NANOCRYSTALLINE PHASES AS AN EFFECT OF HEAT-TREATMENT OF IN AL-22AT-PERCENT-ZN ALLOY

The method of production of nanocrystals in an Al-22at%Zn alloy, has b een worked out. It consited in the formation of the semiliquid metasta ble alpha(m)-phase and subsequent solidification of it by cyclic isote rmal heating and cooling at rates about 500 K/s. The nanocrystals of Z n-rich alpha(ner) phase of 20 nm size were formed in the areas of dend ritic microcells during solidification due to precipitation on disloca tion loops. The sequence of phase transformations during such a heat t reatment was as follows: alpha(0) --> alpha(m) alpha(ner) The semiliqu id state was obtained by the superheating of the metastable phase by f ew degrees over the solidus temperature, which was resulting in the fo rmation of the phases enriched with zinc of the composition near liqui dus line. The structure analysis were carried out by TEM and XRD. Mech anical properties were examined using Vickers hardness test HV5 in the 635-735 K temperature range. The method allows to obtain nanocrystals in specimens few milimeters thick.