Microstructural development in the modeling and commercial Al-Cu based alloys during equal-channel angular pressing at elevated temperature Part I. Microstructural evolution and continuous dynamic recrystallization in a model Al-3 %Cu alloy

This study (Part I) investigates the microstructural evolution in a model Al-3 %Cu alloy during equal-channel angular pressing at an elevated temperature of 300°C (0.6Tm). The use of a binary model alloy aims to isolate the fundamental grain refinement mechanisms without the confounding effects of transition metal dispersoids. Through scanning electron microscopy with electron backscatter diffraction and X-ray diffraction analysis, it is demonstrated that grain refinement occurs via continuous dynamic recrystallization. This process is primarily driven by the formation of permanent structural elements — microshear bands. The boundaries of these bands accumulate dislocations over successive equal-channel angular pressing passes, leading to a progressive increase in misorientation and their eventual transformation into high-angle grain boundaries. The θ-phase (Al2Cu) precipitates play a critical dual role: they stabilize the deformation-induced structures by pinning dislocations and exerting Zener drag on boundaries, while simultaneously controlling local dislocation rearrangement that aids the formation of more equilibrium subgrain structures. Despite intense dynamic recovery and competing static softening processes during inter-pass annealing, dynamic refinement remains dominant. This work establishes microshear band-driven continuous dynamic recrystallization as a fundamental grain refinement mechanism in simple Al-Cu alloys, providing a crucial baseline for understanding the enhanced refinement in commercial alloys containing dispersoids, as will be reported in Part II.

1. the Ministry of Science and Higher Education of the Russian Federation within the framework of the state assignment of IMSP RAS -