Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding (FSW). The microstructures and mechanical properties of the welded joint were investigated. The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains. The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone. The ultimate tensile strength of AZ31B magnesium alloy added with 0.5 wt.% Ce was 270.41±4.48 MPa, and its elongation to fracture was (17.71±0.60)%. The ultimate tensile strength of FSW joint was 237.97±2.53 MPa, and its elongation to fracture was 6.63±0.60%. The fracture locations of FSW joint were in the heat-affected zone. The ductile fracture was the main fracture mode. The ultimate tensile strength of the sample along the direction of the weld was 270.02±1.45 MPa, and its elongation to fracture was (17.08±0.39)%. The microhardness in the weld nugget zone was slightly lower than that in the base metal. The microhardness in the thermo-mechanical affected zone and heat affected zone was lower than that in the weld nugget zone. The microhardness increased from the surface to the bottom of the weld.