2009 Volume 50 Issue 3 Pages 622-630
An alternating current (AC) of 60 A with a frequency of 1 kHz was imposed on the hypereutectic Mg-4.8 mass% Si melt during solidification in order to modify the primary Mg2Si crystals. The liquidus and eutectic temperatures of the Mg-4.8 mass% Si alloy are 761°C and 638°C, respectively. In order to investigate the effect of temperature ranges with application of AC on the modification of the primary Mg2Si crystals, six temperature ranges from 770°C to 740, 700 and 630°C, and from 700°C to 680, 650 and 630°C were adopted. The temperature ranges examined had an obvious influence on the modification of the primary Mg2Si crystals. For a starting temperature of 770°C, the average size of the primary Mg2Si crystals could be significantly reduced with further decrease in the ending temperature to 700 and 630°C, with agglomeration of the refined primary Mg2Si crystals in these two samples was observed. For a starting temperature of 700°C, the average sizes of the primary Mg2Si crystals could also be reduced, although no obvious agglomeration of the refined primary Mg2Si crystals was observed. The sample treated in the temperature range between 700 and 630°C had primary Mg2Si crystals with the lowest average size and the highest uniformity of size.