Kinetics of transformation during supersaturation and aging of the Al-4.7mass%Cu alloy: Grain size, dilatometric, and di
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Basic and Applied Research: Section I
Kinetics of Transformation during Supersaturation and Aging of the Al-4.7Mass%Cu Alloy: Grain Size, Dilatometric, and Differential Thermal Analysis Studies Ignacy Wierszyłłowski, Sebastian Wieczorek, Andrzej Stankowiak, and Jarosław Samolczyk
(Submitted July 21, 2005; in revised form August 15, 2005) The processes taking place during supersaturation of the Al-4.7mass%Cu alloy have been studied by the methods of quantitative metallography and dilatometry. The grain growth activation energy was about 95 kJ/mol, and the exponent of time, n, was close to 0.4. Dissolution of precipitates caused two-stage shrinkage of the sample, which had activation energies of 90 kJ/mol (first stage, n = 0.8) and 63 kJ/mol (second stage, n = 0.4).The kinetics of the phase transformation during aging of the Al-4.7mass%Cu alloy has been studied by the dilatometry and differential thermal analysis The activation energy of the precipitation processes within the range of 50-320 °C varied between 50 and 100 kJ/mol and confirmed the results obtained previously. For the precipitation processes within the range of 320-462 °C, the activation energy varied from 226 to 300 kJ/mol. The results obtained were compared with literature data with good agreement.
1. Introduction The processes of precipitation in aluminum-copper alloys are well known. After supersaturation consisting of annealing at about 520 °C, quick cooling down to room temperature, and aging, G-P (Guinier-Preston) zones first appear, then are followed by ⌰⬙ precipitates, which nucleate on the most stable G-P zones. The other G-P zones dissolve in the solid solution, and the copper atoms diffuse to the growing nuclei. When the temperature increases, because of aging, the ⌰⬙ dissolves, and ⌰⬘ nucleates at defects in the solid solution. Finally, the equilibrium phase Al 2 Cu (⌰) nucleates at the boundaries of the solid solution grains, ⌰⬘ dissolves, and the copper atoms diffuse to the growing ⌰.[1-4] The saturation process precedes aging and comprises dissolving excess precipitates enriching the solid solution with copper atoms, grain growth, and quick cooling to the ambient temperature. The amount of copper atoms in the solid solution influences the quantity of precipitates during aging and determines the properties obtained after aging. The grain boundaries of the solid solution are privileged places for precipitate nucleation, so grain size can influence the This article is a revised version of the paper printed in the Proceedings of the First International Conference on Diffusion in Solids and Liquids—DSL-2005, Aveiro, Portugal, July 6-8, 2005, Andreas Öchsner, José Grácio and Frédéric Barlat, eds., University of Aveiro, 2005. Ignacy Wierszyłłowski and Andrzej Stankowiak, State College of Leszno, ul. Mickiewicza 5, 61-100 Leszno, Poland; Sebastian Wieczorek, Poznan´ University of Technology, Pl. Marii Sklodowskiej – Curie 5, 60-965 Poznan´, Poland; and Jarosław Samolczyk, Institute of Metal Forming, ul. Jana Pawła I I, 14, 61-139 Poznan´, Polan
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