Solidus composition in Mg side phase diagram of Mg-Zn binary system and its estimation method

Abstract

Eutectically solidified portion, which should be liquid at 673 K, remained in alloys containing more than 7.8 mass% Zn. From change in area fraction of the liquid phase with Zn content, boundary composition between L+α and α regions at 673 K was estimated as about 6.7mass% Zn. Resistivity of a specimen containing 7.8 to 8.6 mass% Zn increased with descending temperature treatment starting from 673 K and saturated at 633 K. Treatment at 613 K, the reported eutectic temperature, prolonged for 602 ks gave a nearly same saturating resistivity which suggested a maximum equilibrium solubility of Zn to Mg to be about 8.5 mass%. Details to be paid attention are described for resistivity measurement of large cross section specimens requiring a large electric current to generate enough electromotive force. When the resistance was measured in liquid nitrogen, effect of Joule heat was scarcely observed. The heating effect was clearly observed when the resistance was measured in a kerosin bath. Even in this case, the effect can be eliminated easily by extrapolation of square of current versus measured resistance plots to zero current.