Microstructures and Mechanical Properties in Friction Stir Zone of Thixo-Molded AS41 Mg Alloy

摘要

The friction stir weldability of thixo-molded AS41 Mg alloy was investigated, and the microstructures and mechanical properties in friction stir zones were examined and evaluated. The non-destructive inspection by means of X-ray radiography shows that the optimum FSW condition range of AS41 alloy exists between AZ61 and AE42 alloys, and it seems that the optimum welding condition range increases with decreasing Al content in the Mg alloys. There are mainly three kinds of compounds, i.e. Mg_2Si, MnSi and Al_(12)Mg_(17), in the thixo-molded AS41 base metal, while only two kinds of compounds are found in SZ except Al_(12)Mg_(17) phase. This is because of the decomposition of Al_(12)Mg_(17) phase at the higher temperature caused by the FSW heat input. Furthermore, the average diameter of compounds in SZ decreases with increasing the traveling speed at constant rotation speed due to less heat input. The hardness in SZ is higher than that in BM, and tensile strength and elongation are both improved after welding because the stirring refines and uniforms the microstructure and intermetallic compounds.