Study On Preparation Process And Microstructure Morphology Of Al-5Ti-1B Alloy

As a typical grain refiner,the Al-Ti-B master alloy have been widely used in aluminum industry.However,due to the poor internal control ability of the master alloy,the domestic production of Al-5Ti-1B master alloys are weaker than that of foreign products,and it will seriously hinder the production of high-quality aluminum products.Therefore,it is of great significance to study the control of internal structure of Al-5Ti-1B master alloy for improving the quality of domestic grain refiner.In this paper,the method of aluminum fluoride thermal reaction was used,and the Al-5Ti-1B master alloy was prepared by changing the process parameters,such as cooling rate,reaction time.In order to study the influence of different reaction time and cooling rate on microstructure and particle morphology of Al-5Ti-1B master alloy,the analysis and characterization methods,such as X ray diffractometer,ICP-AES emission spectrometer,optical metallographic microscope and scanning electron microscope with energy dispersive spectroscopy,were used.What's more,the formation mechanism of the second phase particles with different morphology in the alloy was analyzed.The experimental results indicated that the order of cooling rate of different mold can be summarized as follows.?1?The cooling rate of copper mold is larger than that of graphite mold,and the cooling rate of graphite mold is larger than that of steel mold,and the cooling rate of sand mold is the smallest one.It's also found that the ratio of Ti to B in the Al-5Ti-1B master alloys,which are prepared in this experiment,is close to5:1.It's showed that the cooling rate and reaction time have no effect on the type of the second phase particles,and the Al-5Ti-1B master alloys are consists of?-Al,TiAl₃ and TiB₂ phase.?2?Within the ranges of our study,in order to obtain a better internal Al-5Ti-1B master alloy,the process parameters of cooling rate should be equal to the cooling rate of copper mold,and the reaction time should be ten minutes,approximately.What's more,the degree of agglomeration of TiB₂ particles decreases with the increase of cooling rate,but the average size of TiAl₃ particles slightly decreases with the increase of cooling rate.Furthermore,the average size of the aggregation of TiB₂particles increases linearly with the prolongation of reaction time.The average size of TiAl₃ particles increases with the prolongation of reaction time,and the trends like a parabola.?3?The micromorphology of the particles of Al-5Ti-1B master alloys prepared in this research was observed,and the growth model of particles also was established.It can be found that there is a reason for the formation of the square block TiAl₃ particles which has a large aspect ratio.The reason is that the atomic density on?001?plane is larger than that on?100?and?010?planes,and the growth rate of the[001]direction is suppressed to a certain degree.However,there are two reasons for the formation of the cross-like TiAl₃ particles.The first one also can be described as the larger atomic density of?001?plane,and the second one is that the constitutional supercooling on the?001?plane,which caused by the enrichment of Ti atom.Similarly,there are also two kinds of morphology of TiB₂ agglomerates.Firstly,it can be found that there are some TiB₂ particles grow together on the surface of TiAl₃ particles.Because the more stable TiB₂ particles are generated by the reaction between TiAl₃ and AlB₂ particles.And then,the TiB₂ particles pile up into a dendritic cluster on the?0001?plane of TiB₂ particles one by one.Secondly,the TiB₂ agglomerates with an irregular shape caused by the phagocytosis of TiB₂ particles which happened at the solid-liquid interface.