One Goal,One Expectation——Do a good job as host of the 69th World Foundry Congress

As a traditional metal-forming technology, casting/foundry has written a brilliant history chapter in the long development process of human society and

等轴球晶凝固多相体系内热溶质对流、补缩流及晶粒运动的数值模拟 Ⅰ．三相流模型

基于Eulerian-Eulerian方法和体积元平均技术,建立了模拟等轴球晶凝固过程的液、固、气三相流模型．液、固两相处理成相互分离、相互扩散的介质,气相与液、固两相只存在热量及动量的相互作用,三相(凝固前)作为自由流体共享一个统一的压力场．分别求解三相的质量、动量、溶质、热焓守恒方程;相间的热量交换和摩擦拖拽以及液／固界面上的溶质再分配和凝固潜热释放,通过定义对应守恒方程的源项和交换项而加以考虑;另外,单独求解一个晶粒密度守恒方程．晶粒的形核生长(相变) 也加以模型化并体现在对应的源项中,模型中所用的密度定义为溶质与温度的函数,因此可综合考虑热溶质对流、晶粒运动及凝固收缩所引起的补缩流动．凝固过程的体积收缩及补缩流动将体现在气／液自由表面的波动上．

等轴球晶凝固多相体系内热溶质对流、补缩流及晶粒运动的数值模拟 Ⅱ．模型的应用

利用等轴球晶三相凝固模型模拟了A356铝合金半固态浆料冷却斜槽法制备过程,研究了晶粒密度、尺寸及固相分数的分布与工艺参数的关系．结果表明,在斜槽浇注处晶粒形核密度最大,在斜槽末端晶粒尺寸、固相分数最大,在铸型中这三者的最终分布大致均匀．适当降低浇注温度有助于提高斜槽上形核密度和固相分数及降低晶粒尺寸．此外,还模拟了热溶质对流及补缩流在Al-4％Cu(质量分数)合金等轴球晶凝固过程所起的作用,以及晶粒运动及补缩流对合金自由表面和宏观偏析形成的影响．结果表明,凝固初期热对流及补缩流为主导,凝固中期热溶质对流为主导,凝固后期补缩流为主导;晶粒运动受阻程度直接影响自由表面形状,补缩流考虑与否导致完全不同的宏观偏析图．实验测得晶粒尺寸与模拟结果分布较相似,但其绝对值存在较大差异．

Temperature evolution and grain defect formation during single crystal solidification of a blade cluster

In order to investigate the asymmetry of thermal conditions during directional solidification, the temperature evolution and correspondingly developed undercooling in a simplified single crystal blade cluster were numerically simulated. Simulation results demonstrate that the temperature distribution at the blade platforms is obviously asymmetrical. On the outside of the blade which directly faces the heating element, the liquidus(TL) isotherms progress relatively smoothly. On the inside of the blades facing the central rod, however, the TLisotherms are in concave shape and the slope goes upwards to the platform extremities. The average undercooling extent ?T and undercooling time ?t at the inside are much higher than those at the outside. It was then predicted that the inside platform extremities have significantly higher probabilities of stray grain formation compared to the outside ones. A corresponding experiment was carried out and the metallographic examination exhibited the same side-and height-dependence of stray grain formation in the blades as predicted. On the inside of the blades, all platforms are occupied by stray grains, while the platforms on the outside are nearly stray grain free. The simulation result agrees very well with the experimental observation.

Experimental determination of grain density function of AZ91/SiC composite with different mass fractions of SiC and undercoolings using heterogeneous nucleation model

The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation,which is based on chemical elements diffusion and grain interface kinetics,can be used to predict casting quality and its microstructure.Nucleation models have parameters,which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composites with 0,1,2,3 and 4wt.% of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple,to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles,and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.

