Essential Readings in Magnesium Technology

Electrolytic magnesium production has been the mainstay of the world’s magnesium industry since magnesium was first discovered by Davy in 1808. Many of the early workers developed small advances until the electrolysis of anhydrous magnesium chloride became the standard method of production. From the very first days, the importance of anhydrous magnesium chloride has been recognized. It remains the major problem area of economic and efficient electrolytic magnesium production.There has been a dramatically increased usage of magnesium in the past ten years by the automotive industry. This usage is projected to continue a large growth as automakers continue to strive for better fuel economy with reduced emission. The use in die casting alone has been projected to increase at 10–15% per year for the next 10 years.Cost of magnesium and its alloys is constantly compared to aluminum and its alloys by the automakers on all continents. Magnesium usually loses this battle, in spite of the different densities. Aluminum is 50% heavier than magnesium, hence for the same casting shape a pound of magnesium would make three castings while a pound of aluminum would make only two. Automakers feel that to be fully competitive, magnesium should be priced at 1.5 times the price of aluminum. This only takes into account the densities and not the other advantages offered by magnesium such as damping capacity and strength and rigidity.In recent years, the interest in magnesium has grown dramtically and there is a great deal of basic research and pilot plant work going on to identify better and more economic ways to produce electrolytic magnesium metal. There is more technical brainpower being applied to magnesium than ever before at anytime in history. The work has no boundries or restrictions and can be found on all the major continents (except maybe Antartica).

World demand for magnesium will show a decline in 2009. The outlook for 2010, which is guardedly optimistic, will be for a resumption of slow growth. The industry has seen marked changes in the sources of supply for primary and alloyed magnesium in recent years. Technological advances in magnesium continue at a strong pace as does interest in the material as a substitute for other light metals. The automotive segment remains the end-use area with the largest growth potential, if for no other reason than the size and quantity of the potential materials substitution applications. However, the shrinkage of that market, particularly in North America will have a definite impact on expectations for magnesium. The 3C market (computers, communications & consumer electronics) will continue to show above average growth. Other niche markets related to medical and construction industries also offer potential.

The present paper reviews the present potential of magnesium and its alloys as structural light-weight material in transportation industry. An overview will be given on the state of the art in casting technologies of magnesium alloys in order to broaden possible applications in light weight construction. Further, wrought magnesium will be emphasized as a challenge for developing magnesium towards a competitive constructional material. Future needs in all regards involve further alloy development which has to need the special requirements for each process. An overview on actual research activities in Europe and also especially in Germany will be given.

In this paper, the material properties, structural performance, mass saving potential, design and manufacturing characteristics of magnesium are compared with various competing materials such as cast iron, steel sheet, aluminum alloys and polymers. The current and potential automotive applications of magnesium are reviewed, and the technical challenges for these applications are also discussed. Recent alloy development for powertrain applications and the creep resistance of several experimental magnesium alloys are reviewed.

This paper summarizes the monograph, “Magnesium Vision 2020. A North American Automotive Strategic Vision for Magnesium”1 prepared under the auspices of the United States Automotive Materials Partnership The objective was to understand the infrastructural and technical challenge that can increase the use of magnesium in the automotive industry. One hundred sixty three (163) Research and Technology Development Themes (RTDTs), or RTD projects were developed that addressed issues of corrosion, fastening, and processing-other-than-high pressure die casting to produce automotive magnesium parts. A major problem identified in the study is the limited ability of the current magnesium industrial infrastructure to supply RTD and implementation-ready automotive magnesium components. One solution is to create a magnesium cyber center wrhere globally networked experts would be able to innovate in process and product development, model metalworking and non-HPDC foundry processes, and integrate theoretical predictions/models of metallurgical structure with component function.

The Magnesium Front End Research & Development (MFERD) project is an effort jointly sponsored by the United States Department of Energy, the United States Automotive Materials Partnership (USAMP), the Chinese Ministry of Science and Technology and Natural Resources Canada (NRCan) to demonstrate the technical and economic feasibility of a magnesium-intensive automotive front end body structure which offers improved fuel economy and performance benefits in a multi-material automotive structure. The project examines novel magnesium automotive body applications and processes, beyond conventional die castings, including wrought components (sheet or extrusions) and high-integrity body castings. This paper outlines the scope of work and organization for the collaborative (tri-country) task teams. The project has the goals of developing key enabling technologies and knowledge base for increased magnesium automotive body applications. The MFERD project began in early 2007 by initiating R&D in the following areas: crashworthiness, NVH, fatigue and durability, corrosion and surface finishing, extrusion and forming, sheet and forming, high-integrity body casting, as well as joining and assembly. Additionally, the MFERD project is also linked to the Integrated Computational Materials Engineering (ICME) project that will investigate the processing/structure/properties relations for various magnesium alloys and manufacturing processes utilizing advanced computer-aided engineering and modeling tools.

This paper provides an overview and progress report for an international collaborative project which aims to develop an ICME infrastructure for magnesium for use in automotive body applications. Quantitative processing-micro structure-property relationships are being developed for extruded Mg alloys, sheet-formed Mg alloys and high pressure die cast Mg alloys. These relationships are captured in computational models which are then linked with manufacturing process simulation and used to provide constitutive models for component performance analysis. The long term goal is to capture this information in efficient computational models and in a web-centered knowledge base. The work is being conducted at leading universities, national labs and industrial research facilities in the US, China and Canada. This project is sponsored by the U.S. Department of Energy, the U.S. Automotive Materials Partnership (USAMP), Chinese Ministry of Science and Technology (MOST) and Natural Resources Canada (NRCan).

This paper describes a lightweight automobile body concept utilizing a hybrid materials approach with emphasis on a magnesium and aluminum structure to support a high fuel-efficiency vehicle project. This approach resulted in a more than 40% weight reduction over a conventional steel body-in-white while achieving significantly improved staictural performance as evaluated through CAE simulations. A business case analysis was conducted and showed promising results. One concept vehicle was built for the purpose of demonstrating concept feasibility.

Although weight reduction in aircrafts is a fundamental matter, use of magnesium alloys is not widespread in airplanes due to “traditional” problems with corrosion resistance. Though there is creation of new magnesium alloys with improved corrosion resistance, these alloys are mostly designed for automotive industry. Alloys for aerospace industry must combine high performance regarding mechanical properties and corrosion resistance. A review is given here on the use of magnesium in aircrafts in the past. The paper then presents requirements of modern aircraft industry from magnesium castings regarding mechanical properties as well as corrosion resistance. Today the drawback is a lack of sufficient number of available alloys fulfilling the needs of modern aerospace industry. The methodology used in an international research project (IDEA) to develop new magnesium alloys for special use in aircrafts is described here, as well as the experimental and virtual methods utilised in this development.

Since the 1940’s Mg-alloys have been used for military applications, from aircraft components to ground vehicles. The drive for usage was primarily availability and lightweighting of military systems. But the promise of widespread military usage was not met largely based on corrosion and flammability concerns, poor mechanical behavior and inferior ballistic response. This review paper will cover historical, current and potential future applications with a focus on scientific, engineering and social barriers relevant to integration of Mg-alloy. It will also present mechanical and physical property improvements solutions which are currently being developed to address these issues.

One of the current main challenges in green-power storage and smart grids is the lack of effective solutions for accommodating the unbalance between renewable energy sources, that offer intermittent electricity supply, and a variable electricity demand. Energy management systems have to be foreseen for the near future, while they still represent a major challenge. Integrating intermittent renewable energy sources, by safe and cost-effective energy storage systems based on solid state hydrogen is today achievable thanks to recently some technology breakthroughs. Optimized solid storage method made of magnesium-based hydrides guarantees a very rapid absorption and desorption kinetics. Coupled with electrolyzer technology, high-capacity storage of green-hydrogen is therefore practicable. Besides these aspects, magnesium has been emerging as environmentally friend energy storage method to sustain integration, monitoring and control of large quantity of GWh from high capacity renewable generation in the EU.

Primary magnesium production just prior to WWII was around 32,000 tonnes with most of it coming from Germany and England with smaller amounts from France and the U.S.A. Peak production during the war was 232,000 tonnes with most of it coming from the 15 plants that had been built in the United States. By 1946 worldwide demand had fallen back to pre-war levels until 1980. The paper will identify the various plants built round the world since WWII and the impact of exports from Russia and China beginning in the early 90’s. "The presentation will be by country in chronological order. We will not discuss the 15 or 20 potential projects going on around the world since this was well covered by Bob Brown at the Nashville Conference in the year 2000.

Lloyd Montgomery Pidgeon was an unusual man in an unusual time. His contributions to the development of the magnesium industry have never been appreciated (or even known) by many of today’s magnesium followers. Dr. Pidgeon, working with one technical graduate, achieved commercial development of a process to produce magnesium by reducing calcined dolomite with ferrosilicon, i.e. the silicothermic process. He also received patents for electrolytic magnesium processes. He worked with engineers to design and build six magnesium production plants in a very short period of time. The original plant at Haley, Ontario is still operating. Dr. Pidgeon received many technical honors, but was always quick-witted, with a humorous approach to life.

Norsk Hydro has been continuously engaged in development of magnesium electrolysis all since the start of production in Porsgrunn, Norway, in 1951. The first technology was inherited from IG Farben. Later, Norsk Hydro has developed its own diaphragmless electrolyser, now being used for a number of years in the Norsk Hydro’s plants in Porsgrunn as well as in Bécancour (Québec), Canada.A presentation is made of the Norsk Hydro high-amperage monopolar electrolysis cell. Its performance is described, as basis for the conclusion that this type of cell presently is very competitive compared to other cell technologies, although it has a higher electrical energy consumption than bipolar cells.Publications of performance data from magnesium plants in operation are scarce. Norsk Hydro hopes by presenting this paper to invite other producers to release comparable data.

