Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > Rolling > Non-ferrous metal rolling

Research on Differential Speed Rolling and Equal Channel Angular Rolling of AZ31 Magnesium Alloy

Author JiangJunFeng
Tutor XiaWeiJun
School Hunan University
Course Materials Processing Engineering
Keywords AZ31 magnesium alloy finite element method differential speed rolling equal channel angular rolling texture formability
Type Master's thesis
Year 2010
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Deformed magnesium sheets have great potentials for industrial applications owing to their superior combination properties. However, the room formability of magnesium produced by conventional preparation and/or plastic processing is poor due to their intrinsic hexagonal close-packed lattice, which greatly limits the application and development of magnesium sheets. Therefore, the present study aims to improve the room formability of magnesium sheets by differential speed rolling (DSR) and equal channel angular rolling (ECAR). Moreover, a novel method called equal channel angular cross rolling (ECACR) is introduced. The deformation behaviors, microstructures and mechanical properties were systematically investigated by the combination of simulation by Deform 3D finite element method (FEM) and experimental researches including optical microscopy (OM) observation, X-ray diffraction pattern analysis, macro-texture measurement, scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) observation and tensile test at ambient temperature, etc. The temperature field, stress field and strain field during the rolling processes were analyzed, and the evolution of microstructure, grain orientation and mechanical properties of the sheets were illustrated. The main conclusions can be drawn as follows:(1) The FEM of differential speed rolling (DSR) shows that temperature field, stress field and strain field are asymmetrical along the thickness of the sheet. The temperature of the plane on the side of the low speed roll is lower than that of the plane on the side of the high speed roll, as well as equivalent stress and equivalent strain. The effect of shear strain during DSR with a lower speed ratio is larger than that with a higher speed ratio. The FEM of ECAR indicates that the temperature of the sheet decreases sharply from the entrance of the die to the angle, but increases at the angle, and the equivalent stress and equivalent strain also increase at the angle.(2) The grains of AZ31 magnesium alloy sheet can be significantly refined by DSR, and the (0002) basal texture is weakened by tilting some degrees. As the strain per pass is increased, the microstructural homogeneity along the thickness of the sheet is improved, but the ability of tilting the basal texture is weakened. With 10% reduction per pass, compared with conventional rolling, the ultimate tensile strength (UTS) is increased from 235MPa to 278MPa, and the elongation is increased from 17.6% to 22.5%, and the yield ratio is decreased from 0.77 to 0.66. The effects of grain refinement and weakening of basal texture are the primary reasons to enhance the mechanical properties of sheet produced by DSR.(3) As the passes of ECAR are continued, the (0002) basal texture of the sheet is weakened gradually, and the yield strength (YS) and UTS are decreased, and the elongation is increased and the yield ratio is decreased. The elongation of the sheet processed by ECAR with 8 passes is up to 31% with yield ratio of only 0.39, which is greatly enhanced the room formability of AZ31 magnesium alloy sheet. After cross ECAR, the c axes along both rolling direction (RD) and transverse direction (TD) are tilted, and the spread of the texture is increased with the enhancement of symmetry. The elongations of ECARed sheet along RD and TD are 26.5% and 27.6%, and the yield ratios are 0.50 and 0.49 respectively, which means that the anisotropy on the rolled plane is reduced remarkably.

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