The mystery of molten metal

Recent advances in scientific understanding of high-temperature materials processing using novel experimental methodologies have shed light on the complex role of surface and interface phenomena. New in-situ studies on molten metal/solid ceramic interactions using a unique experimental complex at the Foundry Research Institute, Krakow, have revealed a number of unusual observations in materials processing at high temperatures. We present some such unusual observations and their explanation with reference to liquid metal processing of Al, Ni, and Ti, and their alloys in contact with oxide ceramics. In particular, we focus on the following aspects: primary oxidation of Al from residual water vapor or oxygen, capillary purification to remove surface oxide, substrate protection by CVD carbon, roughening due to spinel whisker formation, inclusions in castings due to mechanical detachment, floatation due to buoyancy forces, and segregation due to directional solidifciation, modification of the solid surface morphology by metal vapor ahead of the liquid, and the complication due to multi-component alloys melted in crucibles made from complex oxide-based ceramics. In the case of Ti, rapid reactions with oxides result in undesirable volumetric changes that create difficulty in casting high-quality Ti parts, particularly by investment casting. Nanoscale (e.g., colloidal) coatings based on Y2O3 protect crucibles and hold ladles against such attack. Practical insights and recommendations for materials processing emerging from the fundamental studies on high-temperature interfacial phenomena have been described.

Casting of microstructured shark skin surfaces and possible applications on aluminum casting parts

Within the project "Functional Surfaces via Micro-and Nanoscaled Structures" which is part of the Cluster of Excellence "Integrative Production Technology" established and financed by the German Research Foundation (DFG),an investment casting process to produce 3-dimensional functional surfaces down to a structural size of 1μm on near-net-shape-casting parts has been developed.The common way to realize functional microstructures on metallic surfaces is to use laser ablation,electro discharge machining or micro milling.The handicap of these processes is their limited productivity.The approach of this project to raise the efficiency is to use the investment casting process to replicate microstructured surfaces by moulding from a laser-microstructured grand master pattern.The main research objective deals with the investigation of the single process steps of the investment casting process with regard to the moulding accuracy.Actual results concerning making of the wax pattern,suitability of ceramic mould and core materials for casting of an AlSi7Mg0.3 alloy as well as the knock-out behavior of the shells are presented.By using of the example of an intake manifold of a gasoline race car engine,a technical shark skin surface has been realized to reduce the drag of the intake air.The intake manifold consists of an air-restrictor with a defined inner diameter which is microstructured with technical shark skin riblets.For this reason the inner diameter cannot be drilled after casting and demands a very high accuracy of the casting part.A technology for the fabrication and demoulding of accurate microstructured castings are shown.Shrinkage factors of different moulding steps of the macroscopic casting part as well as the microscopic riblet structure have been examined as well.

Simulation of cooling channel rheocasting process of A356 aluminum alloy using three-phase volume averaging model

The cooling channel process is a rehocasting method by which the prematerial with globular microstructure can be produced to fit the thixocasting process. A three-phase model based on volume averaging approach is proposed to simulate the cooling channel process of A356 Aluminum alloy. The three phases are liquid, solid and air respectively and treated as separated and interacting continua, sharing a single pressure field. The mass, momentum, enthalpy transport equations for each phase are solved. The developed model can predict the evolution of liquid, solid and air fraction as well as the distribution of grain density and grain size. The effect of pouring temperature on the grain density, grain size and solid fraction is analyzed in detail.

Structural and thermophysical properties characterization of continuously reinforced cast Al matrix composite

In this work the process of manufacturing a continuously reinforced cast Al matrix composite and its properties are presented. The described technology permits obtaining a structural material of competitive properties compared to either heat treatable aluminum alloys or polymer composites for several types of applications. The examined thermophysical properties and structural characterization, including material anisotropy, coupled with the results of previous measurements of the mechanical properties of both Al2O3 reinforcing filaments and metallic prepregs have proven the high quality of this material and the possibility of its operation under special loading modes and environmental conditions. Microscopic examinations (LM, SEM) were carried out to reveal the range of morphological homogeneity of the microstructure, the anisotropy of the filament band distribution, and simultaneously the adhesive behavior of the metal/fbier interface. The 3D morphology of the chosen microstructure components was revealed by computed tomography. The obtained results indicate that special properties of the examined prepreg materials have been strongly influenced, on the one hand, by the geometry of its internal microstructure, i.e. spatial distribution and volume fraction of the Al2O3 reinforcing filaments and, on the other hand, by a very good compatibility obtained between the individual metal prepreg components.

