The Preparation And Refining Performance Of Al-Ti-B Grain Refiner

Refinement of grains increases the strength,ductility and toughness of metallic materials.Adding Al-5Ti-1B grain refiner to aluminum alloys and the melt of aluminium is the most common method of grain refinement in aluminium industry at present.However,due to the late start of research on Al-5Ti-1B grain refiner in China,there is still a certain gap between the domestic Al-5Ti-1B grain refiner and the refined performance of imported similar products.This is related to the fact that the amount of TiAl₃ and TiB₂ in the domestic Al-5Ti-1B grain refiner is small,large in size and unevenly distributed.Therefore,it is of great practical significance to study the Al-Ti-B grain refiner with fine dispersion characteristics of the second phase.For this reason,the preparation process of fluoride salt method was studied in this paper.The effects of reaction temperature,reaction time and fluoride salt size on the microstructure and refining properties of the refiner were studied,the optimum preparation temperature,time,and fluoride salt particle size were determined.On this basis,the effect of ultrasound on the structure and refining properties of Al-5Ti-1B grain refiner was studied.The Al-5Ti-1B grain refiner with better refining properties was prepared,and the refining process parameters were studied.In addition,the Al-Ti-B grain refiner for the preparation of nanometer second phase by powder method and its refining properties were also studied.The main results are as follows:The process parameters of Al-5Ti-1B grain refiner prepared by fluoride salt method were studied.The results show that the Al-5Ti-1B grain refiner prepared by the two-step process does not contain AlB₂ phase,and the optimal reaction temperature is 800?,the optimum reaction time is 70min,the optimum fluoride salt size is more than 500 mesh,and the optimal ultrasonic treatment time is 3min.The content of Ti and B in the Al-5Ti-1B grain refiner prepared by the optimal preparation process is 4.8wt.%and 0.86wt.%,respectively;TiAl₃ is small block and the size is less than 20?m;TiB₂ is granular and the size is about 1.2?m.The composition and microstructure of the self-made and imported Al-5Ti-1B grain refiner were compared.The results show that the content of Ti and B in the imported Al-5Ti-1B grain refiner is 4.96wt.%and 0.94wt.%.The content of Ti and B in the grain refiner of the self-made Al-5Ti-1B is increased by 3.5%and 9.4%.TiAl₃ in imported and homemade Al-5Ti-1B grain refiner has two forms of block and rod,and the diameter is less than 20?m.The average size of TiB₂ particles in the imported Al-5Ti-1B grain refiner is 0.586?m,and the particle size distribution range is 0.087³.905?m.The average size of TiB₂ in the self-made Al-5Ti-1B grain refiner is 1.23?m,and the particle size distribution range is 0.197⁶.72?m.The effects of refining time,addition amount and refining temperature on the refining performance of Al-5Ti-1B grain refiner were studied.The results show that the addition amount of self-made Al-5Ti-1B grain refiner is 0.4wt.%.When the refining temperature is 720?,the grain size of pure aluminum reaches a minimum?224?m?after 5min refining.However,the grain size of pure aluminum reached a minimum?173?m?after 3minutes of refining of the imported product.Self-made and imported Al-5Ti-1B grain refiner to stabilize the grain size for about 25min and 40min respectively.When the refining time is 5min and the refining temperature is 720?,the addition of 0.4wt.%of the self-made Al-5Ti-1B grain refiner can meet the industrial requirements,and the grain size of the refined pure aluminum is 218?m.Add0.3wt.%of imported products,refine the grain size of pure aluminum 232?m.The self-made Al-5Ti-1B grain refiner is added in an amount of 0.4wt.%,the refining temperature is 700?,and the refining time is 5min,which is the best refining process.The Al-Ti-B grain refiner was prepared by powder method.The results show that Al and Ti can be combined to form TiAl₃ after heat treatment at 550?for 24h.When the refining temperature was 700?,the refiner addition amount was 0.4wt.%,and the refining time was5min,the refining agent which was not subjected to heat treatment had almost no refining property,and the grain size of the refined pure aluminum was 1632?m.The heat-treated refiner refines the grain size of pure aluminum to 877?m,which has a certain refinement performance but is not significant.The reason is greatly related to the serious agglomeration of Ti and TiB₂.When the ball milling mixture was used for 2h,the refining performance was improved under the same refining process conditions,and the grain size of the refined pure aluminum was reduced to 628?m.