Hydrogen trapping and embrittlement in high-strength Al-alloys

TL;DR

This study combines atomic-scale analysis and ab-initio calculations to understand hydrogen trapping in high-strength Al-alloys, revealing mechanisms that influence embrittlement and guiding improved alloy design.

Contribution

It provides the first near-atomic scale analysis of hydrogen in Al-alloys and links atomic observations with computational models to elucidate embrittlement mechanisms.

Findings

Hydrogen co-segregation at grain boundaries promotes decohesion.

Hydrogen trapping in second-phase particles prevents matrix embrittlement.

Insights guide new alloy design strategies to mitigate hydrogen embrittlement.

Abstract

Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles. High-strength Al-alloys often used in aircrafts could help reduce the weight of automobiles, but 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 ab-initio 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.