Influence of Metal Transfer Modes on Pore Formation during the Welding Process of AA6082/A360 Dissimilar Aluminum Alloys

In the present study, the dissimilar welded joints of AA6082/A360 aluminum alloy were prepared by cold metal transfer (CMT) mode, cold metal transfer with pulse (CMT + Pulse) mode, and pulse (Pulse) mode. The influence of the metal transfer modes on the porosity distribution, microstructure, and mechanical properties of dissimilar welded joints were analyzed. The results show that the formation and distribution of weld pores are mainly determined by the hydrogen content of the base metals, cooling rate of the molten pool, driving force, and escaping distance of bubbles. For all the prepared dissimilar welded joints, the regions with the highest porosity appear at the A360 side fusion lines due to the higher hydrogen content of the casting A360 aluminum alloy, followed by the AA6082 side fusion lines and the central regions. With the application of Pulse mode in the welding process, the driving force of bubbles increases and the escape time shortens. The escape time of a bubble was reduced from 4.0 to 3.0 ms compared to CMT welding mode. Therefore, the average porosity of the joints decreases significantly, and the tensile stress increases accordingly. The microstructure of the weld zone gradually changed from long strip grains to equiaxed grains. The tensile stress of the dissimilar welded joint prepared by Pulse mode is 59.2% higher than that of the CMT welded joint.