PREPARATION OF Mg-6Zn AND A STUDY ON ITS RESISTANCE-SPOT WELDING MICROSTRUCTURE AND MECHANICAL PROPERTIES

This article investigates the effect of different welding currents on the microstructure, nugget diameter, and tensile strength of a 1.5-mm-thick Mg-6Zn magnesium alloy through resistance-spot welding. A detailed analysis is conducted using various experimental techniques, including tensile testing, microhardness testing, optical microscopy, and scanning electron microscopy. When the current is 16 kA, the hardness and peak value are 62.45 HV and 1.108 kN, respectively. Therefore, when the current is 16 kA, the hardness in the fusion zone is the smallest and the peak value and fusion diameter are the largest, which is the optimal spot-welding parameter. The welded joint is mainly composed of a fusion zone and a heat-affected zone. The microhardness of the fusion zone is the highest, significantly higher than that of the heat-affected zone and the base material. The fusion zone is mainly composed of equiaxed and columnar dendrites, and grain coarsening is observed in both the fusion zone and the heat-affected zone. There are two types of fracture modes for welded joints. When the size of the weld core is small, it is the joint surface fracture, and when the size of the weld core is large, it is the button fracture. We conducted in-depth research on the microstructure characteristics, fracture morphology, and microhardness distribution of the joint.