Microstructure and mechanical property of dissimilar material resistance spot welded joint of steel and aluminum alloy with electrode plate

Dissimilar materials of H220YD high strength steel and 6008-T66 aluminum alloy had been joined by resistance spot welding with electrode plate. Microstructure and mechanical property of the dissimilar material welded joint were investigated. The results indicated that the welded joint was achieved by means of wetting and spreading of liquid aluminum alloy on solid steel surface, hence it could be regarded as a special weldedbrazed joint. A thin dual-layered intermetallic compound layer composed of Fe₂Al₅ and FeAl₃ was formed on the steel/aluminum alloy interface. The diameter of aluminum alloy nugget of the welded joint reached the maximum value of 9.5 mm at welding speed of 14 kA and welding time of 300 ms. With the increase of welding current(8-14 kA), the tensile-shear load of the welded joint increased rapidly first(8-12 kA) and then became calm gradually(12-14 kA). The tensile-shear load was up to 4.3 kN at welding current of 12 kA and welding time of 300 ms, which was about 30% higher than that of the welded joint obtained without electrode plate. During tensile shear testing, the cracking developed through the brittle intermetallic compound layer and partially in the aluminum alloy nugget.