Kinetic Analysis of Recovery, Recrystallization, and Phase Precipitation in an Al-Fe-Si Alloy Using JMAEK and Sesták–Berggren Models

Abstract

When studying the phase changes process in a rolled AA8011 alloy using DSC, we find that the peaks associated with phase precipitation under this microstructural condition are different from those obtained in homogenized microstructures. The differences observed are attributable, first, to the recovery process occurring at temperatures below 423 K (150 °C), which interacts with the precipitation of Si-rich precipitates or with Guinier–Preston zones both coexistent in that temperature range; and second, to the recrystallization above 473 K (200 °C), which coexists with precipitation of the α-AlFeSi phase. In this work, the precipitation and recovery–recrystallization kinetics are experimentally obtained and deconvoluted in peaks characteristic for each of the mechanisms involved; i.e., precipitation of GP zones, recovery, precipitation of α phase, and recrystallization. The deconvolution is achieved using functions of Gauss, Weibull, and Fraser–Suzuki; and the characterization of each reaction deconvoluted is realized through both Jhonson–Melh–Avrami–Erofeev–Kolmorokov kinetic models and Sesták–Berggren combined kinetic model. The kinetic study evinces that in addition to the expected reactions, other reactions, necessary for good experimental adjustment, appear. An isoconversional study is undertaken to numerically evaluate the kinetic triplet of every process.

Appendix

This Appendix presents Wi deconvolution parameters for each transfer function used, as described in the text. Table XII reports Wi values obtained for the experimental kinetic measurements at T < 423 K (150 °C), where the main reactions correspond to the precipitation of Guinier–Preston zones and to the restoration reaction. Table XIII presents the values obtained for the experimental kinetic for T > 473 K (200 °C). In this case, the main reactions are associated with both a phase precipitation and the recrystallization reaction. Note that the W1 parameter corresponds to the maximum temperature of the reaction, and its value changes when different reactions are involved in the total kinetic. Figure A1 shows comparatively different FTs involved in reproduction of the total kinetics in a homogenized sample heated at 10 °C/min.

Table XII Deconvolution Parameters of the Transfer Function Obtained for Precipitation of Guinier–Preston Zones and Recovery

Table XIII Deconvolution Parameters of the Transfer Function Obtained for Precipitation of α Phase and Recrystallization

Fig. A1

Comparative behavior of the different FTs obtained for HS samples at 10 °C/min. Total kinetics. Squares: Fraser–Suzuki FTs, Circles: Gauss FTs, Triangles: Weibull FTs. The small difference on total kinetic corresponds to the Fraser–Suzuki FTs. In Table XIII are reported Wi parameters for this deconvolution. Note the difference in the peak position (W1) obtained in the second reaction (empty symbols): Gauss FTs 592.6 K (319.6 °C), Weibull FTs 586.3 K (313.3 °C) and Fraser–Suzuki FTs 584.3 K (311.3 °C)

See Appendix Tables XII, XIII and Figure A1.