Effects of Nb and Ta additions on the strength and coarsening resistance of precipitation-strengthened Al-Zr-Sc-Er-Si alloys

Highlights: • Nb and Ta micro-additions are made to a dilute Al-Er-Sc-Zr-Si alloys. • Zr-enriched primary L1₂ precipitates form on solidification. • Secondary L1₂ precipitates form on aging, and show improved coarsening resistance. • Nb and Ta are enriched at the secondary nanoprecipitate/matrix interface. • Micro-additions of Nb and Ta have similar effects as V, previously studied. - Abstract: A dilute Al-0.07Zr-0.02Sc-0.005Er-0.06Si (at.%) alloy was microalloyed with 0.08 at.% Nb or Ta. Atom-probe tomography reveals that, upon aging, Nb and Ta partition to the coherent L1₂-Al₃(Zr,Sc,Er) nanoprecipitates (with average concentrations of 0.2 and 0.08 at.%, respectively), with both segregating at the matrix/nanoprecipitate heterophase interface. This is consistent with the Nb- and Ta-modified alloys exhibiting, as compared to the unmodified alloy: (i) higher peak microhardness, from a higher nanoprecipitate volume fraction and/or lattice parameter mismatch; and (ii) improved aging resistance, from slower nanoprecipitate coarsening due to the small diffusivities of niobium and tantalum in aluminum. Analogous results were previously reported for a V-modified alloy.