Hydrogen trapping and embrittlement in high-strength Al alloys

Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles 1 . High-strength aluminium alloys often used in aircrafts could help reduce the weight of automobiles, but are susceptible to environmental degradation 2 , 3 . Hydrogen ‘embrittlement’ is often indicated as the main culprit 4 ; however, the exact mechanisms underpinning failure are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the durability of the materials. Here we 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 ab initio calculations, which show that the co-segregation of alloying elements and H favours grain boundary decohesion, and the strong partitioning of H into the second-phase particles 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 minimizing cracking and guiding new alloy design. Atom-scale analysis of hydrogen and other elements at the grain boundaries of a 7xxx aluminium alloy shows that co-segregation of elements favours grain boundary decohesion, and that hydrogen embrittlement is prevented by strong partitioning into the second-phase particles.