Microstructural development in model and commercial Al-Cu based alloys during equal-channel angular pressing at elevated temperature Part II. Comparison of grain refinement in the model Al-3 %Cu alloy and the commercial AA2219 alloy

This study (Part II) quantitatively demonstrates the decisive role of thermally stable nanoscale dispersoids in accelerating grain refinement during equal-channel angular pressing of the commercial AA2219 Al-Cu alloy at 300°C, directly comparing it with the model Al-3 %Cu alloy (see Part I). Through scanning electron microscopy with electron backscatter diffraction and transmission electron microscopy, it is shown that the AA2219 alloy achieves a substantially more refined and homogeneous ultrafine-grained structure after a cumulative strain of e =12, with an average grain size of ≈2.5 – 3.0 μm, a high-angle boundary fraction exceeding 55 %, and an average misorientation of ≈24° and a volume fraction of new fine grains of ≈82 %. These values significantly surpass those of the model alloy processed under identical conditions. The accelerated kinetics are attributed to a synergistic effect where fine, thermally stable dispersoids (e. g., aluminides of Zr, Mn, Cr) enhance strain localization via microshear band formation, suppress dynamic recovery by pinning dislocations and subboundaries, and stabilize the deformation-induced structure against static softening during inter-pass holdings. Thus, the introduction of dispersoids is proven to be a critical strategy for overcoming the limitations of dynamic recovery and achieving extensive grain refinement during high-temperature severe plastic deformation. The work establishes that dispersoids are crucial for tailoring a well-developed ultrafine-grained microstructure in commercial aluminum alloys under high-temperature severe plastic deformation conditions.