Calorimetric and resistivity study of formation and redissolution of precipitates in 7050 aluminum alloy

Abstract

Calorimetric and electric resistivity measurements and TEM observations have been performed in order to interpret precipitation and redissolution phenomena in the 7050 aluminum alloy. Reactions of heat absorptions and evolutions in the specific heat vs. temperature curves and changes in the temperature derivative of resistivity vs. temperature curves during heating have been compared. The formation and redissolution of G. P. zones, η′ and η phases are clearly interpreted in the specific heat vs. temperature curves. Thermal stability of G. P. zones increases with aging to near that of the η′ phase, and the thermal stability of the η′ also increases. The η′ transforms to the η having the same habit planes as the η′. The formation of the η with and without habit planes same as the η′ occurs at different temperature ranges, which causes split in the heat evolution due to the η formation in the specific heat vs. temperature curves. In the process of retrogression and reaging (RRA) treatment, a part of G. P. zones and η′ precipitates are redissolved and the η phase is formed at the retrogression stage.