13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- k, the slope of this equation is larger as the angle increases. Fig. 14(b) shows relationship between k and Schmid factor for twinning. In each annealing condition, k become larger as Schmid factor for twinning is larger. When Schmid factor for twinning is large, twinning deformation can easily occur, and AE signals are dominated by twinning deformation. Additionally, slope of Hall-Petch equation is larger in twinning than that in slip [8]. For these reason, there is linear relationship between Schmid factor for twinning and k. Figure 14. (a) Hall-Petch equation and (b) relationship between slope of the equation and Schmid factor for twinning 4. Conclusion In the present study, microstructure effect on mechanical properties of AZ31 extruded magnesium alloy is evaluated by AE test and EBSD test, and following conclusions were drawn; (1) The result of tensile test showed that anisotropy of mechanical properties is weakened by annealing. (2) Nominal stress of AE energy peak and peak of AE energy were dominated by twinning deformation, so these value changed as Schmid factor for twinning changed. (3) Nominal stress of AE start showed strong annealing dependence. After annealing, the stress was less than 20 MPa and anisotropy disappeared. (4) The relationship between nominal stress of AE peak and grain size was well explained by Hall-Petch equation. (5) Slope of Hall-Petch equation changed as Schmid factor for twinning because twinning deformation is main mechanical behavior in this study. References [1] T. Yasutomi and M. Enoki, In-situ evaluation of detwinning behavior in extruded AZ31 mg alloy by AE. Materials Transactions, 53(2012) 1611-1616. [2] Y. P. Li and M. Enoki, Evaluation of the Twinning Behavior of Polycrystalline Magnesium at Room Temperature by Acoustic Emission. Materials Transactions, 48(2007) 1215-1220.
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