Microstructure and properties of resistance spot welded joint of dissimilar aluminum alloys

The resistance spot welding process was used to overlap weld 5182 aluminum alloy and 5754 aluminum alloy with a thickness of 2 mm. The metallurgical characteristics were observed with a metallurgical microscope. And the mechanical properties are tested by the tensile tester and the microhardness tester. The results showed that the welded joint was composed of three typical zones,base metal,heat affected zone and nugget zone. The nugget zone of the welded joints mainly consisted of edge columnar grains and central equiaxed grains,and the volume of central equiaxed crystal zone accounts for about 90% of the entire nugget zone. In the heat affected zone of 5182 aluminum alloy,there appeared many large precipitates and liquefied cracks. However,there existed no obvious precipitates and liquefied cracks in the heat affected zone of 5754 aluminum alloy. The fracture form of the welded joint was a button fracture,and the nuggets on the 5754 aluminum alloy side were peeled off. The hardness of the columnar zone in the nugget was higher than that of the equiaxed crystal zone,and the hardness of the heat-affected zone on both aluminum alloys was higher than that of the corresponding base metal.