Preparation Of Al-Ti-C-Ce From Fluoride Salt And Its Refining Behavior

Aluminum alloy have been widely used in construction,navigation,transportation and food packaging industries,as a result,the requirements for aluminum and aluminum alloy products are becoming increasingly stringent.In which,grain refinement is of great significance for aluminum alloy to improve its own mechanical properties.In industrial production,adding grain refining agent to aluminum melt is one of the most economical and effective methods.Today the commonly used grain refiner in industrial production is Al-Ti-B grain refinement agent,and it has some defects,for example:the grain size of TiB₂ is slight big,the grain of TiB₂ would arises“poisoning”effects with the elements like Cr,Zr of aluminum alloys,which will reduce its ability to refine.However,Al-Ti-C grain refinement agent can overcome the defects of the above refiner,so it has become a research hotspot.In the process of studying Al-Ti-C grain refining agent,because of the poor wettability of graphite particles in aluminum solute,how to prepare Al-Ti-C grain refiner with high TiC particle content is a difficult problem to be solved at present.In this thesis,the wettability between graphite and aluminum solution is improved by adding rare earth elements,which has promoted the formation of TiC particles.Three grain refiner of Al-5Ti-0.2C,Al-5Ti-0.2C-3Ce（group A）and Al-5Ti-0.2C-6Ce（group B）were prepared by using high temperature resistance furnace at 1200℃,and their phase composition,phase morphology and solidification mechanism were discussed by using X-ray Diffraction（XRD）,Scanning electron microscope（SEM）,Energy Dispersive Spectrometer（EDS）and optical microscope（OM）.The performance of grain refiner was judged by changing the amount of grain refinement agent and the time of heat preservation by adding trace grain refiner to pure aluminum.The results shows that the Al-5Ti-0.2C grain refiner consists of TiAl₃,TiC andα-Al phases,and there is extra rare earth phase Ti₂Al₂₀Ce in the group of A,B grain refiner.Meanwhile,comparing the XRD patterns of Al-5Ti-0.2C grain refiner and group A grain refinement,we can see the peak value of TiC has increased indicating that rare earth elements can improve the wettability between aluminum melt and graphite particles.Potassium fluotitanate is added to the aluminum solute to produce TiAl₃ phase,reaction principle is followed by the equation:K₂TiF₆+Al→TiAl₃+KAlF₄+K₃AlF₆;The released heat promotes the reaction of graphite particles with solute Ti atoms in the aluminum melt to produce TiC particles.The Ti₂Al₂₀Ce phases in both group of A,B grain refiners appeared in the phase of wrapping shape and bulk shape,when the content of rare earth elements is low,it mainly plays the role of surfactant,which improves the wettability between aluminum liquid and graphite powder,the extra rare earth element Ce forms the rare earth phase in the aluminum melt;When the content of rare earth elements is high,rare earth phases are mainly formed in aluminum melt:（1）The Al,Ti and Ce atoms in the aluminum solute reach a certain proportion to form the Ti₂Al₂₀Ce phase,which exists in the form of a block shaped phase.（2）Ti₂Al₂₀Ce is wrapped around TiAl₃ phase and formed by diffusion growth of Al and Ti atoms in liquid and solid TiAl₃ phase.In the process of formation,the TiAl₃ with smaller morphology has been dissolved because of its supplement to Ti content in the melt,so there was lefted a plate shaped TiAl₃ phase with larger morphology.Add three sets of grain refiner to pure aluminum,Al-5Ti-0.2C grain refiner can only reduce the grain size of pure aluminum from 710μm to 168μm and the optimal amount of addition is 0.7%,the group of A grain refiner can reduce the grain size as low as 103μm,the optimal amount of addition is 0.4%,the efficiency of group B grain refiner refinement was just after group A grain refiner,can reduce the grain size of pure aluminum as low as 126μm,the optimal amount of addition is 0.7%.When three groups of grain refiners were added to pure aluminium for 15 minutes,their refining ability was as follows:group A grain refiner>group B grain refiner>group Al-5Ti-0.25C grain refiner.The best refining ability can be guaranteed in high temperature aluminum melt for a long time is group of A grain refiner,second is group of B grain refiner.The reduction in the ability to refine may be caused by the distribution of Ti atoms.