THERMOELECTRIC-POWER CHARACTERIZATION OF A 2024-ALUMINUM-ALLOY DURINGSOLUTION TREATMENT AND AGING

The solution treatment and aging of a 2024 aluminum alloy was studied using the thermoelectric power (TEP) measurement technique, and the re sults compared to those obtained by microhardness and optical microsco py. The TEP value changes with solution treatment temperature and dura tion and reaches a maximum value for solution treatment at 500 degrees C. The changes in TEP during solution treatment are caused by changes in the solubility of the alloying elements in alpha-Al. In the artifi cial aging process, the TEP value decreases with increasing aging time , but exhibits different characteristics for different stages of aging . In the initial stage, the TEP value decreases slowly and shows a flu ctuating behavior for aging in temperatures below 190 degrees C. This fluctuation is caused by G.P. zone, G.P.B. zone, theta '', theta', S ' ', and S' formation which make different contributions to the TEP valu e. The TEP values corresponding to maximum microhardness for different aging temperatures are the same for a given solution treatment temper ature. After the peak age, the TEP values decrease very quickly becaus e the solubility of the alloying elements in alpha-Al decreases with a ging time. The micro structural changes caused by precipitation during aging which cannot be observed by the light optical microscope were s uccessfully monitored by the TEP measurement technique.