Effect of Solution Aging Treatment on Microstructure and Properties of 7A52 Aluminum Alloy CMT plus P Welded Joint

Cold metal transfer + pulse welding (CMT+P) method was used to weld 7A52 aluminum alloy, and the effects of different heat treatment processes on the microstructure and mechanical properties of welded joints were studied. The results show that the microstructure dominated by dendrite or equiaxed dendrite in the weld zone is transformed into equiaxed crystal after heat treatment, the grain structure and the size of the second phase of AA (artificial aging) sample are coarser, and there is segregation at the grain boundary. The amount of precipitates in T6 (solid solution+artificial aging) weld zone is more than in AA sample, and the size of eta'(MgZn2) strengthening phase and the width of precipitation free zone decrease in the heat affected zone. The joint strength of AA and T6 samples reaches 315 and 356 MPa, respectively. AA sample has limited improvement on the mechanical properties of the joint, while T6 sample is increased by about 14.10% compared with AW sample (312 MPa). The micro fracture of AA sample is mainly dimple transgranular fracture, while the number of dimples in the fracture of T6 sample is significantly reduced and replaced by an uncharacteristic platform. At this time, the joint is mainly transgranular + intergranular ductile brittle mixed fracture.