Study On The Preparation Of A New Oxygen-bearing Composite Refiner For Aluminum Alloys

Al-Ti-O composite refiner and Al-Ti-B-O composite refiner have been fabricated by direct melt reaction method and semi-solid rotational shear technique using Al-TiO₂ and Al-TiO₂-B₂O₃ system, respectively. The phase composition of two kinds of composite refiner has been investigated by X-ray diffraction; The microstructure and particulate features including morphology, size and distribution have been investigated by Optical Microscopy, Scanning Electron Microscopy and Energy Dispersive Spectroscopy. The grain refining effect of Al-Ti-O and Al-Ti-B-O composite refiner in pure Al and A356 alloy has been analyzed, respectively.The results indicate that, the reaction of Al-TiO₂ and Al-TiO₂-B₂O₃ system was spontaneous exothermic reaction, and the theoretical reaction temperature was about900℃and 950℃, respectively. In the reaction process of two systems, two mixed powders（Al+TiO₂ and TiO₂+B₂O₃） mixing join the semi-solid aluminum melt by mechanical agitator, and coating blade was used to make the powder dispersed evenly in the melt by its rotational shear. The reaction products of Al-TiO₂ system were composed of block-shape or rod-like Al3 Ti particles（about 30μm）and fine Al2O3（about1.5μm）with 15 minutes of shearing time and the reaction temperature 900℃ kept 5minutes. Under the same reaction conditions but the reaction temperature was 950℃,the products of Al-TiO₂-B₂O₃ system were composed of rod-like Al3 Ti particles（about30μm）, bright white Al2O3（about 1.5μm）and the gray fine TiB2（about 1μm）.The dispersibility of the mixed powders Al+TiO₂ and TiO₂+B₂O₃ can be improved by using the coating blade rotational shearing technology, the best shearing time is 15 minutes. Increasing temperature or prolonging holding time could promote the reaction process. In the reaction of Al-TiO₂ system, Unreacted reactants gradually reduce, the fine particles gradually disperse in the matrix and the Al3 Ti particles are irregular bulk when the reaction temperature increase from 850℃to 900℃, and the shape of block Al3 Ti particle become needle when the reaction temperature to 950℃.In the reaction of Al-TiO₂-B₂O₃ system, the mixed powder gradually complete react and gathering particles evenly distribute with increasing holding time, the reactants completely react and products spread to a certain degree at 950℃for 5 minutes, when the holding time increases to 15 minutes, the dispersibility of the fine particles was the best, Al3 Ti particles was oversize and needle, which is bad for the grain refining.For the preparation process of Al-Ti-B-O composite refiner using Al-TiO₂-B₂O₃ system, High-intensity ultrasonic treatment was conducted in reaction process for2 min, 5min and 15 min, respectively. The acoustic cavitation effect and acoustic streaming effect could promote the reaction completely, with the extension of ultrasonic time, the size of Al3 Ti phases reduced and the dispersibility of the agglomerated fine particles was improved. When the ultrasonic time was 5 minutes at950℃, the size of Al3 Ti particle decreased to about 35 μm, Al2O3 and TiB2 particles were relatively disperse, prolonging the ultrasonic time to 15 minutes, organization had little change, and the needle Fe phase was product in the melt, as a result, the best ultrasonic time was 5 minutes.Research on the grain refining performance showed, the grain of pure Al and A356 alloy could be refined effectively by Al-Ti-O and Al-Ti-B-O oxygen-bearing composite refiner. Compared with Al-5Ti and Al-5Ti-B grain refiner, the refinement effect of Al-Ti-O and Al-Ti-B-O composite refiner was better, and with the extension of refining time, the decay resistance of oxygen-bearing composite refiner was better.