Identification of high temperature precipitation reactions in 2024 Al-Cu-Mg alloy through ultrasonic parameters

In situ ultrasonic measurements have been carried out in a 2024 Al-Cu-Mg alloy heat treated from 300 to 623 K. Different specimens have been prepared by (i) solution annealed at 766 K for 1 h, and (ii) water quenched then aged at 463 K for 10 h or 32 h. High temperature ultrasonic measurements from 300 to 623 K reveal the three transitions, (i) formation of GPB zone around 346 K, (ii) dissolution of GPB zones and S phase at 492 K, and (iii) the formation of semi-coherent S' phase at 557 K which have been confirmed by DSC studies and SEM/TEM characterization. The different phase transformations and dissolutions at high temperature have been explained by the ultrasonic method and are compared to DSC and characterization with TEM. The first and second differential plot of the ultrasonic parameters with respect to temperature is identified as an effective tool in clearly identifying the fine scale precipitation/dissolution events. (C) 2012 Elsevier B.V. All rights reserved.