Formability of aluminum-silicon coated boron steel in hot stamping process

Flow behavior of the Al-Si coated boron steel was investigated with Gleeble-3500, in comparison with the uncoated one. Effect of deformation conditions on the coating integrity was characterized by optical microscopy. Facture surfaces of the coated steels were inspected under SEM. Experimental results indicate that the ultimate tensile strength and ductility of the Al-Si coated boron steel are lower than those of the uncoated steel under test conditions. Extensive cracks occur in the coating after tensile tests; the width and density of cracks are sensitive to the deformation temperatures and strain rates. The bare substrate exposed between the separate coating segments is oxidized. Appearance of the oxide degrades the Al-Si coating adhesion. Remarkable difference between formability of the coating layer and the substrate is confirmed. The formability of the Al-Si coating could be optimized by controlling the phase transformation of the ductile Fe-rich intermetallic compounds within it during the austenization.