炉料微观组织对AZ91D镁合金重熔行为的影响

Effect of primary microstructure on re-melting behavior of AZ91D magnesium alloy

通过重熔化学成分相同的AZ91D压铸件和铸锭,研究了炉料组织对镁合金AZ91D金相形貌、晶粒组织及力学性能的影响。结果表明:与铸锭重熔后相比,压铸件重熔后共晶体的离异程度较大,平均晶粒尺寸较小;经过相同保温时间,压铸件重熔后的抗拉强度、屈服强度及断裂延伸率均较高;随保温时间的延长,两种炉料重熔后的力学性能均得到了提高。采用DTA分析了炉料重熔后的凝固过程,凝固过程中过冷度较小是压铸件重熔后晶粒尺寸小于铸锭重熔后晶粒尺寸的热力学原因。

The effect of heredity on structure and properties of AZ91D alloy was investigated using ingots and rejected die-casting parts with the same composition as a furnace charge. After melting the charge, the melts were held for 15, 35 and 65 rain at 720 ℃ and poured into a preheated metal mould. Solidification of re-melted furnace charge was analyzed by DTA. The results show that the different furnace charges show the noticeable difference in the grain size of the alloys and tensile properties; the mean grain size of the samples produced from the die-casting parts is smaller than those produced from the ingots for all holding times. The ultimate tensile strength, yield strength and elongation are correspondingly better for the samples made of the die-casting parts. As the holding time increases, the tensile properties of the samples, made of both kinds of the furnace charge, slightly improve. The grain size also does not noticeably vary with the increase in the holding time.