Resistance spot welding of 5052 Al alloy and DP600 automotive steel is realized by using a Ni interlayer.The interfacial microstructure and mechanical properties ofjoints are investigated by SEM and tensile-shear test.The results show that the Ni interlayer remains integral during the welding process and completely suppresses the interaction between Al alloy and steel base metal.Robust metallurgical bonding is achieved at the Al/Ni interlayer interface by forming Al,3,Ni intermetallic phase.Joining at the Ni interlayer/steel interface is realized by formation of Fe-Ni solid solution via solid state diffusion bonding.However,considerable amount of unbondedzoneexists.The bonding area improves by elevating the welding current.Bonding strength appreciably enhances as welding current increases.The maximum tensile-shear loading of 4.3 KN is obtained at welding current of 11 KA.