Microstructure and mechanical performance of Al-Si coated laser welded hot stamped steel with foils

Al-Si coated hot stamping steel is one of important advanced high strength steel in nowadays vehicle manufacturing. Due to the coating degradation effect, the performance of the laser weld of tailor-welded blanks is lower than that of base metal. This paper chose three different foils with same thickness as filler material to modify the welds. After hot stamping procedure in lab, the microstructure, hardness, tensile strength and fracture morphology are both compared to explain the foil effect. The results indicate Ni foil and Cu foil both reduce the delta ferrite in weld seam, but the joint with Cu foil shows intergranular fracture and low strength and ductility. Ni foil shows a limited increase of the joint strength, because of extra solution enhancement. Fe foil leads to dilution effect of Al coating, which increase martensite fraction.