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Tang C.P.,Central South University | Tang C.P.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering | Deng Y.L.,Central South University | Deng Y.L.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering
Advanced Materials Research | Year: 2014

Superplasticity at high deformation rates is desirable in order to make superplastic forming more practical. High strain rate superplastic behavior and microstructure of the rolled Mg-Gd-Y-Zr alloy sheet were investigated. For the purposes, tensile tests at the strain rate of 0.01 S-1 were conducted, which revealed that the sheet exhibited elongations of 180%~266%. Post-deforming microstructures were characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy, while crystallographic orientation information was obtained from macro-texture analysis. The results show that the high strain rate superplasticity was attributed to class-I creep accommodated by dynamic recrystallization. It is suggested from microstructural analysis results that the interaction between second phases and dislocation facilitated dynamic recrystallization. The macro-texture at the strain of 0.8 still exhibited some characteristics of the crystal rotation arising from dislocation slip despite the occurrence of DRX. © (2014) Trans Tech Publications, Switzerland.


Wu Y.P.,Central South University | Wu Y.P.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering | Wu Y.P.,Deakin University | Zhang X.M.,Central South University | And 6 more authors.
Materials Science and Engineering A | Year: 2014

The effect of secondary extrusion on the microstructure and mechanical properties of a single-extruded Mg-8Gd-4Y-1Nd-0.5Zr alloy has been investigated. The microstructural results from scanning electron microscopy (SEM) show that irregular-shaped β phases in the single-extruded and pre-heated alloy are severely fragmented into small phases during secondary extrusion. Secondary extrusion increases the content of rare-earth (RE) elements in the matrix by dissolving the small phases. Transmission electron microscopy (TEM) analysis confirms that after secondary extrusion the β' strengthening phase formed during ageing is more homogeneously dispersed than that after single extrusion. Precipitate strengthening makes a dominant contribution to a high ultimate tensile strength of 428. MPa with a ductility of 2.8% after peak ageing in the secondary-extruded alloy. In particular, electron backscatter diffraction (EBSD) analysis reveals an unusual texture component after secondary extrusion in which the majority of grains distribute c-axes along the extrusion direction (ED). © 2014 Elsevier B.V.


Wu Y.P.,Central South University | Wu Y.P.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering | Wu Y.P.,Deakin University | Zhang X.M.,Central South University | And 6 more authors.
Materials Science and Engineering A | Year: 2015

The effect of compression conditions on the microstructure and texture of a Mg-8Gd-4Y-1Nd-0.5Zr alloy has been investigated by hardness test, optical microscopy, scanning electron microscopy and electron backscatter diffraction. The post-deformed grain size is directly influenced by the area fraction and the distribution of RE-rich particles. A uniform microstructure of refined grains is accompanied by randomly distributed particles due to particle pinning, while a bimodal grain structure is attributed to the dissolution of particles during compression. The textures of all compressions are weak and the dominant component changes with the compression condition. Compression at temperature 450°C and a low strain rate of 0.0003s-1, the texture is a result of dynamic recrystallization (DRX), such as discontinuous DRX (DDRX) and particle stimulated nucleation (PSN), and grain boundary sliding. The alloy exhibits a typical basal texture of 〈0001〉//ND (the normal direction) after compression at temperature 500°C and a strain rate of 0.2s-1, which suggests that RE-rich particles rather than the high concentration of RE solute atoms in the matrix are necessary to generate the weak and randomized texture during hot compression of the studied alloy. © 2015 Elsevier B.V..


Hu T.-Y.,Central South University | Hu T.-Y.,Hunan City University | Deng Y.-L.,Central South University | Deng Y.-L.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering | And 4 more authors.
Cailiao Gongcheng/Journal of Materials Engineering | Year: 2010

Heterogeneity of microstructure and mechanical properties of the as-extruded EW83 magnesium alloy plate was investigated by means of OM, SEM, EDS, XRD and hardness testing. It is found that heterogenous evolution of the microstructures are affected by the recrystallization and precipitation particle. In the edge of the plate, because of the grain refining effects resulted from the increase of the real Z parameter (heavy shear deformation and quick decrease of temperature), the hindering motion of the grain growth by the precipitation particles, and the recrystallization by particles stimulated nucleation (PSN), the measured grain size is half of the predicted one by the mean parameter (Z). In the middle of the plate, because of the grain coarsening effects caused by the decrease of the real Z parameter, static recrystallization, the measured grain size is twice times as the predicted one by the Z. The hardness value of the specimens cutting from the edge of the as-F plate increases by 5% than those of the middle one. However, after aged at 215°C, the peak hardness of the specimens cutting from the middle of the as-T6 plate increases by 10% than that of the edge one.


Jiang B.,Central South University | Jiang B.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering | Duan X.-C.,Central South University | Duan X.-C.,The Key Laboratory of Nonferrous Metal Materials Science and Engineering | And 6 more authors.
Wuji Cailiao Xuebao/Journal of Inorganic Materials | Year: 2011

A series of bi-layer TiO2/SiO2(ST) and SiO2/TiO2(TS) films were fabricated respectively by changing the coating sequences and rates, via a Sol-Gel dip-coating method. The morphology, light transmittance, photocatalytic activity and hydrophilicity of the obtained products were characterized by FESEM, spectrophotometer, photo-degradation of methyl orange (MO), etc. The experimental results show that SiO2 layer can enhance the light transmittances of ST and TS films due to its lower refractive index. As to the self-cleaning function, the photocatalytic activity and hydrophilicity of TS bi-layer film are both weakened while increasing the dip-coating speed of the overlayer SiO2 film, owing to that more TiO2 is covered by SiO2. However, it is the opposite for ST bi-layer film. When the dip-coating speed of the overlayer TiO2 film reaches 6mm/min, the obtained film exhibits the best photocatalytic activity and hydrophilicity even without UV illumination, which favors greatly the self-cleaning function of the films.

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