Effect of Cu content on HPT-induced grain boundary evolution, decomposition, segregation, and grain refinement in Al-xCu alloys

Abstract

Grain boundaries (GBs) play a crucial role in determining the stability and mechanical properties of ultrafine-grained materials. This research investigates how alloy compositions impact GB evolution in Al-xCu alloys (x = 1, 2 and 4 wt%) under high-pressure torsion (HPT), examining the interplay among precipitation, segregation, and grain refinement. HPT processing induces dynamic precipitation of Al₂Cu (θ) phase and occasionally the unexpected formation of the AlCu (η₂) phase, while generating high-volume-fraction GBs and high-density dislocations with Cu segregation. Notably, GB misorientation angle evolves differently across the alloys with increasing HPT strain, in contrast to relatively stable GB segregation behavior. The study finds a strong correlation between reduced dislocation density and increased high-angle GBs (HAGBs), suggesting that dislocation annihilation at GBs facilitates the transformation of low-angle GBs into HAGBs during HPT processing. These findings demonstrate the potential to engineer GB characteristics in ultrafine-grained Al-Cu alloys by optimizing alloy composition and HPT processing parameters.