Hydrogen embrittlement behavior of Al-Si coated steel laser wire filling welding joint

This study investigated the hydrogen embrittlement behaviors of three laser welding joints for the 1500 MPa Al-Si coated steel using slow strain rate tensile and hydrogen concentration experiments. The results show that LW-HT is fractured in the fusion zone without hydrogen charging because the δ-ferrite reduces the mechanical properties. With the increase in hydrogen concentration, the fracture location is still FZ. The fusion zone of LWF-HT is composed of martensite and retained austenite, and when the hydrogen concentration is 3.4 ppm, retained austenite traps many hydrogen atoms. The newly formed martensite during tensile inheriting the high hydrogen concentration in retained austenite causes cleavage in the fusion zone. When the hydrogen concentration is 13.6 ppm, most hydrogen segregates at the prior austenite grain boundaries, causing an intergranular fracture in the fusion zone. The fusion zone of LWF-HS is composed of martensite and carbide, and grain refinement and nanoscaled Fe₃C can reduce HE susceptibility. With the increase in hydrogen concentration, the fracture location is still base materials. The significantly increased hydrogen concentration compared to LWF-HT is mainly trapped in carbides without reducing the banding force of dislocations and grain boundaries. This work provides a scientific basis and technical direction for realizing high-quality laser wire-filling welding of Al-Si coated steel.