Effect of coating on fiber laser welded joints of DP980 steels

Advanced high strength steels (AHSS), specifically dual phase (DP) steels, are extensively used to reduce the weight of vehicles. Fiber laser welding (FLW) has been shown to provide welds with superior mechanical properties made at high welding speeds. Galvannealing (GA) and galvanizing (GI) coated sheet steels are extensively used for auto bodies to improve corrosion resistance. As such, the effect of coating type on the microstructure, mechanical properties and fatigue properties of FLW similar joints of DP980 was assessed. There existed spherical tempered martensite in the GA coated DP980 base metal (BM), most likely caused by the galvannealing process. Coating type did not present a noticeable effect on the microstructure of the welded zones. The GI coating, however, could evaporate violently during welding, resulting in high concavity and other welding defects which negatively affect the high-cycle fatigue property. Measures to mitigate the negative effects of the GI coating were discussed.