Electrical conductivity and
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(a) r-~ Cooauot,ng m
Ph.,.
(b)
Insulating Phase
Fig. 10--Schematic representation of the possible impediment to electron flow by (a) a fine structure and (b) a coarse structure.
Nevertheless, it should be noted in Figures 1 and 7 and Tables I and II that the changes in the electrical conductivity values are not of orders of magnitude, indicating conduction in the metallic regime of a percolation curve. Furthermore, due to the determined chemical composition of second-phase particles, it is believed that the aluminum silicon eutectic phase acts as the best insulating phase. In conclusion, the changes in electrical conductivity in aluminum alloys can be correlated to the characteristics of the metallurgical structure, i.e., modification of the eutecfic phase and refinement of the structure through either the addition of a grain refinement element or high solidification rates. However, since these changes are not of orders of magnitude and knowing that the chemical composition of the conducting phase does not change, the changes in those properties are ascribed to the size and distribution of the second-phase particles. Nevertheless, it has been observed that the changes are enough to indicate different microstructural conditions; therefore, it is believed that the measurement of either electrical conductivity or resistivity can be used as a reliable method to assess metal quality.
The authors wish to acknowledge A.R. Chan for the SEM analysis and Dr. M. Mendez for providing laboratory facilities.
REFERENCES I. J. Charbonnier, J. Morice, and R. Partalier: Int. Cast Met. J., 1979, vol. 4 (3), pp. 39-44. 2. D. Apelian, G.K. Sigworth, and K.R. Whaler: AFS Trans., 1984, vol. 92, pp. 297-307, 3. J. Charbonnier: AFS Trans., 1984, vol. 92, pp. 907-23. 4. Thermal Analysis of Molten Aluminum, Proc. AFS Conf., Rosemont, IL, 1984. 5. International Molten Aluminum Processing, Proc. AFS Conf., City of Industry, CA, 1986. 6. H. Oger, B. Closset, and J.E. Gruzleski: AFS Trans., 1983, vol. 91, pp. 17-20. 7. D. Argo, R.A.L. Drew, and J.E. Gruzleski: AFS Trans., 1987, vol. 95, pp. 455-64. 8. M.H. Mulazimoglu, R.A.L. Drew, and J.E. Gruzleski: Metall. Trans. A, 1987, vol. 18A, pp. 941-47. 9. M.H. Mulazimoglu, R.A.L. Drew, and J.E. Gruzleski: Metall. Trans. A, 1989, vol. 20A, pp. 383-89. 10. M.H. Mulazimoglu and J.E. Gruzleski: Modern Casting, 1990, vol. 80 (1), pp. 29-31. 1 I. T.J. Hurley: AFS Trans., 1986, vol. 94, pp. 159-72. 12. A. Manzano, E. Nava, E. Carrasco, and J. Mendez: CINVESTAVIPN Unidad Saltillo, Saltillo, Coahuila, MExico, unpublished research, 1993. 2358--VOLUME 24A, OCTOBER 1993
Synthesis of TiC Particulates and Their Segregation during Solidification in In Situ Processed AI-TiC Composites M.K. PREMKUMAR and M.G. CHU High modulus aluminum materials are being increasingly sought after by designers for many aerospace and automotive applications, both from the point of view of the ability to save weight by down-gaging, as well as other mechanical design limitations. A class of materials that has the ability to provid
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