Papers by Author: Xu Yue Yang

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Authors: Xu Yue Yang, Hiromi Miura, Taku Sakai
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Authors: Xu Yue Yang, Hiromi Miura, Taku Sakai
Abstract: Grain refinement taking place in a magnesium alloy AZ31 was studied in a single- and multi-directional compression at a temperature of 573K. The structural changes observed by SEM/EBSD analysis can be characterized by the evolution of many mutually crossing kink bands at low strains, continuous increase in their number and misorientation angle in moderate strain and finally full formation of a fine-grained structure in high strain. The characteristics of new grain evolution process are sensitively affected by initial grain size (D0) and strain path. New grains are developed faster with decrease in D0. Multi-directional compression accelerates the evolution of fine grains and the improvement of plastic workability. The mechanism of new grain formation is discussed in detail.
1632
Authors: Xu Yue Yang, Masayoshi Sanada, Hiromi Miura, Taku Sakai
Abstract: Hot deformation and associated structural changes were studied in compression of a magnesium alloy AZ31 with initial grain sizes (D0) of 22 µm and 90 µm at a temperature of 573K. D0 influences significantly the flow curve and the kinetics of grain refinement during hot deformation. For D0 = 22 µm, grain fragmentation takes place due to frequent formation of kink bands initially at corrugated grain boundaries and then in grain interiors in low strain, followed by full development of new fine grains in high strain. For D0 = 90 µm, in contrast, twinning takes place in coarser original grains, and then kink bands and new fine grains are formed mainly in finer ones at low strains. Then new grains are formed in necklace along the boundaries of coarse original grains, followed by their development into the grain interiors. Grain refinement in the Mg alloy can be concluded to result from a series of deformation-induced continuous reactions, they are essentially similar to continuous dynamic recrystallization (cDRX).
223
Authors: Xu Yue Yang, Hiromi Miura, Taku Sakai
Abstract: The deformation behavior and structure changes of magnesium alloy AZ31 were studied in compression at temperatures ranging from 523K to 673K and at a strain rate of 3 x 10-3 s-1. They depend sensitively on deformation temperature. At high temperatures, grain fragmentation takes place due to frequent formation of kink bands initially at corrugated grain boundaries and then in grain interiors, followed by full development of new grains in high strain. At lower temperatures, in contrast, twinning takes place in rather coarse grains and kink bands are formed mainly in finer original ones in low strain. It is concluded that new grain evolution can be controlled by a deformation-induced continuous reaction resulting in grain fragmentation by kink bands, i.e. continuous dynamic recrystallization (cDRX). The latter is discussed comparing with conventional, i.e. discontinuous, DRX.
531
Authors: Jie Xing, Xu Yue Yang, Hiromi Miura, Taku Sakai
Abstract: Grain refinement in a magnesium alloy AZ31 was studied in multi-directional forging (MDF) at a strain rate of 3×10-3s-1 with decreasing temperature from 623K to 423K. The MDF was carried out up to large cumulative strains with changing the loading direction during decreasing temperature from pass to pass. The structural changes were characterized by generation of many mutually crossing kink bands at low strains, followed by development of very fine grains at large strains. The results showed that MDF with decreasing temperature can accelerate uniform generation of much finer grains, resulting in the minimal grain size of 0.36µm in a cumulative strain of 4.8 at 423K. The mechanism of grain refinement was discussed.
597
Authors: Xu Yue Yang, Hiromi Miura, Taku Sakai
611
Authors: Jie Xing, Xu Yue Yang, Hiromi Miura, Taku Sakai
Abstract: Low temperature superplasticity (LTSP) was studied in a fine-grained magnesium alloy AZ31 which was processed by multi-directional forging (MDF) under decreasing temperature conditions. Tensile specimens were cut from MDFed Mg alloy parallel to the final compression axis (CA), and the tensile axis perpendicular to the CA. Tensile tests was carried out at temperatures from 393K to 473K and at various strain rates. Superplasticity appears even at a low temperature of 393K with a stress exponent (n) of about 0.56 and a total elongation of 370%. The relative large stress exponent can be connected with grain coarsening taking place during deformation. The initial texture hardly takes place during deformation. This suggests that grain rotation does not occur during superplasticcity.
467
Authors: Hiromi Miura, Taku Sakai, H. Nogawa, Xu Yue Yang, Yoshimi Watanabe, Seiji Miura
Abstract: Orientation-controlled Mg single crystals were tensile tested at temperatures between 473 K and 673 K at a strain rate of 4.2 x 10-4 s-1 in vacuum. Though all the single crystals showed high ductility compared with that of polycrystals, the ductility of the single crystals strongly depended on the crystal orientation. The [27 -1 -26 1] single crystal showed 0.57 fracture strain, while the [3 8 -11 -1] single crystal showed superplastic behavior of ductility over 1.8 strain. The observed strong orientation dependence of ductility seemed to be caused by orientation dependence of ease occurrence of dynamic recrystallization (DRX) in the single crystals during high-temperature deformation. The orientation dependence of ductility of Mg single crystals will be discussed in detail concerning crystallographical orientations of the single crystals, occurrence of DRX and fracture.
193
Authors: Xu Yue Yang, Jie Xing, Hiromi Miura, Taku Sakai
Abstract: Strain-induced grain refinement in a magnesium alloy AZ31 was studied in multi-directional forging (MDF) at a temperature range from 423K to 623K and at a strain rate of 3x10-3s-1. MDF with a pass strain of 0.8 was carried out to high cumulative strains of around 5 with changing of the loading direction during decreasing temperature from pass to pass. The structural changes can be characterized by the evolution of many mutually crossing kink bands at low strains followed by increase in their number and misorientation, finally resulting in a fully developed fine-grains at high strains. MDF with decreasing temperature can accelerate the evolution of much finer grains and the improvement of plastic workability. An average grain size of 0.3 μm is formed at an accumulative strain of 4.8 and at 423K. It is concluded that grain refinement under MDF conditions occurs by a series of deformation-induced continuous reactions; that is essentially similar to continuous dynamic recrystallization (cDRX).
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