Structure Macro Kinetics Of Combustion Synthesis Al-T-C And Grain Refining Performance Evaluation

Combustion Synthesis(SHS,CS)is a novel technology for preparing the advanced materials, such as ceramics,intermetallic compounds and composite materials.This technique offers many advantages to synthesize Al-Ti-C master alloys according to a wide choice in titanium and carbon content and a fast and a energy efficient production.There have been numerous studies on TiC/Al compounds fabricated by Combustion Synthesis(CS)technology,but,there are few literatures on taking Al-Ti-C compounds as a master alloys grain refiner to refine aluminum and its alloys.Up to now,little systemic investigation was carry out on the key processing parameters in the Synthesis processes,formation of the productions and their characteristics.The Al-Ti-C master alloys fabricated by Combustion Synthesis(CS)technology have not been applied in modem practical large-scale production lines.Based on the project(863 programe)"Al-Ti-C master alloys grain refiner for aluminum and its alloys and wire Processing ",the combustion Synthesis mechanism and preparation technology of Al-Ti-C master alloys was studied.According to the thermodynamics theory,the adiabatic temperature under ideal state of Al-Ti-C were calculated.It shows that adiabatic temperature was increased with the raising of the preheat temperature,the minimum preheat temperature in combustion Synthesis Al-Ti-C master alloys is 633K.The Al-Ti-C master alloys are synthesized by self-propagating combustion mode,thermal explosion mode and thermal explosion in molten Al respectively,between which a comparison of the reaction process has been made.The effect of some processing parameters in preparation Al-Ti-C master alloys by self-propagating combustion mode were investigated on combustion processing, phase compose and morphology of product.These parameters include Ti/C ratio,green-compact pressure,pellet diameter,preheat temperature,Al and graphite granularity.The morphology of product obviously changes with Ti/C ratio,green-compact pressure,preheat temperature,Al and graphite granularity.The effect of some processing parameters in preparation Al-Ti-C during thermal explosion in Al melt were investigated on the phase compose and morphology of product,the combustion temperature increase with raising molten Al temperature and reducing Al content of specimen,A further experiments of Combustion Front Quenching(CFQ)in cylindrical steel die and compact quenching of thermal explosion in AI melt was brought to success,the microstructure of every region of the different reaction extent was observed.The physical and chemical changes of all region in the quenched samples during the combustion synthesis were followed by scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS)and x-ray diffraction(XRD).High temperature X-ray diffraction were carried out to investigate the phase transformation of Al-Ti-C system at different temperature and the microstructure of reaction product were analyzed by SEM. The results show that the reaction process of Al-Ti-C master alloys combustion synthesis could be expressed as:(â…°)Al melting in the preheat phase;(â…±)formation of Al₃Ti in Al-Ti reaction phase;(â…²) Al₃Ti dissolved,TiC_x layer formed and TiC;(iv)cooling and crystalling of the product after the reaction.And it was found that the Al₃Ti formation in combustion synthesis Al-Ti-C master alloys could be described with a reaction-dissolution-precipitation mechanism.Namely,the melting of Al into Ti particles,and took place 3Al(l)+Ti(s)=Al₃Ti(s),then Al₃Ti precipitate,however,TiC formation exist diffusion- precipitation mechanism and dissolution-precipitation mechanism at the same time.(â…°) diffusion- precipitation mechanism,Al₃Ti dissolved into Al-Ti melt,carbon particles adsorb Ti atom, Ti,C diffuse another on to form TiC_x,occurred[Ti]+C(s)=TiC(s),TiC particles precipitate from Ti-C layer;(â…±)dissolution-precipitation mechanism,at the higher temperature,after Al3 Ti melting,Al-Ti melt formed,C gradually dissolve into the Al-Ti melt,and TiC particles precipitate from the Al-Ti-C melt.The effect of some processing parameters in diluting Al-Ti-C master alloys were investigated on the,these parameters include green-compact pressure,temperature and insulation time.Based on the evaluation about Al-Ti-C master alloys preparation,morphology and grain refining performance, 20kg casting ingots were prepared by self-propagating combustion and thermal explosion in Al melt, subsequently,they were extruded and drawn out into F 9.5mm grain refiner alloy wire.The Al-Ti-C master alloys grain refiner alloy wire was applied successfully in modern practical large-scale production line.They were added in the 1235,5052,8011 aluminum alloys,then the grain size of those casting roll ingots got first rank.The chemic component and mechanical performance accorded with the national standard.Production experimental results indicated that Al-Ti-C grain refiner presented correspondingly fine effect as imported Al-5Ti-B.The refining product counts up to 17 ton.Such as double nil foil,home foil,foil for beer wrap page,timber accorded with the national standard,and all products were sailed to users.