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Session Chairpersons: A.K. Ghosh, University of Michigan, Ann Arbor, MI; J.V. Wood, Department of Materials Engineering and Materials Design University of Nottingham, UK
SPRAY FOAMING OF HIGH PERFORMANCE ALUMINIUM GOES FOR VOLUME PRODUCTION: Klaus Hummert, PEAK Werkstroff GmbH, Velbert, Germany
Very recently the major break-through in spray forming of high performance aluminium has been achieved. After many years of intensive alloy and process development, the first long time volume application could be realised. The use of PM aluminium for cylinder liners in gasoline passenger car engines gives strong improvements in the system of piston, piston rings and liner running surface. Furthermore the engine emissions have been reduced drastically. Based on the progress made with respect to technical and economical aspects this first volume production will have great impact on other application in automotive and aircraft industries or for leisure equipment. The paper describes the state of the art spray forming of aluminium based alloys under technical and metallurgical aspects. Examples will be given several applications in different market sections with functionally relevant test results. Finally the economical situation of spray forming will be discussed in comparison to competitive technologies.
FABRICATION OF LOWER THERMAL EXPANSION ALUMINIUM ALLOYS BY SPRAY-CASING PROCESS: Chong-Sung Park, Hyun-Hp Park, Myung-Ho Kim, R.A.S.O.M., Department of Metallurgical Engineering, Inha University, Inchon 402-751, Korea
Spray-casting process is becoming increasingly attractive as an alternate production route for particulate reinforced metal matrix composites, and the coefficient of thermal expansion (CTE) of the composites can be controlled by altering the level of reinforcement. In this study, performs of Al-Si matrix composites reinforced with SiCp were fabricated by spray-casting process, and the coefficient of thermal expansion (CTE) of the composites were investigated using thermal mechanical analysis (TMA) after hot-extruded. It was found that the CTE of the composite with SiCp reduced with increase in volume fraction of SiC particles, and the Al-Si performs without SiCp also exhibited reduced CTE compared to mold-cast specimen. The effect of the grain and Si phase size, and the aspect ratio of Si phase, as well as the volume fraction of the SiCp on the CTE of the Al-Si composite have also been examined.
PRODUCTION OF CONTINUOUS POLYCRYSTALLINE Al-Cu RIBBONS BY PLANAR FLOW CASTING AND SOLIDIFICATION STRUCTURES: Department of Metallurgical Engineering, Yonseu University, 134 Shinchon-dong, Seodaemun-gu, Scoul, Korea
The geometry and microstructures of ribbons spun by planar flow casting have been investigated as functions of processing parameters adapting various kinds of crucial material and slot design. Microstructural transitions from segregation free zones to cellular/dendrite regions increased with increasing wheel velocity and the superheat of molten metal before ejection. X-ray diffraction spectra indicated an increasing tendency towards a (200) preferred orientation on the wheel-side surface of the ribbon with increasing the superheat of molten metal. A model based on a two-dimensional cellular automaton technique coupled with the control volume method was developed for the prediction of dendrite grain structures in planar flow casting. The calculated grain structures were in good agreement with those obtained from experimentation.
COLUMNAR-EQUIAXED TRANSITION OF SOLIDIFICATION STRUCTURES IN SQUEEZE CASTING: I.S. Cho, C.P. Hong; RASOM, Department of Metallurgical Engineering, RASOM Yonsei University 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, Korea
The CET(Columnar-Equiaxed Transition) of solidification structures in squeeze casting of Al-Cu alloys was investigated. The interfacial heat transfer coefficient between the casting and the mold was evaluated using an inverse problem method. Solidification sequences in squeeze casting were simulated using the calculated interfacial heat transfer coefficients. The cellular automaton coupled with the control volume method was developed for the predication of solidification grain structures and was applied to evaluate the CET in squeeze casting. The effects of casting process variables, such as pressure, pouring temperature, mold temperature and inoculation on the CET in squeeze casting were investigated. The solidification parameters, solidification rate and thermal gradient at the solidification front, were also analyzed in regard to their effects on the CET. The calculated results were also compared with those obtained experimentally.
SEMI-SOLID PROCESSING OF A356 Al ALLOYS: C.P. Chen, C.-Y.A. Tsao, Department of Materials Science and Engineering National Cheng-Kung University Tainan, Taiwan
A356 Al alloys were synthesised and processed in the semi-solid state. The alloys with a non-dendrite structure were synthesised via electromagnetic stirring in the semi-solid state and then subsequently cast into billet form. The billets with non-dendrite structure were then reheated to semi-solid re gime and isothermally upset-deformed. The effects of the solid fraction during semi-solid deformation, deformation rate, and deformation temperature on the morphology, macrostructure, and stress-strain relationships of semi-solid deformed billets were investigated and compared to those of conventional deformed billets. A phenomenological model was developed to help explain the different behaviours of the semi-solid deformed billets.
