ВЛИЯНИЕ ТЕРМИЧЕСКОЙ ОБРАБОТКИ НА СПЛАВЫ СИСТЕМЫ Al‒Mg‒SiС ИЗБЫТКОМ КРЕМНИЯ И МАЛЫМИ ЦИРКОНИЕВЫМИ ДОБАВКАМИ

Abstract

The study is aimed at studying heat treatment for the formation of physical and mechanical properties in the Al-Mg-Si system with an excess of silicon and small zirconium additives. The study was carried out on the example of three alloys with different Mg/Si ratios with a zirconium content of 0.15%. The alloys were subjected to both one and two-stage heat treatment. In the course of a single-stage heat treatment, the alloys were annealed at a temperature of 375–550 °C and holding, which ranged from 10 seconds to 100 hours, followed by fixation of the microstructure in water. In addition, a multi-stage heat treatment was carried out, the annealing temperature of the first stage was varied in the range of 425–550 °C with an 8-hour exposure and subsequent fixation in water, after which the metal was subjected to a 3-hour artificial aging. After completion of the heat treatment, the microhardness and electrical conductivity were investigated. Based on the data on the change in the latter depending on the mode of heat treatment, C-curves of the decomposition of the supersaturated solid solution were constructed. For some modes of heat treatment, studies of intermetallic particles were carried out using scanning microscopy. Using scanning electron microscopy, particles were found in the alloys, similar in their chemical composition to Mg2Si, Al3(FeSi) and Zr2Si. The obtained C-curves show that the decomposition of a supersaturated solid solution begins already at a temperature of 375 °C. Using the constructed C-curves, the influence of the content of silicon, magnesium elements on the rate of decomposition of a supersaturated solid solution is shown. It has been established that the annealing temperature of 375 and 425°C adversely affects the microhardness in the alloys under consideration. After an increase in the annealing temperature to 550°C, there is practically no decrease in microhardness. The performed studies made it possible to choose the optimal mode of multi-stage heat treatment, namely heating to 550 °C for 8 hours with cooling in water, and subsequent 3-hour exposure at a temperature of 180 °C. In general, zirconium additives give an increase in microhardness by 11-25 HV compared to base alloys.