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Abstract
Controlling the segregation behavior of primary Si in the solidification process of hypereutectic Al-Si alloy is crucial for enhancing the design ability of the solidification structure. To explore the separation condition and morphological evolution of primary Si in detail, a series of experiments concerning the coupling effect of a temperature field and electromagnetic stirring on the segregation behavior of primary Si were carried out. Experimental results show that the temperature field and fluid flow in the melt are two key points for controlling the segregation behavior of primary Si. The establishment of a temperature gradient in the Al-Si melt is a precondition for realizing the separation of primary Si. On the basis of the temperature gradient, the electromagnetic stirring can further strengthen the separation effect for primary Si, forming a Si-rich layer with 65~70 wt.% Si content. The formation of the Si-rich layer is a continuous growth process of primary Si by absorbing Si atoms from Al-Si melt with the help of electromagnetic stirring. The separation technology for primary Si is proposed to realize the segregation control of primary Si, which not only broadens the application of Al-Si alloys in the functionally gradient composites but also provides a low-cost supply strategy of Si raw materials for the solar photovoltaic industry.
Highlights
Hypereutectic Al-Si alloys are recognized as excellent candidates for structural application in the aircraft, automotive and electronic packaging industries, due to their excellent wear resistance, high heat resistance and low thermal expansion coefficient [1,2,3]
The uneven growth of the primary Si occurs in the casting solidification process of Al-Si alloy with increasing Si content, resulting in severe macro-segregation in large ingots
The research of Yoshikawa et al, [11,12,13] indicates that the bulk flow forced by an intermediate frequency magnetic field can directionally drive primary Si particles, resulting in the axial macro-segregation of primary Si during the directional solidification of hypereutectic Al-Si alloy
Summary
Hypereutectic Al-Si alloys are recognized as excellent candidates for structural application in the aircraft, automotive and electronic packaging industries, due to their excellent wear resistance, high heat resistance and low thermal expansion coefficient [1,2,3]. The uneven growth of the primary Si occurs in the casting solidification process of Al-Si alloy with increasing Si content, resulting in severe macro-segregation in large ingots. The research of Yoshikawa et al, [11,12,13] indicates that the bulk flow forced by an intermediate frequency magnetic field can directionally drive primary Si particles, resulting in the axial macro-segregation of primary Si during the directional solidification of hypereutectic Al-Si alloy. There are many disputes about the understanding of the separation mechanism, especially regarding the issue for the separation condition and morphological evolution of primary Si, which greatly limits the implementation of electromagnetic separation technology to large commercial ingot production. The present work aims to confirm the separation condition and morphological evolution of primary Si during the solidification of hypereutectic Al-Si alloy under electromagnetic stirring. On the basis of fundamental understanding of the electromagnetic separation mechanism, the electromagnetic separation technology for primary Si was further developed, and its potential perspective in future industry was proposed
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