Enhancing P removal from primary Si by P-containing Al2Si2Sr phase during Al–Si solvent refining

Abstract

In this paper, adding small amounts of Sr in Al–Si solvent to enhance the P removal from primary Si by the formation of P-containing Al2Si2Sr phase has been developed. By microstructure and EDS analysis, it is determined that the Al2Si2Sr phase precipitated in the melt is enriched with 0.8–1.2 at% P. The precipitation of the P-containing Al2Si2Sr phase consumes a large amount of P in the melt, which makes the P content in the primary Si decrease. With the addition of Sr-16000 ppmw, the P removal fraction in the primary Si is all over 93% and the highest removal fraction reaches 94.66%. The B content in primary Si does not change significantly with the increase of Sr addition. Some of the Al2Si2Sr phases are trapped and engulfed by the primary Si, which leads to the accumulation of Sr impurity in the primary Si. Moreover, the possibility of P behaving as the solute atom in the Al2Si2Sr solid solution is analyzed through first-principle calculations. The result shows that P replaces Si at its the atomic position in the Al2Si2Sr phase to achieve a more stable crystal structure. Finally, an evolution model of the interaction between the P-containing Al2Si2Sr phase and the primary Si in the Al–Si melt is established.