Mg基Mg-Ag合金の時効に関する研究（第1報）多結晶試料による研究

Abstract

As the first step to clarify the mechanism of precipitation from a solid solution having close-packed hexagonal structure, the age-hardening has been studied using polycrystalline specimens of the Mg-Ag alloy containing 12.6%Ag, aged at room temperature, 100°, 150°, 175°, 200°, 250° and 300°, by means of hardness measurement, microscopic examination and X-ray investigation. At high temperatures, from 150° to 300°, hardening is related to the precipitation of a new phase. At low temperature, 100°, no evidence of precipitation has been found, though hardening occurs with prolonged aging. In general cases, the number of precipitated phases is one, i.e. continuous precipitation occurs, throughout the period of aging. However, two-phase precipitation, that is, a pearlitic precipitation of the depleted matrix and a gamma phase have also been observed locally when the aging temperature is higher than 200°. The mode of growth of the two-phase precipitation in this alloy resembles that of the so-called grain boundary reaction, but its microstructure is different from that in the latter case: the precipitated particles in the pearlitic structure are smaller than in the case of the continuous precipitation. From Debye-Scherrer patterns, it has been deduced that the structure of the gamma phase (Mg3Ag) is complicated but not simply hexagonal such as proposed by Ageew and Kuznetzow.