TEMPERATURE DEPENDENCE OF VISCOSITY OF Al-Si ALLOY MELTS

1. IntroductionLiquid m etalsare in com m on use in m odern industry/area such ascasting, m etallurgy, w elding,glassform ing,the nuclearindustry and crystalgrow th.In addition,the relation ofthe physicalpropertyand structure change w ith tem perature, concentration and pressure isofgreatinterestto researchersinphysics and m aterials. V iscosity is a basic param eterin discussing the nature and behaviourofm etalm elts,and isone ofbasic propertiessensitive to the m eltstructure. V iscosity m ea…     

电磁搅拌下铝合金的力学性能研究

研究了无搅拌铸造和电磁搅拌铸造下的Al-24%Si过共晶合金和Al-6.6%Si亚共晶合金常温下的力学性能,并运用扫描电镜对其拉伸断口进行了分析。结果表明:在搅拌作用下凝固的合金相比同成分非搅拌时凝固的合金,Al-24%Si过共晶合金强度提高了约11%,伸长率提高了约12%;Al-6.6%Si亚共晶合金强度提高了约5%,伸长率提高了约46%。过共晶合金在相同搅拌强度下,其硬度是随着降温速率的增大而增大的。亚共晶合金在搅拌强度相同时,降温速率越小,硬度就越高;合金降温速率相同时,搅拌强度越高,硬度就越高。     

Al-Si合金熔体热处理的结构转变

用示差扫描量热分析了Al-Si合金温度处理的熔体结构变化规律及结构变化温度。结果表明,在升温阶段的Al-7%Si亚共晶、Al-12%Si共晶及Al-20%Si过共晶合金的熔体中均存在额外的热效应,范围均在798～850℃之间,额外热效应温度范围与含硅量无关,结构转变焓值随合金的硅含量增加而增加,氢含量不影响结构转变的温度;而在降温过程中仅在Al-20%Si过共晶合金中发现了额外热效应,额外热效应的出现及温度范围取决于降温速度。分析认为,升温阶段的额外热效应体现了Al的熔体结构变化,降温阶段的额外热效应与熔体中的Si-Si原子团簇的行为有关。     

MICROSTRUCTURE AND MACROSEGREGATION OF Al-7%Si ALLOY SOLIDIFIED UNDER COMPLEX EFFECTS OF ELECTROMAGNETIC AND CENTRIFUGAL FORCES

1.IntroductionElectromagneticcentrifugalcasting(EMCC)isanewtechnologydevelopedfromcentrifUgalcastingandelectromagneticstirringprocessing.WithaseeofEMFgeneratingdeyicemountedonacentrifugalcastingmachine,liquidmetalssolidifyunderthecomplexeffectsofEMFandcentrifugalforce.ThequalityofthecastingsiscontrolledbymodifyingtheparametersofEMFandcentrifugalcasting.Thistechnologyprovedveryeffective...inimprovingthemacrostructureandpropertiesofthecastings['].WiththeeffectoftheEMF,thereisalwaysaconve…     

INFLUENCES OF TRACE ADDITIONS OF STRONTIUM AND PHOSPHORUS ON ELECTRICAL RESISTIVITY AND VISCOSITY OF LIQUID Al-Si ALLOYS

ＩＮＦＬＵＥＮＣＥＳＯＦＴＲＡＣＥＡＤＤＩＴＩＯＮＳＯＦＳＴＲＯＮＴＩＵＭＡＮＤＰＨＯＳＰＨＯＲＵＳＯＮＥＬＥＣＴＲＩＣＡＬＲＥＳＩＳＴＩＶＩＴＹＡＮＤＶＩＳＣＯＳＩＴＹＯＦＬＩＱＵＩＤＡｌＳｉＡＬＬＯＹＳ①ＧｕｉＭａｎｃｈａｎｇ，ＪｉａＪｕｎ，...     

On the modification of hypereutectic Al-Si alloys using rare earth Er

Hypereutectic Al-17.5Si (wt pct) and Al-25Si (wt pct) alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.     

电磁搅拌对铝硅合金显微组织的影响

研究电磁搅拌对亚共晶、共晶及过共晶Al—Si合金显微组织的影响，并对其在EMS作用下的液淬组织和凝固组织进行研究。试验表明：电磁搅拌能够改变正常的铝硅合金凝固行为。本试验条件下EMS作用下非树枝晶存在异常长大、聚集和缩颈熔断现象；对亚共晶Al-Si合金凝固主要表现为共晶组织发生粗化；对过共晶Al-Si合金凝固主要表现为初生硅的聚集与偏聚。     

Eutectic nucleation in Al-25wt.%Si alloy through DSC

Eutectic nucleation in hypereutectic Al-25wt.%Si alloy with the addition of P was studied by calculating the activation energy and nucleation work. The results indicate that P refinement, which can decrease the activation energy as well as nucleation work of eutectic solidification, can increase the eutectic nucleation frequency of Al-25wt.%Si alloy, so the addition of P can refine the eutectic structures of hypereutectic Al-Si alloys. According to the calculations, there is a certain relationship between the precipitation of primary silicon and eutectic solidifica-tion, and the eutectic nucleation mode is independent of morphology transition.     

