Features of thermal expansion of special-purpose aluminum alloys after treatment of melt and heat treatment

Abstract

A combination of corrosion resistance, low specific gravity, and high dimensional stability over a wide temperature range is necessary for alloys for special purpose. The dimensional stability is determined, first of all, by the low temperature coefficient of linear expansion (TCLE). The paper presents the results of studies on the effect of melt treatment on TCLE of aluminum alloys for special purpose on the basis of the system Al-(11÷40)%Si. It is shown that melt treatment with an aqueous solution of CuSO4 and modification of melt with a mixture of (CaCO3⋅MgCO3) leads to the decrease in TCLE for all alloys under consideration in the low-temperature test interval ttest = 50÷150 °C. Treatment of the melt by CO(NH2)2 vapours leads to the decrease of TCLE of alloys Al-40%Si in the whole temperature range from 50 to 450 °C. For high silicon alloys it is established that the decrease in TCLE occurs in the interval ttest = 350÷450°C after additional heat treatment