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^1-3. Intermetallic compound particles in Al alloys can trap hydrogen and mitigate HE⁴, 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 Al₃Sc nanoprecipitates and in situ formed core-shell Al₃(Mg, Sc)₂/Al₃Sc nanophases with high hydrogen-trapping ability. The two-step heat treatment induces heterogeneous nucleation of the Samson-phase Al₃(Mg, Sc)₂ on the surface of Al₃Sc nanoprecipitates that are only above 10 nm in size. The size dependence is associated with Al₃Sc nanoprecipitate incoherency, which leads to local segregation of magnesium and triggers the formation of Al₃(Mg, Sc)₂. 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.