Segregation behavior and its regulating process in as-cast magnesium alloy containing heavy rare earth

Abstract

Specific gravity segregation that occurs during the smelting process always leads to the low composition homogeneity and poor performance stability of the magnesium-rare earth (Mg-RE) alloys. In this study, the segregation behavior of Mg–Gd alloy was investigated by sampling from different locations in the ingot fabricated in a resistance furnace without a pouring process. The combined application of induction-heating and mechanical stirring with various speeds (0–130 r/min) was applied to promote the distribution homogeneity of Gd atoms. In the resistance-heating fabricated ingot, Gd content at the bottom section reaches 407% of that at the top. The coarse dendrites surrounded by the network-like eutectic structures are responsible for the brittle fracture with a poor elongation of 3.7%. By the combined employment of the induction heating and mechanical stirring with the speed of 87 r/min at 740 °C for 40 s, the variation of the Gd content within the whole ingot can be reduced to be the minimum of 0.23 wt%. Corresponding formation and regulating models of segregation were also proposed. However, the cooling rate of the melt is reduced by the continuous increase of the stirring speed to 130 r/min, which results in the grain coarsening and lower homogeneity of the ingot.