Effect of Bismuth and Lead on the Phase Composition and Structure of the Al–5% Si–4% Cu–4% Sn Alloy

Resumo

This article is devoted to the topical problem of developing antifriction aluminum alloys economically alloyed with low-melting metals. It was found in earlier experiments that an alloy containing about 5% Si, 4% Cu, and 6% Sn (wt %) has a balanced complex of manufacturing and physicomechanical properties. The possibility of decreasing the tin concentration to 4% and its partial substitution by other low-melting metals such as bismuth and lead is considered because of the high cost of tin. The joint and separate influence of these elements on the phase composition of the Al–5% Si–4% Cu–4% Sn alloy is studied using thermodynamic calculations (in the Thermo-Calc program), including the construction of polythermal and isothermal sections. It is shown that additives of lead and bismuth cause the appearance of an extensive area of fluid stratification, so their total concentration should not exceed 1–2%. The phase composition and microstructure of the Al–5% Si–4% Cu–4% Sn–0.5% Pb–0.5% Bi alloy are studied using scanning electron microscopy and X-ray spectral microanalysis. It is revealed that low-melting metals are uniformly distributed in the structure of the alloy in the cast state and, in totality of properties, this material surpasses BrO4Ts4S17 antifriction bronze. Heat treatment according to the T6 mode leads to a significant increase in the hardness of the alloy under study. However, local fusion of the low-melting component occurs during heating for quenching at 500°C, which causes the deterioration of the microstructure during recrystallization and, consequently, causes alloy embrittlement.