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ISSN: 1820-0206 First published in 1950
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doi: 10.5937/str2600003M Vol. 75, No.2 (2025), Pages: 18 - 22 Impressum Contents
Influence of
Retrogression and Reaging Heat Treatment on Calorimetric Behavior of
EN AW-7049A Alloy
Aluminum alloy EN AW-7049A samples in artificial (T6 temper) and after multi-stage aging (T77 temper, i.e. retrogression and reaging treatment - RRA), were investigated by means of differential scanning calorimetry (DSC). DSC was employed to distinguish the dissolution behavior of different metastable and Cu-enriched precipitate populations in EN AW-7049A alloy in the T6 and T77 tempers. DSC thermographs exhibited two consecutive endothermic peaks in the T6 temper, which correspond to the sequential dissolution of metastable semi-coherent phases. First peak corresponds to the main strengthening η' phase, the second peak is associated with the dissolution of thermally more stable Cu-enriched η′/incipient η precipitates. These Cu-rich precipitates enhance yield strength and hardness by increasing dislocation resistance and significantly improve thermal stability by retarding precipitate coarsening and overaging. In the T77 temper, only a single endothermic peak was observed, indicating a reduced concentration of metastable η′ precipitates and the predominance of coarser η′ or incoherent equilibrium η precipitates formed during the retrogression and reaging treatment. The dissolution and transformation of metastable semi-coherent precipitates during RRA promote the nucleation and growth of the stable incoherent η phase, particularly at grain boundaries, leading to strength reduction. Consequently, the increased fraction and coarsening of η precipitates account for the lower strength of the EN AW-7049A alloy in the T77 temper compared with the initial T6 temper.
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