CHARLES UNIVERSITY PRAGUE Department of Physics of Materials Effect of microstructural parameters on twinning activity of magnesium alloys K. Máthis, J. Čapek, Z. Zdražilová Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University Prague
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Effect of microstructural parameters on twinning activity of magnesium alloys
Effect of microstructural parameters on twinning activity of magnesium alloys. K . Máthis , J. Čapek, Z. Zdražilová Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University Prague. Motivation. - PowerPoint PPT Presentation
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CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Effect of microstructural parameters on twinning activity of magnesium alloys
K. Máthis, J. Čapek, Z. Zdražilová
Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University Prague
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Motivation
• Magnesium alloys – twinning is one of the
main deformation mode
• Twinning has impact on e.g. ductility or tension-
compression asymmetry
• Investigation of influence of initial texture and loading
mode on twinning activity
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CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Experimental
Continuous cast AZ31 alloy
Mg + 3 wt.% Al + 1 wt.% Zn
• Tensile and compression tests at RT, strain rate : 10-3 s-1
• Two orientations:
Specimen axis || RD, TD
• In-situ acoustic emission (AE) measurements
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
ExperimentalAcoustic emission
In-situ technique – sensitive on twin nucleation
Information from the entire volume of the specimen
Two threshold levels: Count 1 – 302 mV – all effects
Count 2 – 600 mV – mostly twinning
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Initial microstructure
Elongated grains in RD
Strong initial texture
RD TD
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Influence of the initial texture
• Higher strength for TD direction
• AE indicates higher twinning activity
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Influence of the initial texture
• Micrographs show larger amount of twins for TD
RD TD
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Influence of the initial texture
• Twin boundaries are impenetrable for basal dislocations twin boundaries are non-penetrable obstacles
• Dislocation pile-ups at the twin boundaries stress concentration could initiate non-basal slip
• Interactions of non-basal dislocations with basal dislocation results sessile dislocations increased forest dislocation density
• As a consequence of above mentioned larger amount of twin boundaries in TD direction causes more significant hardening
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
Influence of the loading mode
• Significant tension – compression asymmetry
• Compression – twin nucleation at the beginning than their growth
• Tension – twin growth is limited twinning during the entire test
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
ConclusionsInfluence of the texture
• Larger amount of twins is observed for TD direction interaction
of basal dislocations with twin boundaries causes hardening
Influence of the loading mode
• Compression – twin nucleation at the beginning of the deformation
• Tension – twinning during the entire test
Good agreement between AE measurement and the micrographs
CHARLES UNIVERSITY PRAGUE
Department of Physics of Materials
AcknowledgementThis work received a support from the Grant 106/09/0712 by the Czech Science Foundation.