Influence of cryogenic deformation on second-phase particles, grain structure, and mechanical properties of Al–Cu–Mn alloy

Abstract

To refine the coarse second-phase particles (Al2Cu) and grains of Al–Cu–Mn alloy, 10% and 20% compression deformation at cryogenic and room temperatures was applied, followed by a T8 heat treatment process consisting of solution treatment, 3% cold deformation, and artificial aging. The microstructures of the compressed and heat-treated samples were investigated using a combination of scanning electron microscopy, X-ray diffractometry, electron backscattering diffractometry, and transmission electron microscopy, with the results showing that coarse Al2Cu particles are fragmented during cryogenic compression. Further, the higher dislocation densities in the cryogenically deformed samples, which lower the activation energies for atomic diffusion, promote the dissolution of particles during subsequent heat treatment. After heat treatment, the volume fraction of coarse particles decreased from 2.5% for a sample processed without deformation, to 0.5% for the sample cryogenically compressed at a ratio of 20%. Meanwhile, the higher dislocation density provides more nucleation sites for recrystallization during heat treatment. Consequently, at 33 μm, the average size of the grains in the 20% cryogenically compressed sample was much smaller than the size of the grains in the uncompressed sample (500 μm). This microstructural refinement increased the ultimate tensile strength, yield strength, and elongation from 445 MPa, 363 MPa, and 7.1% in the undeformed sample, to 471 MPa, 377 MPa, and 13.4%, respectively, in the cryogenically compressed sample.