Titanium Institute/VAMI propose two variants of magnesium electrolytic production process.The first variant is based on two-stage preparation of magnesium raw material — carnallite (KCl · MgCl₂ · 6H₂O) for electrolysis. At the first stage, carnallite is dehydrated in fluidized bed dryers with on output of 400 t/day. Operation and control of the drying process has a high level of automation.The second stage of carnallite dehydration is carned out in electric chlorinators with an output of 150-200 t/day. In chlorinators, carnallite is melted and chlorinets treated. Molten carnallite flows to the electrolysis cells. Electrolysis cells are connected in a flow line which operates as one highly productive electrochemical unit. By electrolyte flow, magnesium moves through electrolysis cells and accumulates in a separator cell from where it is extracted and transferred to the casting house for casting magnesium and magnesium alloys into ingots.Electrolysis cells current intensity is ∼ 200–300 kA.Magnesium and magnesium alloys are refined in continuous refining furnaces with the capacity up to 100 t/day.His process is adopted at magnesium and titanium-magnesium plants of Russia, Kazakhstan Ukraine. The best modem projects are realised at DSM Magnesium Plant (Israel).The second variant of magnesium electrolysis production process is based on high dehydration of carnallite in fluidized bed dryers by HCl injection into chambers together with combustion gases, HCl is gained from fuel burning in chlorine gas magnesium electrolysis cells. Solid highly dehydrated carnallite is charged into cells connected into flow lines having centralized magnesium collection.The process has passed pilot-commercial tests and is ready for industrial realization.Above mentioned carnallite processing variants can be used for different types of raw material: magnesite, magnesium chloride solutions, sea water, dolomite and carnallite.

A new technique of magnesia direct electrolysis to produce magnesium with the LaCl₃-MgCl₂ system as support electrolyte published in Magnesium Technology 2004 has low energy consumption, high current efficiency and less pollution for the environment. In this paper, pilot experiments of the new technique of magnesia direct electrolysis in a 5kA magnesium electrolysis cell are conducted. The electrolyte is also the LaCl₃-MgCl₂ system. The experiment results indicate that the LaCl₃-MgCl₂ system is promising. These pilot experiments lay a good foundation for industrial comprehensive utilization of bischofite from Qinghai Lakes in China. In the meantime, the physico-chemical properties of LaCl₃-MgCl₂ bath system, electrolyte ionic species and electrode reactions of the magnesia direct electrolysis in the LaCl₃-MgCl₂ system are studied. The operational parameters of the new process are also compared with those of the common aluminum production process and MgCl₂ electrolysis process.

The effects of cathode materials and electrolyte additives on magnesium wetting were studied with the goal of improving current efficiency in a magnesium electrolysis cell. The study consisted of static wetting and electrolysis tests, both conducted in a visual cell with a molten salt electrolyte of MgCl₂-CaCl₂-NaCl-KCl-CaF₂. The wetting conditions were tested using high resolution photography and contact angle software. The electrolysis tests were completed to qualitatively assess the effect of additives to the melt and were recorded with a digital video camcorder. Results from the static wetting tests showed a significant variation in wetting depending on the material used for the cathode. Mo and a Mo-W alloy, with contact angles of 60° and 52° respectively, demonstrated excellent wetting. The contact angle for steel was 132° and it ranged from 142°–154° for graphite depending on the type. Improvements to the cathode wetting were observed with tungsten and molybdenum oxide additives.

Magnesium production in China has been growing steadily over the past 10 years. Most of the metal has been produced by the Pidgeon process. This process uses horizontal steel tubes called retorts, in furnaces and under vacuum. In the retorts mixtures of finely ground calcined dolomite and ferrosilicon formed into briquettes react to form magnesium vapors which are condensed and later remelted into ingots. The Pidgeon process was long thought to be uneconomic and obsolete. The Chinese have used the advantages of excellent raw material, location, large skilled labor supply, and low capital costs to produce magnesium by this process. The Chinese magnesium is being sold at the lowest prices in the world and lower than aluminum on a pound for pound basis.

A new magnesium reduction technique has been developed to improve the Pidgeon reduction process. A demo-plant of l000t magnesium per year succeeds in applying this new technique. Firstly, a new furnace is developed and a larger-diameter vertical settled vacuum retort is used instead of traditional horizontal retort. So the furnace can be designed with more compact structure to raise the magnesium output per furnace volume. Secondly, calcined dolomites and ferrosilicon is compressed into given unitary shape for enhancing heat and mass transfer during the reduction and shorten remarkably the reduction time. The shape is designed with reference to the numerical simulation result. Demo operation shows that, with application of the technology, significantly production capacity increases in the same furnace, reduction period decreases (only two thirds of the traditional reduction period), energy consumption decreases too, retort’s life extends, operation becomes easy and the total production cost reduces.

A new method of magnesium production was proposed that using a mixture of calcined dolomite and calcined magnesite as raw materials with the molar ratio of MgO to CaO was 6:1 by vacuum aluminothermic reduction. The reduction process was studied by thermodynamic analysis and X-ray diffraction analysis of reduction residue. The reaction of reduction process was CaO+6MgO+4Al=CaO·2Al₂O₃+6Mg. The effect of briquetting pressure, reduction temperature, time and CaF₂ (MgF₂) on reduction ratio of MgO was investigated. And the reduction residue that the main phase of CaO·2Al₂O₃ was leached in alkaline solution for producing sodium aluminate-the raw material for special alumina. The results show that the reduction ratio is increased with increasing of the temperature, time, briquetting pressure in range from 40 to 100 MPa and addition of CaF₂ or MgF₂ in range from 0 to 3%. The alumina leaching ratio of reduction residue reached 88% at the conditions of leaching temperature 95 °C and the concentration ratio of Na₂CO₃ to NaOH was 100:75 in leaching solution.

Carbothermal production has been recognized as conceptually the simplest and cleanest route to magnesium metal, but has suffered from technical challenges of development and scale-up. Work by CSIRO has now successfully demonstrated the technology using supersonic quenching of magnesium vapor (the MagSonic™ Process). Key barriers to process development have been overcome: the experimental program has achieved sustained operation, no nozzle blockage, minimal reversion, and safe handling of pyrophoric powders. The laboratory equipment has been operated at industrially relevant magnesium vapor concentrations (>25% Mg) for multiple runs with no blockage. Novel computational fluid dynamics (CFD) modeling of the shock quenching and metal vapor condensation has informed nozzle design and is supported by experimental data. Reversion below 10% has been demonstrated, and magnesium successfully purified (>99.9%) from the collected powder. Safe operating procedures have been developed and demonstrated, minimizing the risk of powder explosion. The MagSonic™ Process is now ready to progress to significantly larger scale and continuous operation.

The two major problems with using sulphur hexafluoride (SF₆) as a cover gas component for protecting molten magnesium are its high cost and extremely high Global Warming Potential of approximately 24,000. Sulphur dioxide (SO₂) is a viable alternative to SF₆. In comparison, SO₂ is relatively inexpensive and has a Global Warming Potential of zero.However, there has been some concern regarding the safety of SO₂ cover gases, particularly when used in die casting melting furnaces. During the 1940s and 1950s, numerous incidents were reported in magnesium die casting operations, where sulphur domes were used to protect the magnesium die casting alloys. This “Sulphur Dome Effect” was attributed to the presence of SO₂ above the melt, with the suggestion that the incidents were associated with formation of magnesium sulphate.To optimise the conditions for use of SO₂, experiments were conducted to assess the performance of various SO₂-based cover gas mixtures for ingot casting. Ingots of pure and alloyed magnesium were cast under cover gases of SO₂ diluted with air, carbon dioxide, argon and nitrogen. A wide range of SO₂ concentrations was examined, and the ingots were ranked on the basis of visual appearance, dross formation and mould-coat interaction.To determine the significance of the Sulphur Dome Effect, melts of magnesium alloys were exposed to cover gas mixtures of 0.5% SO₂ + dry air, CO₂ and N2 at 660, 680 and 700°C. The scale that deposited on the crucible wall was then scraped with a mild steel spatula, simulating the de-sludging procedure used for crucible cleaning. Samples of the melt surface film and the crucible scalewere collected for chemical analyses by X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD).For both pure and alloyed magnesium, scraping of the crucible scale produced significant sparking and burning, with litth difference noted when changing the diluent gas or melt temperature. Chemical analyses revealed the presence of MgO and MgSO4 in the surface film and the crucible scale. The highly unstable compound A12(SO₄)3 was also detected in the crucible scale. These findings support the currently proposed mechanism for the “Sulphur Dome Effect”, of a highly exothermic reaction between molten magnesium and magnesium sulphate.

In the late 60’s, Norsk Hydro started to develop a process for production of anhydrous MgCl₂ based on dehydration of MgCl₂ brines. The development of the dehydration process has continued, and today an improved third generation process is ready for implementation in brown-field expansions or green-field projects. Several elements of the improved process have already been installed in the Norsk Hydro Bécancour plant. Compared to the previous generation, this new technology offers a minimized energy consumption of 6 kWhi/kg Mg in a large scale mass and energy integrated plant, fully automated and continuous operation with a typical productivity of 1 t Mg/man hour. The Norsk Hydro dehydration technology (considered BAT in EU) offers an environmentally sound solution with minimal emissions of chlorine and chlorinated hydrocarbons, high productivity and improved quality of the anhydrous MgCl₂ feed, ensuring a significantly improved performance of the electrolysis.

