Actual Problems in Machine Building Vol.5 N1-2 2018

Actual Problems in Machine Building. Vol. 5. N 1-2. 2018 Materials Science in Machine Building ____________________________________________________________________ 138 MODIFICATION EFFECTS ON MICROSTRUCTURE AND PHYSICAL PROPERTIES OF Al-(20÷40)% Si ALLOYS Popova M.V. , D.Sc. (Engineering), Professor, e-mail: m.popova@rdtc.ru Malyuh M.A. , Post-graduate Student, e-mail: starostina_ma1976@mail.ru Siberian State Industrial University, 42 Kirov str., Novokuznetsk, 654007, Russian Federation Abstract This paper presents the results of the research of the effect of alloy modification with Cu sulfate on microstructure, thermal expansion and density of aluminium alloys with 20÷40% Si. Modification was carried out in the following way. Alloy melts were purged for 5-15 minutes with vapors of 3-7% water solution of CuSO 4 at a temperature 800–1100ºС. Crystallization was carried out in the aluminum chill mold whereby liquid stamping was imitated. The metallographic analysis has shown that the alloy modification proposed in the current paper induces the formation of finely dispersed structure of Al-(20÷40) % Si alloys, especially after high- speed crystallization. At the same time the size of both the primary crystals of Si as well as of the eutectic Si decreases. The conducted research has shown that the treatment of alloys with vapors of water solution of Cu sulfate affects the temperature coefficient of linear expansion, microhardness and density of alloys Al-(20÷40) % Si. The TCLE goes down by 3-16% in the temperature range 50–250ºС whereas it increases in the temperature range 300–450 ºС. As a result of modification the microhardness of alloys increases whereas their density goes down by 3-6%. The aforementioned changes of alloy properties become more pronounced when the content of Si is increased. Keywords aluminum, silicon, modification, microstructure, temperature coefficient of linear expansion, crystallization, density.