Effect of the Melting Behavior of the Coating Layer on Weldability in the Bolt Projection Resistance Welding of Al-Si Coated Hot-Stamped Boron Steel

In this study, the effect of Al-Si coating melting behavior and weldability during the resistance spot welding of hot stamped boron steels was investigated. In the case of the Al-Si coated hot-stamped boron steel, high heat was generated on the surface and the oxide layer by the intermetallic coating, and the molten coating layer pushed toward the outer edge of the weld like a film of liquid. The liquid coating layer accumulated at the periphery, preventing current flow and extension of the contact area, and this influenced the height of the nugget growth. As a result of the limited nugget growth, weld strength decreased. However, in the case of bare hot stamped boron steel, relatively low heat was generated due to the large contact area, and the nugget grew in the longitudinal direction. Compared to the nugget diameter of Al-Si coated hot-stamped boron steel, this can result in superior weldability. Key words: Bolt projection welding, Al-Si coated hot stamping steel, Melting behavior, Weldability, Heat generation