镁/镀锌钢异种金属电阻点焊接头显微组织与力学性能OA

Welding experiments on dissimilar metals of AZ31B magnesium alloy and HC260YD+Z galvanized steel were conducted using resistance spot welding.The effects of welding current on the mechanical properties,fracture modes,and microstructure of the joints were investigated.The results show that as the welding current increases,the nugget diameter of the joint gradually increases,while the indentation depth and tensile shear force first increase and then decrease.When the welding current is low(less than 8 kA),the fracture mode of the joint is interfacial fracture.As the current increases to 10 kA,the failure mode changes to button fracture with partial nugget pull-out.The joint achieves the maximum shear strength of 3.83 kN under the welding conditions of 10 kA current,24 cycles welding time,and 2.0 kN electrode pressure.In the heat-affected zone on the magnesium side,the microstructure mainly consists of coarse equiaxed grains,while the nugget center is composed of fine equiaxed dendrites,and the edge zone is dominated by columnar dendrites.A small amount of the Mg₁₇Al₁₂ second phase precipitates at the grain boundaries within the nugget zone.Intermetallic compounds,mainly Fe₂Al₅,form at the joint interface,leading to an average hardness in the interfacial region that is higher than that on the magnesium side.