Re-determination of γ/(γ + α-Mg) phase boundary and experimental evidence of R intermetallic compound existing at lower temperatures in the Mg-Al binary system

摘要

Equilibrated phase compositions at 250-400 °C in the Mg-Al binary system have been determined by means of both diffusion couple technique and alloy method. The results show that the solubility of Al in the Mg_(17)Al_(12) (γ) intermetallic compound is ~36.6 at.% when the Mg_(17)Al_(12) phase is in equilibrium with the γ-Mg solid solution, i.e., γ/(γ + α-Mg) phase boundary remarkably shifts to the Mg-rich side. The R intermetallic compound (R3) does stably exist at 250 °C, and its composition range is 51.2-54.5 at.% Al, which is completely different from the presently accepted Mg-Al phase diagram. Moreover, the composition region of β phase (Fd3) is determined in the range of 57.5-60.5 at.% Al below 400 °C.