Strengthening and Joining by Plastic Deformation

Thick-walled cylindrical components are used in many industries, e.g. oil and chemical industries, artillery industries and nuclear power plants for withstanding high pressure or thermal gradient. Such components are subjected to autofrettage prior to their use in service, which increases their load carrying capacity as well as fatigue life. The fatigue life of the cylinder is important when the cylinder is subjected to a fluctuating or repeated pressure. Thermal autofrettage is a potential process capable of increasing the pressure carrying capacity as well as the thermal gradient capacity of thick-walled cylinders. This is achieved by employing a radial thermal gradient across the wall thickness of the cylinder. Due to the beneficial compressive residual stresses generated at and around the inner wall of the cylinder as a result of unloading of the thermal gradient, the thermally autofrettaged cylinder enhances the load carrying capacity as well as the fatigue life. Further enhancement in the fatigue life can be achieved by combining thermal autofrettage with shrink-fit. In this work, the fatigue life analysis of the thermally autofrettaged cylinder with shrink-fit is carried out. The analysis of thermal autofrettage is based on the assumptions of a generalized plane  strain condition and Tresca yield criterion.

This chapter highlights the fundamental deformation and fracture mechanism of an engineered ultrafine-grained (UFG) material developed by a combination of cryorolling and short-annealing treatment. The UFG material developed by cryorolling possesses superlative tensile strength. However, the ductility and strain hardening potential of the material is found to be low, reducing its manufacturing capabilities. Controlled post-deformation annealing results in a combination of good strength and ductility. The anisotropic property of the material is also improved after short-term annealing. These properties have been attributed to the unique equiaxed, thermally stable microstructure comprising of high-angled nanometric grains. The various mechanical properties have been experimentally evaluated by performing the tensile test at all three different processing conditions (base, cryorolled, annealed) and the corresponding strain hardening potential, fracture behaviour and anisotropic properties have been systematically investigated. These properties have been correlated with the microstructural features of the material. This has been achieved by mechanical testing and characterisation of the material by employing transmission electron microscopy, fractographic analysis and determination of mechanical anisotropy coefficient (Lankford coefficient). Finally, a case study on the improved microforming abilities of UFG material over coarse-grained material has been presented.

The electromagnetic pulse crimping is a high energy, high strain rate, high velocity, and green materials joining or surface coating technique. Joining of dissimilar materials is difficult due to their physiochemical properties that are seldom compatible or similar. Therefore, electromagnetic pulse crimping which is solid-state joining technique can be an alternative for joining dissimilar materials. In the present work, composite rods were produced by the electromagnetic pulse crimping technique, which was characterized by a uniform crimping of the flyer tube on the base rod perimeter. The materials used were Al 1050 as flyer tube and dual-phase (DP) steel as a base rod. Numerical simulations were carried out for finding out the optimized parameters for crimping and then experiments were conducted on the optimized parameters. The results obtained from the simulations revealed that for the successful crimping, a minimum value of collision velocity, plastic strain, electromagnetic pressure, and standoff distance must be maintained. The post-process current obtained from the simulations and first peak of the discharge current measured in the experiments was compared. The variation in the maximum value of discharge currents in simulations from the experimental values was found to be 2, 3, and 7% at 2.5, 2.6, and 2.9 kJ of discharge energy. The outer diameter of the successfully crimped samples was measured and compared with the outer diameter obtained from the simulations and found a maximum of 6.6% variation in the simulation value from the experimental value. The optical microscope image was analyzed and it was found that the Al-tube was crimped on the DP steel rod with a negligible gap. Further, pullout tests and hardness tests at the interface were performed to test the strength and hardness of the joints, respectively.

