The effect of heating stage parameters on AlSi coating microstructure and fracture at high temperatures

Abstract

AlSi coating fracture during press hardening of boron steel can significantly increase tool wear and reduce the product quality. During heating of AlSi-coated press hardening steel, the coating layer evolves due to diffusion. This results in various Fe − Al intermetallic compounds (such as FeAl, Fe2Al5), voids throughout the coating and rise in surface roughness. The goal of this study is to investigate the effect of heating parameters on AlSi coating micro-structure and thereby on its fracture behavior during deformation at elevated temperatures. Heating and quenching experiments are performed and later the coating layer is inspected under the microscope to check the distribution of intermetallics, voids and surface roughness. Subsequently, the coating fracture for the micro-structures resulting from different heating parameters is investigated during uniaxial tensile deformation at 700 °C. After the test, the severity of coating cracks is correlated in terms of the percentage of Fe-rich compounds and void distributions in the AlSi coating. The results show that by increasing the amount of Fe-rich compounds in the coating, its crack density is significantly reduced. Finally, it is shown that by adjusting the heating stage parameters, it is possible to further improve the ductility of coating micro-structure and minimize coating fracture upon tensile deformation.