The Study On Preparing Process And Grain Refining Performance Of Al-5Ti-1B Master Alloy

The fine equiaxed crystal structure can improve the mechanical properties of aluminum alloy castings,reduce hot cracks,eliminate shrinkage,and improve the performance of aluminum alloys.Adding Al-Ti-B grain refiner can make the aluminum alloy castings transform from coarse columnar crystals to fine equiaxed crystals,which can refine the aluminum alloy crystal grains.Al-5Ti-1B master alloy is considered to be the best Al-Ti-B refiner for pure aluminum and aluminum alloys,and it is widely used.At present,the preparation of Al-5Ti-1B master alloy mainly use the fluorine salt reaction method,that is,K₂Ti F₆ and KBF4 are added to the 800?Al melt,and Al-Ti-B master alloy is prepared by the interfacial reaction between the two fluoride salts and the Al melt.The advantages are low raw material prices,relatively simple preparation process,and low-density reaction products in the molten state floating on the melt,which facilitates removal.However,there are also great shortcomings,such as the slow reaction rate of the interface,resulting in a long time for the alloying reaction and a low production efficiency;the molten fluoride salt floating on the melt is volatile and causes environmental pollution;The impurities of the potassium fluoroaluminate salt by-products and the introduced metal compounds,as well as the inclusions generated by molten salt corrosion on the refractory material can not be completely removed,resulting in poor cleanliness of the final prepared Al-Ti-B master alloy.In this paper,the problems existing in the preparation of Al-5Ti-1B grain refiner by fluoride salt method are optimized.The preparation process is optimized by improving the process parameters such as fluoride addition sequence,alloying reaction temperature and reaction time.The Al-5Ti-1B master alloy was prepared by melt treatment with high-energy ultrasonic vibration.The effects of various alloying process parameters and high energy ultrasonic application methods and time on the microstructure of Al-5Ti-1B grain refiner were studied.Through refinement experiments,the influence of preparation parameters on the grain refinement of Al-5Ti-1B master alloy was further investigated.Sponge Ti,as the previous product of K₂Ti F₆,is the main raw material for the production of K₂Ti F₆.On the basis of the traditional fluoride salt reaction method,the Al-5Ti-1B master alloy refiner was prepared by substituting K₂Ti F₆ with Ti as a raw material,and the effect of substitution ratio on the microstructure and the refinement effect of the master alloy was studied.The microstructure of the prepared Al-5Ti-1B grain refiner was observed and analyzed by XRD,OM,SEM and EDS.The results show that in the preparation process of Al-5Ti-1B grain refiner,the Ti Al₃ size in Al-5Ti-1B master alloy obtained by mixing K₂Ti F₆ and KBF₄ is smaller and the distribution is more uniform.However,the order of addition has little effect on the morphology of Ti Al₃ and Ti B₂ particles in Al-5Ti-1B.Most of Ti Al₃ is in the form of a block,while most of Ti B₂ is hexagonal and a few are regular polygons.When the alloying reaction temperature is 850?,the Ti Al₃ phase size of the prepared Al-5Ti-1B master alloy is relatively small.When the alloying reaction time is 60min,the content of Ti element in the prepared AI-5Ti-1B master alloy is 5.01%,the content of B element is 0.88%,and the yield of Ti and B elements reaches the maximum value.In the process of preparing Al-5Ti-1B master alloy,applying ultrasonic vibration to the molten metal can significantly improve the microstructure and refinement effect of the refiner.After the fluoride salt was added into the aluminum liquid,ultrasonic vibration was applied to the molten metal for 3.5 min.Compared with no ultrasonic treatment,The thick lath-like Ti Al₃ is inhibited,the size of pin-like and block-like Ti Al₃ are significantly reduced,and the distribution is more uniform.The aggregation of the bulk agglomerated Ti B₂ phase in the refiner decreases,the isolated Ti B₂particles increase,and the Ti B₂ cluster also becomes looser,but the Ti B₂ particle size does not change significantly.In the mixed ultrasonic treatment process,the alloy liquid is subjected to ultrasonic treatment again before solidification,and the Ti Al₃grown during the heat preservation process can be crushed to reduce its size.In addition,the circulation current generated in the alloy liquid by acoustic current effect of the ultrasonic wave can effectively disperse Ti Al₃.The distribution of Ti Al₃ is more uniform and the Ti B₂ particles tend to diffusely distribute.The Ti Al₃ phases in the Al-5Ti-1B grain refiner prepared by continuous ultrasonic treatment for 10 min are all in fine blocks with an average size of 12.4?m.The Ti B₂ particles have clear outlines and regular polygonal shapes with no adhesion to each other.The Ti Al₃phases and Ti B₂ particles are all scattered on the Al matrix.Using industrial pure aluminum as a object,refinement performance of the prepared Al-5Ti-1B master alloy was tested.The results show that the pure aluminum microstructure refined by the refiner prepared by applying ultrasonic vibration for 3.5minutes is all fine equiaxed crystals.Compared with no ultrasonic treatment,the grain of pure aluminum was significantly refined and the average size was 472?m.With refinement of the refiner prepared by applying ultrasonic vibration,the grain size of pure aluminum is further reduced to 398?m,indicating that the mixed ultrasonic vibration can further improve the refinement effect of the prepared Al-5Ti-1B refiner.The refinement effect of Al-5Ti-1B master alloy prepared by continuous ultrasonic treatment for 10 min is best,and the pure aluminum grain can be refined to 307?m.The Al-5Ti-1B master alloy refiner prepared from the Ti sponge instead of K₂Ti F₆was used.When the substitution ratio was 25%,the microstructure of prepared master alloy is better,and the Ti Al₃ is all block and distributed evenly.Refinement experiments show that the refinement performance is closest to that of the Al-5Ti-1B master alloy prepared by the fluoride salt method.The use of sponge Ti instead of K₂Ti F₆ to prepare Al-5Ti-1B master alloy can reduce the amount of fluoride salt,reduce the release of fluoride salt vapor and the generation of toxic gases,and environmental protection can be maximized.It save the process of producing K₂Ti F₆with sponge Ti,save energy,save costs,protect the environment,and have high industrial application value.