The plastic deformation and recrystallization behavior of the commercial magnesium alloys WE54 was analyzed using the strain rates 0.01, 0.1, 1, and 5 s−1 in the temperature range from 400 to 550 °C. The dependence of the flow stress on the temperature and the strain rate was modeled using the Garofalo hyperbolic sine equation. Thereby, the activation energy for plastic deformation of 224 kJ mol−1 was determined considering the flow stress at a strain of 0.5. The analysis revealed a stress exponent of 3.2. Furthermore, processing maps were generated by plotting the efficiency of power dissipation and the instability parameter considering different instability criteria as a function of the temperature and the strain rate. Depending on these parameters the extent of the recrystallization and the localization of the nucleation varied, significantly. At 400 °C, the recrystallization is very limited and was observed at grain boundaries (GB), shear bands (SB), and twin boundaries (TW). Increasing temperatures result in an increased recrystallized fraction, while lower strain rates promote grain boundary nucleation and reduce the amount of SBN and TW. The prediction of the processing map was verified by large scale extrusion trials, which proof that the evaluation of hot compression data can provide an effective tool to establish viable processing parameters.
Shear Band High Strain Rate Grain Boundary Power Dissipation Strain Rate Sensitivity
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The authors are grateful for the financial support of the Deutsche Forschungsgemeinschaft (DFG) under the Contract Number RE 688/67-1.