The thermal stability of strongly saturated solid solution of hyper-eutectic Al-Mn alloys

Studies on hyper-eutectic Al-Mn alloys (4th Report)

Abstract

The thermal stability of strongly saturated solid solution obtained by rapid cooling from the molten state of Al-3% Mn alloys containing each one of the following 3rd elements (Ag, Cu, Mg, Si and Zn) was studied by means of dilatometer, electron microscope, hardness test etc.
The results obtained were as follows; The curves obtained by differential dilatation were showed that two stages of the decomposition of supersaturated solid solution by the precipitation of Al₆Mn and other compounds were evident in Al-3% Mn-2% Cu and Al-3% Mn-0.5% Si alloys. However, only one stage was evident in other alloys.
The change in length by isothermal heat-treatment was not found at 300°C for 500hr, in Al-3%Mn and Al-3%Mn-2% Zn alloys. However, expansion and contraction were observed in other alloys. In any of test alloys, no remarkable age-hardening effects were found and the hardness as cast was maintained for a long period at high temperature independent of the change in expansion or contraction by aging.