Improving microstructure uniformity and mechanical properties of Al-Si coating 22MnB5 steel welded joints by pulsed Laser-TIG hybrid welding

Abstract

The 22MnB5 steel with Al-Si coated exhibits high strength, robust corrosion resistance, and outstanding high-temperature formability, making it a crucial material for automotive lightweight and safety enhancement. However, traditional continuous laser welding (CLW) encounters limitations due to the molten pool’s rapid solidification, which hampers the complete and uniform diffusion of Al elements from the coating into the molten pool. Consequently, Al element segregation occurs in the fusion zone, forming α-ferrite − a critical factor in welded joint failure. To address this issue, the study introduced a novel technology, pulsed laser-TIG hybrid welding (PLTW), designed to overcome these challenges. The novel technology integrates an arc heat source to decelerate the solidification rate of the molten pool. Furthermore, the pulse laser stirs the molten pool, facilitating the complete diffusion of Al elements within it. Consequently, without removing the coating, the formation of α-ferrite was minimized, thereby enhancing the strength and ductility of the welded joint. After hot stamping, compared to CLW, the PLTW welded joint exhibited a more homogeneous microstructure and suppressed fusion zone softening, significantly increasing tensile strength by 13.3% and elongation by 39.1%. Nevertheless, due to the higher heat input from the arc heat source, thinning occurred on both sides of the fusion zone of the PLTW joint. Future research will investigate the use of PLTW with filler wire to address the thinning issue on both sides of the weld, aiming further to enhance the strength and ductility of the welded joint.