Effects of Operating Parameters on Modification of Primary Mg<SUB>2</SUB>Si Crystals in Hypereutectic Mg-Si Alloy Treated by Imposition of Alternating Current

Abstract

An alternating current (AC) was imposed upon the hypereutectic Mg-Si melt during solidification to modify the primary Mg 2 Si crystals in the fixed temperature range between 700 and 630 C. The effects of current intensity and frequency have been investigated in the present study. For every sample, 200 primary Mg 2 Si crystals were measured and 200 data were then statistically analyzed. The average size and standard deviation were used to evaluate the modification effect, including the refinement and uniformity of sizes of the modified primary Mg 2 Si crystals. The results show that both frequency and current intensity were significant to determine the modification effect. When the current intensity was fixed at 60 A, the average size increased and uniformity of sizes of the primary Mg 2 Si crystals improved with the increase in the frequency to 2 kHz. However, in the case that the frequency was fixed at 1 kHz, the statistical average size increased and uniformity of sizes improved with the increase in the current intensity to 60 A. With the further increase in the current intensity to 90 A, the statistical average size and uniformity of sizes had no obvious changes. The average size drastically decreased and uniformity of sizes remarkably improved with the increase in the estimated electromagnetic force to a critical value of about 126 Nm À3 , corresponding to the current intensity of 60 A and frequency of 1 kHz. However, the average size was constant if the electromagnetic force exceeded the critical value.

Microstructures and mechanical performance of Mg–4Si–6Ni–xY in situ composite after extrusion process

“…Despite the reliable properties of the Mg 2 Si phase, Mg–Mg 2 Si in situ composite shows low tensile properties (low strength and ductility) due to the presence of both large primary Mg 2 Si phase with dendritic morphology and brittle eutectic phase (eutectic Mg/Mg 2 Si) [17,18]. Consequently, modification of such phases is necessary with the application of proper techniques such as modifying elements during casting [19]. Among useful elements that are employed for modification, Ca [20], Ba [21], and Gd [17] are so important.…”