Effect of spherical electrode radius on crack in resistance spot welding of aluminum alloy 2A12

Selecting 100, 75, 50 and 25 mm as the radius of spherical electrode, spot welding experiment of the aluminum alloy 2A12 sheet with thickness of 1 mm was performed on the three-phase secondary rectification welding machine. Using optical microscopy and scanning electron microscopy, the microstructure and crack characteristics of the nugget were observed. The low-magnification measuring microscope and the tensile test machine were used to test the nugget diameter and the tensile-shear strength of the weld, and then the effect of spherical electrode radius on the crack distribution, formation mechanism, nugget diameter, and the tensile-shear strength of spot welding joint of the aluminum alloy 2A12 were investigated. The results show that as the spherical electrode radius increases, more likely the cracks occur in the nuggets, and nugget diameters present decreasing tendency. When the spherical electrode radii are 75 and 100 mm, respectively, the intergranular longitudinal solidification crack locates in the middle of the nugget, which almost transverse across the whole weld nugget, and liquation crack is visible in the heat-affected zone (HAZ), but there is no transverse crack in the nugget.