Evolution of precipitates of Al-Cu alloy during equal-channel angular pressing at room temperature

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.