The 5Cu40Zn55Al and 15Cu20Zn65Al alloys were prepared in the Al-Zn-Cu system. There exist the metastable phases ε and θ in the two alloys after homogenization treatment and furnace cooling,respectively. It is shown that the particles are refined from 3 mm to less than 10 μm after hammering the two alloys but there are still metastable phases. This means that the phase constituents of the two alloys have no changes by the deformation,which is different from that by balling. The phase constituents are not changed at room temperature by hammering,which is dependent on the deformation mechanism of hammering.
The room temperature phase diagram of Al-Zn-Cu system is the important basis for judging the phase constituents of the materials at the usage condition. New results about the room temperature phase diagram of the low copper side in the Al-Zn-Cu systems have been shown in this study. Miscibility gap of fcc phase in the Al-Zn-Cu system has also been studied by experimental diffusion-couple method and thermodynamic calculation. Properties of this miscibility gap have been known. It is practically significant for the study on the aging behavior and for the control of the microstructure and properties of the Al alloys with Zn and Cu element.
The phase constitutes and phase compositions in the eight alloys designed with different compositions of Al-Zn-Cu system have been determined after the homogenous treatment and then equilibrium cooling to 20℃ by use of optical microscope, electron probe microanalysis and X-ray diffraction. It has been found that there existed the T phase in the seven alloys. Consequently, it was testified that the T phase was stable at room temperature. At the same time, the phase relationship was not locally right for the isothermal section of 20℃ of Al-Zn-Cu system of the ASM published in 1997.
After diffusion couples were annealed at 260-360 ℃, the concentration profiles of Zn element were measured by EPMA. It has been first quantitatively determined by Matano method that the interdiffusion coefficient in A1-Zn fee solid solution containing high Zn contents is remarkably decreased due to the small addition of Cu. Also, the interdiffusion coefficient in A1-Zn fee solid solution clearly increases with the increasing of Zn concentration. The interdiffusion activity energy remarkably decreases with the increasing of Zn contents. On the other hand, the interdiffusion activity energy markedly increases due to the small addition of Cu in the A1 Zn fcc solid solution containing high Zn contents.
