Experimental investigation of the Mg-Al phase diagram from 47 to 63 at% Al

The purpose of this work was to investigate the Mg-Al phase diagram in the composition range from 47 to 63 at.% Al which has not previously been consistently determined. The rhombohedral epsilon phase near 56 at.% Al is found to form at 410 degrees C following a peritectoid reaction (gamma + beta --> epsilon) and not a peritectic reaction as reported by Schurmann and Voss (Giessereiforschung, 33 (1981) 43). The respective homogeneity ranges of the gamma phase in the Al-rich part and of the beta phase have been determined. Besides the gamma, beta and epsilon phases, the existence of a high temperature phase (named lambda) between 435 and 445 degrees C is suggested. The existence of the zeta phase and of the relevant invariant reactions reported by Schurmann and Voss are not confirmed by the present results.