Microstructures and properties of welded joint of aluminum alloy to galvanized steel by Nd:YAG laser + MIG arc hybrid brazing-fusion welding

According to the differences in melting point between aluminum alloy and steel, 6013-T4 aluminum alloy was joined to galvanized steel by large spot Nd:YAG laser + MIG arc hybrid brazing-fusion welding with ER4043(AlSi5) filler wire. The microstructures and mechanical properties of the brazed–fusion welded joint were investigated. The joint is divided into two parts of fusion weld and brazed seam. There is a zinc-rich zone at fusion weld toe, which consists of α(Al)–Zn solid solution and Al–Zn eutectic. The brazed seam is the Fe–Al intermetallic compounds (IMCs) layer of 2–4 μm in thickness, and the IMCs include FeAl2, Fe2Al5 and Fe4Al13. FeAl2 and Fe2Al5 are located in the compact reaction layer near the steel side, and Fe4Al13 with tongue shape or sawtooth shape grows towards the fusion weld. The tensile strength of the joint firstly increases and then decreases as the welding current and laser power increase, the highest tensile strength can be up to 247.3 MPa, and the fracture usually occurs at fusion zone of the fusion weld. The hardness is the highest at the brazed seam because of hard Fe–Al IMCs, and gradually decreases along the fusion weld and galvanized steel, respectively.