The Microstructure And Grain Refining Performance Of Al-Ti-C Master Alloys Prepared By SHS

Self-propagating High-temperature Synthesis(SHS) technology is a novel technology for preparing the advanced materials,such as ceramics,intermetalic compounds and composite materials.This technology offers many advantages to synthesize Al-Ti-C master alloys according to a wide choice in titanium and carbon content and a fast and an energy efficient production.Although TiC/Al compounds fabricated by Self-propagating High-temperature Synthesis(SHS) technology have been numerous studied,Al-Ti-C master alloys fabricated by Self-propagating High-temperature Synthesis technology as a grain refiner to refine aluminum and its alloys has been rarely researched.Up to now,little systemic investigation was carried 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 Self-propagating High-temperature Synthesis technology has not been applied in modern practical large-scale production lines,and much problem needs to solve.The Al-Ti-C master alloys prepared by Self-propagating High-temperature Synthesis technology adopts laser to ignite.The effect of laser parameters on combustion processing, composing and morphology of SHS Al-Ti-C master alloys are studied.The laser operational parameter has the very tremendous influence on the microstructure characteristics of the production master alloys.Through control the laser operational parameter,Microstructure of preparation master alloys are excellent.The morphology of Al-Ti-C master alloys prepared by SHS and its formation mechanism was studied by means of XRD,EPMA,SEM and DTA.The results show that, firstly,the block-typed TiAl₃ phase is formed in Al melt at 680℃;at 700℃,TiAl₃ is transformed block-typed into approximate globularity;at 850℃,acicular TiAl₃ goes into decompose and a spot of TiC are appeared,and then C is not wettability in the liquid aluminum;at 1000℃,C takes on obvious wettability,TiAl₃ is decomposed completely. Simultaneously,TiC is produced.Ultimately,TiAl₃ is separated out from over-saturated Al-Ti melt and takes on particle-shape.The microstructures of Al-Ti-C master alloys are composed of Al matrix,block-typed TiAl₃ phase,TiC particle and Al after SHS.Effect of adding TiH₂ to Al-Ti-C prefabrication on microstructure of Al-Ti-C master alloys is quite tremendous.In this master alloys,the size,characteristic and distribution of TiC and TiAl₃ are nicer,and TiC is less than 1μm in diameter.The effects of the microstructures of Al-Ti-C master alloys,adding quality of Al-Ti-C master alloys,holding time,holding temperature the dilution parameters on refining character were studied.The refining experiments indicate that the holding temperature is about 750℃and the holding time is 5 min in the process of refiner,considering and character form of Al-Ti-C master alloys,industrial production and so on.Under this condition,the Al-Ti-C master alloys with value of Ti/C is 8 and adding 0.1%is expected to be most excellent for refining performance(average grain size 110μm).The refining test on aluminum indicates that Al-Ti-C master alloy of prefabrication with TiH₂ possesses more excellent grain refining property(average grain size 100μm).Adding 0.1%diluting master alloys is expected to be most excellent refining performance(average grain size 95μm).According to the experimental results,the mechanism of "Intergradations' crust of AlTi₃C induced by the concentration of Ti on the surface of TiC particles act as nucleuses" has been verified.