The Characteristic Of Solid-liquid Interface And Microstructure Of Al-12.5Si Alloy In DC Casting

In this work, in-situ temperature measurements were performed on the Al-12.5Si alloy during direct chill (DC) casting of billets of different parameters. Cooling curves and first-order differential cooling curves of Al-12.5Si alloy were obtained in different casting conditions. Studies on the macrostructure and microstructure corresponding to different cooling and first-order differential cooling curves were carried out to find the effects of the cooling intensity and temperature gradient on the solid-liquid interface and microstructure. The following conclusions may be drawn from the results of the present investigation:(1) The temperature gradient and cooling intensity of Al-12.5Si alloy were lower at the higher casting velocities and the microstructure was better. The primary silicon particles were less and smaller and the morphology of eutectics was coral-like. The temperature gradient and cooling intensity of Al-12.5Si alloy were higher at the lower casting velocities and the microstructure was worse. The primary silicon particles were more and larger and the morphology of eutectics structure was polyhedral.(2) From the edge to the center of billets the temperature gradient and the cooling intensity became smaller and smaller, primary silicon particles became more and larger and the morphology of eutectic structure changed from coral-like to coral-like and polyhedral.(3) The eutectic temperature was lower and eutectic reaction time was longer during DC casting in the center of billets at lower temperature gradient and cooling intensity. The eutectic temperature was higher and eutectic reaction time was shorter during DC casting in the center of billets at higher temperature gradient and cooling intensity.(4) Solid-liquid interface was closed to a straight line and had a smooth bottom. Solid-liquid interface was steeper and deeper under the condition of lower temperature gradient and cooling intensity. Solid-liquid interface was gentler and shallower under the condition of higher temperature gradient and cooling intensity. Solid-liquid interface in the side of the larger cooling water flow rate was deeper than the other.(5) Secondary dendrite arm spacing was larger in the side of developed a-Al dendrites and tertiary dendrites were developed along the upward direction. The a-Al dendrites grew to halo and eutectic structure appeared to be coarse. Primary silicon particles became more and larger and the morphology of eutectic structure was polyhedral in the corrosion area.