CaO added Eco-Mg alloy has the potential to maximize the environmental benefits provided by lightweight, unlimited, and recyclable Mg alloy by eliminating global warming SF₆ or other protective gases as well as Be addition. It is possible to ensure the safety during manufacturing and application, especially without sacrificing process abilities and mechanical properties and increasing the cost of Mg alloy. However, the one limitation of CaO is prone to moisture absorption during storage. Instead of CaO, it is attempted to use Ca(OH)₂, which does not absorb moisture during storage, for Eco-Mg alloy. This paper discusses the effect of Ca(OH)₂ on oxidation and ignition resistances of pure Mg and to compare the results with them of CaO addition. The purpose of this study is to investigate effects of CaO and Ca(OH)₂ on pure Mg through micro structure observation, ignition test and phase analysis. With increasing Ca(OH)₂ content, the hardness of Ca(OH)₂ added Mg alloy increased by grain refinement. From oxidation test by TGA, the oxidation behavior of Ca(OH)₂ added Mg was comparable to that of CaO added Mg alloy for the previous study. Consequently, it seems that reduction of fluidity and mold adhesion could be minimized by adding small amount of Ca(OH)₂ which is cheap and easy to be handled due to its stability in application for Eco-Mg alloy.

As the production of magnesium die-castings for automotive applications increases, the recycling of inhouse scrap and post consumer scrap plays a more and more important role in the supply of magnesium in the long term.An innovative recycling concept for low-cost recycling of magnesium scrap is presented. The operation of this new fluxless conti-process for the recycling of return material class I is introduced. The components of the remelting unit are explained.Recycled material from flux-based processes is compared with fluxless recycled material in terms of mechanical properties.It is shown that the used gas atmosphere in the furnace during melting process has an influence on the inclusion content. The mechanical properties differ markedly depending on the atmosphere and the ratio of surface to volume of the used scrap.

Magnesium recycling now becomes a very important subject as magnesium consumption increases fast around the world. All commonly used magnesium die-casting alloys can be recycled and recovered to the primary metal quality. The recycled materials may be comprised of biscuits, sprues, runners, flash, overflows, dross, sludge, scrap parts, and old parts that are returned from service, An innovative magnesium recycle method, vacuum distillation, is developed and proved out to be able to recycle magnesium scraps, especially machining chips, oily magnesium, smelting sludge, dross or the mixture. With this process at a specific temperature and environment condition, magnesium in scraps can be gasified and then solidified to become crystal magnesium crown. This ‘recycled’ magnesium crown is collected and used as the raw material of magnesium alloys. The experimental results show the vacuum distillation is a feasible and plausible method to recycle magnesium. Further, the cost analysis will be addressed in this paper.

A mathematical model has been developed to simulate the occurrence of heat transfer in vertical retorts. The simulations were run to determine the effect of varying parameters, such as the diameter and thickness of the compound, and slot angle, on the magnesium reduction time. The model predicted the temperature distributions, the heating curves, the recovery ratio of magnesium, and the total process time. The predictions were used to optimize the magnesium reduction process parameters, which consist of dimensions of the retort, shapes of charged materials, and reduction cycle time. The computed results show that the utilization of the optimized process parameters leads to a decrease in reduction time and energy consumption, and an increase in production capacities and recovery rates. Consequently, the magnesium thermal reduction process is significantly improved in the vertical retort.

With a focus on the global warming impact, this paper deals with the cradle-to-gate life cycle study of the following two practical production systems for producing magnesium ingots: (i) Magnesite ore is processed using the Australian Magnesium process to produce anhydrous magnesium chloride, which is then electrolysed to produce magnesium; and (ii) Dolomite ore is calcined to produce magnesium oxide, which is then thermally reduced with ferrosilicon using the Pidgeon process, based on the current practice used in China for magnesium productionThe global warming impact of the ingots produced by the Australian Magnesium process is ∼ 24.3 kg C02-eq/kg of Mg ingot, assuming to HFC-134a is used as the blanketing gas, and electricity and steam are co-generated using Australian black coal. The impact of the magnesium ingots produced in China using the Pidgeon process is ∼ 42 kg C02-eq/kg Mg ingot. This value is based on the current usage of sulphur powder for blanketing molten magnesium while casting. The values of GHG impact for the two systems are discussed in light of energy consumption and process contributions.

The development of magnesium applications for automotive industries is receiving significant attention. One aspect of this attention is the assessment and reduction of the cradle-to-grave environmental impact of magnesium components.The study investigates detailed impact of magnesium converter housing for automotives starting from the production of magnesium ingots to the manufacture and assembly, use and recycling.Extensive sensitivity analysis is conducted to examine the impact of key process parameters that can improve the environmental performance of the component. The parameters include: cover gases other than SF6, improvements to product yield and use of secondary magnesium. From this analysis, a number of environmental performance scenarios are proposed and used to compare the impact of similar functional components made using of magnesium produced in China, aluminium and iron.The investigations clearly show a significant reduction in the greenhouse gas impact may be achieved from the lighter weight of the magnesium components. Also, process improvements to reduce the impact improve the break-even distances in the use of automobiles at which magnesium becomes comparable with other competing metals.

The solubility of fluorine in molten magnesium was measured at temperatures between 700°C and 950°C. The experimental approach involved equilibrating molten magnesium in a MgF₂ crucible under argon. Samples of the equilibrated melt were taken using alumina tubes and a syringe. The fluorine solubility was determined employing the “Sintalyzer method”, an electrochemical method developed at SINTEF, Norway. The fluorine content in liquid magnesium was described by an exponential function of inverse temperature and varied between 10 and 100 ppm by weight in the measured temperature interval. The standard Gibbs free energy of the fluorine dissolution reaction: 1/2 F₂ (gas) = F (in mass %), in the temperature range 700°C to 950°C, was determined to: <math display='block'> <mrow> <mi>&#x0394;</mi><msup> <mi>G</mi> <mo>&#x2218;</mo> </msup> <msub> <mrow></mrow> <mn>3</mn> </msub> <mo>/</mo><mn>2</mn><mo>=</mo><mo stretchy='false'>(</mo><mo>-</mo><mn>473</mn><mi>&#x0020;</mi><mn>000</mn><mo>&#x00B1;</mo><mn>3250</mn><mo stretchy='false'>)</mo><mo>+</mo><mo stretchy='false'>(</mo><mn>53</mn><mo>&#x00B1;</mo><mn>3</mn><mo stretchy='false'>)</mo><mi>T</mi> </mrow> </math>$$\Delta {G^ \circ }_3/2 = ( - 473 000 \pm 3250) + (53 \pm 3)T$$

There is intense research effort into the development of high pressure die cast-able creep resistant magnesium alloys. One of the difficulties encountered in magnesium alloy development for creep resistance is that many additions made to improve the creep properties have reportedly resulted in alloys that are difficult to cast. It is therefore important to have an understanding of the effect of alloying elements on the castability. This paper gives a review of the state of the knowledge of the castability of magnesium alloys.

A description of the key solidification steps in the formation of the as-cast micro structure of magnesium alloys is presented. The focus is on the two common magnesium alloy groups: Mg-Al alloys and Mg-Zn-rare earth alloys. The key elements described are: nucleation (including grain refinement), growth of the primary phase and the formation of the eutectic phases. In addition the effect of casting process (e.g. high-pressure die-casting and sand casting) on the outcomes from solidification are discussed. This includes consideration of the formation of banded defects during solidification in the dynamic environment of high-pressure die casting.

Solidification behavior and as-cast microstructure have been analyzed in a series of ternary Mg alloys consisting of Mg — Al — X: (Ca, Sr, Ce, La). Thermodynamic calculations of the Mg — Al — Ca, Mg — Al -Sr, and Mg — Al — Ce ternaries were conducted to predict the solidification path of the Mg — 4 Al — 4 X and Mg — 4 Al — 2 X systems. Thermal analyses of the solidification process and accompanying electron microscopy studies of as-cast microstructure were conducted on the same alloys. Scheil calculations and the experimental measurements of liquidus and solidus temperatures are compared. All microstructures consisted of primary α-Mg grains with intermetallic phases along the grain boundaries. Additions of Ca and Sr widen the solidus to liquidus gap to a much greater degree than equivalent levels of Ce and La.

The susceptibility of binary Mg-Al alloys in permanent mold casting was tested, including Mg-0.25Al, Mg-0.6Al, Mg-1Al, Mg-2Al, Mg-4Al and Mg-8Al (all in wt %). A steel mold was used for constrained rod casting (CRC), in which rods of various lengths were cast with sudden enlargement at both ends of each rod to prevent it from free contraction during solidification and thus induce hot cracking. The cooling rate near the location of cracking was measured. The hot cracking susceptibility was evaluated based on the widths and locations of the cracks observed. The curve of crack susceptibility vs. Al content was determined and compared with previous curves based on ring casting in steel molds and constrained rod casting in sand molds. The Scheil model of solidification was used to calculate the curves of temperature vs. fraction solid (T-f_S) of the alloys. The crack susceptibility curve based on a simplified hot cracking criterion and the T-f_S and cooling curves was compared with that based on CRC.

It is usually believed that formation of gas and shrinkage porosity has different dependencies on the process conditions, and consequently, the gas and shrinkage pores are usually regarded as independent microstructural features. In this contribution, it is shown that in high-pressure die-castings, gas pores can lead to the formation of shrinkage porosity under specific conditions. This is because the air/gas in the gas pores is an efficient heat-insulating medium. Therefore, presence of gas porosity can retard heat transfer in the liquid melt as compared to similar regions without gas porosity. Consequently, the local solidification rate is lower in such regions, leading to shrinkage porosity formation. Two and three-dimensional (3D) microstructural observations using digital image analysis and numerical simulation for heat transfer support such a hypothesis. Finite element (FE)-based simulations have also been performed on the 3D microstructures to reveal the variations of local stresses caused by gas induced shrinkage porosity.

The deformation and fracture behavior of die-cast AM50 and AM60 magnesium alloys have been examined to determine the processes leading to fracture in bending and tension and to elucidate the influences of microstructure and porosity on ductility. Damage accumulation in terms of crack initiation, growth, linking and eventual failure was quantified as a function of strain for as-cast plates with section thicknesses of 2, 6 and 10 mm. Microstructure and porosity distribution are dependent on section thickness, with bands of high porosity resulting from the nature of the die filling process. In both tensile and three-point bend studies, damage accumulation and subsequent ductility at fracture are strongly influenced by the heterogeneous porosity distribution, with early crack formation occurring in regions of highest porosity. A model is presented that relates the observed ductility of these alloys with porosity distribution, crack size, crack tip radius, and elastic modulus.

