Effect of electrode morphology on steel/aluminum alloy joint

Microstructure characteristics of dissimilar-metal resistance spot welded joints of SUS301L austenitic stainless steel and 6063-T6 aluminum alloy, and effects of electrode morphology were studied. Results indicated that welded joints of dissimilar materials between austenitic stainless steel and aluminum alloy had characteristics of welding-brazing. The aluminum nugget consisted mainly of the cellular crystal, cellular dendrites and dendrites. The interface between austenitic stainless steel and aluminum alloy had a two-layered structures：a flat front surface θ-Fe2Al5 on the steel side and a serrated morphology θ-FeAl3 on the aluminium alloy side, and it was the weakest zone of the joints. The electrode morphology had great effects on spot welded joints of stainless steel and aluminum alloy. The custom electrodes were a planar circular tip electrode with tip diameter of 10 mm on the stainless steel side and a spherical tip electrode with spherical radius of 35 mm on the aluminum alloy side. When the custom electrodes were used, the nugget diameter, tensile shear load and indentation ratio of spot welded joint were 7.22 mm, 3 606 N and 10.71%, respectively. The nugget diameter and joint tensile shear load increased by 34% and 102% respectively, and the indentation ratio decreased by 65% compared with the F-type electrodes (nugget diameter: 5.384 mm, tensile-shear load 1 783 N, indentation rate 30.94%). Therefore, it was more favorable to use the custom electrodes for improving the mechanical properties and appearance quality of resistance spot welded joints of stainless steel and aluminum alloy.