Double-side friction stir welding of thick magnesium alloy: microstructure and mechanical properties

A two-step double-side friction stir welding (DS-FSW) technique was proposed to join 20 mm thick Mg-Y-Nd magnesium alloy plates. FSW was first carried out on one side of the butt joint, and then the plates were left-right reversed for the other side welding. The DS-FSW joint was free of defects and the weld nugget zone (NZ) showed fine equiaxial grains. An overlap zone with ultrafine grain (∼2.19 µm) and dispersive particles existed between the two welding tracks, beneficial to the integrity of the joint. The ultimate tensile strength (σ UTS ), yield strength (σ 0.2 ), and elongation rate (δ) of the joint were 277. 6, 204.1 MPa, and 7.27%. A high joint efficiency (σ UTS ratio between the joint and parent material) was achieved at ∼82.6%.