Fabrication of Al-Ti-B Grain Refiner Using Machining Ti Chips, Reaction Mechanisms and Grain Refinement Performance in Pure Al

Al-5Ti-1B grain refiner was successfully prepared with the reaction of Ti chips produced during machining and KBF4 in pure aluminum melt. In order to illustrate the reaction mechanism of Ti chips, the effect of different feeding ways and reaction times of Ti chips on microstructure and refining performance of Al-5Ti-1B was systematically investigated by optical microscope, scanning electron microscopy and X-ray diffractometer. The results show that, in three feeding ways, including adding Ti chips firstly, adding KBF4 firstly and adding both Ti chips and KBF4 in the form of prefabricated blocks, the best refining performance of Al-5Ti-1B is the feeding way of using the prefabricated block. TiB2 and TiAl3 as effective heterogeneous nuclei are formed simultaneously around the Ti chips. The average grain size of pure aluminum is refined to about 206.80 mu m. The reaction time mainly affects the dissolution process of Ti chips and the average size of TiAl3. With the reaction time from 60 min to 90 min and then to 120 min, the average size of TiAl3 increases from 10.74 mu m to 14.30 mu m and then to 15.39 mu m. During the dissolution process, Ti chips undergo a transition from a thermal isolation layer to a supersaturated zone of Ti atoms. Based on the analysis of the dissolution process of Ti chips, the dissolution model is proposed. Al-5Ti-1B has the best refining performance at 90 min of the reaction time, which can refine pure aluminum to about 223.65 mu m.