Study On The Refining Mechanism Of Al-Ti-B-O Composite Refiner

Al-Ti-B-O refiner is a combination of Al-Ti-B refiner with Al₂O₃ particles.Therefore it is clear that we could study on the refining mechanism of Al-Ti-B refiner and Al₂O₃ particles on aluminum alloys separately as we want to know how Al-Ti-B-O refiner has an effect on aluminum alloys. In case that the refining mechanism of Al-Ti-B refiner has made more progress so that we can use it for reference, what we need to do is just having a research on the refining mechanism of Al₂O₃ particles to aluminum alloys, and then adding the mature refining mechanism of Al-Ti-B refiner into it to explore the refining mechanism of Al-Ti-B-O refiner.Semi-solid mechanical stirring and ceramic knife cutting were used to synthesize Al₂O₃ particle reinforced Al-8Si matrix composites from SiO2 powers and Al-7Si aluminum alloy successfully. Microstructures of the composite were analyzed by optical microscope（OM） and scanning electronic microscope（SEM）. It was shown that SiO2 particles can be drawn into the matrix by using the steel impeller, but they never dispersed uniformly but in the form of aggregation. Then the ceramic blade was used to cut the molten matrix, and made Al₂O₃ particle disperse more uniformly through the Al-8Si aluminum alloy grain boundaries. The primary α-Al dendrites tended to be equiaxed. At the same time, eutectic silicon turn into small lumps near Al₂O₃ particle.γ-Al₂O₃ particles with different sizes and weight percentages were added into the Al-8Si alloy by semi-solid mechanical stirring and ceramic knife cutting process. The results showed that the small-sized γ-Al₂O₃ particles distributed in a wider range under the same weight percentage, and the ability to refine the eutectic phase was stronger, but the reunion was worse than large γ-Al₂O₃ particles. 1wt.% is the best adding percentage for γ-Al₂O₃ to distribute in the matrix under the same particle size,as adding too much made the agglomeration serious. The larger the size of Al₂O₃ particles, the worse effect to refining α-Al grain of Al-8Si alloy. Small size of Al₂O₃ particles is good to α-Al grain refinement. Besides, adding 1wt.% Al₂O₃ particles is most useful to refine a-Al grain.Different weight percentages of Al-5Ti-1B refiner and Al-5Ti-1B-6O refiner were added into Al-8Si alloys. It can be seen that refiners had the best adding quantity which can refine the grain size to the best effect, and the grain size can not be smaller beyond the best adding quantity. The best adding quantities of Al-5Ti-1B refiner and Al-5Ti-1B-6O refiner are 0.6wt.%. The alloy grain size of adding Al-5Ti-1B-6O refiner was smaller than that adding Al-5Ti-1B as adding the best adding quantity.After adding grain refiner, the grain shape turned to flower shape, and it could be found that there were Al₂O₃ particles inside α-Al phase and the size are about 1μm.And the Al₂O₃ particles could act as nucleates to refine the grain size.