Microstructures and mechanical properties of thick AZ31 magnesium alloy welded joint by friction stir welding

10 mm thick AZ31 magnesium alloy was successfully welded by friction stir welding.The good welded joints without porosity and crack were obtained.The microstructure of friction stir welded joint and its mechanical properties were studied.The results show that fine grains formed in the center of weld zone, the grain size was different and there existed a plastic fluidity grains in the thermo-mechanical affect zone.The strength of the welded joint is more than 80% of the base metal, the impact toughness of the welded joint is better than that of the base metal, the microhardness of the welded joint is a little lower than that of the base metal.The welded joint has good mechanical properties, and friction stir welding is one of the effective method to weld thick magnesium alloy.