Effects of Si contents in filling wires on microstructure evolution and properties of Al-steel dissimilar joint by laser welding-brazing

Abstract

The overlap joints of 6061 aluminium alloy and galvanized DP590 steel were made by the laser welding-brazing technology. Effects of Si contents in filler wires on weld appearances, microstructure and mechanical properties of the welding-brazing joints were studied. The well-formed joints could be obtained under the optimized welding-brazing parameters. The interfacial intermetallic compounds (IMCs) could divided into five zones from the steel side to the Al side: the R-IMCs and G-IMCs mainly composed by Fe(Al,Si) phases, the S-IMCs mainly consisted of Fe2(Al,Si)5 phases, the P-IMCs mainly made up of Fe(Al,Si)3 phases and the Fe2Al8Si phases formed at edges of the P-IMCs. Various ranges and morphologies of IMCs within different zones were attributed to the element diffusion and microstructure evolution affected by thermal interactions. Formation of the Fe–Al–Si ternary compounds softened the hardness of interfacial zones compared to the Fe–Al binary compounds. Harness of the Fe2(Al,Si)5 phase was highest, followed by the Fe(Al,Si)3 phase and then the Fe(Al,Si) phase. Addition of Si element significantly improved tensile properties of the welding-brazing joints, optimal tensile strength and ductility could be achieved when the AlSi10 wire was adopted, owing to the dispersion strengthening of the soft G-IMCs distributed discretely within S-IMCs.

Keywords

• Al/steel dissimilar joint
• Laser welding-brazing
• Microstructure
• Mechanical properties