Hydrogen Trapping at Grain Boundaries and Embrittlement in High-Strength Al-Alloys

High-strength Al-alloys help reduce the weight of automobiles, but they are susceptible to environmental degradation. Hydrogen (H) embrittlement is often pointed as the main culprit, however, the mechanisms underpinning failure are elusive: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the materials’ durability. Here we successfully performed near-atomic scale analysis of H trapped in second-phase particles and at grain boundaries in a high-strength 7xxx Al-alloy. We used these observations to guide atomistic <i>ab-initio</i> calculations which show that the co-segregation of alloying elements and H favours grain boundary decohesion, while the strong partitioning of H into the second-phases removes solute H from the matrix, hence preventing H-embrittlement. Our insights further advance the mechanistic understanding of H-assisted embrittlement in Al-alloys, emphasizing the role of H-traps in retarding cracking and guiding new alloy design (1).<br/><br/>(1) Zhao, H., Chakraborty, P., Ponge, D. <i>et al.</i> Hydrogen trapping and embrittlement in high-strength Al alloys. <i>Nature</i> <b>602, </b>437–441 (2022)