CALPHAD-aided design and model prediction achieve the strength and quench sensitivity balance of Al-Zn-Mg-Cu alloys

Abstract

Balancing strength and quench sensitivity in Al-Zn-Mg-Cu alloys through traditional composition optimization is difficult. This work proposes a novel approach to control the Zn/Mg ratio (R_Zn/Mg) by employing a simplified CALPHAD-aided equivalence precipitation (EP) model of η-type precipitates to balance strength and quench sensitivity. Alloys with varying R_Zn/Mg but the same theoretical mass fraction of η-type precipitates (M_η) were designed and investigated. The results show that alloys with equivalent M_η have similar strength across different R_Zn/Mg due to the comparable transformation activation energies of the η′ phase. When the M_η and total (Zn + Mg) content remain constant, alloys with R_Zn/Mg above the critical R_Zn/Mg show lower quench sensitivity, attributed to the lower nucleation rate of quench-induced η phase. The EP model improves predictions for precipitation strengthening and quench sensitivity by accounting for R_Zn/Mg effects on η-type precipitates. This optimized model accurately predicts yield strength and quench sensitivity, providing a strategy for achieving a balance between strength and quench sensitivity in Al-Zn-Mg-Cu alloys.