Intermediate layer, microstructure and mechanical properties of aluminum alloy/stainless steel butt joint using laser–MIG hybrid welding–brazing method

Butt joining of AA6061 aluminum (Al) alloy and 304 stainless steel of 2-mm thickness was conducted using laser–MIG hybrid welding–brazing method with ER4043 filler metal. To promote the mechanical properties of the welding–brazing joints, two kinds of intermediate layers (Al–Si–Mg alloy and Ag-based alloy) are used to adjust the microstructures of the joints. The brazing interface and the tensile strength of the joints were characterized. The results showed that the brazing interface between Al alloy and stainless steel consisted of double layers of Fe₂Al₅ (near stainless steel) and Fe₄Al${}_{13}$ intermetallic compounds (IMCs) with a total thickness of 3.7 $\mu$m, when using Al–Si–Mg alloy as the intermediate layer. The brazing interface of the joints using Ag-based alloy as intermediate layer also consists of double IMC layers, but the first layer near stainless steel was FeAl₂ and the total thickness of these two IMC layers decreased to 3.1 $\mu$m. The tensile strength of the joints using Al–Si–Mg alloy as the intermediate layer was promoted to 149 MPa, which was 63 MPa higher than that of the joints using Al–Si–Mg alloy as the intermediate layer. The fractures occurred in the brazing interface between Al alloy and stainless steel.