Effect of Ni foil thickness on the microstructure of fusion zone during PHS laser welding

Abstract In this present, hot-rolled Al-Si coated press hardened steel (PHS) with 1.5 mm thick was laser tailor welded using Ni foil as an interlayer. The effect of Ni foil thickness on the microstructure evolution of fusion zone (FZ) was studied. With the Ni foil thickness increased, Al had a uniform profile in the FZ but Ni had a segregation in the fusion boundary. JMatPro analysis results showed that the fraction of δ-ferrite at high temperature was decreasing and the primary solidification phase was changed from δ-ferrite to γ phase. The fusion boundary and FZ center had the similar solidification phase evolution during laser welding. The microstructure was the composition of δ-ferrite and lath martensite when the Ni foil was 30 μm, but it was full martensite with the Ni foil increased to 60 μm. Austenite was present in the fusion boundary with the Ni foil increased to 100 μm but it was still lath martensite in FZ center.