Research On The Preparing Process Of Low-Ti Al-Ti-B Master Alloys For The Casting Alloys

Metals or alloys with small grains can achieve fine surface structure, which can avoid hot tearing, improve the yield strength, and reduce particle inclusion, avoid damaging to the elongation, thus resulting in good processing and molding properties. The method which inoculate master alloy (grain refiner) to the matrix is regarded to the most economic, convenience and practice way. Therefore, master alloys were always produced into ingots, pill ingots and silk shape in large scales.In this paper, the Al-3Ti-3B master alloys were produced by halide salts method. The influence of processing parameters such as the reaction temperature, holding time and stirring practice on microstructures and their grain refining performance were discussed in detail, which can give direct suggestions to the commercial use. In addition, based on these, a new type of Al-3Ti-3B master alloy was developed. This master alloy can get over some disadvantages such as the poor grain refining and easy fading performances which usually existed in traditional master alloys.The results revealed that:the reaction temperature and stirring process had more influences on the master alloy, while the holding time was not. When the reaction temperature is low. i.e.750, the recovery of Ti was low and the microstructures of intermediate were presented as big hunk shape and in turn resulted in poor grain refining performance; with the reaction temperature increasing, i.e. in850℃and950℃, reactions between the salts and melt trended to more fierce and complete which lead to a high Ti recovery. Meanwhile, the characters of the intermediates were small and the grain refining performance of the master alloy was thus improved. The holding time had less impact on the master alloy, therefore holding5min in preparation can achieve a good effect. Stirring practice can have a big influence on the microstructure and refining performance of the master alloy. If the stirring practice was added to preparation process, the effective particles (Ti.A1)B2can be trapped in the salts, the nucleation efficiency of these particles were thus lost. Besides, the new formed hunks can easy settle in the melt which impair their grain refining potency further.A novel Al-3Ti-3B grain refiner was produce by mixing Al-Ti master alloy and Al-B master alloy. This master alloy had a different microstructure which contains TiB2, TiA13and A1B12particles. T1A13can be fast acting and AlB12can be fading-resistance. The result showed that inoculate0.005%B such master alloy into Al-Si melt which can reduce the grain size of a-Al to160μm.As for low-Ti Al-B master alloy, when it produces on850℃-5min. A1B2exhibit fine equiaxed morphology. At the same reaction temperature, when the holding time was60min, A1B2grows up to hexagonal crystals and the size becomes larger. With a higher preparing temperature and faster cooling rate, A1B2exhibit noodle-like. The grain refinement efficiencies of these master alloys are different on Al-7Si alloy. The fine equiaxed AIB2can well grain refining Al-7Si alloy, while the noodle-like A1B2are not.