Abstract:

Lap joining between wrought 6061-T6 and cast A356-T6 aluminum alloys plates by direct current pulse MIG welding is investigated. The mechanical property, microstructure and composition of the joints are analyzed. The tensile results indicate that the maximum tensile strength of the joints is 95 MPa with the welding speed of 10mm/s and joint design with A356-T6 aluminum alloy as upper plate. The samples during tensile test fail mainly in weld through mixed fracture mode. The analysis on the microstructure and composition of the joints shows that the segregation of Fe and Mg occurs in the partially melted zone on A356 aluminum alloy side, resulting in formation of flake-like Al-Fe-Si phases and Al-Fe-Mg-Si particles, and these Fe-rich phases can weaken the joints. Grain boundary liquation occurs in the partially melted zone on 6061 aluminum alloy side, which is composed of Al-Mg-Si-Cu phases and solute-depleted α-Al zone, and a little Fe segregated near this structure. The weakest position locates at the root of the lap joint, where the tensile samples crack and finally fracture through the weld.

Key words: lap joint, mechanical property, microstructure, pulse MIG welding, dissimilar aluminum alloy