Solidification microstructure and temperature field during direct chill casting of Al-16Si alloy

By properly controlling casting parameters such as pouring temperature, casting velocity and water flux, direct chill (DC) casting can be employed to produce refined microstructure in the hypereutectic Al-Si alloys without chemical modification. This refined microstructure is characterized of fine primary Si particles, fully developed dendritic Al halos and fine coupled eutectics. In this work, in situ measurements of temperature field in the mould during DC casting of Al-16Si alloy at casting velocity of 2.17 mm/s, 3.5 mm/s and 4.34 mm/s at a pouring temperature of 800°C were performed. The results show that the primary Si phase nucleated at considerable undercooling (about 27°C to 38°C) and the growth temperature of dendritic Al halos was 7°C to 8°C below the equilibrium eutectic temperature. In the center regions of the DC cast billet, halos are fully developed because the Gl/R value is low.