Microstructure evolution of Cu-12.58%Mg hypereutectic alloy at constant and abruptly increasing velocities in directional solidification

Directionally solidified microstructures of Cu-Cu ₂Mg hypereutectic alloy were investigated in different solidification conditions. At the pulling velocity ranging from 5 μm/s to 100 μm/s, the interface morphologies of Cu-Cu ₂Mg hypereutectic were observed changing from the coarse dendrite with less side-branch to refined dendrite. As the pulling velocity increased abruptly from 2 μm/s to 20 μm/s, the primary dendrites of Cu ₂Mg phase were thinned and some ceased growing. The branch of Cu phase in coupled eutectics led to reduction of the lamellar spacing during the pulling velocity abruptly changing process. Simultaneously, the experimental results show that the abruptly increasing velocity process enable the coupled eutectics more refined compared to the constant pulling velocity process.