Isothermal precipitation of commercial 3003 Al alloys studied by thermoelectric power
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INTRODUCTION
DUE to its industrial and commercial characteristics, commercial wrought, no heat treatable 3003 Al alloy has been thoroughly studied and reported in the literature. The principal components of 3003 are Mn, Fe, and Si, which, through the strain hardening process, control the structure changes and the very important mechanical properties of this alloy. The studies concerning this alloy have been done using Al-Mn binary alloy as a starting point. By adding other alloying components, we were able to determine their effect upon the different metallurgical properties of the alloy with respect to the binary base. Thermal and mechanical treatments applied to the material give rise to significant microstructural changes which control the kinetics of precipitation and the recrystallization of grains in the alloy. The knowledge of these facts and the way to regulate them allow the optimization of the properties of the 3003 Alalloy. It is useful to cite the works of Goel et al.,[1,2] Nes and Embury,[3] Diallo et al.,[4] Kiss et al.,[5] and Howe[6] related to recrystallization and precipitation of Al-Mn alloys. All of these authors use direct and indirect techniques to determine the kinetics and magnitude of the precipitation as well as the identification of precipitates. In the 1989 Hungary workshop, which covered aluminum and its alloys, the results of the aforementioned works were deeply analyzed by Vo¨ro¨s and Kova´cs,[7] Chinh et al.,[8], Moricz et al.,[9] and Kova´cs-Csete´nyi et al.[10] In only one of the works cited previously was the thermoelectric power (TEP) used as a technique to characterize the alloy. The work by Moricz et al. shows the qualitative effect of Fe and Si on the behavior NEY JOSE´ LUIGGI, Professor, is with the Department of Physics, Universidad de Oriente, Cumana´, 6161 Venezuela. Manuscript submitted September 11, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS B
of the precipitation of Mn in Al. The use of TEP as a technique to characterize the precipitation effect on alloys is spreading due to the precise information it provides about the impurities in solid solution.[11] In this work, we used a procedure similar to the one used by Borrelly et al.[12] in his studies of the 3004 alloy. The samples, adequately treated, are annealed at a fixed temperature and the thermoelectric power measured at ambient temperature. The isothermal precipitation curves are analyzed through time-temperature-transformation (TTT) diagrams, which allow us to predict the physical and metallurgical parameters of interest during the precipitation process. In a future work, we will give details of the evaluation of those parameters using the multiphase theoretical model for the precipitation process of Luiggi and Betancourt.[13,14] II.
THEORETICAL AND EXPERIMENTAL DETAILS
A. Alloy Description In this work, we will study a commercial 3003 Al alloy, from Aluminios del Caroni S.A. (ALCASA), Guacara, Venezuela. The samples were provided in as-cast condition, with nominal chemical composition, as indicated in Tab
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