Study On The Phase Equilibria Of The Al-Cu-Mg-Zn System In The Al-rich Corner

7xxx aluminum alloys with high strength and modulus, good corrosion resistance and high toughness, are a new type of rigid structural materials of aeronautics and astronautics. A complete and accurate Al-Cu-Mg-Zn alloy phase diagram which can describe its alloy composition, temperature and phase equilibrium relations have not yet established because of its complexity, and therefore a lot of alloy development is used to adjust alloy composition trially. In the Al-Cu-Mg-Zn quaternary system, the important three constituent ternary systems, Al-Mg-Cu, Al-Mg-Zn and Al-Cu-Zn ternary phase diagrams are also not perfect, in which some phase equilibra and phase compositions remain controversial.The main purpose of this study is to perform experimental measurements to the phase equilibria of Al-Mg-Cu, Al-Mg-Zn and Al-Cu-Zn ternary alloys at the temperatures of300℃、400℃and450℃. The results can provide effective and reliable data for the study of the Al-Cu-Mg-Zn quaternary phase diagram. The detailed results are as follows:(1) The solid solubilities of the (aAl) have been determined in the Al-rich corner of the Al-Cu-Mg, Al-Mg-Zn, Al-Cu-Zn system. Comparing the experimental results with the calculated phase diagrams, we can clealy find that the solid solubilities of the (αAl) determined by experiments and calculation differ greatly, especially in the the phase equilibria of the Al-Cu-Mg and Al-Mg-Zn systems at300℃and Al-Cu-Zn system at450℃.(2) The phase equilibria of the above systems at the temperatures of300℃,400℃,450℃and495℃in the Al-rich region have been well studied. The intermetallic compounds of Al2Cu, Al2MgCu and Al6Mg4Cu have been detected to get equilibrium with (aAl) in the Al-rich corner of Al-Mg-Cu system, At the temperature of495℃, liquid has been found in the Al-Mg-Cu system. The intermetallic compounds of MgZn2and Mg3Zn3Al2have been detected to get equilibrium with (αAl) in the Al-rich corner of the Al-Mg-Zn system. The intermetallic compounds of Al2Cu have been detected to get equilibrium with (aAl) in the Al-rich corner of the Al-Cu-Zn system. A comparison has been done between the calculated and the experimental results, where we can see that the calculated phase compositions are different from the experimental results. For example, the experimentally determined composition range of Al6Mg4Cu phase has lower Mg and more Cu comparing with the calculation.(3)Through the study on the phase equilibria of the Al-Mg-Zn and the Al-Cu-Zn systems, the solubilities of Al in MgZn2and Zn in Al2Cu have been well studied. The calculated solubility of Al in MgZn2is less than the experimental results.The research results above are very important to develop the Al-Cu-Mg-Zn alloys. Based on these experimental results, a thermodynamic database of the Al-Cu-Mg-Zn system can be established, which will help the alloy design of the7xxx aluminum alloys.