Effect of Cooling Rate on the Microstructure of Semi-Solid Al–25Si–2Fe Alloy During Electromagnetic Stirring

The effect of cooling rate on the microstructure of semi-solid Al–25Si–2Fe alloy was investigated during electromagnetic stirring. It was found that as the cooling rate was increased from 7 to 21 °C/min, the equivalent diameter of the primary Si particles decreased from 70 ± 5 to 25 ± 2 μm. The primary Si particles form a fine blocky structure when the cooling rate is 21 °C/min. When the cooling rate is increased to 30 and 33 °C/min, the primary Si particles coarsen and adopt plate or other irregular shapes. As the melt cools to 690 °C, Fe inter-metallic phases present different morphologies at different cooling rates during EMS. These phases in the Al–25Si–2Fe alloy are mainly in the form of δ-Al4FeSi2 at higher cooling rates.