Thermodynamic analyse on equilibrium precipitation phases and composition design of Al-Zn-Mg-Cu alloys

The solidification paths of Al-Zn-Mg-Cu alloys and its precipitation behavior are analyzed using software package JMatPro 6.0 for material property simulation of Al-base alloys. The microstructures of the experimental alloys are analyzed; the experimental results of microstructural analysis are in agreement with the thermodynamic prediction. Through orthogonal experimental method, this paper designs the composition of Al-Zn-Mg-Cu alloys by studying the variation of ?? (MgZn₂) phase, S (Al₂CuMg) phase, T (AlZnMgCu) phase amount and precipitation temperatures with different Zn, Mg and Cu contents. It is found that with the optimum mass fraction of Zn of 6.7%, Mg of 2.2%?C2.5% and Cu of 1.6%?C2.0%, the mass fraction of ?? phase can be up to 8.7%?C9.22% and that of S phase and T phase can be lower than 0.5%.