Enhancing resistance to hydrogen embrittlement in high-strength hot-press-forming steel sheets through Al-Si-Zn coating optimization

This study addresses critical issues of hydrogen embrittlement (HE) and liquid metal embrittlement (LME) in Al-Si-coated and Zn-coated hot-press-forming (HPF) steel sheets, respectively, by proposing an innovative approach of incorporating (24–30) wt% Zn into the conventional Al-Si (AS) coating to mitigate HE issues while leveraging the absence of LME associated with Zn coating. To the best of the authors` knowledge, no other paper has considered this subject. The optimal Al-Si-Zn (ASZ) sheet formed a surface oxide layer and Zn-enriched zone, acting as local trap sites to reduce H intrusion, while the AS sheet lacked this zone, leading to continuous H intrusion. The ASZ sheet reached complete H emission in 4 weeks, whereas significant H remained in the AS sheet even after 4 weeks due to higher H intrusion. This result emphasizes the crucial role of Zn addition in impeding H diffusion and ensuring excellent resistance to HE. Bending angles at peak load, crucial for assessing bending and sheet forming properties, were adversely affected by diffusible H contents within the sheets. When austenitized at 900 °C for 3 min and then cooled to 800 °C for tensile testing, the ASZ sheet experienced abrupt premature fracture due to selective Zn diffusion from the liquid alloy to grain boundaries, inducing LME. However, prolonged austenitization to 6 min mitigated LME, with no expected issues on LME. These findings underscore the significance of the tailored Al-Si-Zn coating in enhancing resistance to HE, making it suitable for broad applications in high-strength HPF steel sheets.