Microstructural Refinement and Mechanical Property Improvement of Copper and Copper-AL₂O₃ Specimens Processed by Equal Channel Angular Extrusion (ECAE)

Abstract

Pure copper and copper alloys containing different volume fractions of nano size A1₂0₃ dispersoids were processed by ECAE at 25–250°C, annealed at 25–500°C, and microstructural refinement and mechanical property improvement were studied. In samples processed by ECAE to strains of 5, hardness values increased by 100% in copper specimens and 40–50% in Cu-Al₂0₃ specimens. A drastic increase in hardness was observed after a strain of 1, and hardness values leveled off beyond a strain of 2. Samples were annealed at 25–500°C, to determine the extent of recovery of hardness values. In ECAE processed copper samples, significant reduction in hardness occurred between 100–200°C, and higher temperature annealing resulted in hardness values close to the values before ECAE processing. However, in Cu-Al₂0₃ specimens, the increased hardness was maintained in samples annealed at as high as 500°C. Strength and ductility values determined from 3 point bend tests showed strength values of 150–200 MPa for copper and 650–800 MPa for Cu-Al₂0₃ samples with excellent ductility in copper as well as Cu-Al₂0₃ samples. The observed results were analyzed in terms of the magnitudes of strengthening contributions from dislocation substructure, fine grains, and incoherent dispersoids.