Resistance Spot Welding Of Magnesium Alloy Sheets with Cover Plates

Abstract

Lightweight materials such as high-strength steels and aluminum alloys are widely used in automotive components for the purposes of weight reduction and consequent higher fuel efficiency. As new alloys have been developed, magnesium alloys have become attractive for the production of automotive components due to their unique properties, such as high specific strength, damping capacity, and recyclability. In the assembly process of these materials, resistance spot welding (RSW) is used to construct thin sheet structures. Although RSW of steel sheets with high weld quality has already been established, the following problems remain with regard to RSW of magnesium alloys: high welding current, degeneration of electrodes, and blowholes and expulsion in or around the nugget. In this study, RSW with cover plates was applied to magnesium alloy sheets to investigate the performance of spot-welded joints. The weld quality was evaluated based on the tensile shear strength of the joints, the shape and the size of the nugget, and the appearance of blowholes and expulsion. Since RSW with cover plates is similar to conductive heat resistance seam welding (CHRSMW), the results showed that RSW with cover plates enabled the spot welding of a magnesium alloy with a large nugget and high tensile shear strength in the joint. It was also shown that blowhole-free spot welds with a large nugget and high tensile shear strength were obtained for welding currents above 8 000 A with a long down-slope time of welding current and a high electrode force.