Macroscopic Shear Banding in an Aluminum-Based Alloy During Equal-Channel Angular Pressing
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Macroscopic Shear Banding in an Aluminum-Based Alloy During Equal-Channel Angular Pressing Jingtao Wang, Yuzhong Xu, Lizhong Wang*, Xicheng Zhao and Haibo Wang School of Metall., Xi’an Univ. of Arch. & Tech., 710055, P.R.China (*Now at School of Mech. Engineer., Xi’an Jiaotong University, 710049, P.R. China;) ABSTRACT Equal-channel angular pressing is now recognized as an effective technique for fabricating materials with ultrafine structures. It is generally considered that the strain is homogeneously distributed in the materials after ECA pressing. The present investigation shows, however, that severe macroscopic shear band, which extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45o, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and the total volume fraction of macroscopic shear bands may well surpass 50%. I. INTRODUCTION It is a general observation in many of the industrial forming processes, that plastic instability develops at high strain levels (generally >1.0 of true strain), and shear bands, or s-bands as some authors termed form [1, 2]. Macroscopic shear bands were observed in various single and polycrystalline metals with low to high stacking fault energy [1-3], and in various metalworking processes including rolling[4-7], extrusion[8], plane strain compression[9], tensile testing[10,11], torsion testing[12,13] and cutting[14] etc. Equal-channel angular (ECA) pressing, during which specimen is subjected to pure shear deformation[15], is successfully applied in the fabrication of ultrafine grained materials[16,17]. Grain scale shearing characteristics during ECA pressing was observed and analyzed by Furukawa et al. [18,19]. Semiatin et al. [20-22] observed macroscopic shear banding and specimen failure of TiAl intermetallic compound. Detailed investigation on macroscopic shear banding in ECA pressing was need. This paper reports our investigation on the macroscopic banding characteristics occurred during ECA pressing of an aluminum alloy. II. EXPERIMENTAL PROCEDURES Y
An Al-3%Mg solid solution alloy was used in the present investigation. The alloy was prepared through conventional IM process. The average grain size in the annealed state before ECA pressing is ~50 µm. ECA pressing was carried out at room temperature, without any intermediate annealing, as described earlier[23,24]. In the present study, the intersecting angle between the two equal channels is π/2. BB3.1.1
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Figure 1. Orientation of the three orthogonal sections observed
Optical microscopy was used for the microstructure characterization of the macroscopic shear bands on three orthogonal sections (S--Horizontal section; L--Longitudinal section; T--Transverse cross section), as shown in Fig.1. The specimens were anode oxidized in a solution of 38% H2SO4, 42% H2PO4 and 19% H2O, and observed under polarized light. True shear strain that a shear band ac
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