Abstract:

Microstructural characteristics of dissimilar resistance spot welded joints of 6061-T6 aluminium alloy and SUS301L stainless steel, and effects of electrode morphology are studied. Results indicate that spot welded aluminium-steel joints have welding-brazing characteristics. The aluminium nugget consists mainly of the cellular crystal, cellular dendrites and dendrites. The aluminium/steel interface zone has a double layer structures：The needle-like Fe₄Al₁₃ layer at aluminum side and the Fe₂Al₅ intermetallic compound (IMCs) at steel side, and it is the weakest zone of the joints. The electrode morphology has great effects on spot welded joints of aluminium alloy and stainless steel. The optimised electrodes are 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 aluminium alloy side. When the optimised electrodes are used, the nugget diameter, tensile shear load and indentation ratio of spot welded joint are 7.5 mm, 4.7 kN and 13.5%, respectively. The nugget diameter and joint tensile shear load increases by 53.1% and 56.7% respectively, and the indentation ratio decreases by 47.3% compared with F-type electrodes. Therefore, it is more favorable to use the optimized electrodes for improving the mechanical properties and appearance quality of spot welded joints of aluminum alloy and stainless steel.

Key words: mechanical properties, microstructures, resistance sport welding, stainless steel, aluminium alloy