Research On Electromagnetic Stirring And Grain Refining Performance Of Al-3Ti-0.2C-5Sr Grain Refiner

With the rapid development of the aerospace and automotive industries, theperformance of Al-Si alloys have become increasingly demanding.Currently, addinggrain refiner and eutectic silicon modifier to Al-Si alloys is the most direct andeffective method of improving its performance.Al-3Ti-0.2C-5Sr master alloys as akind of double-effect modifier with refinement and modification, not only effectivelyimproves the performance of hypoeutectic Al-Si alloys, but also greatly simplifies themelting process.However, the sizes of TiAl3phase, Al-Ti-Sr phase and Al4Sr phaseare relatively large, TiC particles are easy to assemble in microstructure ofAl-3Ti-0.2C-5Sr master alloys under static conditions, which greatly reducing itsrefined performance and prone to refinement recession phenomenon.Studies haveshown that the external magnetic field to improve morphology and distribution roleof phases is very clear.So this paper uses electromagnetic stirring method to improvethe Al-3Ti-0.2C-5Sr refinement modifier in the form of distribution of each phase,to improve its refining performance.This paper studies the effect of casting temperature, the cooling rate and holdingtime under static conditions on each phase species distribution of Al-3Ti-0.2C-5Srrefinement modifier, and its solidification phase transition was in-depth studied,which provide a theoretical basis for the selection and optimization ofelectromagnetic stirring parameters; Put the Al-3Ti-0.2C-5Sr melt under staticconditions into electromagnetic stirrer to electromagnetic stirring, the effect ofstirring process parameters on Al-3Ti-0.2C-5Sr microstructure was deeply studied;Put the Al-3Ti-0.2C-5Sr grain refiner after stirring into Al-7Si alloys to studing thebehavior of Al-3Ti-0.2C-5Sr refining performance, and compared with the refiningperformance of Al-3Ti-0.2C-5Sr without stirring.The results show that, under static conditions, the effect of casting temperatureon TiAl3phase morphology is the most obvious, with declining of castingtemperature, the long strip TiAl3phase gradually transformed into block phase, The coated like Al-Ti-Sr phase morphology changes with TiAl3phase morphology; theeffect of cooling rate on TiAl3phase and Clad like Al-Ti-Sr morphology is the mostobvious, and the effect of block Al-Ti-Sr phase is very little, With the decreasing ofthe cooling rate, TiAl3phase decreases slowly, Clad like Al-Ti-Sr phase becomesbigger; the effect of holding time on TiAl3phase and block Al-Ti-Sr morphology isthe most obvious, with the extending of holding time, TiAl3phase graduallydisappeared, small block Al-Ti-Sr grew up to big block.The precipitates order of eachphase in Al-3Ti-0.2C-Sr master alloys is TiAl3phase, Al-Ti-Sr phase, Al4Sr phase;And liquid-solid phase temperature range of650～800℃; The initial precipitationtemperature of TiAl3phase is800℃, The initial precipitation temperature of Al4Srphase is740℃; Massive Al-Ti-Sr phase and block Al-Ti-Sr phase are also formed byperitectic reactions between TiAl3phase and liquid phase.The electromagnetic stirring parameters were: stirring frequency is3Hz,5Hz,7Hz,9Hz, stirring time is2min,5min,10min,15min, The srirring initialtemperature is800℃. With the extension of electromagnetic stirring time, inAl-3Ti-0.2C-5Sr grain refiner, TiAl3phase slowly disappears, big block or lathAl-Ti-Sr phase turn into small pieces phase, massive Al4Sr phase turns into fineneedle phase, the distribution of TiC particle is more uniform.However, when thestirring time more than ten minutes, stirring effect is not obvious.With the increase ofthe electromagnetic stirring frequency, the size of block Al-Ti-Sr phase becomessmaller, and its distribution is more uniform, when the electromagnetic stirringfrequency reachs7Hz, the size of Al-Ti-Sr phase reduces to about20μm20μm.Optimal scheme of electromagnetic stirring is stirred for10min with7Hz at800℃.When refining alloy Al-7Si by Al-3Ti-0.2C-5Sr grain refiner afterelectromagnetic stirring, the best refinement time is15min, the best addition is0.8%,the best refinement temperature is720℃～750℃; The grain refining performanceof Al-3Ti-0.2C-5Sr refiner is better than that of Al-3Ti-0.2C and Al-10Sr; The grainrefining performance of Al-3Ti-0.2C-5Sr refiner which contained little block Al-Ti-Srphase is better than that of Al-3Ti-0.2C-5Sr refiner which contained massive Al-Ti-Srphase, and the smaller the size, the greater the n μmber, the better the performance refinement.Compared with Al-3Ti-0.2C-5Sr grain refiner without stirring, refining responsetimes of Al-3Ti-0.2C-5Sr grain refiner after stirring reduce, refining recession doesnot appear after hoilding60min, the best addition of Al-3Ti-0.2C-5Sr grain refinerafter stirring saves ratio of30%.