Al-Si和Al-Si-Sc合金的界面能各向异性的研究

平衡液滴法(Equilibrium shape measurement)是一种确定晶体-熔体界面能各向异性参数的有效方法。本文利用平衡液滴法测量单相固体中夹带的平衡液滴的形状,得到了Al-Si和Al-Si-Sc合金的界面能各向异性参数计算值。通过定向凝固方法制备Al-2wt.%Si和Al-2wt.%Si-0.2wt.%Sc合金杆状试样,使用光学显微镜表征Al-2wt.%Si和Al-2wt.%Si-0.2wt.%Sc合金内部液滴手工连续磨样抛光后多个二维截面形状,计算了二维界面能各向异性参数的大小。利用FIB(Focused ion beam)技术连续切割了Al-2wt.%Si合金内部液滴,并用Image-J软件重构液滴三维形状,获得了三维界面能各向异性参数值以及三维界面能分布和界面刚度的分布。在此基础上,讨论了平衡温度和Sc元素对界面能各向异性参数的影响。     

Al－l8％Si过共晶合金熔体结构特征及磷的影响

用ＤＳＣ热分析和快速凝固方法对过共晶Ａｌ－１８％Ｓｉ合金熔体结构特征进行了分析研究，着重考察了液态过热温度和元素Ｐ对熔体结构特征的影响．结果表明，在液态区域其结构特征存在三个区域：低温微观不均匀区域、中温微观不均匀向微观均匀过渡区域和高温微观均匀区域．Ｐ增加低过热过共晶Ａｌ－ｌ８％Ｓｉ熔体的微观不均匀性．     

Effects of high magnetic field on modification of Al-Si alloy

1INTRODUCTIONAmong Al-Si alloys,the Al-Si eutectic alloyhas the best foundry capability.The mechanicalproperties of Al-Si eutectic and hypoeutectic alloyhighly relates to the shape,size and distribution ofSi phase in eutectic structure.Coarse acicular-likeeutectic Si dissevers Al matrix badly to inducestress concentration and debase the mechanicalproperties,especially the tenacity.Modification isthe process to change the shape and size of eutecticSi,namely to change the shape of eutec…     

Effects of electromagnetic stirring on microstructures of solidified aluminum alloys

1　INTRODUCTIONPractically ,mechanicalstirringandelectromag neticstirring (EMS)arewidelyusedtogenerateforcedflowinsolidificationandcastingofmetalsandalloys,resultingin greatchangesofthesolidifiedstructures,segregationsand propertiesofthecast ings .Muchattentionhasbeenpaidtosolidificationofdendriticalloyssuperposedwithforcedflow ,andmanypreviousworkshavebeenfocusedontheeffectsoffluidflowonthestructuraltransitions,suchascolumnar equiaxedtransitions(CET)ormacro segre gationinthealloys[13] .…     

复合变质对Al-20%Si合金耐磨性能的影响

在不同P、RE添加量下对P-RE复合变质和未变质的过共晶铝硅合金的耐磨性进行了研究。结果表明:P-RE复合变质明显提高了合金的耐磨性,当加入0.08%P和0.6%RE时,合金的耐磨性达到最佳,磨损失重量从未变质的5.2mg降低到4.225mg,减少了19%。磨损主要为磨粒磨损,磨粒来源是硅相的破碎剥落。合金耐磨性能的改善与复合变质引起的共晶硅和初晶硅颗粒的细化和合金强度、塑性的提高有关。     

Temperature-dependence of electrical resistivity of Cd-Sn, Bi-Sn, and Al-Si eutectic and Al-3wt.%Si hypoeutectic alloys

Cd-Sn, Bi-Cd, and Al-Si eutectic and Al-3wt.%Si hypoeutectic alloys of high-purity (99.99%) metals were produced in a vacuum atmosphere. Current-voltage (I-V) characteristics of these specimens were measured at various temperatures between 100 and 475 K. The electrical resistivity (ρ) and temperature coefficient (α) for each specimen, depending on the temperature, were calculated using results obtained from the I-V measurements. The electrical resistivities and the residual resistivity of the specimens increase with increasing temperature for each alloy system. These results are compared with literature results.     

