EFFECTS OF HOLDING TIME ON MICROSTRUCTURE AND SHEAR STRENGTH OF RESISTANCE SPOT-WELDED JOINTS BETWEEN MILD STEEL AND ALUMINUM WITH ZINC POWDER FILLER

Abstract

This study aimed to determine effects of holding time on microstructure and shear strength of resistance spot-welded joints between mild steel and aluminum with zinc powder filler. The materials used are 0.9 mm thick mild steel, 1.2 mm thick 3000 series aluminum, and 200 mesh zinc powder. Welding parameters were selected as welding time of 0.5 seconds (s), electric currents of 8000 A and 9000 A, with holding time variations of 1 s, 3 s, and 5 s. Macro and scanning electron microscope (SEM) images follow ASTM E3-01, while ASME IX was used as tensile test standards. The macro images showed that holding time affected quality of the welded joints. Applying a longer holding time was able to reduce defects on the welded joints. SEM energy-dispersive X-ray spectroscopy (SEM-EDX) analysis exhibited that the holding time of 1 s produced a lack of density in the spot-welded joint, resulting in the existence of porosity. In contrast, increasing the holding time to 5 s gives a denser spot-welded joint with no defects found. The tensile test results showed that applying electric current of 8000 A, welding time of 0.5 s, and holding time of 1 s produced the joint with the weakest shear strength of 130 N. The highest joint shear strength of 790 N is obtained with the condition: electric current of 9000 A, welding time of 0.5 s, and holding time of 5 s.