Abstract: 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%—2.5% and Cu of 1.6%—2.0%, the mass fraction of phase can be up to 8.7%—9.22% and that of S phase and T phase can be lower than 0.5%.
0 Introduction
Possessing high strength and toughness, 7xxx series aluminum alloy is a vital structural material, which can be applied widely in the aviation and aerospace fields. In recent years, many internationally recognized scholars have done much research on the composition design and the relationship between the microstructure of the precipitation phases and the properties of the material[1-2]. By controlling the content of the main phases such as (MgZn2) phase, S (Al2CuMg) phase and T (AlZnMgCu) phase, the strength and stress corrosion resistance of Al-Zn-Mg-Cu alloys can be greatly improved[3-4].
In resent years, the use of thermodynamic modelling via the multi-platform software has been extensively applied to the complex alloys of many types, including Al-based alloys. Many software packages were developed for multicomponent phase equilibrium calculation in the past few decades, such as Thermo-Cal, Pandat and JMatPro. These software packages were developed based on the CALPHAD approach, which can be used to calculate the phase equilibrium and model the properties of multicomponent alloys by incorporating various theoretical models and relevant thermodynamic database[5-6]. In this paper, we use the CALPHAD method and JMatPro software to calculate the solidification paths of Al-Zn-Mg-Cu alloys and optimize the alloy composition of Al-Zn-Mg-Cu alloys by using the orthogonal experimental design. Moreover, the simulations are compared with the microstructural analysis to verify the reliability of the thermodynamic calculations.
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