切欠きを有する多結晶アルミニウム合金の繰返し引張り挙動に及ぼす結晶方位分布と相対結晶粒径の影響

抄録

The microstructure of aluminum (Al) alloy is changed by the material process, and it strongly affects the mechanical property of the material. The final goal of our present study is to establish the mechanical model predicting the performance of the material under practical use. For this purpose, the mechanical behavior of the polycrystalline Al alloy having a notch under the monotonic and cyclic uniaxial tensile tests is investigated experimentally and numerically. A6061 Al alloy specimens obtained from T4 and T6 heat treatments are prepared which have different grain sizes and textures. The stress level of the T6 specimen in the uniaxial tensile test is larger than that of the T4 specimen whereas the elongation of the T4 specimen is larger. The clear deformation bands developed from the notch front during the cyclic test of the T4 specimen. By contrast, the deformation concentration is relaxed by polycrystalline structure-induced nonuniform deformation in the T6 specimen. The Crystalline Plasticity-Finite Element Method (CP-FEM) simulations of monotonic and cyclic tensile tests are performed using the two-dimensional plane stress polycrystalline model having different crystalline orientations and grain numbers. The stress for the model without a notch under the uniaxial tensile test decreases with increases in the deviation of crystalline orientation and grain numbers. By contrast, the decrease in the stress due to the introduction of the notch is reduced by nonuniform deformation induced by crystalline anisotropy. Localized plastic deformations occurred by crystalline anisotropy and stress concentration around the notch front induce the residual strain during the cyclic test with the maximum stress smaller than the 0.2% proof stress. A further extension of the computational model based on the back stress is required to accurately predict the mechanical behavior under cyclic loading-unloading conditions.