Study on Al migration, microstructure and hardness in fusion zone of Al-Si coated press-hardened steel by various laser powers

In this paper, the influence of Al distribution in the fusion zone (FZ) on microstructures and properties of welded joints was studied under 13 different laser powers (300 W→3000 W). The results show that Al can quickly accumulate at the upper surface of the FZ and the fusion line. Due to the stirring action of the beam and the dilution of the molten pool metal, Al becomes gradually uniform with the increase of laser power. This work guides the welding process parameters of lap welding the second layer steel plate to obtain uniform weld. In addition, with the decrease of Al content, the microstructure and hardness of the FZ change as follows: Al-based solid solution (Al > 60.2 wt%, 80 ∼ 120 HV) →Fe-Al intermetallic compound (IMC) (10 wt% < Al < 60.2 wt%, 340 ∼ 980 HV) →Fe-based solid solution (Al < 10 wt%, 350 ∼ 530 HV). Therefore, this work revealed the relationship between the distribution-microstructure-hardness of Al and gave the possible microstructures and properties database of Fe/Al welding joints.