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Microstructural changes upon retrogression, and retrogression and reaging (RRA) treatment to 8090 Al -Li -CuMg -Zr alloy in the peak aged (T8) temper have been studied by XRD and TEM. The variation of hardness with retrogression, and retrogression and reaging (RRA) has been measured to assess RRA behaviour. XRD studies exhibited all the phases that would be expected in the system. Retrogression primarily caused dissolution of matrix strengthening d9 precipitates in the solution. Reaging the retrogressed state caused reprecipitation of the d9 precipitates in the matrix. Retrogression and reaging (RRA) treatments retained the strength of the conventional peak aged temper, but TEM observations revealed some microstructural changes, such as growth of d, T 1 and S9 phases, reduction of the dislocation densities, and generation of more dislocation loops and helices. MST/6039

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