Hydrogen partitioning behavior and related hydrogen embrittlement in Al-Zn-Mg alloys

To develop high strength Al-Zn-Mg alloys, suppression of hydrogen embrittlement is indispensable. The hydrogen embrittlement behavior of different prepared Al-10.1-1.2Mg alloys with various hydrogen trap sites was observed using in situ synchrotron X-ray tomography in this study. Furthermore, we quantified the hydrogen partitioning based on hydrogen occupancies and hydrogen trap site densities in the prepared alloys. The combined analysis of hydrogen embrittlement and hydrogen partitioning showed that initial trapped hydrogen content in grain boundaries, vacancies, and dislocations before deformation was not crucial for inducing both intergranular fracture and quasi-cleavage fracture. However, hydrogen accumulates at grain boundaries and precipitate interfaces during deformation, inducing intergranular and quasi-cleavage fracture, respectively. Due to hydrogen accumulation, intergranular and quasi-cleavage fracture initiate when the hydrogen content at the grain boundary enriches 10³–10⁴ times the initial content and hydrogen content at the precipitate interface enriches 3.9 × 10² times the initial content, respectively. The change in hydrogen trap sites by processing and heat treatments did not suppress the intergranular and quasi-cleavage fracture. We conclude that generating new hydrogen trap sites (e.g., the interior of the intermetallic particle) in which hydrogen trap site density and binding energy are higher than the precipitate interface (>33.87 kJ/mol) is beneficial to suppress hydrogen embrittlement.