Studies on Two Failure Modes and Shear Strength of Various CMT Brazed Lap Joints of Dissimilar Materials

Cold metal transfer (CMT) is a promising method to join steel/Al dissimilar materials together in vehicle body assembly. In this paper, shear strength and failure mode of CMT brazed lap joint of steel/Al dissimilar materials are investigated in detail by both experimental and numerical simulating method. Two failure modes, including interface fracture and fusion line fracture are found out. Failure mode transition and the factors influencing joint strength and failure mode are discussed in detail. Finally, a numerical model to estimate shear strength and failure mode of CMT brazed lap joint of dissimilar materials, is developed based on the failure criteria of interface layer and fusion line fracture. It is shown that the numerical model including interface layer and fusion line failure criteria can be used to predict shear strength and failure mode of CMT brazed lap joint of dissimilar materials. Steel sheet thickness and strength grade can have an obvious effect on joint strength of interface layer fracture because of stress concentration status variation at interface layer element. And joint strength of fusion line fracture can be improved by reducing micro defects in weld metal