热处理对AZ91D铸造镁合金疲劳性能的影响

Influences of Heat Treatment on Fatigue Properties of AZ91D Cast Magnesium Alloys

研究了固溶和固溶后时效处理对铸造AZ91D镁合金显微组织、常规力学性能和高周疲劳行为的影响。结果表明:AZ91D镁合金经固溶处理后,抗拉强度、疲劳强度和伸长率大大增加,但屈服强度降低;合金经固溶+时效处理后,抗拉强度、屈服强度提高,但伸长率和疲劳强度稍有下降;疲劳断口分析表明:疲劳裂纹萌生于合金表面或亚表面的气孔、夹杂或缩松处,未处理合金疲劳断口表现为准解理断裂,固溶处理后的合金具有较多的韧性特征,而固溶+时效处理的合金表现为脆性解理断裂形式。

The effect of solid solution and solid solution plus aging treatment on the microstructure, conventional mechanical properties and high cycle fatigue behaviors of cast AZ91D magnesium alloys were investigated. The results show that the tensile strength, fatigue strength and elongation of cast AZ91D magnesium alloy are increased by solid solution treatment. However, the yield strength decreases after solid solution treatment. The tensile strength and yield strength of the alloy increase after solid solution plus aging treatment, while the elongation and fatigue strength slightly decrease. The analysis of the fatigue fracture surface of test alloys shows that the fatigue crack of AZ91D alloys initiates at the gas hole, inclusions and dispersed shrinkage under surface and subsurface. The fatigue fracture surface shows the quasi-cleavage fracture for as cast alloy, while shows the toughness fracture features for the alloy after solid solution treatment and the brittle cleavage fracture characteristics for the alloy after solid solution and aging treatment.