Structurally complex phase engineering enables hydrogen-tolerant Al alloys.

Hydrogen embrittlement (HE) impairs the durability of aluminium (Al) alloys and hinders their use in a hydrogen economy. Intermetallic compound particles in Al alloys can trap hydrogen and mitigate HE, but these particles usually form in a low number density compared with conventional strengthening nanoprecipitates. Here we report a size-sieved complex precipitation in Sc-added Al-Mg alloys to achieve a high-density dispersion of both fine AlSc nanoprecipitates and in situ formed core-shell Al(Mg, Sc)/AlSc nanophases with high hydrogen-trapping ability. The two-step heat treatment induces heterogeneous nucleation of the Samson-phase Al(Mg, Sc) on the surface of AlSc nanoprecipitates that are only above 10 nm in size. The size dependence is associated with AlSc nanoprecipitate incoherency, which leads to local segregation of magnesium and triggers the formation of Al(Mg, Sc). The tailored distribution of dual nanoprecipitates in our Al-Mg-Sc alloy provides about a 40% increase in strength and nearly five times improved HE resistance compared with the Sc-free alloy, reaching a record tensile uniform elongation in Al alloys charged with H up to 7 ppmw. We apply this strategy to other Al-Mg-based alloys, such as Al-Mg-Ti-Zr, Al-Mg-Cu-Sc and Al-Mg-Zn-Sc alloys. Our work showcases a possible route to increase hydrogen resistance in high-strength Al alloys and could be readily adapted to large-scale industrial production.