Thermal stability of Al-Mg alloys after solidification under high pressures

The thermal stability of Al-32Mg and Al-42Mg alloys prepared by solidification under high pressures, which contain a large amount of Al(Mg) solid solution, was investigated in the present paper. With increasing Mg content in the Al(Mg) solid solution, the mechanism of phase transformation has a remarkable difference compared to that prepared by other techniques. The GP zones first dissolve, then the γ phase is formed; the stable β phase is finally formed during the heating of Al(Mg) solid solution. By comparing formation of the precipitation phase of Al(Mg) solid solution prepared by different methods, it can be concluded that vacancy concentration may determine whether the β′ phase is formed, and whether the high Mg content is the necessary condition for the formation of γ phase. The γ phases that are precipitated from the Al(Mg) solid solution and formed during the solidification process all transform to the β phase in the Al-32Mg alloy; however, a part of the γ phase stably exists in the Al-42Mg alloy according to the equilibrium phase diagram.