Modeling the Effects of Cu Variations on the Precipitated Phases and Properties of Al-Zn-Mg-Cu Alloys

This paper investigates the influence of Cu contents on the precipitated phases and the resultant properties of Al-Zn-Mg-Cu alloys. The quantities of three major precipitated phases and phase diagrams of Al-Zn-Mg-Cu alloys with various Cu contents have been calculated based on materials models and properties database. The results show that the amount of the main hardening η (MgZn₂) phase increases with an increase in Cu content up to 1.4% (wt.%), whereby the maximum amount of η phase can be obtained. S (Al₂CuMg) phase forms markedly as Cu content increases and the precipitation process occurs rapidly at early stage with temperature between 430 and 480 °C. T (A1₂Mg₃Zn₃) phase reduces significantly as the Cu content increases, and the presence of T phase in the alloy largely depends on the Cu:Mg ratio. The experimental verification for the presence of major phases is in good accordance with the modeling results. The physical and mechanical properties of the alloys under various heat treatment conditions have also been simulated.