Since its discovery over thirty years ago, semisolid processing is mainly applied to alloys with relatively low melting temperatures, particularly aluminum. Although historically an interest in magnesium reaches back to the early 1970’s, compared with aluminum, investigations of semisolid magnesium alloys are still scarce. This report presents the origin of semisolid processing, rheological behaviour of semisolid slurries and the key technologies, available in today’s industry, based on thixo- and rheo-routes. Particular attention is being paid to emerging techniques of injection molding. The major requirements imposed on potential alloys and typical components, manufactured commercially, are characterized.

The fatigue behavior of the Thixomolded® magnesium alloy AZ91D has been examined using ultrasonic fatigue testing techniques at frequencies of approximately 20 kHz and for lifetimes as long as 109 cycles. An apparent endurance limit of approximately 65–70 MPa is observed. Comparison with the fatigue behavior of AZ91 produced by conventional die casting indicates that the Thixomolded® material has an endurance limit substantially higher than that of die cast material. This is attributed primarily to reduced porosity associated with the thixotropic processing technique. Fractographic analyses indicate that fatigue cracks leading to failure initiate at internal porosity in approximately 75% of tests and at the as-molded surface in the remainder of tests. Fractographic studies indicate that, in general, longer fatigue lifetimes are associated with smaller fracture initiation sites. It was also observed that a bimodal distribution of fatigue lives occurred, especially at lower stresses. This was analyzed using cumulative distribution functions, which confirmed the existence of dual failure populations.

Development of wrought Mg alloy, particularly in sheet form, are essential to support the growing interest for lightweight components in the automotive industry. However, development of Mg alloy sheets has been quite slow due to the complexity of sheet production originated from limited deformability of Mg. In this respect, strip casting, a one-step processing of flat rolled products, can be an alternative for the production of Mg alloy sheets. In this study, AZ31 and experimental alloys are strip cast into 2 mm thick strips. The microstructure of the as-cast AZ31 alloy strip consists of columnar zones near the roll side and equiaxed zones in the mid-thickness region. On the other hand, as-cast MX1 alloy strip shows equiaxed dendritic structure through the thickness of strip. The cooling rate estimated from the secondary dendrite arm spacing is around 102 K/s. These alloys were subjected to various thermomechanical treatments and their tensile properties were evaluated. Strip cast AZ31 alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast AZ31-H24 alloy, indicating that strip casting is a viable process for the fabrication of Mg alloy strips. The experimental MX alloys have a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of strip casting on microstructural refinement. It has been shown that the experimental MX0 alloy has superior tensile properties compared to commercial ingot cast AZ31-H24 alloy, suggesting the possibility of the development of new wrought Mg alloy sheets by strip casting.

Magnesium alloy AZ31, AZ61, AZ91, AM50 and AM60 sheets were produced by twin roll casting first time in Turkey. Sheets of 4.5–6.5mm thick and 1500mm width were successfully achieved. Microstructure of the sheet was analyzed by optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Semi-quantitative analyses were performed by SEM-EDS. In addition, X-ray studies were performed for both characterization and texture purposes. Mechanical properties were investigated by tensile tests and also hardness measurements. Homogenization and annealing heat treatments were performed on the produced sheets.

Grain formation during solidification of magnesium and Mg-Al alloys has been studied with a focus on grain refinement mechanisms, solute and particle effects. The variation in grain size with increased aluminium content in hypoeutectic Mg-Al alloys showed a continuous decrease in grain size up to 5 wt% Al, and a stabilisation at higher Al contents (above 5 wt%). Strontium additions to both low- and high-aluminium content magnesium alloys showed that Sr had a significant grain refining effect in low-aluminium containing alloys. However, strontium had a negligible effect on grain size in the Mg-9Al alloy. Additions of Zr, Si, or Ca to pure magnesium produced significant grain refinement, probably because these elements have high growth restriction effects during solidification. An attempt was made to identify the grain refinement effect of particles added directly to the melt that are considered to be powerful nucleants in Al based alloys (TiC) and in Mg based alloys (AlN, Al₄C₃). Most of these particles produced grain refinement, probably because of enhanced nucleation due to the small lattice disregistry between their crystal structures and that of magnesium. However, it is not clear whether the grain refining mechanism of the effective particles was catalysis of primary crystal nucleation or simply restriction of crystal growth during solidification.

This paper investigates the effect of ZrB₂ particles on the grain refinement of an Mg-Al alloy. A comparison, with respect to grain size, of the effect of ZrB₂ particles formed in situ and commercially obtained synthetic ZrB₂ particles, which are subsequently added to the melt, was made. In situ ZrB₂ particles were formed by reacting conventional Al-Ti-B and Al-Zr alloys. Samples were taken in accordance with the TP1 test procedure and the resulting grain size of the primary Mg measured using the intersect method. An SEM equipped with EDS was employed to elucidate the effect of the Zr. Results show that the ZrB₂ successfully grain refines the Mg-Al alloy resulting in ultimate grain sizes of 100 and 60 μm for the in situ and synthetic ZrB₂ particles respectively. Mg-Al alloys can be successfully grain refined using ZrB₂ heterogeneous particles and the resultant effect should be beneficial in improving the mechanical properties of the alloy.

Solute in solution hardens the basal planes but causes solid solution softening on the prismatic (and possibly pyramidal) planes in dilute (< 0.5 at.% Zn) Mg-Zn alloys. Solid solution softening lowers the strain-hardening rate and increases the ductility of the alloys with respect to the pure Mg metal. In the concentrated (0.5 ∼ 2.4 at.% Zn) alloys, solid solution hardening of the basal planes is extensive but it is not clear whether solid solution softening of the secondary slip systems still occurs. Therefore, solid solution effects on the strain hardening rate and ductility of cast polycrystalline Mg-Zn alloys, with Zn contents between 0 and 2.4 at.% have been studied. A constant grain size was obtained in all alloys by adding a small amount of Zr to the melt. The strain-hardening rate is low for dilute concentrations increasing monotonically above 1 at.% Zn. The ductility goes through a maximum at very low concentrations of Zn, decreasing for higher concentrations. This suggests that the solid solution hardening gradually offsets the solid solution softening effects at high concentrations of Zn.

We have investigated the age hardening behavior of Mg-1.2at.%Sn (T5) based alloys, which are solution treatable at lower temperature as compared to the previously studied Mg-2.2Sn (T10) based alloys. To enhance the age hardening response with the reduced Sn content, Zn and Al were alloyed with the Mg-1.2at.%Sn alloy. Particularly, Mg-1.7Zn-1.2Sn-2.0Al alloy (TZA543) showed the peak hardness of 79 VHN at 200°C. The peak aged Mg-1.2Sn-1.7Zn-2.0Al alloy consisted of cuboidal β₂’ precipitates with the size of less than 50 nm, rod shaped precipitates, and lathplate shaped Mg₂Sn phase.

Microstructural analysis of die cast AE42 reveals a correlation between microstructure and creep strength. A lamellar phase Al₁₁RE₃ which dominates the interdendritic microstructure of the alloy partly decomposes above 150°C into Al₂RE and Al (forming Mg₁₇Al₁₂). The creep strength decreases sharply with these phase changes. A mechanism for the decrease in creep strength of AE42 is proposed whereby reduced presence of lamellar Al₁₁RE₃ and/or the presence of Mg_l7Al₁₂ contribute to the observed poor creep strength at the higher temperature. The increased solubility of AI in Mg at higher temperature may also promote the decomposition of Al₁₁RE3.

There have been attempts since in the 70’s to develop creep resistant magnesium diecasting alloys for automotive applications such as automatic-transmission case and engine components. The earliest die casting alloys developed as a result of these activities were the Mg-Al- RE and Mg-Al-Si systems (AE and AS alloys). The shortcomings of these two alloy systems related to high cost or borderline properties have led to renewed activity in the 90’s in the development of magnesium alloys with improved elevaied-temperature properties. This paper presents the development of a new family of creep-resistant Mg alloys based on the Mg-Al-Sr system. Creep resistance, the tensile yield strength and the bolt-load-retention of these alloys at 150°C and 175°C show improvement over Mg-Al-RE and Mg-Al-Si system. The microstructure of the alloys is characterized by Al-Sr-(Mg) containing intermetallic second phases. The absence of the Mg₁₇Al₁₂ phase in the microstructure, either creep-induced or as-cast, is one of the factors that contribute to improved creep-resistance of these alloys over the Mg-Al based diecasting alloys. Furthermore, the alloys exhibit better salt-spray corrosion resistance (0.09-0.15mg/cm2/day) than other commercial magnesium diecasting alloys such as AM60B, AS41, AE42 and the aluminum diecasting alloy A380.

The microstructure and microstructural stability of die-cast AC53 (Mg-5Al-3Ca) and AXJ530 (Mg-5Al-3Ca-0.15Sr) have been investigated in detail by transmission electron microscopy (TEM). Both alloys have an as-cast microstructure of α-Mg with (Mg, Al)₂Ca (dihexagonal C36) eutectic at grain boundaries. During aging at 573 K, the C36 phase transforms to Al₂Ca (cubic Cl5) phase. These two phases have a crystallographic orientation relationship of (0001)_C36//{111}_C15 and [2110]_C36//[011]_C15, and the transformation from C36 to C15 occurs by a shear-assisted process. Despite this change in the phase constitution, the network structure of the intermetallic compound(s) surrounding α-Mg grains is fairly stable, morphologically, even after prolonged exposure at elevated temperature. In the α-Mg matrix phase, precipitation of Al₂Ca was observed after aging for 360 ks at 573 K. The precipitates are disc-shaped with a habit plane of {111}_C15//(0001)_α. AXJ530 shows higher creep resistance than AC53. The dislocation substructure that evolved during creep deformation was investigated in both alloys, and the basal and non-basal slip of a-dislocation and other slip modes of a+c- dislocations were observed. The relationship between creep properties and microstructure is discussed.

