Results of a large set of tensile and compressive creep tests on pure Al were reanalyzed for the influence of low-and high-angle grain boundaries on the deformation resistance at the temperature T = 473 K = 0.51 Tmwhe...Results of a large set of tensile and compressive creep tests on pure Al were reanalyzed for the influence of low-and high-angle grain boundaries on the deformation resistance at the temperature T = 473 K = 0.51 Tmwhere Tm is the melting point.Thermomechanical treatment by equal channel angular pressing followed by heating to T led to strong increase of areal fraction of high-angle boundaries in a structure of subgrains of ≈10^-6m in size,accompanied by significant reduction of subgrain strengthening and of the stress sensitivity of the deformation rate.（Sub）grain strengthening by low-angle boundaries is most effective;the strengthening effect virtually disappears during creep as the boundary spacings coarsen toward their stress-dependent,quasi-stationary size wqs.The same type of coarsening is found for（sub）grain structures with large fraction of high-angle boundaries;in the quasi-stationary state they lead to softening at low and strengthening at high stresses,and a significant increase in tensile fracture strain to values up to 0.8.The results are analogous to former results for Cu and are explained in the same way by the influence of boundaries on storage and recovery of crystal defects and the homogenization of glide.展开更多
The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain rates.The tensile tests were carried out at the tempera...The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain rates.The tensile tests were carried out at the temperature range of 300-500 ℃ and at the strain rates of 0.0005-0.01 s^（-1）.The microstructure evolution was characterized using optical microscopy,transmission electron microscopy and X-ray diffraction technique.The influences of the microstructure after SPD,thermomechanical parameters（temperature and strain rate） and specimen size on the hot formability of this alloy were then analyzed.The results show that a decrease in grains/subgrains exhibited significant effect on the hot ductility of SPDed samples.The constitutive equations were then developed to model the hot formability of the studied alloy.The developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation form.Both the changes of elongation to failure and Zener-Hollomon parameter indicate that the hot ductility of the alloy is more sensitive to the temperature rather than to the strain rate.The uniform elongation is independent of the specimen size,but the postnecking elongation increases dramatically as the ratio of l/A^（1/2） decreases.展开更多
基金support by the Central European Institute of Technology CEITEC(Project CZ.1.05/1.1.00/02.0068 and the European Regional Development Fund)
文摘Results of a large set of tensile and compressive creep tests on pure Al were reanalyzed for the influence of low-and high-angle grain boundaries on the deformation resistance at the temperature T = 473 K = 0.51 Tmwhere Tm is the melting point.Thermomechanical treatment by equal channel angular pressing followed by heating to T led to strong increase of areal fraction of high-angle boundaries in a structure of subgrains of ≈10^-6m in size,accompanied by significant reduction of subgrain strengthening and of the stress sensitivity of the deformation rate.（Sub）grain strengthening by low-angle boundaries is most effective;the strengthening effect virtually disappears during creep as the boundary spacings coarsen toward their stress-dependent,quasi-stationary size wqs.The same type of coarsening is found for（sub）grain structures with large fraction of high-angle boundaries;in the quasi-stationary state they lead to softening at low and strengthening at high stresses,and a significant increase in tensile fracture strain to values up to 0.8.The results are analogous to former results for Cu and are explained in the same way by the influence of boundaries on storage and recovery of crystal defects and the homogenization of glide.
文摘The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain rates.The tensile tests were carried out at the temperature range of 300-500 ℃ and at the strain rates of 0.0005-0.01 s^（-1）.The microstructure evolution was characterized using optical microscopy,transmission electron microscopy and X-ray diffraction technique.The influences of the microstructure after SPD,thermomechanical parameters（temperature and strain rate） and specimen size on the hot formability of this alloy were then analyzed.The results show that a decrease in grains/subgrains exhibited significant effect on the hot ductility of SPDed samples.The constitutive equations were then developed to model the hot formability of the studied alloy.The developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation form.Both the changes of elongation to failure and Zener-Hollomon parameter indicate that the hot ductility of the alloy is more sensitive to the temperature rather than to the strain rate.The uniform elongation is independent of the specimen size,but the postnecking elongation increases dramatically as the ratio of l/A^（1/2） decreases.
