熔体过热处理对AZ91D镁合金组织与性能的影响

Influences of Melt Superheating Treatment on Microstructure and Properties of AZ91D Magnesium Alloy

摘要:

本文采用采用自制的电阻炉研究熔体过热温度对AZ91D镁合金凝固组织和力学性能的影响规律。结果表明：AZ91D镁合金的铸态组织随着熔体过热温度的提高由树枝晶形态向等轴晶转变，晶粒尺寸逐渐减小，超过850℃后晶粒尺寸变化不大。AZ91D镁合金的抗拉强度、条件屈服强度和伸长率均随熔体过热温度的提高呈先增大后减小的变化趋势，力学性能在850℃时达到最大值。DSC分析表明，提高熔体温度使凝固开始点温度降低，凝固区间缩小，临界晶核半径减小，增加了熔体中的过冷度，提高了熔体中非均匀形核率，是镁合金晶粒细化的主要原因。熔体过热温度的提高导致共晶温度提高，使共晶相粗大。

Abstract:

In this paper, the influences of the melt superheating temperature on the solidification structure and mechanical properties of AZ91D magnesium are studied by a home-made electrical resistance furnace. The results show that, with the increase of melt superheating temperature, the as-cast structure of AZ91D alloy changes from dendrite morphology into equiaxed grain morphology, the grain size gradually decreases, while the change of the grain size is not obviously when the melt superheating temperature exceeds 850℃. With the enhancement of melt superheating temperature, the tensile strength, offset yield strength and specific elongation increase firstly and then decreases. The mechanical properties of AZ91D reach the maximum. The analysis of DSC show that the increase the melt superheating temperature makes the beginning solidification temperature reduce, shrink the freezing range, decrease the critical nucleus radius, increase the degree of supercooling of the melt and enhance the heterogeneous nucleation rate, these are the primary reason of grain refinement in magnesium alloy. Increasing the superheating temperature will lead to the increase of the eutectic transformation temperature, hence the eutectic phase is coarse.