The effect of electropulsing on the mechanical behaviors and microstructures of Ti-6Al-4V titanium alloy was investigated by an uniaxial tensile test. Compared to the value measured in cold tensile test, the alloy exh...The effect of electropulsing on the mechanical behaviors and microstructures of Ti-6Al-4V titanium alloy was investigated by an uniaxial tensile test. Compared to the value measured in cold tensile test, the alloy exhibits lower ultimate tensile strength when the tensile deformation is assisted by electropulsing. The tensile elongation is found to vary non-monotonically with increasing root mean square(RMS) current density. Though decreasing at first, the tensile elongation increases with current density once the value exceeds 8.1 A/mm^2. Through applying current with RMS current density of 12.7 A/mm^2, the tensile elongation at strain rate 0.001 s^(-1) can be improved by 94.1%. In addition, it is observed that more remarkable electroplastic effect is induced by the higher peak current density under similar thermal effect. Microstructure analysis reveals that the low plasticity at 8.1 A/mm^2 is attributed to the micro-void easily formation near the tips of acicular β phases. The enhanced ductility at higher current densities, on the other hand, is attributed to the dynamic recrystallization.展开更多
In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse cur...In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse current can effec-tively reduce the springback and the bending force compared to the experiments without current. The frequency has a moresignificant influence on bending force and springback than electric current density. Electroplastic （EP） effect begins towork when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, themicrostructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current canpromote the occurrence of dynamic recrystallization （DRX） of magnesium alloy compared to traditional hot formingprocess. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture withincreasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanismof pulse current to promote DRX is studied and athermal effect is proved to exist.展开更多
The tensile tests of AZ31 magnesium alloy were carried out under room temperature, 100, 150 and 200 ℃ with andwithout pulse current. The effect of temperature on dynamic recrystallization （DRX） of AZ31 alloy was st...The tensile tests of AZ31 magnesium alloy were carried out under room temperature, 100, 150 and 200 ℃ with andwithout pulse current. The effect of temperature on dynamic recrystallization （DRX） of AZ31 alloy was studied at differentconditions. One-parameter approach was used to analyze the critical conditions of DRX, the critical stress was obtainedunder different temperatures, and the related results were validated by metallography observation. The results showed thatDRX of AZ31 alloy occurred at 200 ℃ without pulse current. When pulse current with 150 Hz/50 V parameter wasapplied at room temperature, DRX occurred, while DRX was not completed until temperature over 150 ~C. With theanalysis result of critical conditions of DRX based on one-parameter approach, the relationship between critical stress andpeak stress obtained in this present study is σc = （0.746-0.773）σp.展开更多
The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were r...The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were revealed,as well as underlying micromechanical factors.Phenomenology and machine learning-based constitutive models were developed.Both models were formulated in the framework of a temperature-dependent linear combination regulated by a transition function to capture the evolution of strain-hardening behavior with increasing temperature.Novel mathematical functions for describing temperature and strain rate sensitivities were formulated for the phenomenological constitutive model.The threshold temperature related to microstructure evolution was considered in the modeling.A data-enrichment strategy based on extrapolating experimental data via classical strain hardening laws was adopted to improve neural network training.An efficient inverse identification strategy,focusing solely on the transition function,was proposed to enhance the prediction accuracy of post-necking deformation by both constitutive models.展开更多
基金supported by the Natural Science Foundation of Shandong Province(No.ZR2016EEM25)
文摘The effect of electropulsing on the mechanical behaviors and microstructures of Ti-6Al-4V titanium alloy was investigated by an uniaxial tensile test. Compared to the value measured in cold tensile test, the alloy exhibits lower ultimate tensile strength when the tensile deformation is assisted by electropulsing. The tensile elongation is found to vary non-monotonically with increasing root mean square(RMS) current density. Though decreasing at first, the tensile elongation increases with current density once the value exceeds 8.1 A/mm^2. Through applying current with RMS current density of 12.7 A/mm^2, the tensile elongation at strain rate 0.001 s^(-1) can be improved by 94.1%. In addition, it is observed that more remarkable electroplastic effect is induced by the higher peak current density under similar thermal effect. Microstructure analysis reveals that the low plasticity at 8.1 A/mm^2 is attributed to the micro-void easily formation near the tips of acicular β phases. The enhanced ductility at higher current densities, on the other hand, is attributed to the dynamic recrystallization.
基金financial support from the Natural Science Foundation of Shandong Province (No. ZR2016EEM25)
文摘In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse current can effec-tively reduce the springback and the bending force compared to the experiments without current. The frequency has a moresignificant influence on bending force and springback than electric current density. Electroplastic （EP） effect begins towork when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, themicrostructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current canpromote the occurrence of dynamic recrystallization （DRX） of magnesium alloy compared to traditional hot formingprocess. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture withincreasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanismof pulse current to promote DRX is studied and athermal effect is proved to exist.
基金financial support from the Natural Science Foundation of Shandong Province(Grant No.ZR2016EEM25)the China Postdoctoral Science Foundation(2016M592184)
文摘The tensile tests of AZ31 magnesium alloy were carried out under room temperature, 100, 150 and 200 ℃ with andwithout pulse current. The effect of temperature on dynamic recrystallization （DRX） of AZ31 alloy was studied at differentconditions. One-parameter approach was used to analyze the critical conditions of DRX, the critical stress was obtainedunder different temperatures, and the related results were validated by metallography observation. The results showed thatDRX of AZ31 alloy occurred at 200 ℃ without pulse current. When pulse current with 150 Hz/50 V parameter wasapplied at room temperature, DRX occurred, while DRX was not completed until temperature over 150 ~C. With theanalysis result of critical conditions of DRX based on one-parameter approach, the relationship between critical stress andpeak stress obtained in this present study is σc = （0.746-0.773）σp.
文摘The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were revealed,as well as underlying micromechanical factors.Phenomenology and machine learning-based constitutive models were developed.Both models were formulated in the framework of a temperature-dependent linear combination regulated by a transition function to capture the evolution of strain-hardening behavior with increasing temperature.Novel mathematical functions for describing temperature and strain rate sensitivities were formulated for the phenomenological constitutive model.The threshold temperature related to microstructure evolution was considered in the modeling.A data-enrichment strategy based on extrapolating experimental data via classical strain hardening laws was adopted to improve neural network training.An efficient inverse identification strategy,focusing solely on the transition function,was proposed to enhance the prediction accuracy of post-necking deformation by both constitutive models.
