Effect of coating weight on fiber laser welding of Galvanneal-coated 22MnB5 press hardening steel

Abstract

Tensile strengths of up to 1.5 GPa and fracture elongation of 8% in press-hardening steel (PHS) opened up a great opportunity to improve the crash performance of vehicles. However, due to the increased susceptibility to welding defects and undesired transformation as a result of coating mixing into the weld pool, laser welding of PHS is still challenging. Hence, the present study focuses on the effect of Galvanneal (GA)-coating weight on the microstructure and mechanical performance of fiber laser welded PHS. It was observed that GA-coating weight considerably affects the laser welding process window as well as weld geometry. Weld penetration decreased and concavity increased with increasing coating weight, which is attributed to intensified Zn-plasma and laser interaction at higher coating weights. Moreover, a model has been developed to interpret the correlation between the GA-coating weight of the PHS and the penetration depth based on the heat input per unit thickness of the sheet. The size of fusion zone and heat affected zone decreased slightly with increasing coating weight due to lower energy absorption by the material. Furthermore, GA-coating weight did not affect the tensile strength of all welded joints as the failure happened in the base metal.