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<p>Research on Al-Si coated press-hardening (PH) steel has predominantly focused on resistance spot (RS) welding performed after hot stamping, while the weldability and microstructural evolution of as received sheets welded beforehand remain insufficiently understood. This study investigates the RS welding behavior of Al-Si coated PH steel in the as-received condition and further evaluates how subsequent hot stamping modifies the weld microstructure and mechanical response. The results show that the as-received sheet maintains a relatively wide weldability window and stable tensile shear (TS) peak load prior to hot stamping. After hot stamping, the maximum TS peak load increases significantly to 53% above the pre-stamping level, while the fracture displacement and energy decrease notably, indicating improved load carrying capacity but reduced deformation and energy absorption. Microstructural characterization reveals strong heterogeneity in the joint before hot stamping, including martensite in the nugget and upper critical heat-affected zone, and a dual-phase constitution of martensite and ferrite in the intercritical heat-affected zone. Hot stamping eliminates this heterogeneity by producing fine and nearly uniform martensite across the entire joint. Fracture shifts from initiating in the softened heat-affected zone before hot stamping to originating at the unfused interface at the nugget edge after hot stamping, resulting in a high strength but low ductility failure mode. Meanwhile, compared with the welded joint produced via the conventional processing route, the martensite at the nugget edge of this joint exhibits finer prior austenite grains, thereby suppressing brittle crack propagation and promoting ductile failure in this region. These findings clarify the distinct RS welding behaviors of coated press hardening steel under different processing conditions and offer guidance for improving weld performance in patch welded blank applications.</p>

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Hot stamping-induced microstructural and mechanical evolutions in resistance spot welds of As-received Al-Si coated steel

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Zhengxian Li,
  • Fei Cheng,
  • Yuqian Wang,
  • Dapeng Yang,
  • Guangming Xie,
  • Hongliang Yi

摘要

Research on Al-Si coated press-hardening (PH) steel has predominantly focused on resistance spot (RS) welding performed after hot stamping, while the weldability and microstructural evolution of as received sheets welded beforehand remain insufficiently understood. This study investigates the RS welding behavior of Al-Si coated PH steel in the as-received condition and further evaluates how subsequent hot stamping modifies the weld microstructure and mechanical response. The results show that the as-received sheet maintains a relatively wide weldability window and stable tensile shear (TS) peak load prior to hot stamping. After hot stamping, the maximum TS peak load increases significantly to 53% above the pre-stamping level, while the fracture displacement and energy decrease notably, indicating improved load carrying capacity but reduced deformation and energy absorption. Microstructural characterization reveals strong heterogeneity in the joint before hot stamping, including martensite in the nugget and upper critical heat-affected zone, and a dual-phase constitution of martensite and ferrite in the intercritical heat-affected zone. Hot stamping eliminates this heterogeneity by producing fine and nearly uniform martensite across the entire joint. Fracture shifts from initiating in the softened heat-affected zone before hot stamping to originating at the unfused interface at the nugget edge after hot stamping, resulting in a high strength but low ductility failure mode. Meanwhile, compared with the welded joint produced via the conventional processing route, the martensite at the nugget edge of this joint exhibits finer prior austenite grains, thereby suppressing brittle crack propagation and promoting ductile failure in this region. These findings clarify the distinct RS welding behaviors of coated press hardening steel under different processing conditions and offer guidance for improving weld performance in patch welded blank applications.