New growth area for automotive use of magnesium is powertrain applications such as the transmission case and engine block. These applications see service conditions in the temperature range of 150–200C under 50–70 MPa of tensile and compressive loads. In addition, metallurgical stability, fatigue resistance, corrosion resistance and castability requirements need to be met. A decade of research and development has resulted in a number of creep- resistant magnesium alloys that are potential candidates for elevated-temperature automotive applications. These alloys are mostly based on rare-earth and alkaline earth element additions to magnesium. This paper gives an overview of the various magnesium alloy systems for use in elevated-temperature applications.

Mg products are easily oxidized and burned when they are exposed to high temperature or fire by accident. In order to solve these problems, the fire-proof solution has been developed by adding CaO in Mg alloys. The fire-proof was evaluated by three methods: quantitative DTA for small sphere specimen, furnace ignition test for burrs and machined chips, and torch ignition test for products. DTA was carried out for obtaining quantitative ignition temperature data with respect to specimen geometry and test environment; the furnace ignition test for burr and chip ignition temperature data; and the torch test for ignition temperature data for manufactured products. This paper discusses the results of fire-proof properties of 1wt.%, and 1.5wt.% CaO added Mg-3Al, Mg-6Al, and Mg-9Al Mg alloys compared with other high temperature Mg alloys such as AE44, AS21, MRI153, and MRI230. Eco-Mg alloy will be low-cost and fire-proof Mg alloys for airplane and train applications in terms of preventing poisonous gas generation, inhalation bum, and ignition generation.

The performance of magnesium die cast parts is governed by the microstructure and by the distribution of structural features which occur as a result of the chemical composition and processing history of the alloy. The elevated temperature properties, especially mechanical strength under creep conditions, are primarily determined by the grain structure, the elements in solid solution and the effectiveness of second phase particles in stabilizing the grain boundaries. The current emphases in alloy development focus on the utilization of elements with low solubility in the solid state, leading to the formation of stable precipitates during solidification. Such elements include the rare earths, as well as silicon, strontium and calcium. A detailed analysis of the various microstructural features and attributes is given for a new family of rare earth-containing alloys. The optimization of alloy composition is addressed in terms of blending advantageous microstructural characteristics with phase equilibria considerations.

Precipitation strengthening in Mg-Zn-Y alloys occurs via the formation of a fine dispersion of β’₁ (Mg₄Zn₇) rods aligned parallel to the hexagonal axis. In this study, texture and controlled deformation have been used to control the directionality and morphology of the precipitates and their effect on the ageing response. The resulting precipitates were studied via conventional and high-resolution transmission electron microscopy.Texture was developed through extrusion at 300°C, followed by controlled room-temperature deformation to generate microstructures where yield occurred either with, or without, twinning. The ageing response was monitored using hardness testing. Both compressive and tensile deformation accelerated the ageing response. Compression parallel to the extrusion axis generated a high volume fraction of twins. Precipitates on the twin boundaries assumed a low aspect-ratio morphology different from the usual high-aspect ratio rods.

Commercial magnesium alloys have a great potential for structural applications in automotive due to their significant weight saving. However, they have poor creep resistance at temperature over 125°C, thus making them inadequate for power train applications such as engine pistons, which are operated at temperature up to 300°C. Recently, creep resistant magnesium alloys with rare-earth elements and Zn have been developed, hence the applicability of Mg-Zn-(Y, Gd) alloys for engine pistons was investigated in this paper. Gravity casting was performed with Mg-Zn-(Y, Gd)-Zr alloy, followed by T6 treatment. Effects of the amount of alloying elements on the mechanical properties of tensile strength and creep strain were evaluated. Nominal composition of Mg-2Zn-11Y-5Gd-0.5Zr was selected for the actual piston cast trial and its high cycle fatigue test was conducted comparing to the current aluminum cast alloy of A336 (JIS AC8A) for pistons. At room temperature, the fatigue strength is 27% lower than A336, while it is 35% higher at 300°C. It is suggested that Mg-2Zn-11Y-5Gd-0.5Zr alloy shows attractive high temperature mechanical properties higher than A336, hence it is promising as a candidate material for the engine piston application.

A detailed investigation of the deformation mechanisms plays an important role for a better understanding of texture evolution and anisotropic behavior of magnesium wrought alloys. Therefore, room temperature deformation tests of AZ31 hot rolled sheets and extruded bars have been performed. The experimental tensile textures of the rolled sheets show a reorientation resulting in a {0001}〈101;¯0〉 main component.The results were compared with simulations using a viscoplastic self-consistent model to gain further information about deformation mode activities, texture evolution and mechanical properties. Thereby three simulation sets were executed: The first set included the results of both the rolled sheets and the extruded bars, while the others considered the results separately.Based on the simulations, it will be demonstrated that the activity of the basal, prismatic, pyramidal slip and the twinning mode is required to achieve comprehensive results for the mechanical properties as well as for the texture evolution.

The data on the hot workability of the magnesium alloy AZ61 available in the open literature are based on the tests over narrow ranges of temperatures and strain rates and thus are of limited use for bulk-forming processes. The objective of the present research was to perform a detailed constitutive analysis of the alloy, on the basis of the results obtained from uniaxial compression tests at temperatures from 250 to 450 °C and strain rates from 0.01 to 100 s−1. The shape of the flow curves suggested the occurrence of twinning followed by dynamic recrystallization. The alloy did not display steady-state flow stress behavior such that the constitutive analysis of the alloy using the hyperbolic equation must take strain into account. It was found that the constitutive constants were indeed strain dependent. A method to apply the hyperbolic constitutive equation at given strains was developed, with which an accurate strain-stress database for the alloy could be established.

Understanding deformation mechanisms is a prerequisite for the development of more formable magnesium alloys. We have developed a novel approach based on analysis of in-grain misorientation axes which allows identification of the dominant slip system for a large number of grains. We investigated the effects of orientations and temperatures on active deformation mechanisms during the rolling of AZ31, including slip, deformation twinning and deformation banding. The IGMA analysis suggests that increasing rolling temperature promotes activation of prism <a> slip which enhances the rollability of the plate favorably oriented for this slip mode. The approach also reveals an orientation-dependent occurrence of deformation banding and its crystallographic relationship with parent grain. It is concluded that IGMA analysis can be effectively used to study deformation mechanism in hcp metals, and can be used as a criterion for validating some crystal plasticity models.

The anisotropic plastic responses of commercial magnesium alloy AZ31B sheets in the stress-relieved and soft-annealed conditions are found to be similar. Measurements of the r-value (r = d□_w/d□_t) for tensile samples oriented 0, 45, and 90° from the rolling direction highlight a strong in-plane anisotropy, with r(0°)∼1 and r(90°)∼3.5. This in-plane anisotropy is somewhat surprising given the nearly ideal basal texture present in the material. Simulations of the plastic response which incorporate the initial texture and the strain hardening of the individual grain-level deformation modes enable us to conclude that the slight off-basal character of the texture is enough to induce a change in the balance between the activities of basal and prismatic slip. The tendency of the grain’s basal poles to tilt from the normal direction towards the rolling direction is enough to enable easy basal slip to accommodate the majority of the strain during tension along the rolling direction (0°). During tension along the transverse direction (90°), however, the majority of the strain is accommodated by the harder prismatic slip mode, which induces little change in the thickness, while producing a strong reduction in the width.

The commercial application of magnesium alloy sheets is hindered by their low formability and therefore technological and economic constraints. Tailoring the texture has been identified as playing a major role in enhancing the formability of magnesium sheets. In this study, the formability of magnesium sheet ZE10 and AZ31 was investigated. While the texture of AZ31 is of unfavourable basal type, ZE10 shows a significantly different texture with the basal planes being randomly distributed. More basal planes are oriented favourably for basal slip, promising higher formability and thus, lower process temperature. Formability is assessed by means of forming limit diagrams as a representation of material response to various strain paths. Nakajima tests were carried out from room temperature to 250°C. Local strain data is correlated with the microstructural evolution. This study reveals a significant influence of texture on formability with ZE10 sheet showing superior formability compared to AZ31.

Unalloyed Mg and Mg-0.2%Ce alloy were extruded as solid rounds at 400°C in a 500 ton vertical extrusion press at 10 mm/sec. Tensile tests revealed a significant increase in elongation with only a small Ce addition of 0.2%. The addition of cerium caused a decrease in yield strength and an increase in work hardening delaying the onset of instability. EBSD analysis shows that the small Ce addition markedly alters the texture of the extruded rods during recrystallization, and orients the c-axes of the grains at an angle to the extrusion axis whereas they are mostly normal to the extrusion axis in Mg. This reorientation favors basal slip activity leading to higher elongation. While Mg deforms mainly by twinning and fracture initiates due to voids nucleating at twin intersections, the Mg-0.2Ce alloy shows void nucleation along nonintersecting shear bands parallel to the tensile axis. The results of this study point to a design approach that combines alloying and processing to alter the slip distribution which can enhance the formability of Mg alloys.

The evolution of flow stress and microstructure for wrought magnesium alloy AZ31 was characterised using torsion and compression testing. Temperatures ranging between 300°C and 450°C and strain rates between 0.001s−1 and 1s−1, were employed. Constitutive equations were developed for the flow stress at a strain of 1.0 for torsion, and 0.6 for compression. The flow stress was found to be strongly dependent on deformation mode at low strains. This can be explained in terms of the influence of the deformation accommodating processes of prismatic slip and dynamic recrystallisation (DRX). At higher strains, when the change in flow stress with strain is lower, the flow stress was relatively insensitive to deformation mode. Optical microscopy carried out on torsion samples quenched after twisting to strains between 0.2 and 2 revealed dynamically recrystallised (DRX) grains situated on pre-existing grain boundaries. The average grain size was reduced from 22.5µm down to 7.3 µm after a strain of 2, with the initial grain size being halved after a strain of 0.5.

