Papers by Keyword: Large Strain Rolling

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Authors: Dae Guen Kim, Hyeon Taek Son, Jae Seol Lee
Abstract: The aims of this study are to investigate the microstructure evolution of AZ31 Mg alloys with normal rolling and cross rolling as the large strain hot rolling affects microstructure, texture and mechanical properties of AZ31 Mg alloys. In the microstructures of as-rolled both samples, twins are clearly apparent, small and recrystallized grains are visible along some grain boundary and twinned regions. The Lankford values of large strain cross rolled sample obviously demonstrate the higher average r-value and lower planar anisotropy value. The press formability of cross rolled Mg alloy might be improved due to control of texture and grain size by severe deformation.
Authors: Tetsuo Sakai, Yohei Watanabe, Hiroshi Utsunomiya
Abstract: The present authors have succeeded in single pass large draught rolling of AZ31 and ZK60A magnesium alloy sheet below 200°C without heating rolls by raising the rolling speed above 1000m/min. Maximum reduction attained in single pass rolling was 60%. Among magnesium alloys, AZ31 is known as the most ductile alloy. It remains uncertain whether the high limiting reduction by high speed rolling can be attained in other magnesium alloys that are less ductile but stronger than AZ31. In this study, AZ80A (Mg-8.1%Al-0.63%Zn) sheets with the thickness of 2.7mm cut from the extruded sheets were used. Rolling temperature was varied from RT to 350°C. Rolling speed was 1000m/min. The limiting reduction in thickness increases with rolling temperature, and the maximum reduction of 52% is obtained at 250°C. The fracture surface of sheet rolled at 100°C shows ductile fractured surface, while it shows brittle fracture surface at 350°C. This difference in fracture mode is attributed to the precipitation of -particles at grain boundaries during holding at 350°C before rolling. From this result, high speed rolling can also be an effective tool for improving the rolling deformability of AZ80 sheet. The hardness of the rolled sheets measured on the transverse plane increases with increasing temperature and reduction. The variation of hardness with rolling temperature and reduction indicates the occurrence of dynamic recrystallization (DRX). The sheet rolled at 200°C with the reduction of 50% shows the tensile strength of 353MPa and the elongation of 29%, which is an excellent strength-ductility balance. By applying high-speed rolling process to AZ80 magnesium alloy, we can obtain a remarkable improvement in the material characteristics as well as rolling deformability.
Authors: Maria Teresa Pérez-Prado, F. Salort, Ling Jiang, Oscar A. Ruano, M.E. Kassner
Abstract: A coarse grained Zr-Hf alloy has been subjected to one rolling pass with different thickness reductions ranging from 10% to 80%. Rolling was performed at three temperatures: 300°C, room temperature (RT) and liquid nitrogen temperature (-196°C). It has been found that, with increasing strain per pass, i.e., with increasing strain rate, the deformation mechanism changes from twinning to dislocation slip. The minimum strain per pass necessary to trigger the transition in deformation mechanism decreases with decreasing temperature. High strain, high strain-rate deformation leads to the development of an ultrafine grained structure. Simultaneously, a basal type rolling texture forms. At the higher temperatures (RT and above) a recrystallization texture component is also present. Thus, nanostructuring of this Zr-Hf alloy during severe rolling is attributed to a combination of grain subdivision by the formation of geometrically necessary boundaries and to nucleation and growth phenomena taking place as a consequence of rapid adiabatic heating.
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