The Research On The Preparation Process And Grain Refining Property Of Aluminum Alloy Grain Refiner

Al-Ti-B master alloy grain refiner was prepared in an induction furnace by the reaction of molten aluminum with halide salts, namely, K2TiF6 and KBF4. Impact of different processing parameters on the morphology, distribution, size and formation rule of the second phases in Al-Ti-B master alloy was investigated. The refining specialties of Al-Ti-B master alloy self-prepared were studied with comparison to the import Al-Ti-B master alloy in the refining test of pure aluminum. The grain refining mechanism of Al-Ti-B master alloy was discussed primarily according to thermodynamic knowledge and interrelated papers.The impact of superheating temperature of aluminum melt, salt addition seque- nce, holding time, and melt stirring during the fabrication of the master alloy on the morphology, size, and distribution of the second phases in the Al-Ti-B master alloy were discussed in the preparation test. The results indicated that superheating temperature of Al melt and salt addition sequence were the major factors, the rest were the ordinary ones. With the temperature increasing, the morphology of TiAl3 particles changed from blocky to needle-like (length stick). Different salt addition sequence resulted in the different distribution of TiB₂ in Al-Ti-B master alloy. The holding time and the melt stirring during the fabrication of the master alloy had a big impact on the second phases of Al-Ti-B master alloy.The formation laws and mechanism of second phases (TiAl₃, TiB₂) in Al-Ti-B master alloys prepared using different salt addition sequence were investigated. The kinetic models corresponding to the three different salt addition sequences were put forward.When the additional quantity of the master alloy was 0.2wt%, and the temp- erature was ranging from 710℃to 730℃, the grain refining performance of the master alloy was excellent. Complete conversion of coarse columnar grain structure to fine equiaxed grain structure occurred within 5min. When the refining time was beyond 60min, the fading phenomena occurred markedly. The master alloys prepared using different salt addition sequence had similar microstructure, but the refining performance was different obviously. The refining properties of the master alloy prepared by pre-mixed salts were better than that of the other two master alloys. In the test of grain refinement, it was found that the size ofα-Al refined by self-prepared A1-Ti-B master alloy was smaller than that refined by the import Al-Ti-B master alloy.Finally, the grain refining mechanism of Al-Ti-B master alloy was discussed according to the existing grain refining mechanisms.