Yield surface prediction of Aluminum on rolling

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Abstract

Rolling of polycrystalline aggregates of Aluminum was investigated by employing the Visco-plastic self-consistent polycrystal (VPSC) model. The starting texture is a series crystals represented by five hundred random orientations. Rolled texture and yield surfaces at rolling strain levels of -0.5, -1.0, -1.5, -2.0 and -2.5 were captured by VPSC modeling. The predicted texture showed a typical rolled texture components and the yield surfaces showed anisotropic shape and a saturation tendency.

Author(s): Q. Ma, E.B. Marin, M.F. Horstemeyer


Methodology

Magnesium has a hexagonal close-packed (HCP) structure whose deformation modes are different from those of aluminum. Typical deformation modes in magnesium are basal <a>-{0002}<11-20> slip, prismatic <a>-{10-10}<11-20> slip, second pyramidal <c+a>-{11-22}<11-23> slip and extension twinning {10-12}<10-11>. In this study, a commercial extruded AM30 alloy (mass %, 2.54% Al, 0.40% Mn, Mg in balance) was selected as the HCP experimental material to conduct channel die compression at high temperature 200C and at strain rate of 0.001/S to strain 30%. At these loading conditions, twinning would not be profuse and, hence, only slip will be the predominant deformation mode. The hardening parameters of the three slips modes were obtained using material point simulations to fit the experimental stress-strain curve recorded from the channel die compression test as shown in Figure 1d.


The texture of AM30 was measured by X-ray diffraction method (XRD). The recalculated pole figures were calculated based on the orientation distribution functions (ODFs) which was obtained using the measured six incomplete pole figures {10-10}, {0002}, {10-11},{10-12}, {11-20} and {10-13}. The initial and the channel die compressed texture of AM30 plotted by the texture software MTEX [1].

The commercial finite element software ABAQUS 6.9 and a user subroutine UMAT incorporating the crystal plasticity constitutive theory and the magnesium AM30 materials parameters were used to simulate texture evolution and mechanical response. The initial texture used in this CPFEM simulation was measured in the undeformed sample and was represented by 343 discrete orientations as shown in Figure 1a. The 3D polycrystal is represented by the 3D Voronoi grains created by the code Neper [2]. The undeformed polycrystal and the channel die compressed 3D polycrystal up to a strain of 30% are presented in Figures 1b and 1c.The simulated and measured channel die compression stress-strain curves are presented in Figure 1e.

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