Compressive Deformation of Semi-Solid AZ91D Magnesium Alloy

The compression tests of semi-solid AZ91D Mg alloy have been conducted on a parallel-plate viscometer. The results are as follows. With increasing the compression temperature, the deformation rate or the strain rate of the specimens rises, but the compressive stress continuously decreases; the deformation strain is obviously linear with the compressive stress and independent on compression temperature under a given compression load. In the wake of the compression load being added, the compressive strain increases but the compressive stress decreases clearly; the deformation strain is obviously linear with the compressive stress under different compression load. The mathematical apparent viscosity model about the semi-solid compressed AZ91D Mg alloy has been established, i.e ηapp =2004.2exp（15.61 fs）γ^1.317.fn^-1.3511

连续增强铸造铝基复合材料的结构特征和热物理性能

介绍了连续增强铸造铝基复合材料的性能及其制造过程。该工艺能获得一种在某些应用场合中性能优于可热处理的铝合金或聚合复合材料的结构材料。检验得到的热物理性能和结构特征,包括材料的各向异性以及以前Al2O3增强纤维及金属预浸料坯力学性能的测定结果都证明了该材料的高质量及其在特定的载荷模式和环境条件下工作的可能性。显微观察(光学显微镜,扫描电子显微镜)显示了微观组织的形态均匀性范围,纤维带分布的各向异性,以及金属/纤维界面的粘着特性。用计算机层析X射线照相法来显示所选取的微观组织组元的三维形态。结果表明:预浸料坯的特殊性能一方面受到其内在的微观组织几何形态,即Al2O3增强纤维体积分数和空间分布的强烈影响,另一方面还受到金属预浸料坯的各组元之间达到非常好的相容性的强烈影响。

Thixocasting combination spanners using stainless steel X39CrMo17

Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with high mechanical load capacity.Moreover,forging is a cost-effective mass production process but,in spite of all its advantages,it has its limitations,e.g.in the freedom of designs.However,because of the extreme thermal loading(particularly with regard to permanent moulds) and the frequently unavoidable casting defects,hand tools are not cast.By means of thixocasting steel,technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging.Through near-net shape production,manufacturing steps and costs can be reduced.Furthermore,steels,which are difficult to forge but nonetheless have high potential for specific applications(such as high strength or corrosion resistant steels),can also be processed.In cooperation with industrial partners,X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast.Forming dies were designed and optimized by simulation,the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys.The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition(PECVD).During the experiments,combination spanners were successfully cast in the semi-solid state.Cast parts were heat-treated to enhance the toughness of components,which was subsequently measured by a standardized torque test.Moreover,a hypothetical approach of a possible,industrial batch process was carried out using the simulation software MAGMAsoft.

Hot cracking susceptibility of AlSi7MgCu alloys and effects of alloying elements magnesium and copper

Hot cracking during solidification can be a serious problem in aluminium casting alloys under certain conditions.This feature is well known,but still insuffi ciently investigated in shape casting.This study gives a brief overview of the factors inf luencing hot cracking during shape casting.Five different AlSi7MgCu alloys with varying Mg and Cu contents were examined.Theoretical models,including the cracking susceptibility coeffi cient(CSC)from Clyne and Davies,were considered.Thermodynamic calculations(terminal freezing range,TFR)of the behavior of the solid fraction during solidif ication were compared to an experimentbased hot cracking indexing(HCI)method.Scanning electron microscopy(SEM)was used to compare the existing microstructure and precipitated thermodynamic phases using the software ThermoCalc Classic(TCC).Furthermore,SEM was used to investigate crack surfaces initiated by a dog-bone shaped mold during casting.A good correlation between theoretical models and the experimental hot cracking index method was observed.

