Study on microstructures and fatigue behavior of dissimilar Al/steel resistance spot welded joint

Abstract The microstructures and fatigue behavior of dissimilar resistance spot welded joint between 5083 aluminum alloy and DP980 high strength steel are studied. Al/steel joint has fusion‐brazing characteristics composed of Al nugget and intermetallic compound (IMC) layer. The microstructure, microhardness, static tensile/shear property, and fatigue test of welded joints are carried out. The number of fatigue cycles increases with the decreasing of load level, and the fatigue limit load is 1.08 kN about 21% of static tensile/shear force. The fatigue test results reveal that different fatigue load levels lead to different fracture mode. It can be summarized as nugget pullout failure (fatigue load > 3.5 kN), interfacial failure (1.5 kN < fatigue load < 3.5 kN), and aluminum alloy base metal fracture (fatigue load < 1.5 kN). Furthermore, the fatigue fracture mechanism under different load levels is analyzed.