Prevention of peeling of Al-Si coated layer in hot stamping using corner thickening by planar compression

Hot-stamped products are widely used for the body in white of an automobile to enable lightweight design and improve crashworthiness. Al-Si coated 22MnB5 steel sheets are applied to prevent oxide scale and adhere to a painting in hot stamping. To strengthen the bent member, corner thickening by planar compression in hot stamping was applied. However, the Al-Si coating layer peels off by large deformation due to corner thickening. The effect of corner thickening on the peeling of the Al-Si coating layer was investigated in hat-shaped bending. The coating layer on the outer corner was cracked by tensile deformation and the peel of the coating layer was observed above 5% in the thickening ratio. Deformability of the coating layer without crack was investigated in V-shaped bending. The sidewall angle was changed to taper to prevent peeling failure. In addition, to improve the elongation of the coating layer during hot stamping, the heating temperature was increased. The peeling and crack of the coating layer were reduced by heating at 1050 °C for 4 min.