Characterization of aluminum flow during friction element welding

Multimaterial use in automotive body structures has become essential for continuing vehicle mass reduction. This has created challenges in joining of these materials. Friction element welding (FEW) is a joining process capable of joining aluminum to high strength steels. In this process, the element is driven through the aluminum sheet and friction welded to the steel, securing the aluminum under the head of the fastener.

The flow of aluminum during the FEW process is a critical parameter. Poor aluminum flow conditions can result in the protrusions of aluminum chips from the underhead of the fastener. These chips can accelerate corrosion and generate contamination. The flow of aluminum material was observed experimentally and modeled in order to better understand the FEW process and guide parameter selection. Two aluminum alloys, 6061 and 7075, were selected for this study due to their differences in ductility and strength and for their widespread use in the automotive industry. Various experimental methods were explored for revealing the flow of aluminum during processing and validating simulations. The results of this testing reveal that there is minimal radial and vertical mixing within the aluminum substrate. It was also found that the 6061 material exhibits much greater upwards flow of aluminum, while the 7075 alloy experiences more outward flow.