中文摘要：

研究机械振动对消失模铸造AZ91合金微观组织和力学性能的影响，并分析凝固过程中机械振动细化晶粒的机制。结果表明：机械振动能显著地细化消失模铸造AZ91合金的组织，合金组织由α-Mg固溶体、沉淀Mg17Al12和新相Al13Mn12组成，其铝锰相有别于不施加振动时的Al32Mn35相；机械振动较大幅度改善了合金的力学性能，当激振力为1．5kN时，AZ91合金抗拉强度相对于不振动时提高27％，其合金力学性能最优；而当激振力进一步增加时，由于组织中存在着微观缩松，强度有所降低。机械振动法通过增大过冷度、剪切力碎化枝晶和使枝晶臂熔断来细化晶粒。

英文摘要：

The effects of mechanical vibration on the microstructure and mechanical properties of AZ91 magnesium alloy were investigated via lost foam casting （LFC）. The refining microstructure mechanism of the casting alloy under vibration force was also analyzed. The results show that mechanical vibration can produce finer dendrite in AZ91 alloy. The microstructure of AZ91 alloy via LFC consists of dominant α-Mg and β-Mg17 Al12 as well as a new phase A113 Mn12 which is different from Al32 Mn25 in the untreated AZ91 alloy via LFC. The mechanical vibration can also strongly improve the mechanical properties of AZ91 alloy. The value of tensile strength of AZ91 alloy produced under vibration force of 1.5 kN is increased by 27% compared to that under vibration force of 0 kN and the mechanical properties is ultimate. However, the strength of AZ91 alloy drops due to the presence of the microporosity in the casting when the vibration force is increased. Mechanical vibration produces finer dendrite by increasing the undercooling degree, breaking dendrite into pieces by shear stress and melting the secondary dendrite arm.