Effect Of Preparation Technology And Rare Earth On Refining Performance Of Al-TiO₂-C Refiners

Aluminum and its alloy is currently widely used in all aspects of industrial production and daily life, which is the most important metallic materials in national construction. Increasing comprehensive performance of aluminum by grain refinement plays an important role in prolonging service life and expanding the scope of its application. The refinement agent is the most simple and effective method to refine the grain of aluminum alloys. At present, the application technology of refiner is immature and its refining effect is unstable. Thus, it is necessary to further study in the preparation process and mechanism of refiner.Al-TiO₂-C refiners were synthesized by the in-situ exothermic dispersion method. In the grain refiner performance test, the refiners were added to industrial pure aluminum. Effect of TiO₂ contents, sintering rate, adding amount, holding time and rare earth contents on refining performance were discussed. The microstructure under different conditions was investigated by OM, SEM, XRD and EDS analysis. The refining effect was analyzed by the KBI ring mode method and line transect method. The sesults as follow.Al-TiO₂-C refiners are composed of Al₃Ti、Al₂O₃ and TiC. The effect of TiO₂ content on the microstructure and refinement effect of Al-TiO₂-C was remarkable. When the content of TiO₂ is 8-12%, Al₃ Ti is wrapped in large number of Al₂O₃ and TiC particles, Al₃ Ti is separated from each other by the particles, Al₃ Ti is massive and the microstructure is distributed uniformly. The Al-TiO₂-C refiners have a better refining effect on pure aluminum when the content of TiO₂ is 8-12%. The average grain size of aluminum refined by Al-TiO₂-C refiner with 12% TiO₂ is about 140 μm.In a certain range, the heating rate has a great influence on the microstructure and refining effect of Al-TiO₂-C refiners. When the heating rate at 40-50 degrees /min, there is no needle like Al₃ Ti in Al-TiO₂-C refiners, Al₃ Ti all become block. Al₂O₃ and TiC distributive uniformly. The Al-TiO₂-C refiners has a better grain refinement effect when the heating rate is 40-50℃/min.In this paper,the effect of refining becomes better with the increase of the refiners in a certain range. When the adding amount is 0.3%, the refining effect of Al-TiO₂-C grain refiner is best. Then the refining effect is not significantly improved with further increasing refiners. The grain structure refined by Al-TiO₂-C refiner becomes finer within 10 min and remains the same in 30 min and 60 min. The grain structure goes bad until 120 min.The composition of master alloys is different, the second phase particles are different, and refining effect on industrial pure aluminum is also different. Al₂O₃ and TiC can not only refine the grain size, play an important role in changing the morphology of Al₃ Ti and improving the refining efficiency of Al₃ Ti. The refining effect of Al-TiO₂-C master alloy is better than Al-Ti, Al-TiO₂ and Al-Ti-C master alloys because it contains Al₂O₃ and TiC particles and blocky Al₃ Ti.La₂O₃ plays an important role in improving the refining effect of Al-TiO₂-C. The Al-TiO₂-C-La refiner is composed of Al₃ Ti, Al₂O₃, TiC and Al20Ti2 La phases. The addition amount of La₂O₃ is different, the microstructure and the refining effect of Al-TiO₂-C-La is also slightly different. When the content of La₂O₃ was 0.2%, the majority of Al₃ Ti is massive, and Al₂O₃ and TiC particles increase obviously and their distribution is relatively dispersed, which has a better refining effect on aluminum. An excellent grain refining performance is obtained when adding 0.2wt% Al-TiO₂-C-RE refiner with 0.2%La₂O₃, the average grain size is about 80μm and there is no refiner recession when holding 120 min.