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Effect of microstructural parameters on twinning activity of magnesium alloys

Effect of microstructural parameters on twinning activity of magnesium alloys

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Effect of microstructural parameters on twinning activity of magnesium alloys

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  1. 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

  2. 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

  3. 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

  4. Experimental Acoustic 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

  5. Initial microstructure TD RD Elongated grains in RD Strong initial texture

  6. Influence of the initial texture • Higher strength for TD direction • AE indicates higher twinning activity

  7. Influence of the initial texture RD TD • Micrographs show larger amount of twins for TD

  8. 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

  9. 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

  10. Influence 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 Conclusions

  11. Acknowledgement This work received a support from the Grant 106/09/0712 by the Czech Science Foundation.