Synergistically enhanced strength and plasticity of a 6061 aluminum alloy using hot corrugated constrained groove pressing

In this study, the annealed 6061 aluminum alloy was subjected to multi-pass conventional corrugated constrained groove pressing (Conv-CCGP) deformation at 100–300 ℃. The Conv-CCGP deformation led to grain refinement. After the alloy was deformed at 100 ℃/ two-pass, the minimum grain size was refined from 37.4 to 23.0 μm. Electron backscattered diffraction and transmission electron microscopy (TEM) were used to analyze the evolution of microstructure and dislocation patterns. Results showed that the evolution of microstructure at 100 and 200 ℃ was governed by dynamic recovery, whereas grain refinement was dominated by dynamic recrystallization at 300 ℃. TEM analysis revealed that high-density dislocations exhibited a long and straight distribution at lower temperatures. As the temperature increased, irregularly arranged dislocations decreased, evolving into regular substructures with fishbone-like or interwoven network-like shapes. The Mg₂Si and iron-containing phases pined dislocations, thus improving the strength of the alloys. The ultimate tensile strength (UTS) and yield strength (YS) along the rolling direction increased to some extent at different temperatures, whereas the elongation decreased. The strengthening effect of the alloy was stronger at lower temperatures. The YS of the alloy increased from 52.9 MPa to 124.7 MPa (135.7 % increase) after the 100 ℃/four-pass Conv-CCGP process, while elongation decreased by 71.9 %. Higher temperatures are beneficial for improving the plasticity of the alloy. The YS of the Conv-CCGPed alloy at 300 ℃/one-pass increased by 38.4 % with a high plasticity of 22.1 %. The tensile fracture surface analysis results showed that the Conv-CCGPed alloy underwent plastic fracture, but the fracture mode transitioned from tensile fracture to shear fracture.