Thermodynamic Investigation on K₂TiF₆ and C Powder to Prepared in-situ TiC_p in Molten Al-Si-Fe Alloy

In this study, K₂TiF₆ and C powder (Ti:C atomic ratio 1:1) are introduced into Al-Si-Fe alloy by contact reaction method. The focus of this study is to investigate the reaction and precipitation behavior of Ti source in the alloy melt, and the effect of reaction products on the microstructure and properties of Al-Si-Fe alloy. The results show that the reaction products formed between Ti and the matrix alloy can destroy the acicular β-Fe phase in the original alloy. The transformation results in the a morphological change of the alloy from needle-like structure to Chinese script and fishbone-like structure, which effectively improves the mechanical properties of the alloy. The DSC analysis results indicate that Al-Si- Fe powder, K₂TiF₆ powder, and C powder undergo significant exothermic reactions at around 950 °C, corresponding to the formation of TiC. Further microscopic morphology observations support the inference that TiC powders formed in this temperature range. Firstly, the synthesis of the matrix takes place at 580 °C. K₂TiF₆ mixed with alloy powder shows an obvious exothermic peak at 660 ℃, corresponding to the formation of the second phase Al₃Ti by wetting and chemical reaction. However, it is worth noting that the reaction intermediate product(Al₄C₃ phase) consumes three times as much Al₃Ti as itself. As a result, the exothermic peak generated by Al₃Ti disappears. Lastly, a long-term exothermic reaction that takes place above 850 °C lead to the gradual replacement of the Al₃Ti phase by TiC particles. The mechanical properties test indicates that the needle-shaped Al₃Ti to some extent deteriorates the alloy’s properties. But the final product (TiC) can offset the deteriorating effect of Al₃Ti and restore the alloy’s property.