Simultaneous improvement of strength and plasticity for LA103Z dual-phase Mg–Li alloy welded by friction stir welding

LA103Z magnesium-lithium alloy is a new type of ultra-light metallic alloy, which is widely used in defense, military and civilian fields. In this paper, LA103Z joints with superior tensile strength and plasticity were fabricated by friction stir welding (FSW). The relationship between microstructure and tensile strength of the joints is investigated. Though the existing the phases, namely α-Mg, β-Li, γ and θ are not changed, due to recrystallization effects, the α-Mg phase morphology is transformed from block to spherical shape, while being also refined. Moreover, the content of nano-scale θ phase increases, with a concomitant decrease of the γ phase, occurs in both the stir zone (SZ) and heated affected zone (HAZ). Additionally, the β-Li phase is recrystallized and transformed into equiaxed grains from the banding grains. The microhardness is increased from 55Hv to 70Hv and 76Hv in HAZ and SZ, respectively. The ultimate tensile strength and the average elongation of the joint are 216 MPa and 63 %, which reach 124 % and 115 % of the base metals (BM), respectively, since the cooperative effect of the equiaxed β-Li phase and the nano-scale θ phase.