Microstructures and mechanical properties of resistance spot welded joints of 16Mn steel and 6063-T6 aluminum alloy with different electrodes

Highlights: • The interface zone was composed of tongue-like Fe₂Al₅ and needle-like Fe₄Al₁₃. • The excessive welding current and welding time result in decreasing joint strength. • Using the optimized electrodes is more favorable to increase joint strength. The dissimilar resistance spot welding of 16Mn high strength steel and 6063-T6 aluminum alloy was studied by using different welding electrodes and welding parameters. The aluminum alloy nuggets consist of cellular crystals, cellular dendrites and equiaxed dendrites with tangled dislocations and fine Mg₂Si particles. There exist intermetallic compound layers including Fe₂Al₅ layer at steel side and Fe₄Al₁₃ layer at aluminum side in the interface zone, and their evolution process has been summarized. The excessive Fe-Al intermetallic compounds deteriorated the steel-aluminum joint strength. The welding electrode morphology and welding parameters had great effects on the steel-aluminum joints. When F-type electrodes were used, the tensile shear load and indentation ratio of the joint are 2534 N and 28.0%, respectively under the condition of optimized welding parameters. When optimized electrodes were used, the tensile shear load of the joint reached 3623 N and the indentation ratio decreased to 18%, which is related to improving welding temperature distribution. It is more favorable to use the optimized electrodes for increasing the steel-aluminum joint strength and improving its appearance quality.