Microstructure and Mechanical Properties of Laser Welded Joints ofLZ92 Magnesium Lithium Alloy

LZ92 magnesium lithium alloy plate with thickness of 2 mm was welded by CO₂ laser, and the microstructure, phase composition, micro-hardness and tensile properties of the welded joint were studied. The results show that LZ92 magnesium lithium alloy welded joint had good formability, and no obvious pores and cracks were found in the weld. The phase composition of the base metal and the weld was the same, consisting of α phase, β phase and intermediate phase Mg₇Zn₃. The base metal was composed of equiaxed β phase and dendritic and granular α phase; the heat-affected zone was composed of coarse β phase and a few fine granular α phase; a large amount of fine needle and granular α phases evenly distributed in the β phase in the weld and the grain boundaries of β phase disappeared. The hardness of the weld was the highest, followed by the base metal, and the hardness of the heat affected zone was the lowest. The tensile strength of welded joint was 158 MPa, which was 86.8% that of the base metal, and the elongation was 27%. The tensile fracture of the welded joint was located at the fusion line between the heat-affected zone and the weld; the fracture was composed of dimples and cleavage surfaces, indicating the fracture form was a mixed fracture.