Effect of Ca and Sr on the compressive creep behavior of Mg–4Al–RE based magnesium alloys
Introduction
Magnesium alloys such as AZ91D, AZ31 and AM60B are widely applied in the automotive and aerospace industries due to low density, good corrosion resistance, superior die castibility, good balance of ductility and strength at room temperature, high specific strength and specific stiffness [1], [2], [3], [4]. However, the commercial utilization of magnesium alloy is limited by the poor creep resistance and poor mechanical strength at temperature about 150 °C [5], [6], [7]. The poor creep properties of Mg–Al based alloy are caused by the softening of β-Mg17Al12 phase at elevated temperature, and the grain boundary sliding and grain deformation of the magnesium alloy are not hindered by the coarsening β-Mg17Al12 phase.
Attempts were made to improve the creep resistance of magnesium alloys by adding a small amount of alloying elements for the formation of strengthening phases. Zhang et al. [8], [9] concluded that Al11RE3 with relatively thermally stable precipitated along the grain boundary provided a considerable deformation when the alloys underwent high stress and low temperature. The A111RE3 was decomposed to Al2RE with high thermally stable at elevated temperature, and the grain was refined by Al2RE acting as the nucleation site for α-Mg phase [10], [11], and the grain deformation was restrained [12], [13]. Nayyeri and Mahmudi [14], [15] found that the thermally stable second phase particle Mg3Sb2 (1280 °C) occurred in the interior parts of the dendrites and at the grain boundary regions, and it was benefit from both strengthening of the grains and grain boundaries during creep deformation at high temperatures. Zhang et al. [16], [17] revealed that the grain size and polygonal morphology of magnesium alloy was improved by the Mg2Si (1085 °C), and then the mechanical properties of magnesium alloy were increased by precipitation hardening by Mg2Si. Celikin et al. [18], [19] demonstrated that the high thermal stability intermetallic Al–Sr phase in the interdendritic regions exerted a strengthening effect in the primary creep stage, and the growth of grains was hindered by Al4Sr. The alkaline-earth elements (Ca and Sr) and the rare earth elements (La/Pr/Ce or Nd/Pr) are considered as outstanding options to improve the creep resistance of Mg–4Al–RE system alloys. Amounts of effort are made to estimate the creep resistance of Mg–4Al–RE system alloys [20], [21], but the compressive stress method is seldom reported.
In the paper, the compressive creep property of a quaternary Mg–4Al–RE–1.2Ca alloy and a quinary Mg–4Al–RE–1.2Ca–0.2Sr alloy was investigated. The creep parameters and creep constitutive equations of AEC4112 alloy and AECJ411202 alloy were estimated. The effect of Ca and Sr on the compressive creep behavior of AEC4112 alloy and AECJ411202 alloy was discussed.
Section snippets
Experimental details
Three AE41 magnesium alloys were prepared for the compressive creep test and the chemical compositions were tested by inductive coupled plasma (ICP) and listed in Table 1. The alkaline-earth elements and the rare earth elements in the magnesium alloys were conducted into magnesium ingot by adding master alloys of Mg–30Ca, Al–10Sr and Mg–10RE (RE = (Nd, Pr), Nd/Pr weight ratio is about 9:1) alloys. The amount of pure magnesium ingot, aluminum ingot and each master alloy was determined by the
Results
Fig. 2 depicts the compressive creep curves of three AE41 magnesium alloys under the temperature 150 °C and applied stress 100 MPa for 100 h. The compressive creep curve consists of decelerating creep stage and steady state creep stage, and the decelerating creep stages of three alloys are sustained for about 5 h and followed by the steady state creep stage with the characteristic of linear creep curve. The creep resistance of magnesium alloys is evaluated by the creep rate that is defined as the
Creep parameters
The relationship between steady state creep rate , stress exponent n and creep activation energy Qc of the polycrystalline material can be expressed by an empirical equation [22]:where A is the structure-dependent constant, σ is the nominal normal stress, n is the stress exponent determined by deformation mechanism, and Qc is the creep activation energy, R is the gas constant and T is the absolute temperature. Eq. (1) is converted to Eq. (2) by taking the logarithm:
Conclusions
The compressive creep resistance and the constitutive equations of AE41 based magnesium alloys are estimated, and the creep mechanism of the magnesium alloys is analyzed. Following conclusions are drawn:
- (1)
The compressive creep resistance of AEC4112 alloy and AECJ411202 alloy is superior to AE41 alloy. The steady state compressive creep rates are increased with increasing temperature and applied stress.
