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

Equilibrated phase compositions at 250-400 degrees 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 Mg17Al12 (gamma) intermetallic compound is similar to 36.6 at.% when the Mg17Al12 phase is in equilibrium with the alpha-Mg solid solution, i.e., gamma/(gamma + alpha-Mg) phase boundary remarkably shifts to the Mg-rich side. The R intermetallic compound (R (3) over bar) does stably exist at 250 degrees 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 beta phase (Fd (3) over bar) is determined in the range of 57.5-60.5 at.% Al below 400 degrees C. (C) 2012 Elsevier B.V. All rights reserved.