针对3种高Ca/Al比的 Mg-Al-Ca合金(Mg-3.7Al-3.8Ca,Mg-4.4Al-4.5Ca 和 Mg-4.9Al-5.0Ca)的超塑性行为展开研究,研究结果表明,铸态镁合金具有二次相 Al2 Ca分布于晶界的枝晶结构。经挤压后,合金的晶粒被细化,二次相也被细化为更小的粒子。这些合金在400℃时表现出很高的伸长率,Mg-4.9Al-5.0Ca 在400℃时3.6×10-4 s-1应变速率下获得最大伸长率572%。超塑性流变的变形机制为晶格扩散(DL)控制的晶界滑移(GBS)。对于挤压态 Mg-4.9Al-5.0Ca合金,大部分高温稳定相 Al2 Ca粒子尺寸为80 nm,对晶粒长大的抑制作用强烈,在晶界滑移时协调变形,因此在3种合金中 Mg-4.9 Al-5.0 Ca具有最好的超塑性。
The superplastic behavior of three Mg-Al-Ca alloys (Mg-3.7Al-3.8Ca,Mg-4.4Al-4.5Ca and Mg-4.9Al-5.0Ca)with high Ca/Al ratio was studied.The results showed that the as-cast alloys contained dendritic struc-ture with secondary phase Al2 Ca on the grain boundaries.After extrusion,the grains of the alloys were refined and secondary phase was refined into smaller particles.These alloys exhibited remarkably high elongation at 400 ℃.A maximum elongation of 572% in Mg-4.9Al-5.0Ca was achieved at 400 ℃ with the strain rate of 3.6×10-4 s-1 .The deformation mechanism of superplastic flow is lattice diffusion (DL )controlled grain boundary slide (GBS).For ex-truded Mg-4.9Al-5.0Ca,most thermally stable Al2 Ca particles were 80 nm in size,which had strong retardation effect on grain growth and coordinated deformation during GBS.As a result,Mg-4.9Al-5.0Ca has best superplasticity among the three alloys.
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