Effect of Homogenization Process on Microstructure of Al-Zn-Mg-Cu Aluminum Alloys

Herein, the best homogenization process of 466.5 degrees C x 36 h + 490 degrees C x (14-26.4 h) that can completely eliminate the coarse phases sigma[Mg(Zn, Al, Cu)(2)] and S(Al2CuMg) in the Al-Zn-Mg-Cu aluminum alloy is developed. The homogenization process is determined by the method of calculation phase diagram, and the experimental verification. It is shown in the results that, first, in the microstructure of the as-cast alloys, the crystal structure of the sigma[Mg(Zn, Al, Cu)(2)], Al7Cu2Fe, and Mg2Si phases is determined. Second, during the homogenization process, the sigma[Mg(Zn, Al, Cu)(2)] phase dissolves and also transforms into the S(Al2CuMg) phase. Most importantly, the dissolution temperature range of the sigma[Mg(Zn, Al, Cu)(2)], S(Al2CuMg), and Al7Cu2Fe phases is determined from 472.56 to 476.36 degrees C, from 484.09 to 485.39 degrees C, and from 540.18 to 547.23 degrees C, respectively. At best homogenization process, the residual Al7Cu2Fe phase area fraction ranges from 1.28 +/- 0.16% to 1.60 +/- 0.18%. In addition, dispersed eta(MgZn2) phase precipitates in supersaturated Al-matrix during differential scanning calorimeter heating. And, the concentration differences between the grain center and the eutectic of structure of Zn, Mg and Cu regression equations are established, which can provide some reference for the design of experimental parameters, thus reducing the experimental workload.