CALORIMETRIC AND RESISTIVITY STUDY OF FORMATION AND REDISSOLUTION OF PRECIPITATES IN 7050-ALUMINUM-ALLOY

Calorimetric and electric resistivity measurements and TEM observation s have been performed in order to interpret precipitation and redissol ution phenomena in the 7050 aluminum alloy. Reactions of heat absorpti ons and evolutions in the specific heat vs. temperature curves and cha nges in the temperature derivative of resistivity vs. temperature curv es during heating have been compared. The formation and redissolution of G. P. zones, eta' and eta phases are clearly interpreted in the spe cific heat vs. temperature curves. Thermal stability of G. P. zones in creases with aging to near that of the eta' phase, and the thermal sta bility of the eta' also increases. The eta' transforms to the eta havi ng the same habit planes as the eta'. The formation of the eta with an d without habit planes same as the eta' occurs at different temperatur e ranges, which causes split in the heat evolution due to the eta form ation in the specific heat vs. temperature curves. In the process of r etrogression and reaging (RRA) treatment, a parr of G. P. zones and et a' precipitates are redissolved and the eta phase is formed at the ret rogression stage.