Joining Mechanism on Resistance Spot-welding between Aluminum Alloy and Steel and Evaluation of Joining Strength

In this study, joining mechanism of aluminum alloy/steel resistance spot-welding was investigated with micro observation and analysis on joining area by SEM-EDX, comparing with steel/steel and aluminum alloy/aluminum alloy spot joining. Results were obtained as follows. The shear tensile strength of aluminum alloy/steel resistance spot-welding was lower than a half of the maximum value of steel/steel due to the diŠerence in resistance value between steel and aluminum alloy, close to the shear tensile strength of aluminum alloy/aluminum alloy. The aluminum alloy played a major role in joining of aluminum alloy/steel. In the resistance spot-welding of aluminum alloy/ steel, the joining strength depended on aluminum melting at the joining interface and diffusing and adhering to steel. The intermetallics played the important role on the joining between steel and aluminum alloy. The fracture occurred on the aluminum side. On the aluminum alloy/steel resistance spot-welding, the hardness of steel increased by heating. On the other hand, the hardness of aluminum remained unchanged. © 2020 Japan Light Metal Welding and Construction Assoc.. All rights reserved.