Fatigue behavior of spot-welded joints in air and under corrosive environments

A bstract The main aim of the project was to evaluate the influence of combined effects of fatigue loading and exposure to cyclic corrosion testing on the corrosion and the fatigue resistances of coated steel-based materials joined by resistance spot welding. Seven steel-based materials including cold rolled mild steels, high-strength steels, and press-hardened steels (PHS) were selected and provided by steel suppliers with different surface coatings for resistance spot welding. Panels were joined using conventional resistance spot welding in both lap-shear and T-peel designs. Joined samples were painted by e-coating following the industrial process. Metallographic characterization of the steel materials revealed that microstructures and metallic coating composition and thickness were as expected. Cross section of spot welds showed good quality and typical evolutions of hardness. Tensile tests and fatigue tests were performed on reference samples (fatigue in “air,” i.e., nonexposed to corrosion) leading to typical SN-lines as described in part I of this paper. The results were used to evaluate the influence of corrosion on tensile strength of the joined samples. Fatigue tests performed on combined and alternating corrosion and fatigue revealed that fatigue life is affected by extent of corrosion near the spot weld, with a reduction of the fatigue life at higher applied load and slight increase for lower load, compared to tests “in air.” This phenomenon was not observed for lap-shear configuration in alternated fatigue-corrosion mode.