Influence of sheet thickness ratio on fracture mechanisms of Al-steel resistance spot welds produced using multi-ring domed electrode

Resistance spot welds with three aluminium to steel sheet thickness ratios were welded using electrodes featuring a plurality of rings and multiple solidification weld schedules. The average shear strength of the intermetallic layer was measured directly using a mini-shear test while the shear stress at the interface was calculated using finite element analysis. The results demonstrated that the fracture modes changed from interfacial fracture to fracture in aluminium when the steel thickness increased or the aluminium thickness was thinner than the steel. Therefore, interfacial fracture can be minimised by decreasing aluminium to steel thickness ratio. This was due to a reduced shear to tensile stress ratio and a lower shear stress than the shear strength at the weld faying interface.