MICROSTRUCTURAL CHANGES IN THE Al-3 wt. % Cu ALLOY DURING EQUAL-CHANNEL ANGULAR PRESSING AT ELEVATED TEMPERATURE

10.25712/ASTU.1811-1416.2023.04.008

Abstract

The microstructure changes in a coarse-grained binary alloy Al-3 wt. % Cu during equal channel angular (ECA) pressing at T=150 °C ≈ 0.5T_m (where T_m is the melting point of pure Al) were investigated. Prior to pressing, the alloy was heat treated to obtain precipitates of the main strengthening phase Q(Al₂Cu) with an average size of approximately 16 nm. As with low-temperature straining, the main feature of ECA pressing of this alloy at 0.5T_m was the development of banded deformation structures in the initial stage of deformation (e=1), leading to fragmentation of the original grains. However, during further ECA pressing, such dislocation structures were transformed into a mixed (sub)grain structure characteristic of hot deformation, accompanied by grain refinement. At e=8, a bimodal microstructure with about 50 % high-angle boundaries was formed in the alloy, consisting of 60 % new grain regions with a size of about 1 μm and unrecrystallized portions of the original grains with subgrains. It has been shown that, in the absence of transition metal dispersoids, the precipitates of the primary strengthening phase Q significantly influenced the processes of deformation energy accumulation and relaxation. As a result, these precipitates controlled the formation of dislocation structures, the occurrence of dynamic recovery, and the migration of (sub)grain boundaries, determining the nature and kinetics of the process of forming a new fine-grained structure.