THERMAL EXPANSION SPECIAL PURPOSE ALUMINUM ALLOYS AFTER MELT TREATMENT AND HEAT TREATMENT

10.25712/ASTU.1811-1416.2024.02.012

Abstract

This paper highlights the results of studies carried out to determine the effect of various reagents used in melt processing on the temperature coefficient of linear expansion (TCLE) of binary alloys of the Al-(11÷40) % Si system for special purposes. It has been established that the use of an aqueous solution of copper sulfate CuSO4 as a melt treatment agent and a mixture of alkaline earth metal carbonates (CaCO3∙MgCO3) as a melt modifier makes it possible to reduce the thermal expansion coefficients of all the alloys under study in the working temperature range. It was shown that the use of urea vapor for melt treatment leads to a decrease in the thermal expansion coefficient of hypoeutectic alloys over the entire temperature range of tests. It has been established that heat treatment, which consists in heating from 100 to 200 °C for 10 hours, followed by cooling in air, contributes to a further decrease in the values of the thermal expansion coefficient of the alloys under study. An increase in the physical and mechanical characteristics of Al-Si alloys after modification was noted, which can be explained by an improvement in the assimilation of hydrogen and oxygen introduced into the melt. It has been suggested that particles of refractory Ca and Mg oxides contained in the mixture provide additional numerous crystallization centers. As a result, it was concluded that an environmentally safe technology for modifying the melt with a mixture of alkaline earth metal carbonates makes it possible to reduce the overheating temperature of the melt from 1100 to 1200 °C to 900 °C and reduce the duration of the smelting process from 5-6 to 1-1.5 hours.