Improving Strength of Stainless Steel/Aluminum Alloy Friction Welds by Modifying Faying Surface Design

Conventionally in friction welding, the rubbing or faying ends of the base material rods are square turned. For the case of dissimilar friction welding, this design is not optimum because of differential flow behavior of the materials. When, only one of the materials deforms preferentially, the actions of cleaning and expulsion of oxides and impurities from the interface would not be as effective. This will adversely affect the joint properties. In this study, alternate designs of faying surfaces such as providing taper (external and internal) and smoother surfaces are compared with the square cut design. The aim was to study how the faying surface conditions of the stronger material affect the flow behavior of the weaker material. By affecting better flow behavior, the intention was to expel intermetallics and other impurities from the interface, and thereby improve joint properties. Friction welding of stainless steel with aluminum alloy (aluminum-magnesium-silicon) was studied. The joints were evaluated for strength and it is found that the external tapered system has the best strength. Different characterization techniques such as optical microscopy, scanning electron microscopy, x-ray diffraction were carried out to observe different phases, microstructure zones, etc., at the interface. Finally, possible reasons for the better strength of tapered system were discussed.