Microstructure, Mechanical Properties, and Corrosion Behavior of Mg–Al–Ca Alloy Prepared by Friction Stir Processing

Friction stir processing (FSP) was used to modify the microstructure and improve the mechanical properties and corrosion resistance of an Mg–Al–Ca alloy. The results demonstrated that, after FSP, the grain size of the Mg–Al–Ca alloy was decreased from 13.3 to 6.7 μm. Meanwhile, the Al8Mn5 phase was broken and dispersed, and its amount was increased. The yield strength and ultimate tensile strength of the Mg–Al–Ca alloy were increased by 17.0% and 10.1%, respectively, due to the combination of fine grain, second phase, and orientation strengthening, while the elongation was slightly decreased. The immersion and electrochemical corrosion rates in 3.5 wt% NaCl solution decreased by 18.4% and 37.5%, respectively, which contributed to grain refinement. However, the stress corrosion cracking (SCC) resistance of the modified Mg–Al–Ca alloy decreased significantly, which was mainly due to the filiform corrosion induced by the Al8Mn5 phase. SCC was mainly controlled by anodic dissolution, while the cathodic hydrogen evolution accelerated the SCC process.