Mg-zn-al-ca, The Alloy Microstructure And Mechanical Performance

By the effect of calcium on the strength of casting ZA85 alloy ,the optimal content of Ca was ascertained,X(wt%). ZA85CaX as research object, the effect of casting and die-casting on microstructure and mechanical properties of ZA85CaX alloy ,and the effect of heat-treatments on microstructure and mechanical properties of casting and die-casting ZA85CaX alloys were studied. The optimal high temperature properties are ascertained,in order to develop a heat-resistant magnesium alloy of low cost and well die castability.The results show that the addition of a little Ca in ZA85 alloy,new phases don't form,but microstructure is fine-grained and mechanical properties are improved.When the addition of Ca is 0.6wt%,the strength effect is best,microhardness and ultimate strength at room temperature and 150℃ of ZA85 alloy increase from 105HV, 147.4MPa,140.2MPa to 117.5HV,164MPa, 149.5.The grain size of die-casting ZA85Ca0.6 alloy is finer than casting ZA85Ca0.6 alloy.The microstucture of casting ZA85Ca0.6 consists of α-Mg ,Mg₂Zn₁₁, AlMg₄Zn₁₁ and quasi-crystal,but the microstucture of die-casting ZA85Ca0.6 consists of a-Mg ,Mg₂Zn₁₁,Al₁₂Mg₁₇.The volume fraction of grain boundary phase of casting ZA85Ca0.6 decreases clearly and grain size is largened after homogenizing and solid solution treatments;the grain-boundary phase is deposited and the shape of grain-boundary phase turns into net, the second phase in grains distributes dispersively after agreing treatment.The grain size of die-casting ZA85Ca0.6 alloy increases after homogenizing treatment; the volume fraction of grain-boundary phase decreases and the grain size increases,the diffraction intensity of Al₁₂Mg₁₇ phase increases and the diffraction intensity of a-Mg and Mg₂Zn₁₁ decreases;the size and volume fraction of grain-boundary phase increase after ageing treatment.The results of mechanical property tests show:The microhardness and ultimate strength of casting ZA85Ca0.6 alloy get max.139.5HV and 213.8MPa after solid...