中文摘要：

对汽车用AZ91镁合金进行了挤压铸造、等温模锻成形和人工时效处理,研究了不同工艺条件下合金的组织和性能演变规律,并探讨了其作用机理。结果表明,挤压铸造AZ91镁合金主要由初生α-Mg基体、离异共晶β相（Mg17Al12相）和二次析出β相组成;等温模锻处理后的合金中存在难变形区、大变形区和小变形区,随着变形量的增加,在难变形区和小变形区的动态再结晶体积分数有明显增加的趋势,大变形区主要由细小的动态再结晶晶粒组成;等温模锻处理后,不同变形量下合金的力学性能较铸态合金均有所提高,且随着变形量的增大,合金的抗拉强度、屈服强度、断后伸长率和硬度呈现不断增加的趋势;等温模锻和人工时效处理后的AZ91镁合金综合性能明显高于挤压铸态合金。

英文摘要：

Evolution of microstructure and properties of magnesium alloy AZ91 under different technological conditions for automobile were studied by extrusion casting,isothermal die forging and artificial aging treatment,and the mechanism was discussed. The results show that the squeeze cast magnesium alloy AZ91 is mainly composed of primary α- Mg matrix,divorced eutectic phase（ Mg17Al12phase） and βprecipitated phase. After isothermal die forging,the hard deformation zone,large deformation zone and small deformation zone exist in the alloy,and the recrystallization volume fraction in the hard deformation zone and the small deformation zone increases significantly with the increase of deformation. Thus,the large deformation zone is composed of fine dynamic recrystallization grains. Furthermore,the mechanical properties of the alloy with different deformations are improved compared to the cast alloy,and the tensile strength,yield strength,elongation and hardness show a rising trend with the increase of deformation. Finally,the comprehensive performance of magnesium alloy AZ91 after isothermal forging and heat treatment is higher than that of squeeze cast alloy.