Direct laser-filler wire welding of Al–Si coated 22MnB5 steel without removing the Al–Si coating

Abstract

Al–Si coated 22MnB5 steels are one of the most important lightweight materials for automotive weight reduction and safety improvement due to its advantages of light weight, high strength and good formability at high temperature. Considering the formation of α-ferrite caused by the Al–Si coating deteriorating the weld mechanical performance, the common way in the automotive industry is to remove the Al–Si coating prior to laser welding. In this work, a patented laser-filler wire welding process was developed with a high strength steel wire to inhibit the formation of α-ferrite and achieve high quality laser weld in Al–Si coated 22MnB5 without the requirement of removing the Al–Si coating. A formula for calculating the average content of Al element in the fusion zone was provided and verified by experiment. Experimental results show that Al segregation in the fusion zone with the designated filler wire was reduced, and the microstructure was full martensite with high dislocation density. The strain of the welded joint was concentrated in the hot-stamped base metal (HSBM) and fractured in an obvious necking during the tensile shear test. The tensile strength and elongation of the welded joint with filler wire increased by 7.5% and 183.9% compared with that without filler wire.