Dissimilar Joining of Aluminum Alloy and Steel by Resistance Spot Welding 2009-01-0034

This study concerns a dissimilar materials joining technique for aluminum (Al) alloys and steel for the purpose of reducing the vehicle body weight. The tough oxide layer on the Al alloy surface and the ability to control the Fe-Al intermetallic compound (IMC) thickness are issues that have so far complicated the joining of Al alloys and steel.

Removing the oxide layer has required a high heat input, resulting in the formation of a thick Fe-Al IMC layer at the joint interface, making it impossible to obtain satisfactory joint strength. To avoid that problem, we propose a unique joining concept that removes the oxide layer at low temperature by using the eutectic reaction between Al in the Al alloy and zinc (Zn) in the coating on galvanized steel (GI) and galvannealed steel (GA). This makes it possible to form a thin, uniform Fe-Al IMC layer at the joint interface.

Welded joints of dissimilar materials require anticorrosion performance against electrochemical corrosion. A seal spot welding process is proposed here as a solution to that issue. Tests conducted on seal spot-welded joints showed that they provide both the required static tensile properties and anticorrosion performance. In addition to static tensile properties, seal spot-welded joints also satisfy all the other performance requirements for vehicle application, including fatigue properties, high-speed tensile properties, low- and high-temperature tensile properties and anticorrosion performance. The seal spot welding process also has ample tolerance and excellent robustness against production variabilities such as the gaps between body panels and misalignment of the electrode angle.