Suppression of δ-ferrite formation on Al-Si coated press-hardened steel during laser welding

Abstract Mechanical properties of Al-Si coated press-hardened steel laser welded joint can not meet requirement due to the presence of δ -ferrite. This study investigated the suppression mechanism of δ -ferrite using a nickel interlayer during fiber laser welding. The fraction of primary solidification δ -ferrite was reduced to 57% with a 5.85% Ni in welding pool, and completely transformed into austenite during peritectic reaction (L +  δ  →  γ ) and solid phase transformation ( δ  →  γ ). Full martensite microstructure was obtained in welded seam and fusion line without Al-segregation. Tensile strength of welded joint had a ∼17.1% improvement compared to as-received welded, similar to that of removing Al-Si coating.