Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Wednesday afternoon, September 17.
Session Chairs: Harish Merchant, Gould Electronics, 35129 Curtis Blvd., Eastlake, OH 44095-4001; James G. Morris, University of Kentucky, 760 Anderson Hall, Dept. of Metallurgy, Lexington, KY 40506-0046
GRAIN REFINEMENT BY CONTINUOUS RECRYSTALLIZATION: Jian Li, S. Saimoto, Dept. of Materials & Metallurgical Engineering, Queen's University, Kingston, Ontario, Canada K7L 3N6
Recent studies have shown that continuous recrystallization rather than the conventional discontinuous one can result in grain size of about 1 µm. Our studies on nominal pure aluminum alloys have shown that the key element is Fe and its solute content has to be reduced below 1ppm (atomic) in order for grain refinement by continuous recrystallization to occur. To enhance rapid gettering of solutes at low temperatures, the material is pre-strained such that the dislocation density is high enough to reduce the diffusion distance of solutes but not sufficient to initiate recrystallization. This procedure have been used with success for AA3003 nickel and some stainless steels.
AN APPROACH TO THE MICROSTRUCTURE ROLE IN THE REFINEMENT OF MONOPHASIC X-Zn ALLOYS: M.E. Noguez, G. Salas, T. Robert, J. Ramirez, Departmento de Metalurgia, Facultad de Quimica, UNAM, Mexico, D.F. 04510
Three casting refinement methods (mold rotation, chemical additions and cooling rate) have been used in the casting of Mg-5% Zn, Al-5% Zn and Cu-30% Zn alloys. A microstructural evaluation and a comparison among the results obtained for the same method in the three alloys and the three methods for the same alloy was made. The aim was to relate the effect of the refining method on the structure and on the properties including a corrosion behavior. Mold rotations were made from 100 to 500 rpm. A similar microstructural refinement and properties relation were found for the three alloys with the rotation. Chemical additions used were: for Al-Zn the commercial material Ti-B (6:1); for Mg-Zn the recommended hexacloroethane used in Mg-Zr alloys; and Bi for Cu-Zn, recommended for pure Cu which was found effective to a certain extent. Results with this method show dissimilarities discussed in text. Cooling rate from approximate 50°C/s to 1 to 2°C/s were used in all alloys. This method gave the expected results and relations. A final general discussion is made regarding the grain size and secondary dendrite arm spacings (DAS) and the common accepted relations DAS-Cooling rate and Grain size-properties, etc.
SOLIDIFICATION PROCESSING FOR GRAIN REFINEMENT OF NON-FERROUS METALS AND ALLOYS: Goro Aragane, Yoshiaki Osawa, Susumu Takamori, Akira Sato, National Research Institute for Metals, Tsukuba, Ibaraki, 305 Japan
Ultrasonic vibration is applied to molten metals through steel horns coated with Al2O3 and SIALON horns during solidification, and effects of the ultrasonic vibration on the structures of Zn, Al, Al alloys and Cu ingots are investigated. A new process named "Rapid solidification with vigorous agitation" is developed to produce large ingots having fine grain structures. The molten Al-Si alloys are rapidly solidified with water cooled copper molds and at the same time stirred vigorously by graphite rods during falling down of the melt through the gap between the mold and the rod. The mean grain size of primary crystals in slurry obtained become smaller with increasing the intensity of cooling and the rotation speed of stirring rod. Primary and eutectic Si grains are not only small but also globular when the agitation is strong enough.
PHENOMENON OF TEXTURE NONHOMOGENEITY IN GRAIN STRUCTURE OF METALS: O.B. Girin, Yu O. Proshenko, V.I. Bekarev, Dept. of Physics, State Metallurgical Academy of Ukraine, Prospekt Gagarina 4, Dnepropetrovsk 320635, Ukraine
Phenomenon of texture nonhomogeneity in grain structure of metals discovered by utilizing nonconventional techniques of X ray diffraction texture characterization and TEM is covered. The effect studied results from texture development and consists in that the grain size, substructure and defect density differ dramatically in the major axial, the minor axial and the random component of texture. On the average, the grain size and the defect density in the major axial component differ from those in the random component of texture. On the average, the grain size and the defect density in the major axial component differ from those in the random component by one order of magnitude. Features of grain structure evolution during texture development are addressed. It is demonstrated that the phenomenon at hand is to be taken into consideration in discussing the impact of grain size on metal properties.
RECRYSTALLIZATION IN PARTICLE-CONTAINING ALUMINUM ALLOYS: L.M. Pawlowski, J.S. Vetrano*, I.M. Robertson and S.M. Bruemmer*, Dept. of Materials Science and Engineering, University of Illinois, 1304 W. Green, Urbana, IL 61801; *Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
Additions of Sc and Mn have been added to solid solution Al-Mg alloys to study the influence of particle size, shape and type on deformation and recrystallization. Controlled heating experiments both in bulk samples and thin specimens heated in-situ in the transmission electron microscope have been performed to study these effects. Plate-like Al6Mn particles are shown to pin grain boundaries and offer potential sites for nucleation of new grains. The presence of fine (<100 nm), coherent Al3Sc particles, alternatively, inhibits recrystallization through pinning of dislocations and sub-grain boundaries. Processing of these alloys to produce microstructures suitable for superplastic deformation will be discussed. Work supported by the Materials Division, Office of Basic Energy Sciences, U.S. Dept. of Energy under Contract DE-AC06-76RLO 1830
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