Interfacial microstructure and mechanical property of resistance spot welded joint of high strength steel and aluminium alloy with 4047 AlSi12 interlayer

Dissimilar materials of H220YD galvanised high strength steel and 6008-T66 aluminium alloy were welded by means of median frequency direct current resistance spot welding with employment of 4047 AlSi12 interlayer. Effects of interlayer thickness on microstructure and mechanical property of the welded joints were studied. The welded joint with interlayer employed could be recognised as a brazed joint. The nugget diameter had a decreased tendency with increasing thickness of interlayer under optimised welding parameters. An intermetallic compound layer composed of Fe-2(Al,Si)(5) and Fe-4(Al,Si)(13) was formed at the interfacial zone in the welded joint, the thickness and morphology of which varying with the increase of interlayer thickness. Reaction diffusion at the steel/aluminium interface was inhibited by introduction of silicon atoms, which restricted growth of Fe-2(Al,Si)(5). Tensile shear load of welded joints experienced an increased tendency with increasing interlayer thickness from 100 to 300 mu m, and the maximum tensile shear load of 6.2 kN was obtained with interlayer thickness of 300 mu m, the fractured welded joint of which exhibiting a nugget pullout failure mode. (C) 2013 Elsevier Ltd. All rights reserved.