10:10 am BREAK
COMPARISON BETWEEN PLASMA PROCESSED NANOCRYSTALLINE Fe AND ITS PRECURSOR IN POWDER AND COMPACT FORMS: Xiaofu Chen, E.G. Baburaj, Wenxian Zhu*, Patrick R Taylor*, F.H. (Sam) Froes, Peter C. Kong+, Institute for Materials and Advanced Processes (IMAP); University of Idaho, Moscow, ID-83844-3026, USA. *Department of Metallurgical and Mining Engineering, University of Idaho, Moscow, Idaho, 83844-3024 USA; +Lockheed Idaho Technologies Company, Idaho Falls, Idaho 83415-2210
Nanocrystalline Fe powder has been produced from 1-4 mm size initial powder, using non-transferred arc plasma processing. Both the processed and initial powders have been consolidated by HIPing at different temperatures to determine the lowest possible processing temperature-time combination which gives rise to full densification. The fine powders and consolidation products have been characterised in detail for particle size, structure and morphology by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the results have been used as feed-back to improve the processing conditions. The particle size of plasma processed Fe powered is in the range of 10-50 nm. The temperature dependent grain growth of plasma processed and starting Fe powders have also been examined in this study.
STUDY OF MICROSTRUCTURE AND PROPERTIES OF SPRAY FORMED Al-Cr-Zr ALLOYS: A.F. Norman, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK
The technical problems and cost associated with the multi-step PM processing of RS Al alloys have hindered their successful development. Spray forming can obviate these problems by means of the integral inert gas atomisation and deposition operation in which the alloy exists in particulate form only for a few milliseconds. Spray forming experiments have been performed on Al-Cr-Zr alloys studied previously by the combined RS/PM route. The microstructure and the tensile properties of the forged and heat treated deposits will be compared with the RS/PM alloy. The latter exhibits superior properties, not matched by the spray formed alloy.
EFFECT OF ALLOY ELEMENTS ON THE DAMPING CAPACITY OF SPRAY CAST Al-Zn ALLOY: B.C. Moon, Z.H. Lee, Department of Materials Science and Engineering, RASOM, Kaist, Korea
Damping capacity of a material refers its ability to dissipate vibrational energy into thermal energy. In Al-Zn system, damping originates form the interfacial friction between two phases and the damping capacity is proportional to the interfacial area. The microstructure of spray cast alloys are very different from the cast alloys and the damping characteristics of spray cast Al-Zn alloys is expected to be also different. In this study, the effect of third element on the damping behaviour of spray cast Al-Zn alloys was studied. Al-Zn-X alloys were made by spray cast and mold cast. Third elements were Cu, Mg and Mn. Uniformly rolled cast and sprayed specimens were solution treated then quenched by water. Specimens were aged at room temperature for 24 hours. Damping capacity was measured by logarithmic decrement of freely decayed vibration of cantilever beam. Damping capacity of spray cast alloys was higher than cast alloys. Dilute tried elements increased the hardness but decreased the damping capacity alightly.
PRODUCTION OF CONTINUOUS POLYCRYSTALLINE Al-Cu RIBBONS BY PLANAR FLOW CASTING AND SOLIDIFICATION STRUCTURES: S.M. Lee, K.Y. Lee, C.P. Hong; RASOM Department of Metallurgical Engineering, Yonsei University 134 Shinchon-dong, seodaemun-ku, Seoul 120-749, Korea
The geometry and microstructures of ribbons spun by planar flow casting have been investigated as functions of processing parameters adapting various kinds of crucible material and slot design. Microstructural transitions from segregation free zones to cellular/dendritic regions were obsened in Al-Cu alloys. The thickness ratio of columnar layer increased with increasing the wheel velocity and the superheat of molten metal before ejection. X-ray diffraction spectra indicated an increasing tendency towards a (200) preferred orientation on the wheel-side surface of the ribbon with increasing the superheat of molten metal. A model based on a two dimensional cellular automaton technique coupled with the control volume method was developed for the prediction of dendritic grain structures in planar flow casting. The calculated grain structures were in good agreement with those obtained experimentally.
OPERATING PARAMETERS FOR THE CONTINUOUS UNIDIRECTIONAL SOLIDIFICATION OF A 1% Si ALUMINUM ALLOY DRAWN TO FINE WIRE: M.H. Kim, Chungbuk National University and RASOM, Cheongju Korea; T.S. Song, Chungbuk National University, Cheongju, Korea; H.H. Jo, Korea Academy of Industrial Technology, Incheon, Korea; C.S. Kang, Seoul National University, Seoul, Korea; C.R. Loper, Jr., The University of Wisconsin-Madison, Madison, WI
Previous studies have demonstrated the technique of producing continuous cast, directionally solidified castings of a limited number of alloys. These procedures have been successful when the casting conditions are established so that the solid-liquid interface is maintained outside of the mold by insuring a mold temperature in excess of the liquidus temperature and a solid-liquid interface located near enough to the mold so that the molten metal surface tension is able to support the liquid phase. Rods varying from 3 to 10 mm. (0.12 to 0.39 in.) D. have been successfully cast in this manner. This study has expanded that technique to a 1% Si aluminum alloy, and the casting, and the casting conditions which would enable production of an 8 mm. (0.31 in). D. rod having a mirror surface with a highly longitudinally oriented microstructure have established. Furthermore it was demonstrated that this alloy could be wire drawn, without the need of intermediate recrystallization or stress relief, to produce wires of 0.14 to 0.10 mm. (0.0055 to 0.0039 in) D.
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