Microstructure and mechanical properties of 5052 aluminum alloy/mild steel butt joint achieved by MIG-TIG double-sided arc welding-brazing

Unstable weld appearance and uncontrollable interfacial compounds have significant impact on the final properties of Al/steel butt joint obtained by traditional processes. In this study, a novel process – MIG-TIG double-sided arc welding-brazing (DSAWB) was introduced to butt join AA5052 aluminum alloy and Q235 low-carbon steel of 3.0mm thickness without groove. The microstructure and mechanical properties of the joints were investigated and compared with that of the traditional metal inert gas (MIG) joint in detail. The results showed that excellent weld appearance, especially back appearance, was achieved at a welding heat input lower than that in the traditional MIG because of the double-sided heating and gas shielding in the DSAWB process. Needle-like FeAl3 and lamellar Fe2Al5 were found at the brazing interface. Due to the decreased heat input, the maximum thickness of the Fe2Al5 was effectively limited to 2.03μm. However, in the traditional MIG, massive FeAl3 and Fe2Al5 layer of 4.20μm thick with obvious cracks were found when the optimal parameters were applied. Benefitting from the excellent weld appearance and the effective control of the interfacial intermetallic compound, the average tensile strength of the DSAWB joints reached 148.1MPa, which was 2.5 times that of the traditional MIG joints.