Effect of Alloy Insert on Channel Segregation During Solidification of Sn-10 wt pct Bi Alloy

A promising approach is proposed for controlling the channel formation during solidification, which is characterized as inserting alloy inserts into the cavity before pouring the melt. A mathematical model, which couples melting with solidification, is developed for simulating the channel formation during solidification of the Sn-10 wt pct Bi alloy in the cavity with alloy inserts. The validity of the model is tested by real-time X-ray observation and experimental measurement. With different superheats, the effects of insert parameters, such as the amount (0.0 pct and 1.2 pct), shape (rod and particle), and initial position, on the melting process of the insert itself, thermosolutal convection, and channel formation are investigated numerically. Calculated results reveal that at a higher superheat, the extent of channel segregation is reduced with the addition of alloy inserts. Because inserts dissolve quickly, only a slight difference in channel formation is noted when the shape and initial position of inserts are changed. At a lower superheat, no channel is formed by adding the alloy inserts. Results are better with the addition of alloy balls. The local positive segregations around the unmelted inserts, which occur when alloy rods are added, are avoided.