AZ91HP镁合金疲劳裂纹扩展行为与断裂机理

Fatigue Crack Propagation Behavior and Mechanism of AZ91HP Magnesium Alloy

试验分析了AZ91HP镁合金在压铸态(F)、固溶状态(T4)和固溶-时效状态(T6)的裂纹扩展行为,并探讨了压铸态镁合金疲劳断口组织特征与裂纹扩展机制。结果表明:压铸态AZ91HP-F疲劳裂纹扩展行为与ΔK值的大小有关,ΔK值越小,断口越平滑,ΔK值越大,断口越粗糙;裂纹扩展过程存在塑性诱发裂纹闭合效应,这一效应使得裂纹扩展的Kop值增加,ΔKeff值减小,并使疲劳裂纹扩展速率与合金塑性有关,由于AZ91HP的塑性依T6、F、T4状态依次增加,导致裂纹扩展速率依次降低。

The fatigue crack propagation behavior of AZ91HP alloy in as die-cast（F）, solution treatment（T4）, and solution plus aging（ T6 ） heat treatment states was investigated. The characteristics of fatigue fracture structure and the mechanism of crack propagation for the alloy were discussed. The results show that the fatigue crack propagation behavior of the alloy is strongly affected by the value of stress intensity factor（ΔK） . With ΔK decreasing, the fatigue fracture becomes smoother and smoother. But with the increase of ΔK, the fracture becomes rougher. The plasticity-induced crack closeness effect was observed in the process of fatigue crack propagation. This effect makes the value of crack-opening stress intensity factor （ Kop ） larger, and effective stress intensity factor （ΔKef ） smaller. The crack propagation rate was inversely proportional to the plasticity of AZ91HP alloy. Because the plasticity of the alloy was increased in T6 ,F,T4 sequential order, the crack propagation rate was decreased in T6 ,F,T4 sequential order.