Investigation of formability and surface micro-crack in hot deep drawing by using laser-welded blank of Al–Si and Zn-coated boron steel

Abstract

Currently, the automobile industry is focusing all its attention to creating high-strength, ultra low-weight car bodies. Many techniques can be used to decrease the thickness of a steel plate in a car body but increase the strength. Among these, the hot stamping process makes use of boron steel to produce ultra high-strength components. On the contrary, this process has a low elongation that causes a decrease in collision absorptiveness. Therefore, this study examined the material and weldability of components with high collision absorptiveness using boron steel plates welded at different thicknesses, where the thinner steel sheet can absorb the collision, whereas the thicker steel sheet can endure it. This study was conducted using boron steel coated with either Al–Si or Zn. The results showed that satisfactory tensile strength and elongation could be obtained when both sides of the coating layer were removed by the laser. The hardness in the welded area of Zn-coated boron steel was greater than 450 Hv, even when the specimen was welded without laser ablation of the coating layer, but the coating layer peeled off when heated for 5 min at 950 °C.