Effects of grain size and texture on stress corrosion cracking of friction stir processed AZ80 magnesium alloy

The microstructure, mechanical properties, static and electrochemical corrosion, and stress corrosion cracking (SCC) behavior of friction stir processed AZ80 magnesium alloy were investigated, and the effects of grain size and texture on the SCC were analyzed. The results showed that fine-grained (FG) and coarse-grained (CG) specimens with the average grain size of 2.7 and 7.1 mu m was obtained via friction stir processing (FSP) underwater and in air, respectively. Both specimens exhibited the similar characteristics of basal texture. The average microhardness of FG specimen (75.3 HV) was higher than that of CG specimen (69.4 HV) in the stir zone. Grain refinement enhanced both the corrosion and stress corrosion resistances in 3.5 wt% NaCl solution. The FG specimen exhibited obvious anisotropy in SCC susceptibility when tested along the processing and transverse directions during slow strain rate tensile test. Texture softening effect accelerated the formation of pitting corrosion, and decreased the SCC performance. Fracture surface of SCC exhibited transgranular brittle fracture. SCC behavior was controlled by anodic dissolution, and the hydrogen accelerated the SCC.