The deformation in compression of pure magnesium and AZ31B magnesium alloy, both with a strong basal pole texture, has been investigated as a function of temperature, strain rate, and specimen orientation. The mechanical response of both metals is highly dependent upon the orientation of loading direction with respect to the basal pole. Specimens compressed along the basal pole direction have a high sensitivity to strain rate and temperature and display a concave down work hardening behavior. Specimens loaded perpendicularly to the basal pole have a yield stress that is relatively insensitive to strain rate and temperature and a work hardening behavior that is parabolic and then linearly upwards. Both specimen orientations display a mechanical response that is sensitive to temperature and strain rate. Post mortem characterization of the pure magnesium was conducted on a subset of specimens to determine the microstructural and textural evolution during deformation and these results are correlated with the observed work hardening behavior and strain rate sensitivities were calculated.

Magnesium alloys are increasingly being used in automotive industry for weight reduction and fuel economy improvement. Extruded tubular sections provide further opportunities in mass-efficient designs of automotive structural and interior applications. In this paper, microstructural evaluation indicates that twinning is the predominant deformation mechanism for magnesium alloys at room and moderate temperatures. Dynamic recrystallization is observed at temperatures as low as 150°C, leading to the formation of fine grains as a “necklace” at prior grain boundaries. These new grains cause strain localization and instability due to a loss in strain hardening, and result in failure by cavitation.

In order to reduce fuel consumption efforts have been made to decrease the weight of automobile constructions by increasing the use of lightweight materials. In this field of application magnesium alloys are important because of their low density. A promising alternative to large surfaced and thin die casting parts has been found in construction parts that are manufactured by sheet metal forming of magnesium. Magnesium alloys show a limited formability at room temperature. A considerable improvement of formability can be achieved by heating the material. Formability increases above a temperature of approximately T = 225 °C.This paper will give an overview about the heated hydro-mechanical deep drawing process of magnesium sheet metal. It will further show how the process parameters temperature and fluid pressure influence the deep drawing process. The main goal of these investigations was a decrease of the forming temperature by use of the hydro mechanical deep drawing process.

A constrained chip formation technique, large strain extrusion machining (LSEM), was used to produce bulk magnesium alloy (AZ31B) strips with fine grain size (2–6 μm) and non-basal textures. These characteristics are known to enhance the final formability. The deformation temperature during extrusion-machining was varied by preheating the workpiece to a range of temperatures (50°C to 375°C). Microstructural refinement and texture evolution were studied as function of deformation temperature. It was possible to refine the grain size down to ∼2 µm by restricting the dynamic grain growth at low to moderate deformation temperatures (below 320°C). LSEM was shown to be capable of resulting in non-basal textures at low deformation temperatures (below 220°C) as well as at elevated deformation temperatures (above 420°C). The influence of active deformation mechanisms and dynamic recrystallization on the texture development is also addressed.

Thermodynamics has often been viewed applicable to states near equilibrium only although irreversible thermodynamics was already developed in 1950s. The CALPHAD technique of computational thermodynamics developed since early 1970s has helped to change this view. This technique couples the phase diagram and thermochemical properties to explicitly characterize all phases in a system, including stable, metastable, and unstable phases over a wide range of temperature, pressure and composition. The modeling of Gibbs energy of individual phases enables the calculation of driving forces between any intermediate non-equilibrium states for simulating dynamic microstructure evolutions.As same as the most commercial alloys, magnesium alloys are multi-component in nature with many intermetallic phases. To develop robust alloys that are less sensitive to process variability, phase relations under both equilibrium and non-equilibrium conditions are extremely valuable for the design of alloy compositions and processing procedures. In this presentation, the CALPHAD technique will be discussed. Particular attention will be paid to the phase relations in the Mg-Al-Zn ternary alloys.

A complete thermodynamic database for the Mg-Al-Mn-Fe-Be system has been developed. The goal of this work is to develop a better understanding of the chemical interactions occurring during the alloying process of magnesium-based alloys. The database consists of evaluated and optimized model parameters, which give all the thermodynamic properties of all phases as functions of temperature and composition.For the binary systems without beryllium, the parameters were taken from the COST 507 Project (1). The binary systems with beryllium were critically evaluated/optimized in the present work, as were all systems of three or more components. The models are used to predict the properties of the phases in regions of composition and temperature where data are unavailable. The optimized set of model parameters was obtained by considering simultaneously all available literature data for phase equilibria and thermodynamic properties of all phases. Complete details of the optimizations will be presented elsewhere.The database can be used with the FactSage thermodynamic software (2) to calculate complex chemical equilibria involving the solid, liquid and gaseous phases. Phase diagram sections of any type can be calculated and plotted. The alloying process can be followed for temperatures between 500 and 900°C, with calculation of the equilibrium phase assemblage at any temperature. Non-equilibrium (Scheil-Gulliver) cooling can also be simulated. The software and database can be used to search for improved alloying techniques and increased elemental recovery by calculating elemental distributions between liquid magnesium and sludge, enthalpy balances, phase saturation, intermediate phase formation upon alloying, etc.

The thermodynamic properties of the ternary Mg-Al-Ca system are investigated, based on the three binary systems, i.e. the Al-Mg, Ca-Mg and Al-Ca systems. The ternary system contains six different intermetallic compounds with five of them treated as stoichiometric compounds. The calculated ternary system and Scheil simulations are used to understand the microstructures and phase relationships during solidification. Metallographic samples are prepared for the optical microscopy and SEM observations. The phase amounts were measured and compared with the calculated results. The calculations will be used to direct new experiments in the project for fine-tuning of the phase relationships.

The thermodynamic properties of the quaternary Mg-Al-Ca-Sr system are investigated by combining the six binary systems, i.e. the Al-Ca, Al-Mg, Al-Sr, Ca-Mg, Ca-Sr and Mg-Sr. The constructed quaternary database is used to understand the microstructures and phase relationships of the two alloys (Mg-5.7%Al-3.1%Ca-0.15%Sr and Mg-5.0%Al-3.1%Ca-0.07%Sr). Scheil simulations and equilibrium calculations were performed for the solidification process of the alloys and compared with experimental observations.

Mg-Al-Ca alloys exhibit appealing creep strength at temperatures over 100°C. It is believed that it is due to the substitution of the γ-Al₁₂Mg₁₇ phase by laves phases of higher thermal stability. In the literature, the C15-Al2Ca phase in the Al-Ca binary system and the C14-Mg₂Ca phase in the Ca-Mg binary system have been reported. Their relative stability in the ternary system may play an important role in the development of the Mg-Al-Ca alloys. Furthermore, recent experiments and first-principles calculations in the literature revealed the existence of a C36 laves phase in the Al₂Ca-Mg₂Ca pseudo-binary system in addition to the C14-Mg₂Ca and C15-Al₂Ca laves phases. In the present work, special quasirandom structures (SQS) for all three laves phases were constructed. The structures possess local pair and multisite correlation functions that mimic those of the corresponding random structures. First-principles calculations were carried out based on the SQS developed to predict the enthalpy of formation in the Al₂Ca-Mg₂Ca pseudo-binary system. It was observed that the enthalpy of formation of C36 is very close to that of C14 at the Mg₂Ca end and decreases with the addition of small amount of Al, while the enthalpy of formation of C14 increases with the addition of Al. It is thus energetically plausible the C36 is stable in the Al₂Ca-Mg₂Ca pseudo-binary system. Experimental investigations were done using diffusion couple of Mg-Ca alloy and pure Al. EPMA analysis of the diffusion zone found the existence of two ternary phases (Mg,Al)₂Ca and Al₂(Mg,Ca).

A thermodynamic database of Mg-Al-Ca-Sr, a basic quaternary for a number of commercial magnesium alloys such as AXJ530 (Mg-4.5Al-3.0Ca-0.14Sr, weight percent hereafter, unless noted otherwise) was developed. Calculated isopleth from Mg-5Al-3Ca to Mg-5Al-3Sr agrees with experimental data reported in the literature. Moreover, using this database and a simple kinetic model proposed by Scheil, the calculated solidification paths of several alloys are likewise in accord with experimental data. Thus, the availability of this database enables one to exploit new alloy compositions for promising properties which can be rapidly validated with few experiments.

Progress is reported on experimental study and thermodynamic modeling of phase formation in key subsystems pertinent to the Mg-Al-Zn-Mn-Ca-Sr alloy system, or abbreviated as (Mg)-AZMXJ. This ongoing work enables thermochemical calculations, which are an important tool for the focused alloy development and process optimization.As an example, additions of Ca and Sr to alloys of the AZ series may provide improved mechanical and corrosion properties. Understanding the contribution of phase formation to these effects and, based on that, tackling a purposeful optimization is hardly possible without that information. This applies also in the case of Sr-addition to AM, essentially forming AJ alloys or, including the Ca-addition, to the potential offered by the AXJ system.

Ternary Mg-Zn-Ce phase equilibria were investigated by key samples to determine the solubilities, primary crystallizing phases and invariant reactions. Alloys were prepared from pure elements and investigated by DTA/DSC and SEM/EDS. A consistent thermodynamic Calphad-type model of the ternary Mg-Zn-Ce system is developed. Phase diagram sections at constant 300°C, at constant 85 at.% Mg and the liquidus projection of the Mg-Zn-Ce ternary system were calculated and they compare reasonably well with all available experimental data, especially in the Mg-rich region. This work may, thus, form a reliable basis for the application of computational thermodynamics in Mg-Zn-Ce-X multicomponent alloys.

