Research On The Synthesis Process Of Al-Ti-C Grain Refiner Under Flux Assisted Wetting

Al-Ti-C is an efficient grain refiner of aluminum and its alloys with excellent refining effect and anti-refining-attenuation capability. However, due to the difficulties in wetting between aluminum and carbon, It is difficult to synthesize the alloy and realize industrial production and practical application. The thesis laid emphasis on the essential problem in the process of the alloy synthesizing-wetting and reaction behavior between the interface of Al and C, focused on the measurement of Al/C wetting angle under assisted wetting conditions, preparation of aluminum titanium alloy and the wetting behavior of the preparation process under assisted condition to optimize the conditions for the preparation of Al-Ti-C grain refiner. Referring to the document on Al-Ti-C grain refiner, Al-Ti-C grain refiner was prepared by casting in situ reaction under laboratory conditions, and the refining effect of Al-Ti-C grain refiner on Al was studied to assess the quality of Al-Ti-C grain refiner and study on the refining-attenuating mechanism. Main achievements and conclusions of this thesis are as follows:(1) The drop-sitting wetting apparatus and reaction apparatus for gas reaction used for interfacial wetting and reaction were designed and manufactured. The drop-sitting wetting apparatus under vacuum condition and in special structure design was used for the study on the harmful influence of oxide film on wettability between Al and C and the intuitive analysis of magnitude of Al/C, and then the C/Al wetting conditions and interfacial reaction behavior, were analyzed to optimize the preparation of Al-Ti-C grain refiner.(2) In the wetting reactor, the wetting temperature between Al melt in (KF-AlF3)E eutectic salt (excessness) and the flux K2TiF6and graphite chip is850℃(1123K), The contact angle gradually decreased with increasing temperature.When the temperature reached950℃(1223K), the equilibrium contact angle is30°.The contact angle no longer changes obviously with increasing temperature and holding time.(3) In the Al-Ti melt/flux system, the wettability between Al-Ti alloy and wetting agent increases with increasing Ti content and temperature; With the increase of the Ti content, the morphology of the alloy droplets changes from spherical to spheroid in lower temperature, but it changed from spheroid to spherical in higher temperature; After inorganic salt K2TiF6was added to the system, the molten aluminum alloy disperses in molten salt and takes on emulsion state.(4) In the reaction system with wetting agent involved, lots of TiAl3phase in micro-level are generated during reaction process. The morphology of TiAl3is relevant to the temperature. TiAl3phase mainly exists in massive shape at790℃, but exist sin acicular shape at850℃.(5) Al-Ti-C grain refiner was prepared by means of assisted solvent using cast-in-situ reaction method. It is found by comparison that Al-3Ti-O.15C and Al-5Ti-0.25C grain refiners have good refinement effect and anti-refining and anti-attenuation capability. The refining capability of Al-5Ti-0.25C is better than that of Al-3Ti-0.15C.(6) The optimized processing parameters in the refining experiment of Al-5Ti-0.25C grain refiner are as follows:the holding time was8min; The addition content of refiner is0.2%; the smallest grain size was175μm.(7) The refining attenuation mechanisms of the refiner are as follows:First, TiC in the melt is unstable with the prolongation of holding temperature and will promote the formation of Al4C3. Immune phenomenon occurs in TiC and nucleation activity disappears. Second, with the prolongation of holding time, the Ti atoms in Ti enriched region around TiC particles diffuse gradually and distributed uniformly into aluminum melt and hence Ti atoms enriched region around TiC and not completely dissolved TiAl3particles disappears.