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Investigation of deformation mechanisms in textured magnesium alloy
Dittrich, J. ; Čapek, J. ; Knapek, Michal ; Minárik, P.
Advanced in-situ and ex-situ methods were used to reveal active deformation mechanisms during deformation of magnesium alloy with a strong texture. Three sets of samples were prepared from the rolled sheet of commercial AZ31 alloy with respect to its strong basal texture - normal direction (ND), rolling direction (RD) and 45 degrees between RD and ND, and were deformed in both compression and tension. The signal of acoustic emission (AE) was measured concurrently during the deformation. Electron backscattered diffraction (EBSD) was used to study the microstructure after the selected stages of the deformation. It is shown that the extension twinning played an important role during the plastic deformation in the samples having favorably oriented basal texture component, whereas in the unfavorably oriented samples, the role of twinning was marginal. Pronounced activation of twinning only in some samples caused a considerable variation in the deformation behavior and AE response. A consistent link between the energy and amplitudes of the AE signal and the microstructure changes investigated by EBSD was established.
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Mechanical properties of WN43 magnesium alloy prepared by spark plasma sintering
Knapek, Michal ; Minárik, P. ; Greš, A. ; Zemková, M. ; Cinert, Jakub ; Král, R.
The spark plasma sintering (SPS) method was used to prepare bulk materials form WN43 magnesium alloy atomized powder. Compression tests were carried out in order to investigate the effect of different sintering regimes (10 min at 400, 450, or 500 degrees C) on the mechanical properties of the material. Furthermore, complementary in-situ acoustic emission (AE) recording was employed to reveal the dynamics of deformation processes during compression. It was shown that by increasing the sintering temperature, the ultimate compressive strength and ductility were significantly improved. The AE data and microstructure observations suggest that pronounced twin nucleation takes place around the yield point whereas twin growth and dislocation activity are the dominant deformation mechanisms in the later stages of deformation.
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Effect of aluminum content and precipitation on the corrosion behavior and acoustic emission response of AZ31 and AZ80 magnesium alloys
Veverková, E. ; Knapek, Michal ; Minárik, P.
In this study, we investigated the effect of aluminum content and precipitation on the corrosion behavior of the AZ31 and AZ80 magnesium alloys. The investigated alloys were received in the as-extruded condition in order to retain comparable grain size and texture. First, solid solution treatment was performed on the samples of both alloys. Subsequently, the samples were isothermally aged at 200 degrees C for 20 hours. The scanning electron microscopy was used to study the grain size and microstructure. The corrosion properties of samples were studied by potentiodynamic polarization measurements and the AE signal was concurrently recorded. Solution treated AZ80 and AZ31 samples exhibited similar behavior. The aged AZ80 sample showed lower corrosion rate. Also, a strong breakdown appeared in the later (compared to other samples) stage of the potentiodynamic test. The breakdown was found to be easily recognized by AE parameters.
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Numerical modeling of surface elastic wave scattering in polycrystalline materials
Grabec, Tomáš ; Ryzy, M. ; Verres, I. A.
Grain-boundary scattering of acoustic waves in polycrystalline materials is studied with analytical and numerical methods in the presented paper. In particular, the attenuation of Surface Acoustic Waves (SAWs) propagating through a polycrystalline microstructure is investigated. A three dimensional timedomain finite-element method (FEM) is utilized for the numerical simulation, whereby the granular microstructure is modeled by Voronoi tessellation. The resulting frequency-dependent attenuation coefficients are compared to an explicit analytical model.
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