Effect of galvanneal-coating evolution during press-hardening on laser welding of 22MnB5 steel

Understanding phase evolution and growth kinetics of Zn-coating during press-hardening is essential in predicting welding behaviour of press-hardened 22MnB5 steel. The results showed that during press-hardening, the initial delta and Gamma-Gamma 1 phases in the coating transform into alpha-Fe(Zn), Gamma, and ZnO phases. As heat-treating continued at a constant temperature, the alpha-Fe(Zn) thickness grew and the overall Zn-content decreased. This resulted in the full-penetration weld window shifting towards higher heat-inputs. However, when heat-treating at higher temperatures, severe oxidation and Fe-Zn inter-diffusion led to the reduction of Zn-content in the evolved coating. It was found that higher heat-treatment times resulted in wider weld beads, thereby increasing joint strength.