The effect of friction stir processing and post-aging treatment on fatigue behavior of Ca-added flame-resistant magnesium alloy

Friction stir processing (FSP) was applied to the microstructural modification of the extruded flame-resistant magnesium (Mg) alloy, AMX602. The as-received material exhibited microstructure, in which intermetallic compounds (IMCs) were inhomogeneously dispersed in the matrix. FSP broke up some large IMCs and resulted in homogeneous distribution of IMCs and fine grains of the matrix. The micro hardness of the FSPed material was lower than that of the as-received one because the dislocation density and hardening precipitates decreased due to the heat input during FSP. The hardness of the FSPed material increased by the post-aging treatment. However, the fatigue strengths of the FSPed and post-aged specimens were lower than those of the as-received ones. The lower fatigue strengths of the FSPed specimens were attributed to the decrease of hardness by FSP. EBSD analyses revealed that strong texture was developed by FSP. The fatigue cracks of the post-aged specimens initiated at the locations with strong texture, in which basal slip planes had an angle about 45A degrees to the fatigue loading direction. The lower fatigue strengths in the post-aged specimens were attributed to the texture-induced fatigue crack initiation mechanism.