| Equal-channel angular pressing(ECAP) is a severe plastic deformation technology, and can obtain microstructure with ultra-fine grains.ECAP can improve the mechanical properties of materials and achieve either low temperature or high strain rate superplasticity to enhance the forming property of materials at room temperature.To investigate both superplastic deformation behavior and mechanism of the ECAPed magnesium alloys at different temperatures and strain rates can provide the reliable basis for development and application of high ductile magnesium alloys,and also offer the necessary theoretical basis for further application of high ductile magnesium alloys in engineering practice.Through performing tensile tests at different temperatures and strain rates,the influence of temperature and strain rate on the superplastic deformation behaviors of the ECAPed Mg-Zn-Nd alloy has been investigated.The strain rate sensitivity and active energy of plastic flow are determined.Moreover,the suitable pressing route,the optimum temperature and strain rate at which the ECAPed Mg-Zn-Nd can exhibit the superplasticity were obtained.In addition,the microstructures of the ECAPed Mg-Zn-Nd alloys are observed using transmission electron microscope(TEM).And the corresponding mechanism of superplastic deformation for the ECAPed Mg-Zn-Nd alloys is discussed.The experimental results revealed that the grains of the Mg-Zn-Nd alloy got obviously refined after one pass of ECAP.After four passes of ECAP,the finest grains with the size of about 350nm can be attained.At strain rates ranging from 1×10-4 to 5×10-3s-1,the elongation of Mg-Zn-Nd alloy increased with decreasing strain rate.When tested under the temperature range of 200-300℃,the elongation increased with the temperature,but the elongation increased dramatically within 250-300℃.After 4 passes of ECAP by route C, the elongation of Mg-Zn-Nd alloy reached 381.8%at 300℃,indicating that the ECAPed Mg-Zn-Nd alloy exhibited a good superplasticity at lower temperature.After 4 passes of ECAP by route A,the alloy showed a tendency of low temperature superplasticity at 250℃.In the case of the same alloy subjected to 4 passes of ECAP by route BC,low temperature superplasticity was also observed.For the Mg-Zn-Nd alloy processed by ECAP,the dominant mechanism during superplastic deformation is grain boundary sliding controlled by grain boundary diffusion,whereas the nucleation,growth and coalition of cavities take effect as an important accommodating mechanism.
|
PDF Full Text Request