- (2)
The creep constitutive equations of AEC4112 alloy and AECJ411202 alloy are written as = 2.0276
Acknowledgments
This research was financially supported by the funding of the National Natural Science Foundation of China (Grant No. 51275060), the Science and Technology Program of Jiangsu Province of China (Grant No. BK20141228) and the Science and Technology Program of Suzhou (Grant Nos. SYG201421, SYG201348, SYG201251 and 13KJB430001).
References (26)
- et al.
Research for a “new age of magnesium” in the automotive industry
J Mater Process Technol
(2001) - et al.
Applications of magnesium alloys in automotive engineering
- et al.
The microstructure and impression creep behavior of cast AZ80 magnesium alloy with yttrium additions
Mater Des
(2012) - et al.
Effect of substituting cerium-rich mischmetal with lanthanum on microstructure and mechanical properties of die-cast Mg–Al–RE alloys
Mater Des
(2009) - et al.
Microstructural stability and high-temperature mechanical properties of AZ91 and AZ91 + 2RE magnesium alloys
Mater Des
(2011) - et al.
Microstructural analysis of the creep resistance of die-cast Mg–4Al–2RE alloy
Scr Mater
(2008) - et al.
Microstructure and mechanical properties of as-cast Mg–Al–Sn–Y–Nd alloy
Mater Des
(2012) - et al.
Effect of Ca and Sr on microstructure and compressive creep property of Mg–4Al–RE alloys
Mater Sci Eng, A
(2014) - et al.
Comparative study of creep of the die-cast Mg-alloys AZ91, AS21, AS41, AM60 and AE42
Mater Sci Eng, A
(2001) - et al.
Effects of Sb additions on the microstructure and impression creep behavior of a cast Mg–5Sn alloy
Mater Sci Eng, A
(2010)
Effects of Sb addition on the modification of Mg2Si particles and high-temperature mechanical properties of cast Mg–4Zn–2Si alloy
J Alloys Compd
Creep behavior of the die-cast Mg–Al alloy AS21
Scri Mater
High temperature tensile properties of modified Mg/Mg2Si in situ composite
Mater Des
Cited by (39)
Effects of Gd/Nd ratio on the microstructures and tensile creep behavior of Mg–8Al–Gd–Nd alloys crept at 423K
2021, Journal of Materials Research and TechnologyInvestigation of tensile creep behavior of Mg–Gd–Y–Zr alloy based on creep constitutive model
2021, Materials Science and Engineering: ACitation Excerpt :Therefore, doping multiple elements is adopted to improve the elevated temperature mechanical properties of Mg alloys through the formation of precipitated phases with high melting temperature and thermal stability. The common alloying elements for heat resistant magnesium alloys include Al, Si, alkaline earth (Bi, Ca, Sr), rare earth (La, Pr, Ce, Nd, Gd, Y) [7–14], etc. The heat resistance of Mg–Gd and Mg–Y series alloys were obtained by large solubility of Gd and Y in α-Mg matrix that promoted the formation of Mg–Gd and Mg–Y phases [15,16].
Microstructural evolution of Mg-Al-Re alloy reinforced with alumina fibers
2020, Journal of Magnesium and AlloysCitation Excerpt :It shows that the probability of Al-Ce intermetallics decreases from Al11Ce3, Al3Ce to Al2Ce and Al2Ce, where the highest melting point AlxCey phase, seems to be the most unstable and would be presented at the melt first [34–37]. Actually, all those three phases have been observed in various process procedures [10–29]. In those reports, Al11Ce3 has been observed in almost all studies on AE44 and seem to be the most stable phase, for AE44 with a low fraction of Al11RE3 has better high-temperature properties [28,40].
Role of Ca on the corrosion resistance of Mg–9Al and Mg–9Al–0.5Mn alloys
2019, Journal of Alloys and CompoundsInfluences of Al and high shearing dispersion technique on the microstructure and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy
2019, Materials Science and Engineering: AUpdate of thermodynamic descriptions of the binary Al-Sn and ternary Mg-Al-Sn systems
2019, Calphad: Computer Coupling of Phase Diagrams and Thermochemistry