Preparation Process and Phase Transformation of Al-5Ti-0.25C Master Alloy Adopting Ti Machining Chips

The refining performance of Al-Ti-C master alloys is substantially compromised by the inferior wettability between graphite and molten aluminum. In this paper, the Al-5Ti-0.25C master alloy was successfully prepared by reacting Ti machining chips, graphite, and molten aluminum. In order to determine a simple method of improving the wettability, the optimal preparation process and phase transformation of the Al-5Ti-0.25C master alloy were investigated using an optical microscope, X-ray diffractometer, and scanning electron microscope equipped with an energy dispersive spectrometer. The results show that the feeding method using a prefabricated block made from Ti chips, Al chips, and graphite effectively improves the wettability between graphite and molten aluminum and increases the recovery rate of graphite. When the reaction temperature is low (1223 K), the agglomeration of TiAl₃ is caused. When the reaction temperature is high (1373 K), the morphology of TiAl₃ changes from block-like to needle-like and increases its size. Further, a short reaction time (30 min) results in the incomplete dissolution of the Ti chips, while a long reaction time (90 min) causes the TiAl₃ to transform into needle-like morphologies. The microstructural observation of undissolved Ti chips shows that TiAl₃ and TiC are formed around it, which proves the transformation of Ti chips to TiAl₃ and TiC. In addition, the enrichment of TiC and Al₄C₃ was observed in the vicinity of TiAl₃, and a reaction model for the formation of TiC from the reaction of Al₄C₃ and TiAl₃ was presented.