Abstract:The effects of the retrogression heating rates (340, 57, 4.3 oC·min-1) on the microstructure evolution of aluminum alloy 7050 during retrogression heating up were investigated by means of differential scanning calorimetry (DSC), high temperature X-ray diffraction (HTXRD), transmission electron microscopy (TEM), hardness measurement and electrical conductivity testing. The results show that during the process of retrogression heating up, the pre-aged microstructures suffer the process of GP zone and η′ phase re-solution, or the phase transformation from GP zone and η′ phase into η′ phase and followed η phase, respectively. And the heating rate affects evidently the temperature of re-solution and phase transformation. With the heating rates increasing, the temperature of re-solution and phase transformation rises, too. When the retrogression temperature is affirmatory, the microstructures formed during heating up process are different due to the various heating rates. And this kind of microstructure will affect the phase transformation at the retrogression stage. This work thinks that at the medium heating rate, the microstructures formed during heating up process are more propitious to the microstructure transformation at the retrogression stage.