Thermoelectric power characterization of a 2024 aluminum alloy during solution treatment and aging

The solution treatment and aging of a 2024 aluminum alloy was studied using the thermoelectric power (TEP) measurement technique, and the results compared to those obtained by microhardness and optical microscopy. The TEP value changes with solution treatment temperature and duration and reaches a maximum value for solution treatment at 500 °C. The changes in TEP during solution treatment are caused by changes in the solubility of the alloying elements in α-Al. In the artificial 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 fluctuating behavior for aging in temperatures below 190 °C. This fluctuation is caused by G.P. zone, G.P.B. zone, θ″, θ′, S″, and S′ formation which make different contributions to the TEP value. The TEP values corresponding to maximum microhardness for different aging temperatures are the same for a given solution treatment temperature. After the peak age, the TEP values decrease very quickly because the solubility of the alloying elements in α-Al decreases with aging time. The micro structural changes caused by precipitation during aging which cannot be observed by the light optical microscope were successfully monitored by the TEP measurement technique.