Effect of bismuth and lead on phase composition and structure of Al—5%Si—4%Cu—4%Sn alloy

Abstract

The article focuses on the actual problem of creating economically alloyed antifriction aluminum alloys doped 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 technological and physicomechanical properties. Due to the high cost of tin, this paper considers the possibility of reducing its concentration to 4 %, and its partial replacement by other low-melting metals, such as bismuth and lead. Thermodynamic calculations (in the Thermo-Calc program) including the construction of polythermal and isothermal sections are used to study the joint and separate influence ofthese elements on the phase composition of the Al—5%Si—4%Cu—4%Sn alloy. It is shown that the addition of lead and bismuth leads to the appearance of an extensive area of fluid separation, and therefore their total concentration should not exceed 1—2 %. The phase composition and microstructure ofthe Al—5%Si—4%Cu—4%Sn—0,5%Pb—0,5%Bi alloy were studied using scanning electron microscopy and micro X-ray spectral analysis. It was found that in the cast state, low-melting metals are evenly distributed in the structure of the alloy, and in terms of the combination of properties, the experimental aluminum alloys surpass the BrO4Z4S17 antifriction bronze. Heat treatment mode T6 leads to a significant increase in the hardness of the experimental alloy. However, in the process of heating for quenching at 500 °C, local fusion of the low-melting component occurs, which leads to deterioration of the microstructure upon re-crystallization and, as a result, causes alloy embrittlement.