Experimental study of Al-Zn alloy decomposition at various temperature and deformation regimes

Abstract

In this work the evolution of phase composition and microstructural characteristics of Al-50% Zn and Al-60% Zn alloys under different temperature regimes and under deformation was investigated experimentally by X-ray diffractometry and scanning electron microscopy methods. It was found that the full decomposition of the initial homogeneous solid solution of zinc in aluminum is completed within three months at room temperature. At the same time, in the time interval of 10-40 days, a peculiar composition of fcc-solid solutions of different concentrations is formed. The final result of aging is a homogeneous solid solution of equilibrium concentrations and almost pure zinc. The SEM method shows that the microstructure of the Al-50% Zn alloy includes the fields of the same chemical composition with a different appearance of morphology. It was also shown that the morphology of the near-to-alloy alloys in the concentration range of 50-60 percent by weight has significant differences. This can be the result of the threshold nature of the concentration dependence of the processes of structuring. The microstructure of the Al-50% Zn alloy tempered from the two-phase region under the "dome" of the phase diagram of the state is investigated. The existence of two morphological types - depleted matrix and micron formations of complex form with high zinc content is shown. By means of local X-ray microanalysis, the average composition of these regions is determined - 31% Al, 69% Zn. The composition of the matrix is 53% Al, 47% Zn. The samples were cooled from 400C to room temperature with different rates of temperature change. It is shown that in the range of values of cooling rates 1000 K / s - 10 K / s there is an interval at which two concentric types of fcc solid solutions are formed. The diffractograms of Al-60% Zn alloy samples, cooled with the speeds characteristic for quenching in different media and free cooling from the furnace, are presented. The phenomenon of decomposition of the solid solution of Al-50% Zn and Al-60% Zn alloys under the influence of mechanical deformation was recorded. The conditions under which the deformation of these alloys passes through is plastic, and the contribution to the decomposition of the solid solution of the thermal factor is insignificant.