Effects of nugget alloying on microstructures and properties of resistance spot welded joints of aluminum and steel

The resistance spot welding of 6063-T16 aluminum alloy and 16Mn steel was studied by nugget alloying.The results indicated that the Al-steel joint had characteristics of welding-brazing.The nugget zone consisted mainly of α-Al solid solution with dislocations and fine Mg₂Si particles.The interface zone had a double-layer structure:Fe₂Al₅ layer at steel side and Fe₄Al₁₃ layer at Al nugget side.The nugget alloying has a significant effect on the joint properties by changing phase composition and refinement of grains.When alloy elements Cu,Zn,Ti and Ni were added,the tensile shear load of Al-steel joints reached 2 780 N,2 910 N,2 915 N and 2 929 N respectively,which increased by 24.1%,29.9%,30.1%and 30.7%respectively compared with that（2 241 N） of joint without nugget alloying.Therefore,it is an effective way for improving mechanical properties of resistance spot welded Al-steel joints.