Welding Journal Research Supplement

Abstract

Our previous work noted that thinning the coating significantly improves the weldability of Al-Si coated press-hardened steel (PHS). However, an Al enrichment formed at the weld toe of the thin (~16 µm) coating PHS during laser welding at a high welding speed of 7 m/min, originating from the coating outside the weld. In this work, a surface pre-alloying (SPA) technique was applied to the thin Al-Si coating near the weld toe before laser welding. After conducting the SPA process, the fraction of intermetallic compounds (IMCs) in the coating increased significantly, and the IMCs consisted of Fe2SiAl7 (τ5), Fe2Al5 (η), and Fe3Al2Si3 (τ1). When the energy input to SPA exceeded 0.48 kJ/cm, the fraction of IMCs in the coating exceeded 60%. This significantly increased the coating’s liquidus temperature near the weld toe due to the altered chemical composition, reducing the molten amount of the coating and preventing it from entering the weld through the weld toe. In this case, the Al enrichment at the weld toe disappeared after high speed welding, and the tensile joints failed at the base metal. Eventually, the thin Al-Si coating PHS was stably welded at a high welding speed because of the application of SPA.