The Pilot Study Of Al-Ti-C Structural Macro-Kinetics And Optimization Of Preparing Processes Of Al-Ti-C Grain Refiner

Recent year, aluminum has been the second matel material inferior to steel and been used in astronavigation, avigation field and so on. Material capability and structure decide material performance.so that, the direct method to improve material performance was to change material structure.as for aluminum and its alloy, the most efficient and useful method is grain refinement.and to append grain refiner is the directal method.The Al-Ti-C grain refiner for aluminum and its alloy was prepared by thermal explosion method of self-propagating high-temperature synthesis (SHS) in melt aluminum with the aluminum powder titanium powder and graphite powder in this paper. The Al-Ti-C grain refiner phases , configuration of Al₃Ti and TiC and its refining performances for commercial purely aluminum was researched. The powder admixture was making of different Al: Ti: C ratios of the prefabricated block in 710°C which is the temperature of aluminum liquid. The results of XRD show that the ratio of Ti/C was important factor for phases compose in the grain refiner. Along with the ratio of Ti/C transfer form more than 1.5 to less than 1.5 ,the mostly phases transfer form Al₃Ti and Al two mostly phases to Al₃Ti TiC and Al three mostly phases in the grain refiner. The analysis of optical microscope and EPMA show that the shape of Al₃Ti was block in the grain refiner, its refining performances show that this shape was the best shape in all kinds shape. The experiments show that when the ratio of Ti/C is 3/2 (namely: Al: Ti: C=3:3:2) in the prefabricated block was the best component in the refining performances. The conclusion is if the synthesis grain refiner has good refining performances for commercially aluminum, the relatively quantity and configuration of TiC and Al₃Ti are very important factor in the grain refiner. We do some comparison between the Al-5Ti-lB grain refiner and the best grain refiner prepared by our lab. In the same token, our best refiner's refining performance was not superior to the imported Al-5Ti-lB grain refiner. The microstructure observation shows that Al₃Ti particle sizes in Al-5Ti-lB refiner was two times than ours.The heat treatment was studied for improving the refining performance.The influential mechanism of heat treatment processes on micro-structure of Al-3% Ti-0.35% C grain refiner prepared by thermal explosion method are researched in this paper. The analysis results show that the Ti element diffusion is an important factor in heat treatment; precipitation reaction was started firstly when the temperature is 400°Cand lasted 5 hours; When the Al₃Ti particle meet the atomic computation, its configuration will hold for long. But when there is superfluous Ti element in the grain boundary and the border area of Al₃Ti, the diffusion reaction will occur in this field at some condition. When the grain refiner holds more than 12 hours in 600℃, there are some particles substances which contain Ti element come into being in the grain boundary by diffusion reaction, the structure of eutectic-like structure and the product of precipitation reaction will eclipse. The configuration of TiC particle can't transform in the test condition mentioned in this paper. The refining test show that the refiner processed by the heat treatment which was hold 2hours in 400℃ has good refining performance The Combustion Front Quenching experiments show that: along with the hoist temperature in the system, the Al powder was melt first of all and fills in the clearance of prefabricated block, surround the Ti and C powder, the Al₃Ti reaction was react at about 720℃and plentiful of heat was released and accelerate the speed of system temperature hoist. The diffusion ability of Ti was increased, the TiC was come into being in the C surrounding or C dissolved in Al₃Ti can react and synthesize Tic. As the temperature hoist going on, surpass the 1083℃, Ti₈C₅ and AlTi₃C₂ can synthesize in the rich-titanium district. While the system temperature arrive at some temperature non-equilibrium phase AlTi₃C₂ decompounds to Al₃Ti.