Characterization by thermoelectric power of a commercial aluminum-iron-silicon alloy (8011) during isothermal precipitat
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I.
INTRODUCTION
COMMERCIAL 8011 alloy is mainly an Al-Fe-Si alloy, which has a wide variety of end applications owing to the fact that it is possible to control the microstructural evolution of the alloy by means of specific thermal and mechanical treatments. The system Al-Fe-Si has been subjected to a large amount of research in an effort to explain the means by which the relation between thermal treatment and microstructure affects the precipitation, recovery, and recrystallization processes. Miki and Warlimont[1] study the morphology and kinetics of the precipitation process in AlFe and Al-Fe-Si alloys, determining that the addition of only 0.05 wt pct of silicon considerably lowers the activation energy for the diffusion of Fe in Al and increases the rate of Al3Fe precipitation. Ito et al.[2] verify that the addition of silicon to an Al-Fe alloy accelerates the kinetics of both recrystallization and precipitation and that silicon increases random components in the recrystallization textures. Cordovilla and Louis[3] study the recovery and recrystallization of a strained Al-Fe-Si alloy by differential scanning calorimetry, verifying that the stored energy is released in two stages, the first being related to recovery process and to the precipitation of Fe and Si. This interpretation differs from that given by other authors.[4] Bay and Hansen[5] evaluate the variation of the recrystallization parameters in deformed samples of a 0.47 wt pct Fe 0.11 wt pct Si alloy. Dons[6,7] and Turmezey et al.[8] identify the Al-Fe-Si intermetallic particles in commercial pure and industrial cast aluminum alloy, determining in each case the effect of the cooling rate upon the precipitate phases. Oscarsson et al.[9] present an interesting work concerning different procedures for the determination of the quantity of iron, which is in solid solution in an Al-Fe-Si alloy, confirming that wet chemical procedures and analyses of the resistivity or of the thermoelectric power (TEP) all produce NEY JOSE´ LUIGGI A., Titular Professor, is with the Laboratorio de Fı´sica de Metales, Dpto. de Fı´sica, Escuela de Ciencias, Universidad de Oriente, Apdo. Postal 299, Cumana´, Sucre, Venezuela. Manuscript submitted January 3, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
compatible results. Puchi et al.[10,11] investigate the recrystallization of twin rolling cast or deformed AA8011 alloys under different conditions of strain and of impurity supersaturation, reporting two distinct intervals between 325 7C and 400 7C in which the restoration of the mechanical properties shows different behaviors. Their results, at low temperature, are in agreement with those of Cordovilla and Louis. Komatsu et al.[12] measured electrical resistivity under isochrone conditions with an average heating rate of 2 7C/min and demonstrated that the vacancy annihilation was completed below 80 7C. The Si precipitation was confirmed to start above 30 7C and continue up to 350 7C. Redissolution of Si starts at 400 7C and is completed at 500 7C in a 0.43 wt pct Fe 0.14 wt
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