The thermo-physical and physical properties of the liquid and solid phases are critical components in casting simulations. Such properties include the fraction solid transformed, enthalpy release, thermal conductivity, volume and density all as a function of temperature. Due to the difficulty in experimentally determining such properties at solidification temperatures, little information exists for multi-component alloys. As part of the development of a new computer program for modeling of materials properties (JMatPro) extensive work has been carried out on the development of sound, physically based models for these properties. Wide ranging results will presented for Mg-based alloys including more detailed information concerning the density change of the liquid that intrinsically occurs during solidification due to its change in composition.

Multi-component magnesium alloys exhibit a complex constitution, requiring computational thermodynamics for a quantitative treatment that goes beyond “just” phase diagrams. The basis for this approach is a thermodynamic Mg alloy database, which is developed in an ongoing long-term project in our group since many years. Three distinctive features of this database are highlighted in this report: (i) Combination of own key experimental work with theoretical modeling to generate consistent data, (ii) Systematic quality control of the database using a variety of elaborated cross-checks, and (iii) Complete and entire composition range descriptions for all pertinent binary or ternary subsystems whenever possible. The latter point is decisive for the capability to use this tool for new alloys, far beyond the composition limits of conventional Mg alloys. It is demonstrated by correctly predicting the phase formation in aluminum-rich six component alloys. Also, new Mg-solder alloys can be tackled that are essentially Zn-rich.

During direct chill (DC) casting, significant stresses can develop within the material leading to cracking within the cast slab. The situation is made worse for higher strength magnesium alloys, such as Elektron™ WE43, which exhibits high strength at elevated temperatures. Consequently, the temperature and stress field must be well understood during the casting process to avoid failure during casting.

Most applications of magnesium in automobiles are for nonstructural components. However, the light weight properties of magnesium make it attractive in structural applications where energy absorption in a crash is critical. Because most deformation in a crash occurs as bending rather than simple tension or compression, the advantages of magnesium are greater than anticipated simply from tensile strength to weight ratios. The increased thickness possible with magnesium strongly influences bending behavior and theoretical calculations suggest almost an order of magnitude greater energy absorption with magnesium compared to the same weight of steel. The strain rate sensitivity of steel is of concern for energy absorption. Mild steels exhibit a distinct yield point which increases with strain rate. At strain rates typical of vehicle impact, this can result in strain localization and poor energy absorption. Magnesium alloys with relatively low aluminum contents exhibit strain rate sensitivity, however, this is manifest as an increase in work hardening and tensile / yield ratio. This behavior suggests that the performance of magnesium alloys in terms of energy absorption actually improves at high strain rates.

In this paper, a new constitutive framework based on a rate-dependent crystal plasticity theory is presented to simulate large strain deformation phenomena in HCP metals such as magnesium. In this new model the principal deformation mechanisms considered are crystallographic slip and deformation twinning. The new framework is incorporated into in-house finite element (FE) codes. Simulations of uniaxial tension and compression for the magnesium alloy AM30 are performed and the results are compared with experimental observations of the specimens deformed at 200°C. Limitations of the current modelling approaches are also discussed.

Development of new Mg-alloys needs greater efforts in systematic evaluation of corrosion protection methods under service environments. A deeper understanding of microscale and nanoscale metallurgy is needed to slow down corrosion. Results from our multiscale modeling effort will be presented to demonstrate the power of first-principle theories in predicting the composition-dependent kinetics of corrosion reactions. Our recent results show that the corrosion prevention properties of Mg-alloys can be significantly enhanced by doping rare-earth elements such as Cerium that protects the oxide layer from rapid hydrolysis. Furthermore, we are developing kinetic Monte Carlo and finite-element analysis (FEA) based models to extend the predictions from the atomic length scales to nano- and microscale models that will include grains and alloy microstructure. The potential for incorporating mechanical and corrosion performance in continuum length scale combined with the insights from first-principles based surface chemical models can have powerful impact on the development of Mg-alloys.

Atomistic simulations are performed in order to study the Aluminum substitution effect on Magnesium twinning mechanism. Multiple twin boundaries are found in pure Mg single crystal under tensile loading condition along (1012) crystallographic direction. However, no twinning has occurred under compression loading. Al substitution has been done for 2, 5, 7, and 10% doping. For 2 and 5% Al substitution, number of twins increase when the system is monitored under tensile loading. On the other hand, for 7 and 10% Al doping under tensile loading, no twin has been found. We found that dislocation-twin and dislocation-dislocation interaction are majorly responsible for this behavior and it is important that which one is prevalent.

An investigation has been carried out on the friction stir welding of four magnesium alloys. These consisted of one wrought and three die-cast magnesium alloys, including those containing manganese such as AM50 and AM60, and also zinc such as AZ91 and AZ31 (wrought material). All of the alloys have each been successfully welded to themselves and also to each other, without any problems from the trapped gases in the cast materials, but the tolerance box of processing parameters to ensure that sound welds are produced has been found to be more restrictive than those seen in friction stir welding aluminium alloys.

Welding will play an important role in the fabrication of modular lightweight structures based on magnesium alloy die castings, extrusion profiles and wrought products. Minimisation of rejection rates during fabrication requires that satisfactory weldability be established for a particular combination of materials and welding procedures. In this paper, we present the results of a study to quantify the weldability of wrought alloy AZ31B by gas tungsten arc (GTA) and laser beam (LB) welding processes. The susceptibility to weld metal solidification cracking was evaluated using the Circular Patch weldability test. Operating windows of welding parameters for crack-free and porosity-free GTA and LB welding were identified, based on which welding procedures were developed for sheet and plate AZ31B. The microstructure and mechanical properties of welded test plates were assessed, leading to a better understanding of microstructurat development and structure-property relationships in GTA and LB weldments in AZ31B.

The development of new creep resistant and cost effective die casting magnesium alloys such as AE, MRI, MEZ, ACM, AXJ, AJ, WE have emerged as an alternative to fulfil the actual demands in structural relevant applications as engines blocks, gear and converter boxes. However, magnesium components are in most of the cases screwed with aluminium and steel bolts, which lead the screwed joint to lose the preload force due to relaxation. This barrier limits thus the broad use of magnesium within this segment and should somehow find an adequate solution to be implemented and to help overcoming this limitation. In this context Friction Welding (FW) and particularly Friction Hydro Pillar Processing (FHPP), which can be described as a drill and fill process, appears as an alternative to widespread the use of magnesium. In this context, FHPP is intended to be used to locally reinforce mechanical fastened magnesium components.

Friction stir welding and ultrasonic welding techniques were applied to join automotive magnesium alloys to steel sheet. The effect of tooling and process parameters on the post-weld microstructure, texture and mechanical properties was investigated. Static and dynamic loading were utilized to investigate the joint strength of both cast and wrought magnesium alloys including their susceptibility and degradation under corrosive media. The conditions required to produce joint strengths in excess of 75% of the base metal strength were determined, and the effects of surface coatings, tooling and weld parameters on weld properties are presented.

The effective application of Mg alloys as automotive power train components is continuously challenged by the ability of magnesium to withstand fastener clamp load under service condition. The stiffness of a joint is strongly dependent on the elastic moduli of the members of the bolted joint. As deflections on loaded bolted steel components could be ignored at low and elevated temperature condition that of magnesium alloys cannot be overlooked. In this work bolt load retention experiments are carried out on AS41 between stresses of 40 MPa to 70 MPa and temperature of 125 °C to 150 °C. A power law creep relationship coded in finite elemental program is used to describe the time dependent stress-strain response of AS41. The parameters in this relationship are obtained by fitting typical compressive creep test results. A comparison of the model and bolt load retention experiments using load cell measuring techniques shows good agreement.

The applicability of friction stir welding to hot rolled sheet of commercial magnesium alloy AZ31 plates has been investigated. Friction stir weld joint showed mechanical strength comparable to that of base material, though the ductility remained at one half of that of the latter. The results are consistent with the microstructure which is characterized by a fine grained bond layer bounded by-intermediate grained base metals. It is found that both anodizing treatment and insertion of aluminum foil between batting faces do not degrade the joint properties at all. The results suggest that friction stir welding can be potentially applied to magnesium alloy.

Friction stir welding (FSW), being a solid-state process, is an attractive method for joining magnesium die castings. In this study, FSW of AZ91D and AM50A plates was performed both on the individual alloys and to join them together. The welds were sound and free from defects, except for small surface cracks in AM50A; a fine microstructure characterized the weld zones. The tensile properties of specimens transverse to the weld zone were measured, as were the corrosion properties. The tensile properties were somewhat lower than the base metal, with the largest percentage decrease found in the elongation of AM50A, perhaps due to the surface cracking. The corrosion resistance of the weld zone was relatively poor, most likely due to iron contamination from wearing of the tool. Further optimization of the FSW tool design and process parameters must take place to improve the reliability of FSW for magnesium die castings.

An increase in the use of magnesium (Mg) in the car manufacturing industry has raised questions concerning its weldability. Friction Stir Welding (FSW) has the advantage of achieving metallic bonding below that of the melting point of the base material thus avoiding many of the metallurgical problems associated with the solidification process. The present study presents the results of a development program carried out to investigate the response of Mg alloys AZ31 and AZ61 to different FSW tool geometries and process parameters. Temperature development across the weld zone was monitored and the produced welds have been subjected to microstructural analysis and mechanical testing. Defect free welds have been produced with optimised FSW-tool and parameters. The micro structure of the welded joint resulted in similar ductility and hardness levels as compared to that of the base material. The results also demonstrated that tool geometry plays a fundamental role in the response of the investigated alloys to the FSW process.

In this research, the feasibility of FSW dissimilar magnesium alloys was investigated. Specifically, die cast magnesium MRI-153M and AZ31 (plate) were butt-welded using the FSW technique. The effects of weld parameters (tool rotation (rpm) and weld speed) on the weld quality have been quantified in terms of hardness profile across the weld as well as tensile strength. Weld surface and cross section were also analyzed. Tensile testing showed that the welded material failed in the base material (MRI-153M) and not in the weld region. Weld cross section analysis showed void free welds were achieved at weld speeds up to 500 mm/min. Furthermore, a smooth and glossy surface ripple appeared on the weld beads and only a small amount of burr was observed. The Mg alloys were then welded together in an experimental oil pan cast in the USCAR-Magnesium Powertrain Cast Component Project. Finally, the oil pan assembly was successfully water bath-leak tested in water bath at 82.7KPa (12 psi) pressure for 3 minutes to validate the applicability of FSW.

