PSI - Issue 41

Alexander Inozemtsev et al. / Procedia Structural Integrity 41 (2022) 544–549 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3. Structural studies Before metallographic studies, the U-shaped specimens were pressed into conductive bakelite holder on a CitoPress-10 machine (Struers) and then polished on a Tegramin-30 machine (Struers). For rough surface conditioning distilled water was used as a lubricant, while surface finishing was carried out with a lubricant containing highly dispersed silicon oxide particles. Surface etching was made with Keller's reagent for 5-10 seconds at 65-70°C. Electron microscopy of the structure were carried out before all tests and after static deformation test on the Testometric electromechanical testing machine and dynamic loading on the split Hopkinson pressure bar. The structural studies were performed for cross-cut U-shaped specimens using a FEI PHENOM G2 ProX scanning electron microscope at an accelerating voltage of 15 kV and magnification of 2,000-15,000x. The initial structure of AMg6 alloy in specimens Nos. 1-6 was a set of grains of  -phase oriented along the rolling direction. The diametrical size of grains was about 8-18 microns. The microscopic examination of specimens revealed the presence of a second phase in the form of cellular conglomerates located in the grain body; the presence of second phases was characteristic of all samples without exception. Static and dynamic testing of U-type specimens №1-№6 leads (to a greater or lesser extent) to localization of plastic strain in areas with geometric stress concentration in all specimens without exception. Specimens subject to loading tests are shown in Fig.2a-c, 3a-c. Regions with geometric stress concentration are shown as circled areas 1-4 in Fig. 2a and 3a.

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Fig.4. Structure of plastic strain localization in the geometrical stress concentrators of the specimen after dynamic tests at maximum loading level (a-c) and after static tests (d-f); a-f – circled region 2; a,d - x2 000; b, e - x8 000; c, f - x15 000. In Figure 4, the arrows show the localized shear bands.