Exploring the mechanical properties of spot welded dissimilar joints for stainless and galvanized steels

Spot weldability of dissimilar metal joints between stainless steels and nonstainless steels was investigated. The aim was to determine the spot welding parameters for the dissimilar metal joints and to characterize the mechanical properties of the joints. Metallographical investigations, microhardness measurements, peel tests, lap shear tests, cross-tension tests, corrosion fatigue tests, and stress corrosion cracking tests were performed. It was found that in the dissimilar metal joints between stainless steel and nonstainless steel, the failure load of the cross-tension specimens was around 72-78% of that of the lap shear specimens. The weld nugget of the dissimilar metal joints was fully martensitic, but it was ductile enough so that the failure type was plug failure in both lap shear and cross-tension tests. In the case of the corrosion fatigue testing of the spot welded joints, different strength levels of the base materials did not have an effect on the corrosion fatigue strength, but the sheet thickness had a significant effect. The fatigue strength of a spot welded specimen increased with the increasing sheet thickness. Electro-coating of the test specimens did not have an effect on the corrosion fatigue properties of the spot welded joints. Stress corrosion cracking tests showed that the stainless steel EN 1.4318 and zinc-coated nonstainless steel ZStE260BH dissimilar metal joints are susceptible to hydrogen embrittlement in 3.5% sodium chloride solution at room temperature. Comparable cracking was also observed in the stainless-stainless steel joints, when they were galvanically coupled to zinc. The reason for hydrogen embrittlement of the dissimilar metal welds is that the weld nugget is fully martensitic and the corrosion potential is low due to the zinc plating.