13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- composition (mass %) of each alloy is shown in Table 1. The mean grain sizes of the extruded and the drawn alloys were about 13 μm and 18 μm, respectively. Their mechanical properties are shown in Table 2. Figure 1 shows inverse pole figure on the cross section of the bars. The extruded alloy has marked texture on (111) plane, but a specified orientation is not observed in the drawn one. This difference in texture may be related to the difference in severity during fabrication processes. From the material properties of both alloys mentioned above, the important difference in both alloys is the degree of texture. Table 1. Chemical composition (mass %) Si Fe Cu Mn Mg Cr Zn Ti Extruded 0.42 0.3 4.06 0.73 0.58 0.05 0.02 0.05 Drawn 0.41 0.32 3.87 0.7 0.62 0.04 0.03 0.04 Table 2. Mechanical properties σ0.2 (MPa) σB (MPa) σT (MPa) φ(%) Extruded 350 471 638 32.4 Drawn 303 464 718 43.7 σ0.2: 0.2% proof stress σB: Tensile strength σT : True breaking stress φ: Reduction of area Figure 2 shows shape and dimensions of specimens. Prior to fatigue testing, all of the specimens were slightly electro-polished by 40 μm in diameter to remove the work affected layer and secure direct surface observation. The observation of fatigue damage and the measurement of crack length were conducted under a scanning electron microscope (SEM) or under an optical microscope by using the plastic-replica technique. Surface crack length, ℓ, was measured in the circumferential direction of the specimen in both tensile and shear mode propagations. The crystallographic analysis was performed by using Electron Back Scatter Diffraction Pattern (EBSD) method. The fatigue tests were carried out using a 20 kHz piezoelectricity actuated ultrasonic machine in relative (a) Extruded (b) Drawn Figure 1. Inverse pole figure
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