Effect of retrogression and reaging treatment on the microstructure and fatigue crack growth behavior of 7050 aluminum alloy thick plate

Effect of Retrogression and Reaging (RRA) treatment on the microstructure and fatigue crack growth behavior of 7050 aluminum alloy thick plate was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results showed that the RRA microstructure is similar to that for T6 treatment inside the grains, but is slightly denser and coarser and more stable in nature. Also grain boundaries precipitates (GPBs) coarsen obviously, distributing discontinuously and isolated. The precipitation free zones (PFZs) are broadened than that of the T6 sample, and narrower than that of the T7451 sample. And maintaining strength equal to that for the T6 peak-aged treatment and enhanced fatigue crack growth resistance to that for the T7451 overaged treatment can be achieved for RRA treatment.