Segregation and precipitation stabilizing an ultrafine lamellar-structured Al-0.3%Cu alloy

Understanding the coarsening mechanisms and the role of solute atoms during recovery annealing of ultrafine lamellar-structured alloys produced by high strain deformation is crucial to tailor their microstructures and mechanical properties. In the present work, a lamellar-structured Al–0.3%Cu alloy with a boundary spacing of 200 nm was prepared by cold rolling to a von Mises strain of 4.5 (a thickness reduction of 98%), featuring Cu segregation to high angle lamellar boundaries. During recovery annealing in the temperature range of 100–175 °C, precipitation of fine Al2Cu particles occurred preferentially at lamellar boundaries. Recovery kinetics was analyzed based on measurements of lamellar boundary spacings in the annealed samples, showing an increase in the apparent activation energy from 77 kJ/mol at the beginning to 106 kJ/mol at the end of recovery. In situ observations of annealing in a transmission electron microscope revealed that the dominant coarsening process is the motion of Y-junctions formed by lamellar boundaries, which is subjected to various degrees of pinning from dislocations, dislocation boundaries and particles. Furthermore, it was found that this local pinning effect can be reinforced with the increase of misorientation angles of the attached dislocation boundaries, the coarsening of Al2Cu particles and the combined effect of interconnecting boundaries and particles. The results underpinned the importance of alloying elements in stabilizing finely spaced lamellar structures during deformation and annealing, providing guidelines for tailoring stable ultrafine structured alloys.