Cr doping mediates hydrogen partitioning to suppress interfacial hydrogen damage in Al alloys

In aerospace, transportation, and other critical industries, the development of high-strength, high-ductility Al-Zn-Mg Al alloys with superior resistance to hydrogen embrittlement (HE) remains a pivotal challenge with substantial practical implications. However, the long-standing issue of HE induced by H accumulation at susceptible interfaces, including grain boundaries (GBs) and semi-coherent precipitate interfaces, has remained inadequately addressed. Here, we propose a strategy of local H partitioning that leverages Cr doping to introduce the E phase (Al₁₈Cr₂Mg₃) and η phase (Mg(Zn,Cr)₂). The E phase not only consumes Mg segregated at GBs to mitigate H enrichment but also acts as a hydrogen trap. The Cr-rich η phase formed by Cr substitution enables conversion of the weak hydrogen trap MgZn₂ into the strong hydrogen trap Mg(Zn,Cr)₂. The maximum H trapping energy in Mg(Zn,Cr)₂ (0.60 eV/atom) exceeds that at its semi-coherent interface (0.56 eV/atom) and at GB (0.25 eV/atom), driving thermodynamically favorable H migration from hazardous interfaces to the benign interior of nanoprecipitates. Experimentally, Cr-doped Al alloys exhibit nearly threefold enhancement in HE resistance under ∼6.7 ppmw H charging compared to standard-state Al alloys, with the area fraction of hydrogen-induced intergranular fracture (IGF) reduced to zero and complete elimination of IGF. This is mainly attributed to the mitigation of H enrichment at the interfaces, thus inhibiting the H-driven stacking fault (SF) expansion and planar slip at GBs. The strategy of suppressing HE by manipulating local H partitioning via microalloying, rather than preventing H ingress, offers a more reliable and simpler solution to ensure the service safety of high-strength Al alloys in H-related application scenarios.