Papers by Author: Hirofumi Inoue

Abstract: A new rolling process, which combined asymmetric rolling with symmetric rolling, was adopted in age-hardenable 6xxx series Al-Mg-Si alloy promising as automotive body panels in order to develop favorable textures for the deep drawability after solution treatment. Symmetric cold rolling at high reduction and subsequent asymmetric warm rolling at low reduction for AA6022 sheets led to the formation of “TD-rotated β-fiber texture” including moderate {111}<uvw>-oriented components, resulting in noticeable evolution of {111}<110> recrystallization texture during the solution treatment at a high temperature. The results of texture analysis and microstructural observation suggested that the low stored energy after asymmetric warm rolling, the high fraction of high angle boundaries with neighboring deformed matrices and the approximate 40° <111> orientation relationship with deformed matrices would strongly affect the evolution of {111}<110> recrystallization texture.

Abstract: In order to develop favorable textures for deep drawing of Al-Mg-Si and Mg-Al-Zn alloys that are promising as automotive body panels, we have adopted the symmetric/asymmetric combination rolling (SACR) process consisting of conventional symmetric rolling and subsequent asymmetric rolling at relatively low reduction. The combination of symmetric cold rolling and asymmetric warm rolling for AA6022 sheets leads to the formation of “TD-rotated β-fiber texture”, resulting in the evolution of {111} recrystallization texture after solution treatment at a high temperature. The SACR processed and solution-treated sheets show a high average r-value with small in-plane anisotropy, and consequently the limiting drawing ratio increases significantly, compared to that of the cold-rolled and solution-treated sheets. In the case of AZ31 magnesium alloy, the SACR process by hot rolling causes the formation of a unique texture, which shows two (0001) poles with tilt angles of 0 and −40 degrees from the normal direction (ND) toward the rolling direction (RD). In addition, subsequent annealing weakens intensity of the double-peak texture, so that the drawability is greatly improved in comparison with that of the conventional warm-rolled sheets with a strong basal texture. At the same time, yield strength decreases to some extent, but the SACR processed and annealed sheets exhibit a good balance of strength and formability due to a mixed texture with basal and tilt components.

Abstract: Conventional symmetric rolling enhances yield strength by forming basal texture, while asymmetric rolling can improve formability by inclining the c-axis of hcp crystal. In this study, the combination rolling consisting of symmetric and asymmetric hot rolling has been performed to simultaneously improve formability and maintain high strength of AZ31 magnesium alloy sheet. The symmetrically/asymmetrically combination hot-rolled and annealed sheet exhibits a broadened texture having double peaks with tilt angles of 0º and 40º from ND toward RD with respect to the c-axis. Correspondingly, this sheet shows relatively high yield strength of 123 MPa and large elongation of 24.7%. As for cup drawing test, the conventional warm-rolled sheet is barely formed at 175 °C, but the symmetrically/asymmetrically combination rolled sheet can be formed at temperature as low as 75 °C. These results indicate that the symmetric/asymmetric combination hot-rolling leads to a unique texture with good balance of formability and strength.

Abstract: Crystallographic texture of pilgered zirconium alloy tubes was analyzed by neutron diffraction, electron backscatter diffraction (EBSD) and X-ray techniques to study bulk and local texture change with pilgering and heat treatment above re-crystallization temperature. Pilgering resulted in slightly inclining (001) planes to sample normal direction, and aligning effectively (100) planes to the normal of radial direction, respectively. (001) planes of the zirconium tube uniformly exist in radial and tangential directions, however, the (001) planes moved from tangential to radial directions after pilgering followed by heat treatment for 20 hours at 540°C. Some of (001) and (100) planes of pilgered tube were paralleled to longitudinal direction by re-crystallization.

Abstract: Copper-silver quasi-nano filamentary composites prepared by hot isostatic pressing followed by heavy drawing were irradiated in CT hole of a domestic experimental nuclear reactor, HANARO to study the morphological change of the poly-crystalline nano-filaments with irradiation and annealing conditions. The irradiation was carried out for 36 days at 320 o C with the maximum neutron flux of 4.8x10 20 n/cm 2 (E>1.0 MeV). The gamma heating rate was in the range of 2.0-6.45 W/gm. Polycrystalline silver nano-filaments of the composites were equilibrium shape like the faceted sphere shape. Annealing results in the increase of the faceting rate of the irradiated specimen. Nano-indentation results supported that the morphology change of nano-filaments by annealing in this study is more effective on strength change of the irradiated nano-filamentary composites than irradiated hardening.

