Improving the mechanical and dynamic properties of Al-Zn-Mg-Cu- based aluminum alloy: A combined approach of microstructural modification and heat treatment

This study investigates the combined effects of microstructural modification by adding Ti, B, Ni, and Cr alloying elements and heat treatment, homogenization and solid solution (T6), on the mechanical and dynamic properties of Al-Zn-Mg-Cu- based aluminum alloy. The cast alloys were homogenized at 470 °C for 3 h, air cooled and solid solved at 470 °C for 3 h, quenched, and then artificial aged at 120 °C for 24 h. The modified Al-Zn-Mg-Cu- based alloy consistently shows an improved microstructure compared to the unmodified alloy, especially after T6 treatment, as confirmed by SEM analysis. The T6 heat treatment improved the microstructure by dissolving intermetallic phase precipitates and dispersoids, followed by quenching and aging to promote the precipitation of strengthening phases. The improved alloy exhibited 11.4 % enhancement in ultimate tensile strength and a 40 % improvement in elongation compared to the as-cast version. Furthermore, the dynamic young’s modulus of the improved alloy was enhanced by 13.0 % relative to Al-Zn-Mg-Cu- based alloy. The synergistic impact of modification and tempering resulted in the most significant enhancement in dynamic characteristics; thus, the modified alloy exhibited an increase of 11.5 % in first-mode resonant frequency and 25.4 % in dynamic modulus relative to the unmodified alloy. The tempered modified alloy (Al-Zn-Mg-Cu- based -M-T6) exhibits a somewhat superior damping ratio compared to the modified and homogenized alloy. This indicates a correlation between precipitated phases created by tempering and dislocations caused by modification.