The evolution of precipitates and hardness changes in Al-Cu alloys during equal-channel angular pressing(ECAP) at room temperature were investigated by hardness measurement,X-ray diffraction analysis and transmission electron microscopy.The results show that with the increase of the total equivalent strain during ECAP from 0 to 8.4,the hardness of specimens with metastable θ″ phase increases first and decreases in later period.The hardness increases successively in specimens containing metastable θ′ phase and equilibrium θ phase.It is believed that the evolutions of hardness are related to the mechanism of re-dissolution of precipitates.A critical nuclei size concept is provided to express the mechanism of such re-dissolution of three precipitates in Al-Cu alloys.
