Advances in FSW and FSSW of dissimilar Al-alloy plates

Abstract

Numerous industrial applications, particularly those in the transport industry, require the joining of dissimilar materials which offers considerable benefits in terms of low cost, design flexibility, and weight reduction for overall structures. The problems associated with conventional fusion welding processes have stimulated researchers in recent years to develop new joining methods for dissimilar materials which are particularly difficult to join. Friction stir welding (FSW) originally developed for joining difficult-to-weld Al-alloys and FSSW (a variant of FSW for spot welding) have exhibited great potential for obtaining sound joints in various dissimilar alloy systems in different configurations namely butt-, lap- and spot-welding, particularly in dissimilar Al-alloys systems with different properties, which are very difficult to weld using conventional fusion welding techniques. A major difficulty in joining dissimilar Al-alloys by FSW/FSSW lies in the discontinuity in mechanical and technological properties (such as high-temperature strength, plastic deformation capacity, viscosity, etc.) of the materials to be welded across the abutting surfaces. This discontinuity as well as inherent asymmetry in heat generation and material flow of FWS/FSSW processes causes a higher asymmetry in materials flow behavior in dissimilar welding. However, it is relatively easier to implement the FSW/FSSW process to dissimilar Al-alloys in contrast to FSW of dissimilar materials combinations with very differing properties, such as Al-alloy to Mg-alloy or Al-alloy to steel.