Bonding effect of liquid magnesium with open-celled carbon foam in interpenetrating phase composite

The issue of bonding formation in liquid metal/open-celled carbon foam(C_(of))systems was examined,taking into account the practical aspects of the synthesis of a new type of Mg-C metal material composite.The problem is complex due to the strong oxidation and intense evaporation of liquid magnesium,as well as the 3D geometry of the carbon component,where metal transport occurred through the foam cells’windows.Laboratory experiments performed at 700℃ in ceramic crucibles showed that spontaneous carbon foam infiltration by liquid metal is impossible under the applied conditions,either in an air atmosphere coupled with flux protection or under argon protection.Comparative tests performed in a UHV chamber filled with static pure Ar by a sessile drop method,coupled with non-contact heating and capillary purification at a test temperature of 700℃ directly in the UHV chamber,showed non-wetting behavior of the Mg/C_(of)couple with a correspondingly high contact angle of about 135°.The graphite capillary was then moved down,the liquid drop being slightly pressed into the foam,but these changes did not induce effective foam penetration.Despite the short contact time for the sessile drop test under an argon atmosphere,SEM+WDS analysis of the solidified Mg/C_(of)couple revealed the formation of an MgO interlayer at the interface,with a thickness of approx.1μm.The experimentally demonstrated presence of oxygen in the carbon foam sample,both before and after its contact with magnesium,points to oxide-type bonding being established between Mg and C_(of).This observation is in a good agreement with previous reports on the interface characterization of magnesium matrix composites reinforced with glassy carbon materials and carbon fibers by stir casting and pressure infiltration.Based on the findings of this study,a general structural scheme of the bonding process between carbon foam and liquid magnesium,as an important stage in the syntheses of Mg-C composites,was proposed.

Meeting Summary of Composites Committee of FICMES

The working meeting of Composites Committee of Foundry Institution of Chinese Mechanical Engineering Society (FICMES) was held on July 25th, 2004 in Kunming, Yunnan Province. The newly elected committee members attended the meeting. The committee consists of 27 members from universities, research institutions and enterprises. The meeting was presided over by deputy-director of Composites Committee of FICMES, Prof. Ye PAN from Southeast University. He also briefly introduced the Composites Committee development amt academic activities. Prof. Shifang SU,

CM247LC单晶高温合金中MC碳化物对γ/γ′共晶反应的影响

在0.2 mm/min的抽拉速率下对高温合金CM247LC进行了单晶定向凝固实验,观察分析了水淬的糊状区内的组织。结果显示,合金凝固时首先形成g枝晶,然后初生MC碳化物在g枝晶尖端稍后的位置开始形成,γ/γ′共晶在凝固最后阶段析出。值得注意的是,γ/γ′共晶反应是以化学成分和晶体结构都完全不同的MC碳化物作为异质形核核心,而不是依附在形核条件更好的g相上。检测结果表明,在MC碳化物基底上形成的γ/γ′共晶体具有杂乱的晶体取向,与单晶g相基体的取向完全不同,说明宏观上为单晶体的高温合金铸件实际上可能含有许多微小杂晶晶粒,使得铸件的单晶性受到影响。

Metallic Functionally Graded Materials:A Specific Class of Advanced Composites

Functionally graded materials, including their characterization, properties and production methods are a new rapidly developing field of materials science. The aims of this review are to systematize the basic production techniques for manufacturing functionally graded materials. Attention is paid to the principles for obtaining graded structure mainly in the metal based functionally graded materials. Several unpublished results obtained by the authors have been discussed briefly. Experimental methods and theoretical analysis for qualitative and quantitative estimation of graded properties have also been presented. The article can be useful for people who work in the field of functionally graded structures and materials, and who need a compact informative review of recent experimental and theoretical activity in this area.

Determining casting defects in near-net shape casting aluminum parts by computed tomography

Three types of near-net shape casting alumi- num parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die casting （Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy）, die casting （A356, A1-7Si-0.3Mg）, and semi-solid casting （A356, A1-TSi-0.3Mg）, respectively. Unlike die casting （second part）, low-pressure die casting （first part） sig- nificantly reduced the formation of casting defects （i.e., porosity） due to its smooth filling and solidification under pressure. No significant casting defect was observed in the third part, and this absence of defects indicates that semi- solid casting could produce high-quality near-net shape casting aluminum parts. Moreover, casting defects were mostly distributed along the eutectic grain boundaries. This finding reveals that refinement of eutectic grains is necessary to optimize the distribution of casting defects and reduce their size. This investigation demonstrated that computed tomography is an efficient method to determine casting defects in near-net shape casting aluminum parts.