Preparation Of Al-5Ti-0.25C-1Ce Grain Refiner From Al And Ti Chips And Its Refining Effect

With the increasing application range of aluminum,titanium and their alloys,more and more chips are produced in their production and processing.Therefore,the effective recycling of aluminum and titanium chips and the reuse of resources have become an important proposition.The addition of grain refiners is the most direct and effective method to realize grain refinement.At present,the most used grain refiner for aluminum alloy is Al-Ti-B which has the disadvantages of easy decay,coarse Ti B₂ particles and toxic raw materials.Al-Ti-C grain refiner can be used as a excellent substitute for Al-Ti-B.However,the bottleneck of poor wettability between graphite and liquid aluminum is difficult to break through,which limits the development.Improving wettability has become the key preparation technology of Al-Ti-C grain refiner.In this study,Al-5Ti-0.25C-1Ce grain refiner was prepared by melt reaction method using graphite,ceria and aluminum and titanium chips produced in machining process as raw materials.It is expected to achieve effective recycling of aluminum and titanium chips,improve the wettability between graphite and liquid aluminum with the help of rare earth Ce,and solve the key problems of Al-Ti-C series grain refiners.The optimum preparation and refining process of Al-5Ti-0.25C-1Ce grain refiner were studied by optical microscope(OM),X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission/high resolution electron microscope(TEM/HRTEM).The effects of rare earth element Ce on Microstructure and refining performance were investigated.The dissolution kinetic model of Ti chips in aluminum melt was established,it provides a theoretical basis for the recycling of titanium chips.The optimum preparation process of Al-5Ti-0.25C-1Ce grain refiner by regeneration of titanium and aluminum chips is as follows:reaction temperature is 1000?,reaction time is 80min.When the reaction temperature is low or the reaction time is short,only a small amount of Ti Al₃ and Ti₂Al₂₀Ce phases are formed in the microstructure of Al-5Ti-0.25C-1Ce grain refiner.When the reaction temperature is high or the reaction time is long,the morphology of Ti Al₃ and Ti₂Al₂₀Ce phases changes from block and short needle to long needle.The surface activity and catalysis of rare earth element Ce effectively improve the wettability between graphite and molten aluminum,promoting the reaction of graphite and increase the amount of Ti C.1.0 wt%Ce effectively increases the tic content from 0.36 wt%to 0.92 wt%.Rare earth Ce triggers the formation of Ti₂Al₂₀Ce phase,and the formation of Ti₂Al₂₀Ce phase stems form the doping of Ce atoms in Ti Al₃ lattice.There is no clear interface between Ti₂Al₂₀Ce and Ti Al₃ phase,but forms a transition region with a large number of dislocations,in which Ti₂Al₂₀Ce and Ti Al₃ atoms are mixed with each other.The special formation characteristics of Ti₂Al₂₀Ce phase endow Ce with good modification of Ti Al₃ phase.The dissolution kinetics of titanium chips based on two-dimensional Fick's diffusion theory shows that the radius of titanium chips in aluminum melt is an exponential function of its dissolution time.When the addition amount of Al-5Ti-0.25C-1Ce grain refiner is less than 1.0 wt%,the heterogeneous nucleation sites in the aluminum melt increase with the increase of the addition amount,and the average grain size of pure aluminum decreases significantly with the increase of the addition amount,from 3500?m reduced to 76.3?m;After that,increasing the addition amount will no longer significantly reduce the average grain size of pure aluminum,which comes from the saturation of heterogeneous nucleation sites.When the refining time is 2 min,the average grain size of pure aluminum reaches the lowest,which is 60.36?m;After that,the average grain size of pure aluminum increases with the increase of refining time.Therefore,the optimum refining process of Al-5Ti-0.25C-1Ce grain refiner is as follows:the addition amount is 1.0 wt.%and the refining time is 2 min.