Microstructure and Mechanical Properties of Die-Cast Magnesium Alloys

Microstructure and Mechanical Properties of Die-Cast Magnesium Alloys
　　At present, the die casting technology has been widely used for the production of magnesium alloy structural components. However, due to low strength of magnesium alloys at high temperatures, how to improve both room temperature and high temperature strengths has become an important subject in development of magnesium alloys. In this dissertation, the influence of element Y on microstructure, tensile properties and low-cyclic fatigue behavior of die-cast Mg-Al-Y alloys has been studied by microstructure observation, tensile and low-cycle fatigue tests. Neodymium Magnets In addition, the effect of Ca on microstructure and mechanical properties of AE42 alloy have been investigated. The aim of this study is to provide a reliable theoretical reference for both development and engineering application of die-cast magnesium alloys containing RE elements.The observations on microstructure reveal that the grains in die-cast Mg-Al-Y alloys become finer with increasing the content of Y.
　　However, the coarse Al-Mg eutectic structures can be also observed in the microstructure of die-cast Mg-Al-Y alloys. It can be noted that the microstructure of die-cast AE42-Ca consists ofα-Mg, Al11RE3 and Al2Ca.The results of tensile tests indicate that the tensile properties of die-cast Mg-Al-Y alloys not only depend on experimental temperature, but also the content of rare element Y. At room temperature and 200℃, the ultimate tensile strength of the die-cast Mg-Al-0.5wt%Y alloy is the highest, while the die-cast Mg-Al-1.0wt%Y alloy shows the highest ultimate tensile strength at 150℃. At room and 150℃, the yield strength of the die-cast Mg-Al-1.0wt%Y alloy is the http://www.999magnet.com/ highest, while the die-cast Mg-Al-0.5wt%Y alloy shows the best yield strength at 200℃. It has been found that the die-cast AE42-0.8%Ca shows the best tensile strengths at room temperature, while the die-cast AE42-0.5%Ca and AE42-0.2%Ca alloys exhibit the best tensile properties at 150℃and 200℃respectively. In addition, aging treatment can further enhance the tensile properties of the die-cast AE42-Ca alloys.The results of low-cyclic fatigue tests show that the die-cast Mg-7%Al-0.5%Y alloy exhibits the same extent of cyclic strain hardening at various total strain amplitudes. For the die-cast Mg-7%A1-0.5%Y alloy, the relations between the elastic strain amplitude, plastic strain amplitude and reversals to failure can be described by the Basquin and Coffin-Manson equations, respectively. The SEM analysis on the fracture surfaces shows that the fatigue cracks initiate at the casting defects near the surface of the fatigue specimens, and propagate in a transgranular mode.