Al-20％Si中间合金对Al-Si合金共晶Si变质行为的影响

研究了Al-20％Si中间合金对铸造Al-Si合金显微组织的影响.结果表明:向Al-Si合金熔体中加入1％的Al-20％Si中间合金,Al-7％Si合金中的共晶Si由粗大的板片状变为细密的纤维状或点状,变质效果较好,而对共晶Al- 12％Si合金的变质效果较弱;浇注温度对合金显微组织影响较大,适当降低浇注温度,有利于铸件组织的细化;变质温度越低越有利于颗粒状Si相成为形核核心,抑制枝晶组织的形成长大;在变质温度为650℃时,Al-20％Si中间合金对Al-7％Si合金变质有效时间是3h左右.     

Novel image analysis to determine the si modification for hypoeutectic and hypereutectic Al-Si alloys

The aim of this research is to develop a novel analytical approach to determine the level of modification of silicon in Al-Si hypoeutectic and hypereutectic alloys. Two standards to determine the level of modification of silicon particles were investigated: the AFS Si Modification Standard and the Primary Si Grade.^1,2 The first method can only be used for Al-Si hypoeutectic alloys and the second one for Al-Si hypereutectic alloys. In both methods, the determination of the level of modification of silicon is carried out by comparing micrographs of the test sample with the respective standards by simple observation. This results in a method with a bias error and does not take advantage of the analytical accuracy made possible by modern image analysis techniques. This paper presents a method known as image-analysis-based silicon modification level, which provides highly reliable results to determine the level of silicon modification for Al-Si hypoeutectic and hypereutectic alloys. He is formerly a member of the Light Metals Casting Technology Group (LMCTG) at the University of Windsor. For more information, contact J.H. Sokolowski, Mechanical, Automotive and Materials Engineering, University of Windsor, Room 209, Essex Hall, 401 Sunset Avenue, Windsor, Canada, N9B 3P4; jerry@uwindsor.ca.     

Microstructure variation and growth mechanism of hypoeutectic Al-Si alloy solidified under high pressure

The microstructure of hypoeutectic Al-9.21wt.%Si alloy solidified under 5.5 GPa was studied. The results show that the solidification microstructure is refined. The primary a phase is the extended solid solution.The solid solubility of Si in a phase is up to 8.26wt.%. The growth mode of the a phase is cellular, and this cellular growth mechanism is interpreted in terms of the decrease of the diffusivity and the extended solid solution under high pressure. By calculation, it can be known that the the diffusivity of solute in the liquid under normal pressure is as high as two hundred times that under high pressure. The microhardness of the hypoeutectic Al-Si alloy solidified under high pressure is higher than that of solidified under normal pressure. After annealing, Si precipitates from the solid solution, the microhardness of the alloy decrease, but, still higher than that of solidified under normal pressure.     

Sr对Mg-4%Si合金中Mg2Si的变质作用

研究Sr对过共晶Mg-4%Si（质量分数）合金中Mg2Si相的变质作用与机理。Mg-4%Si合金中存在多面体形初生Mg2Si相与汉字状共晶Mg2Si相。添加Al-10%Sr可以明显细化初生Mg2Si相,同时可以将共晶Mg2Si相由汉字状变质为多面体状或者纤维状。对初生Mg2Si相的细化作用主要是由凝固过程中含Sr颗粒的异质形核作用引起的,而对共晶Mg2Si相的变质作用是由在凝固过程中熔体中的Sr原子在Mg2Si晶体生长表面富集,从而改变了其生长优势所致的。     

Effect of phosphor addition on eutectic solidification and microstructure of an Al-13％Si alloy

As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.     

Variation of microstructure of RE-containing AlSi20Cu2Ni1RE0.6 alloy with different cobalt contents

Cobalt is generally considered as the element that can promote the high-temperature mechanical properties of Al-Si alloys. In order to develop new hypereutectic Al-Si alloys that can be used at high temperature, the changes of microstructure of Al-20Si-2Cu-1Ni-0.6RE-xCo alloy with different contents of Co were studied in this paper. The results show that, under P-RE complex modification of the alloy melt, the content of Co varying from 0 to 1.5% had little influence on the refining effect of primary Si and modification effect of eutectic Si, but the amount of acicular RE-bearing Al-RE-Ni-Co-Si compounds gradually increased with the increase of Co content. In addition, Co could also modify the morphology of Fe-bearing phases, which solidified as particles instead of long needles. The addition of Co even has an adverse effect on the tensile strength of this RE-containing hypereutectic Al-Si alloy.