Age hardenable, high-strength aluminium alloys are used majorly in aerospace, defence, marine and automobile components because of their excellent strength-to-weight ratio and better corrosion resistance. To join such nonferrous alloys, friction stir welding (FSW) is a special technique, which uses the phenomenon of friction and deformation while joining in the solid state. The joint sections of 2XXX, 6XXX and 7XXX series of aluminium alloys are susceptible to microstructural changes during FSW due to their ageing characteristics. These changes further aggravate the problem of mechanical engineering properties, and especially the corrosion resistance of these alloys. In the present work, focus is kept on the effect of post-weld heat treatments (PWHT) such as retrogression and re-ageing (RRA) and stabilization with double ageing (SDA) on mechanical properties, electrical conductivity and exfoliation corrosion resistance of AA 7075 aluminium alloy FSW joints.

Metal/polymer/metal multi-layered materials have shown promising properties because of lightweight characteristics in automotive industries. Joining of these materials is difficult by conventional methods due to large difference in their physical and chemical properties. In the present work Friction Stir Spot Welding (FSSW) of AA5052-H32/HDPE/AA5052-H32 sandwich sheet is done. The objective is to analyse the influence of tool plunge depth on the joint behaviour. This is accomplished through joint characterization by evaluating mechanical performance, hook and flash formation, grain size, temperature measurement, and hardness distribution. Lap shear test, cross-tension test, peel test, and uni-axial tensile tests are conducted. A comparison between bimetallic and sandwich sheet has also been done. First, for joining sandwich sheets, the optimum plunge depth is 3.6 mm and greater. Adequate joint strength and extension at failure are obtained in this range. The joint strength does not depend on hook geometry, rather it depends on bond width and joint hardness. Second, though the joint strength of sandwich sheets is reduced as compared to bimetallic, the flash formed is minimised in sandwich sheets. The deformed material gets accommodated in the core layer region to reduce the flash formation. Finer grains are seen in sandwich sheet due to lesser peak temperature. Nugget pull out failure is commonly seen after testing and is independent of test method and the plunge depth.

The chapter focuses on the welding of thermoplastic polymers. The use of thermoplastics has increased tremendously in the manufacturing industries due to their light-weight characteristic. A detailed study regarding the polymers has been presented and the importance of thermoplastics has also been outlined. The joining technique which has been used in the present work is Friction Stir Welding (FSW). FSW has been one of the major achievements in the field of current welding technologies. Since its invention, the process has been under tremendous research and has been employed to join different metallic alloys of aluminium, magnesium, copper, titanium, etc. The process has also been used to join materials in different joint configurations. Recently, it has been used to weld the thermoplastic materials. An introduction to the FSW technique, the working elements of the process and its constituents have been presented in the chapter. Before the discussion of application of FSW to thermoplastic joining, the other available methods to join thermoplastics such as adhesive bonding and mechanical fastening have been discussed. The literature available with respect to the joining of thermoplastics using FSW has been discussed followed by an experimental study on high density polyethylene (HDPE) sheets. The results of the study have been presented and the relevant conclusions have been drawn.

This research presents the enhancement of mechanical properties of friction stir welded portion of aluminium alloy 6061 by incorporating additional reinforcing particulates of silicon carbide and aluminium oxide at weld interface. Friction stir welding (FSW) of AA6061, each plate of 200 mm × 100 mm × 4 mm thickness with silicon carbide and aluminium oxide as reinforcement at weld interface in four different volume proportions and without reinforcement are performed on vertical milling machine. In the present research, comparison has been done between mechanical properties of silicon carbide and aluminium oxide reinforced welded joints. Silicon carbide and aluminium oxide have been added as reinforcement by creating separate geometry, at the edges, where the welding is interfaced with four different volume proportions such as 10, 15, 25 and 30%. Tool steel of H13 grade is used as friction stir welding tool. The tool has outer shoulder diameter of 18 mm, pin diameter at the top of 7 mm and 5 mm at the bottom, and pin length of 3.7 mm. A rotational speed of 1120 rpm and transverse speed of 40 mm/min were selected. Quality assessment is carried out by visual inspection and non-destructive testing using fluorescent and radiography to reveal the surface and volumetric defects. Mechanical testings including tensile test, impact test, bend test and hardness test were conducted to study the behaviour of reinforced and unreinforced friction stir welded joints. Metallurgical evaluation has been performed by capturing the microstructures of base materials and at different zones of nugget, heat-affected zone (HAZ) by optical microscope to reveal the grain size and grain refinement at different zones. The experimental results indicate that the reinforcing particulates and percentage of reinforcing particulates have a major influence on the mechanical properties of friction stir welded joint. From microstructures, it has been shown that the addition of SiC and Al₂O particles decreased the grain size and increased the strength of the joints.

