The Evolution and Dissolution Mechanism of Θ-Al2cu Phase and the Analysis of Precipitation of a Novel Alcu Phase During Elevated Aging

Abstract

The evolution and dissolution mechanism of the θ-Al2Cu precipitates were investigated in this study by transmission electron microscopy (TEM) during the re-aging at high temperatures for a long time. The results advance the current knowledge of dissolution and its associated mechanisms of the θ-Al2Cu phase in Al-Cu alloys. In this study, the coarsening and dissolution of θ-Al2Cu phase in T6 heat-treated Al-4Cu alloy during various times (0–1000 h) of re-aging temperature 420 °C were studied experimentally and theoretically. The morphological characterization revealed that the θ-Al2Cu phases gradually increase in size and decrease in volume density during the aging process, which can be attributed to coarsening and dissolution phenomena occurring during re-aging. Additionally, a body-centered tetragonal AlCu phase is precipitated within the θ-Al2Cu phase during the high temperature re-aging process, which is a characteristic of this phase prior to dissolution. Moreover, the primary mechanisms responsible for the high temperature melting of the θ-Al2Cu phase are the formation of the AlCu phase and the initial melting of the Cu-poor region in the θ-Al2Cu phase. The Cu atoms in θ-Al2Cu phase dissolve and diffuse into the Al matrix, forming L12 ordered AlCu solute clusters through long-range diffusion.

Keywords: Al-Cu alloy, Al2Cu particles, microstructural evolution, Transmission electron microscopy (TEM)