A novel zero tool defect accelerated friction stir thin sheet welding technique for automotive light-weight structural component fabrication with dissimilar material

Abstract

Frequent tool failure and rupturing pose significant challenges in friction stir welding (FSW) of thin dissimilar material sheets with diverse thermal and mechanical properties. These issues exacerbate at higher welding speed (ν), demanding greater precision in welding methodology. This paper presents a novel approach to weld 300 μm thin SS304 and 500 μm thick commercially pure aluminum sheets at ν up to 2400 mm/min using H13 tool without wear, obviating the necessity for expensive high-strength tool materials. Furthermore, the use of a pinless tool negates the requirement for an additional pinhole filling step, which is a prevalent challenge associated with pinned tools. The study unveils that higher tool tilt angle (α) reduces flash formation, leading to a higher effective weld thickness, thereby enhancing weld strength. The increased material extraction (2.048 mm3) from the weld center and higher heat generation (7.6%) compared to the pinless tool imposes a speed limit of 300 mm/min for the pinned tool. The thicker layer (4.9 μm) of inter-metallic compounds (IMC) formed at lower ν showed maximum joint strength (70.03% of base Al). The fracture behavior indicates cleavage facet formation becomes more frequent at higher ν, diminishing joint ductility. With a distortion-free, high lap shear strength and enhanced ν, this novel joining method meets the needs of industrial mass production.