Effect of welding parameters on microstructure and mechanical properties of laser welded Al-Si coated 22MnB5 hot stamping steel

Abstract

Laser lap welding of 22MnB5 with different laser power, welding speed and coating condition were presented. The effect of the welding parameters on microstructure and mechanical properties of the joint was investigated. The fusion zone was composed of lath martensite. Based on the location, the heat affected zone (HAZ) was divided into three regions: inner HAZ was composed of martensite, middle HAZ was composed of martensite and ferrite and outer HAZ was composed of tempered martensite which was the most soften area of the joint. Al-Fe intermetallic phases formed along the fusion boundary due to the agglomerating of the mixture of coating and base metal. The tensile shear load of the weld in coated condition was lower than that in non-coated condition at the same welding parameter due to the Al-Si coating agglomerating along the fusion boundary deteriorating the mechanical properties of the joint. Regardless of the excessive heat input, failure occurred directly at the fusion boundary with a quasi-cleavage pattern in coated condition but took place at the interface with a dimple pattern in non-coated condition. The tensile shear load was increased by increasing laser power or decreasing welding speed in the experimental parameters except the excessive heat input. For the diffusion of Al can be enhanced by the increased flow of weld pool, which results from wider bead width associated with higher laser power and lower welding speed.