Tailoring microstructure and mechanical properties of an AA5454 extruded aluminum alloy with Sc/Zr microalloying and processing conditions

Microalloying with Sc and Zr offers significant potential to enhance the strength, microstructural stability, and corrosion resistance of aluminum alloys. This study investigates the effects of individual Sc and combined Sc/Zr additions on the mechanical performance and microstructural evolution of AA5454 extrusions subjected to two homogenization treatments (350°C/24h and 575°C/4h). Homogenization at 350 °C promoted the formation of fine, coherent Al 3 Sc and Al 3 (Sc,Zr) precipitates, enhancing dispersion strengthening and recrystallization resistance. At the higher homogenization temperature of 575°C, Al 3 Sc precipitation was suppressed in the Sc-containing alloy, while coarse Al 3 (Sc,Zr) precipitates formed in the alloy containing both Sc and Zr. The results revealed a significant increase in yield strength (YS), ranging from 132–139 MPa in the Sc-containing alloy to 132–164 MPa in the Sc- and Zr-containing alloy, with yield strength increments of 49–77 MPa per 0.1 wt.% Sc addition, depending on the processing route. Transmission electron microscopy and electrical conductivity measurements confirm the evolution and reprecipitation behavior of Al 3 Sc/Al 3 (Sc,Zr) precipitates in the Sc- and Sc/Zr-containing alloys. A predictive strength model combining solid solution, grain boundary, and dispersion/precipitation strengthening showed good agreement with the experimentally measured YS values, identifying precipitation strengthening as the primary contributor, particularly after post-aging. These findings reveal pathways for improving the performance of 5xxx-series extrusions.