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Acoustic Emission Study of the Deformation Behavior of Mg-Mn Alloys Containing Rare Earth Elements

100%
Illkova K., Dobroň P., Chmelík F., Letzig D., Bohlen J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
634-638
EN
Magnesium-manganese (Mg-Mn) based alloys with various chemical composition were processed by indirect extrusion at two different speeds. Alloying with Mn and rare earth elements has significant influence on the microstructure and on the texture of the alloys under investigation. This paper deals with the acoustic emission analysis of the deformation behavior of the extruded Mg-Mn alloys. The acoustic emission measurements were performed during the uniaxial tension and compression tests, and the obtained results are discussed with respect to the influence of rare-earth elements on the deformation behavior, particularly in terms of the activation of dislocation glide and twinning.
2
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On the Effect of the Extrusion Speed on Microstructure and Plastic Deformation of ZE10 and ZEK100 Magnesium Alloys - an Acoustic Emission Study

100%
Dobroň P., Chmelík F., Parfenenko K., Letzig D., Bohlen J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
593-596
EN
Mg-Zn-based alloys ZE10 and ZEK100 have been extruded at different speeds varying from 1 m/min to 20 m/min. Specimens taken in the extrusion direction were uniaxially loaded in tension and compression at room temperature. The results are discussed using concurrent acoustic emission monitoring during mechanical testing and the acoustic emission signal analysis that correlates the microstructure and the stress-strain curves to the possible deformation mechanisms. In all tests, the acoustic emission response exhibited a large acoustic emission peak at the beginning of plastic deformation. A small local maximum on the onset of the acoustic emission activity was frequently observed, i.e. at very low stresses. For the alloys with bimodal grain structure tested in compression, an additional acoustic emission peak appeared at larger strains. This peculiar behavior can be explained by interplay of (10-12)-twinning and dislocation slip in samples with various grain size distributions.
3
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The Influence of Rolling Conditions on Deformation Behavior of Magnesium Alloy Sheets

100%
Drozdenko D., Bohlen J., Chmelík F., Letzig D., Dobroň P.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
795-800
EN
The influence of texture on deformation behavior was investigated for conventionally rolled magnesium alloy slabs and rolled twin roll cast magnesium alloy strips in the form of sheets. The Mg-Zn based sheets were deformed at room temperature with the tensile axis oriented in the rolling and transversal directions. The texture with respect to different rolling conditions was characterized by X-ray diffraction. In the case of Mg-Zn-rare earth alloy sheets, the basal pole intensity, aligned with the sheet normal direction, is lower for conventionally rolled sheet in comparison to the rolled twin roll cast strip. Difference in angular distribution of basal planes influences on the mechanical behavior of the sheets. The yield strength is higher for the tension along rolling direction than along transversal direction for the conventionally rolled sheets, whereas the opposite deformation behavior is observed for the rolled twin roll cast strips. Furthermore, the planar anisotropy of the yield strength is less pronounced for the rolled twin roll cast strips. The deformation behavior of the sheets was also investigated by the acoustic emission technique. The acoustic emission signal analysis correlates the microstructure and the stress-time curves with active deformation mechanisms. It highlights the activity of a basal slip and tensile twinning, particularly during the transverse direction tension.
4
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Influence of Pre-Compression on Tensile Behaviour in Wrought Mg-Zn-Ce Alloy Studied by the Acoustic Emission Technique

86%
Dobroň P., Drozdenko D., Bohlen J., Yi S., Letzig D., Chmelík F.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
790-794
EN
Wrought Mg-Zn-Ce alloy (ZE10) has been pre-compressed and subsequently subjected to tensile loading. Due to a fibre texture of the samples, the level of pre-compression stress significantly influences the subsequent tensile behaviour. The acoustic emission technique was used for monitoring active deformation mechanisms during mechanical testing. The obtained acoustic emission results are correlated to the stress-time curves and the differences in the acoustic emission count rate were used to reveal changes in underlying deformation mechanisms. Firstly, a compression-tension cycle was monitored by the acoustic emission technique. Then, the samples were deformed to specific points on the stress-time curve, where acoustic emission exhibits strong changes in the activity. The following microstructure analysis of the samples, deformed to different strain-levels, by using electron back scattered diffraction method brought a detailed insight into active deformation mechanisms. Twinning during the pre-compression was followed by detwinning during the tensile loading. Two consecutive acoustic emission peaks, which appeared at larger strains, are explained by interplay of detwinning and dislocation slip and a nucleation of compression twins, respectively.
5
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The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

86%
Bohlen J., Dobron P., Nascimento L., Parfenenko K., Chmelik F., Letzig D.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 3
444-449
EN
An indirectly extruded round bar of magnesium alloy AZ31 has been subjected to a cyclic test consisting of preloading in compression to different values of maximum stress followed by a single tensile test segment. Concurrent acoustic emission measurements were used to determine the active deformation mechanisms during plastic flow and work hardening. Electron backscattering diffraction was applied to obtain local orientation images in order to reveal twins and twinned fractions of the microstructure. Twins form preferentially in larger grains during the compression test segment and only with increasing stress do smaller grains show twinning. Some grains are completely re-oriented as a result of twinning. During the tensile test segment, untwinning is the most significant deformation mechanism although in some re-oriented grains new twins also nucleate. The acoustic emission count rates confirm that this is only the case after compression to higher stress levels.
6
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The Study of the Behavior of Constrained Groove Pressed Magnesium Alloy after Heat Treatment

73%
Zimina M., Bohlen J., Letzig D., Kurz G., Poková M., Knapek M., Zrník J., Cieslar M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
775-778
EN
In this work twin-roll cast AZ31 magnesium strip of thickness 5.6 mm was subjected to the heat treatment and further constrained groove pressing. A comparison of the microstructure and microhardness of as-cast, constrained groove pressed and annealed material was carried out. The twin-roll cast strip exhibits an inhomogeneous structure which is replaced by a finer and uniform recrystallized one after aging at 450°C for 10 h. A significant increase of the microhardness was observed accompanied by a pronounce grain refinement. Nevertheless, the distribution of the grain size is unequal along the specimen width. Thermal stability of the deformed structure during subsequent annealing was investigated. It was shown that higher annealing temperatures result in a formation of a more uniform recrystallized structure and in a significant drop of microhardness down to the values obtained for as-cast alloy.
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