Ultrasonic welding is considered to be one of the novel and innovative techniques used in semiconductor industries for several years. Recently, it has been a challenging task for the automobile industries to join soft and high thermal conductivity materials like aluminum to copper for lithium-ion battery assembly using conventional fusion welding process. The purpose of this study is to explore the effects of various process parameters like weld pressure, weld time, and vibration amplitude on the weld strength with microstructural analysis of Al–Cu ultrasonic welded joint. The results revealed that the tensile shear and T-peel strength increased with the increase in weld time and attained its maximum at 0.75 s. Afterward, these strengths were gradually decreased. Meantime, different types of microstructures with various properties and morphologies were also observed in the interface zone. The interfacial reaction between Al and Cu produces intermetallic compounds (IMCs) along with swirls and voids. From the energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) scans, it was noticed that at high weld time (0.9 s), a 1.5 μm thick IMC layer composed of Al₂Cu and Al₄Cu₉ was formed. A three-dimensional finite element (FE) model was used to find out the compressive stress distribution beneath the sonotrode knurl and the contact stress on the bottom sheet during the delay time. The present work not only illustrates a better understanding of the welding mechanism and failure behavior but also it provides an insight of ultrasonic welding toward the improvement in the quality of weld.

Magnetic pulse welding (MPW), which is uniquely advantageous in welding electrically conductive similar and dissimilar pipe fittings, is a contactless welding technology based on high-speed magnetic impulse shaping and solid-phase diffusion welding. This has proven to be an effective solution to specific manufacturing problems, especially for leak-proof dissimilar pipe joints required to sustain high pressure, which is very difficult to achieve by conventional techniques. For achieving the successful weldament, it is essential to understand the effect of various process parameters to generate proper weldability window. In the present work, the distribution of electromagnetic force and magnetic field of single-turn circular coil for MPW has been investigated using FE simulation. A three-dimensional (3D) electromagnetic FE model has been developed using commercially available ANSYS-EMAG application software. A single-turn inductor coil of Cu material is chosen for the analysis. Compression joining of tubular metallic assembly with flyer tube as Al6061 and target tube as SS304 is simulated in ANSYS Maxwell 3D to study the influence of varying process parameters like air gap between the tubes, tube thickness, and gap between the flyer tube and the coil with respect to the input voltage. FE simulation results for weld formation are verified with the analytical results and the data available in the literature. The study reveals that for effective welding, estimation of electromagnetic field and electromagnetic force has a significant role which is governed by the process parameters of applied voltage and air gap. The presented information can assist to understand process physics, coil reliability, and prediction of mechanical behavior of the workpiece.

Electromagnetic Welding (EMW) technology is a promising and new manufacturing technology for welding of stainless steel alloys and aluminium alloys for nuclear applications. It has significant advantages over conventional welding techniques. A primary characteristic of this process is the use of non-contact electromagnetic forces to achieve welding of various metal workpieces. In this process, the welding is carried out by impact, when the workpieces are accelerated towards each other by the Lorentz force, produced due to magnetic field and the induced current in workpiece. The capacitor bank is required for generating high pulse discharge current at high frequency in the coil, which generates maximum magnetic pressure on the workpiece to obtain the weld. Electromagnetic Welding machines and weld coils are designed and developed for the welding of aluminium (Al 6061) and stainless steel (SS316L) alloys. This technique enables us to join similar and dissimilar metals, which are very difficult to weld by other conventional welding techniques.