The evolution and dissolution mechanism of θ-Al2Cu phase and the analysis of precipitation of a novel AlCu phase during elevated aging

The evolution and dissolution mechanism of the θ-Al 2 Cu 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-Al 2 Cu phase in Al Cu alloys. In this study, the coarsening and dissolution of θ-Al 2 Cu 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-Al 2 Cu 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-Al 2 Cu 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-Al 2 Cu phase are the formation of the AlCu phase and the initial melting of the Cu-poor region in the θ-Al 2 Cu phase. The Cu atoms in θ-Al 2 Cu phase dissolve and diffuse into the Al matrix , forming L1 2 ordered AlCu solute clusters through long-range diffusion. • The results advance the current knowledge of dissolution and its associated mechanisms of the θ-Al 2 Cu phase in Al-Cu alloys. • Before the dissolution of the θ-Al 2 Cu phase, the body-centered tetragonal AlCu phase first precipitates within it. • The formation of L1 2 AlCu clusters is related to the dissolution of the θ-Al 2 Cu phase.