In this study, the fatigue behavior of a magnesium AZ31 alloy in friction stir spot welds is experimentally characterized. Load control cyclic tests were conducted on single weld lap-shear coupons to determine fatigue crack characteristics. Cyclic failure modes included weld nugget pullout and full coupon separation. Good correlation was obtained between fatigue life and linear elastic fracture mechanics. In addition, in-situ fatigue tests were conducted to determine crack growth rates of the friction stir spot welds via an automated digital microscope. The experimentally measured crack growth rate suggests that the assumption of constant crack growth employed in literature is reasonable.

This paper presents the experimental results of benchmark coupon testing of monotonic and cyclic conditions on friction stir spot welded coupons of Mg AZ31 alloy. The results presented here are a product of a collaborative multinational research effort involving research teams from Canada, China, and the United States. Fatigue tests were conducted in load control at R=0.1 at two different maximum loads: 1kN and 3kN. Good agreement was found between the participating labs regarding the number of cycles to failure. Differences in the failure modes were observed for the two different loading conditions tested. At the higher load, fatigue failure was caused by interfacial fracture. However, at the lower load, fatigue cracks formed perpendicular to the loading direction, which led to full width separation. For additional comparison, the monotonic and cyclic results of the friction stir spot welds are compared to resistance spot welded coupons of similar nugget size.

Due to the negative difference effect, a special electrochemical phenomenon for magnesium and its alloys, significant errors can be introduced into corrosion rate measurements when using traditional electrochemical techniques. Also, the classical weight-loss method only provides final corrosion information (or an integrated corrosion rate), and moreover errors may easily be introduced into the final result during the removal of corrosion products and in the calculation of the corrosion rate.This paper experimentally and theoretically demonstrates the use of a hydorgen evolution method for measuring the corrosion rate of magnesium and its alloys. The following are shown. 1) The amount of hydorgen collected is equal to the amount of magnesium dissolved. 2) The collection of evolved hydorgen can reveal the instantaneous corrosion rate, and the changing corrosion behaviour of magnesium and ists alloys. 3) Smaller theoretical and experimental errors are introduced by the hydrogen evolution collection method. Most important, this method is easy to set up and operate, and is suitable for a quick corrosion behaviour of magnesium and its alloys.

A novel technique for measuring the intrinsic corrosion rate of magnesium alloys has been developed. As a magnesium alloy sample dissolves in a 5% NaCl solution, the dissolution rate is determined by measuring the amount of HCl added to the NaCl solution to control the pH between 5 and 7. The corrosion rate is determined from the slope of the curve where the dissolution rate reaches a steady state. The technique was used to compare the corrosion behavior of newly developed creep resistant Mg-Al-Ca (AC) alloys with several known magnesium alloys. It was shown that the corrosion rate of AC52 (Mg-5%Al-2%Ca) is comparable to AZ91, meeting one of the several design criteria for new, creep-resistant alloys. This technique provides a fast way to screen the effect of small composition changes on corrosion behavior of Mg alloys. Because of the short test time, this technique provides a powerful tool to accelerate alloy and product development with Mg alloys.

Magnesium is easy to be corroded because it has small standard electrode potential (SEP). In magnesium alloys, the corrosion resistance of dispersoids hasn’t yet evaluated quantitatively as the SEP of dispersoids wasn’t almost investigated. This study surveyed the surface potential difference (SPD) between α-Mg in AZ91D magnesium alloy and the dispersoids in that alloy by using Scanning Kelvin Probe Force Microscope (SKPFM). The corrosion resistance was evaluated and correlated with SPD, where this measured SPD represents the difference of work function between α-Mg and the dispersoid. At this experiment, it was obtained that the difference of SEP generally increases as the SPD increases. The good correlation between difference of SEP and SPD was obtained. The SPD between α-Mg and Mg₁₇Al₁₂ or Al₆Mn in AZ91D Mg alloy is measured. In addition, in order to obtain the reference of SPD, the area of α-Mg only and the interface area between Fe and α-Mg were respectively scanned. The result shows that Mg₁₇Al₁₂ has small SPD to α-Mg and that the SPD between Mg₁₇Al₁₂ and α-Mg is mostly the same as that in α-Mg. Therefore, Mg₁₇Al₁₂ is considered of no effect on corrosion. On the other hand, Al₆Mn degrades corrosion resistance because the SPD between Al₆Mn and α-Mg is as large as that between Fe and α-Mg.

Due to the improved corrosion resistance of magnesium alloys brought forward by the development of the high purity grades 20 years ago, the use of die cast magnesium components has moved towards more and more demanding applications. The corrosion resistance is sufficient so that magnesium is used in the under-body environment of vehicles without additional general corrosion protection, although special attention must be given to galvanic corrosion protection. There has recently been an increasing interest in both semi-exterior and exterior automotive parts. Since magnesium alloys are not compatible with standard automotive phosphate treatments, the parts need to be pre-coated prior to assembly. For such components, the challenges are to find efficient, environmentally friendly pre-treatments and robust coating systems that can maintain their integrity through the assembly process. The present paper reviews some of the established and newly developed methods for corrosion protection and finishing of die cast magnesium automotive parts.

Magnesium alloys are susceptible to galvanic corrosion. Consequently, it is often necessary to apply coatings to magnesium components for isolation purposes. However, previous publications suggest the effectiveness of commercial coatings can vary widely. Therefore, an extensive corrosion screening study was performed to evaluate pre-treatment and coating systems currently available for use within the automotive industry. This paper focuses on a selection of conversion and anodized coatings. In many instances, these coatings were used in conjunction with either powder coat or an electro-coat to assess the additional protection offered by a supplemental barrier. Scribe test results and corroded area determination after accelerated corrosion testing are presented and used to quantify the pre-treatment performance. These results are supplemented by DC polarization measurements to determine the level of passivation. Finally, SEM micrographs were used to determine coating thickness variability and morphology. The overall performance of each pre-treatment and coating is then assessed with respect to corrosion protection and robustness.

Magnesium and its alloys have excellent physical and mechanical properties due to their high strength-to-weight ratio and are ideal for various applications in automotive, aerospace and defense sectors. However, Mg alloys are also highly susceptible to corrosion under harsh environments. Owing to this carcinogenicity as well as environmental impact of hexavalent chromium fueled by stringent environmental regulations, an environmentally green alternative to the carcinogenic hexavalent chromium coatings on magnesium is due.In this work, a novel trivalent chromium based conversion coating has been developed to improve the corrosion resistance and paint adhesion properties of Mg alloys. Coating performance characterization has been investigated via hydrogen evolution, weight loss measurement and electrochemical corrosion analysis techniques. Results have shown that the novel environmentally green trivalent chromium based coating on magnesium has indeed performed comparable to hexavalent chromium and thus establishing a viable alternative.

This paper describes the results of a study on the corrosion behaviour of die-cast magnesium alloy type AZ91D coated using the KERONITE™ process. This process is a commercially available and environmentally friendly electrolytic coating method applicable to all types of magnesium alloys. The process involves creation of a hard ceramic oxide layer on the surface of a light substrate alloy by plasma electrolytic oxidation in a low concentration alkaline solution.Corrosion performance was assessed in a 3.5% NaCl solution using an accelerated electrochemical potentiodynamic polarisation method, and a salt spray exposure. Parallel tests were also carried out on an uncoated AZ91D alloy. The study demonstrated an improvement in the corrosion resistance of Keronite coated AZ91D magnesium alloy.

It is well known that magnesium alloys, in close proximity to other alloys, are susceptible to galvanic corrosion. Combined with this fact, in automotive applications, it is rare that magnesium will be present in the absence of other alloys such as steel or aluminum. Therefore, in wet applications, where the galvanic cell is completed, it is necessary to isolate the magnesium in order to prevent accelerated corrosion. There are numerous commercial pre-treatments available for magnesium, however this paper focuses on conversion coatings in conjunction with a spray powder coat. By means of example, results for a hem flange joint on an AM50 die cast magnesium door structure will be presented. The outer door skin is an aluminum alloy hemmed around a cast magnesium flange. An adhesive is used between the inner and outer to help with stiffness and NVH (Noise, Vibration and Harshness). Results from bonded lap-shear coupon tests that have been exposed to accelerated corrosion cycles are presented. A second phase of this work considered a surrogate hem flange coupon, which was similarly exposed to the same accelerated corrosion cycle. Results from both of these tests are presented within this paper along with a discussion as to their suitability for use within automotive applications.

Magnesium alloys are of growing interest for a number of applications in a range of industries because of their low densities and high specific strength. An impediment to their increased application is their low resistance to both wear and corrosion compared to that of steel or aluminium alloys. This is due to their relatively low surface hardness and high chemical affinity for numerous elements respectively.This paper describes the results of experiments investigating Nd:YAG laser cladding of AS21 magnesium alloy with a mixture of aluminium silicon (40 % wt) and tungsten carbide (60 % wt) powder to improve its wear properties. The effects of laser power, scan speed, powder feed rate, and laser spot size on the clad layer thickness were examined. The results indicate that crack and porosity free clad layers up to 2 mm thick can be produced under optimum laser and powder mass flow rate conditions

This manuscript summarizes recent studies on the corrosion behavior of Mg and Mg alloys in simulated biological environments, as well as interactions between corroding Mg (alloy) surfaces and cells. The influence of different types of simulated body solutions on the corrosion behavior of Mg is discussed. The effects of different types of chemical surface treatments on cell adhesion and spreading is presented. Moreover, possible routes to further optimize the corrosion and the biological performance of Mg alloys by surface modification are discussed.