Effects of die- and punch-shaped electrode on formation of the intermetallic compound for Fe/Al resistance spot welding

Abstract

Resistance spot welding has recently been proposed for joining steel and aluminum alloys to reduce the weight and increase the strength of automobile bodies. However, joining Fe and Al results in the formation of intermetallic compounds (IMCs) at the joining interface. A thick IMC layer reduces the joint strength, but it is difficult to control the IMC layer thickness. Therefore, in this study, a joining process that simultaneously achieves resistance heat generation and plastic deformation using die- and punch-shaped electrodes in resistance spot welding equipment is developed. The formation state and extent of IMCs for this process are investigated. The formation state of IMCs is evaluated experimentally for various electrical currents. Numerical simulations are conducted to calculate the temperature variation of the joining interface for various currents. It is found that the IMC is thin at the center of the joint and thick and spike-shaped at the edge of the joint. Furthermore, the cross-tension strength is found to increase with increasing electrical current. The stable formation of IMCs at the center of the joining interface is considered to be due to an increase in temperature in this region with increasing current. Joints with high cross-tension strength form spike-shaped IMCs with differences in thickness. It is considered that the spike-shaped IMCs create a snagging effect, enhancing the strength of the joint interface.

Keywords

• resistance heat
• intermetallic compound
• resistance spot welding
• electrode shape
• dissimilar material joining