Drastic Improvement in Dissimilar Aluminum-to-Steel Joint Strength by Combining Positive Roles of Silicon and Nickel Additions

Abstract

Dissimilar welding of an aluminum (Al) alloy to steel is expected to be effective for weight reduction of automotive car bodies. In this study, an aluminum alloy 1050 sheet was welded to a nickel (Ni)-plated Fe sheet using a silicon (Si)-containing Al filler by gas tungsten arc welding. The effect of the simultaneous addition of Si and Ni on the Al/Fe joint strength associated with the microstructure of the intermetallic compound (IMC) layer was systematically examined. The addition of Si and Ni individually improved the Al/Fe joint strength by the reduction in the IMC layer thickness caused by the Si addition and the refinement of the IMC grains due to the Ni addition, respectively. The most effective improvement in the joint strength was achieved by the simultaneous addition of Si and Ni. The IMC layer at the Al/Fe interface with Si addition consisted of θ-Fe4Al13, η-Fe2Al5, and Al–Fe–Si ternary IMCs, while it changed to θ-Fe4Al13, η-Fe2Al5, and an Al–Fe–Ni ternary IMC after Ni was additionally added. This change in the phase as well as the thickness reduction and grain refinement of the IMC layer probably contributes to further improving the joint strength by the simultaneous addition of Si and Ni.

Keywords

• Gas tungsten arc welding
• Dissimilar welding
• Aluminum alloy
• Steel
• Intermetallic compounds
• Mechanical properties