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The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

100%

Bohlen J., Dobron P., Nascimento L., Parfenenko K., Chmelik F., Letzig D.

Acta Physica Polonica A

2012

vol. 122

issue 3

444-449

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.

Acoustic-Emission Study of Intermittency of Plastic Flow during Twinning and Dislocation Glide

84%

Shashkov I., Lebedkina T., Lebyodkin M., Dobron P., Chmelik F., Kral R., Parfenenko K., Mathis K.

Acta Physica Polonica A

2012

vol. 122

issue 3

430-434

Recent studies of plastic deformation with the aid of acoustic emission techniques proved an intermittent, scale-invariant character of plastic processes, as reflected in power-law statistical distributions. In some cases, the power-law exponents display close values leading to hypothesis of universality of scaling laws for various mechanisms of plasticity. Nevertheless, the accurate determination of the power law may be impeded by some sources of errors inevitable in real conditions, in particular, by superposition of individual acoustic emission events. In the present work, the sensitivity of the apparent statistics to the variation of the parameters of individualization of acoustic emission events is examined using Mg and Al based alloys. Both these alloys exhibit a highly cooperative character of plastic deformation, leading to strong acoustic activity which is governed by distinct microscopic mechanisms - mechanical twinning and the Portevin-Le Chatelier effect, respectively.

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2 Acta Physica Polonica A

2 2012

2 Chmelik F.

2 Dobron P.

2 Parfenenko K.

1 Bohlen J.

1 Kral R.

1 Lebedkina T.

1 Lebyodkin M.

1 Letzig D.

1 Mathis K.

1 Nascimento L.

1 Shashkov I.

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The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

Acoustic-Emission Study of Intermittency of Plastic Flow during Twinning and Dislocation Glide