Abstract: In order to improve deep drawability of 6000 series aluminum alloys for automotive body panels, texture control for increasing r-value of the sheets was attempted by combination of symmetric and asymmetric rolling. Asymmetric warm rolling at relatively low reduction after symmetric rolling made it possible to form TD-rotated β-fiber texture including {111} components. Recrystallization textures of the T4-treated materials varied significantly depending on roll speed ratio and reduction in asymmetric warm rolling. On appropriate rolling conditions, {111}<110> orientation with high r-value was formed as a main component of recrystallization texture. On the other hand, two-stage heat treatment consisting of low temperature annealing and subsequent T4-treatment led to a significant change in recrystallization texture. In the sample annealed for long time at a low temperature, TD-rotated β-fiber rolling texture was retained even after solution treatment at a much higher temperature, because recovery or recrystallization took place to some extent during low temperature annealing.

Abstract: γ-TiAl has a tetragonal structure that is almost cubic (c/a ≈ 1.02). As a result of this, the electron backscatter diffraction patterns (EBSPs) of orientations related by 90°<100] rotations are almost identical. Reliable orientation measurement during automated EBSD mapping requires distinguishing very small differences in the positions of certain bands within the EBSPs. EBSD was used to measure the micro-texture and bulk texture of γ-TiAl hot-deformed under conditions approximating plane-strain compression. The reliability and accuracy of the indexing was assessed by inspecting the orientation maps for misindexing and by comparing the texture measured using EBSD with that measured using X-ray diffraction (XRD). Using Advanced Fit refinement and high-resolution EBSPs produced reliable and accurate results. Substantial misindexing was present when the EBSPs were indexed using the Hough transform method alone.

Abstract: TiNi shape memory alloy thin sheets were produced from titanium and nickel metal sheets by a new processing consisting of repetitive roll-bonding and diffusional heat treatment. TiNi sheets after heat treatment at a relatively low temperature for a long time exhibited fairly isotropic and high shape-recoverable strain, because a near {111} B2-phase texture such as {223}<110> and {332}<113> was developed through reactive diffusion during heat treatment. In the early stage of reactive diffusion, intermetallic layers of Ti2Ni, TiNi and Ni3Ti were formed at once at the Ti/Ni interfaces of the roll-bonded laminate and then growth of a TiNi phase took place with the progress of interdiffusion. Texture of the final TiNi thin sheets, therefore, is derived from that of TiNi layers generated at the Ti/Ni interfaces, which is considered to have inherited rolling textures of Ni and Ti layers in the Ti/Ni laminate prior to reactive diffusion under orientation relationships on close-packed plane and direction between parent and product phases.

Abstract: In order to improve corrosion resistance and mechanical properties of magnesium alloys, titanium with high specific strength was warm roll-bonded on the surface of AZ31 magnesium alloy sheets. Although the AZ31 alloy before roll-bonding had a typical basal texture, the AZ31 layer that constitutes a larger part of the clad sheet clearly showed off-basal texture with c-axis inclined by about 10º from the normal direction toward the rolling direction. This texture significantly affected tensile properties of clad sheets, resulting in lower proof stress and higher elongation at the rolling direction than at the transverse direction. In deep drawing tests, the 2-layered clad sheet with an outer titanium layer could be successfully formed at temperatures considerably lower than the limiting forming temperature of an original AZ31 single sheet. This is probably due to an effect of the outer titanium layer bearing tensile stress at a shoulder part of cup and an additional effect of improved deformability by off-basal texture in the AZ31 layer.

Abstract: In order to improve deep drawability of Al-Mg-Si alloy sheets for automotive body panel by texture control, the effects of Mn addition and warm rolling on recrystallization texture were investigated for rolled and T4 treated sheets and the r-value was related to overall texture through thickness. Recrystallization texture after T4 treatment varied significantly depending on alloy composition and rolling condition. Planar anisotropy of r-value could be predicted relatively exactly from recrystallization texture by the Taylor full constraints model for all specimens. Mn addition led to an increase of average r-value in both cold and warm rolled materials, while warm rolling resulted in a decrease of average r-value in spite of relatively high predicted r-values in the surface layer.