Comparison of precipitation kinetics and mechanical properties in Zr and Sc-bearing aluminum-based alloys

[Display omitted] •Continuous and discontinuous mechanisms of L12-phases precipitation are revealed.•Sc increases precipitation kinetics of Zr-bearing alloy at first annealing step.•Two-step aging weakly influences precipitation and strength of Sc-bearing alloy.•Aging optimization of Sc-free alloy yields higher strength than Sc-bearing one. The study compares the precipitation kinetics of the L12-structured phase, microstructure, and mechanical properties in Al-Mg-Zr and Al-Mg-Sc-Zr alloys with a close atomic concentration of dispersoid-forming elements. Continuous and discontinuous precipitation mechanisms leading to spherical nanoscale and fan-shaped precipitates are revealed in both alloys. Scandium raises the precipitation kinetics of L12-structured dispersoids owing to its high diffusivity in Al. The low effect of two-stage annealing on precipitation and mechanical properties is observed in the Sc-bearing alloy compared to the Sc-free one. Due to heat treatment optimization, the Sc-free alloy exhibits higher yield strength as compared with the alloy containing both Sc and Zr. The Sc-free alloy requires a long-term two-step heat treatment to provide increased precipitates number density and high-strength values.