Effect of repair welding on microstructure and mechanical properties of 7N01 aluminum alloy MIG welded joint

The effect of repair welding on the microstructure and mechanical properties of the welded joint was investigated. The results show that the difference of microstructure in different locations of the original welded joint (OWJ) is mainly related to the production process. The AT5 side is an extruded profile, exhibiting equiaxed grain characteristics, while the AT4 side is a rolled sheet, displaying flat long grain. The grain boundary orientation difference in different positions of repair welded joint (RWJ) is various from that of OWJ, especially the change of proportion of small angle grain boundary in AT4-HAZ II is large. The tensile strength of the OWJ and RWJ are 283 MPa and 280 MPa, respectively, and the corresponding welded joint coefficients are 78.6 % and 77.8 %, respectively, which can fulfill the demands of practical engineering applications. Due to the existence of pores and inclusions, the crack of OWJ originates in the junction of HAZ I near the 7N01-T4 side, then expands along the welded zone, while the RWJ fails in the junction of the original weld and the weld passes.