The thermomechanical behavior of precipitation-hardened aluminum alloy AA7022-T6 was studied using isothermal compression at temperatures of 623−773 K and strain rates of 0.01−1 s^−1.The experimental results indicated...The thermomechanical behavior of precipitation-hardened aluminum alloy AA7022-T6 was studied using isothermal compression at temperatures of 623−773 K and strain rates of 0.01−1 s^−1.The experimental results indicated that dynamic recrystallization(DRX)is a predominant hot deformation mechanism,especially at elevated temperatures and low strain rates.The modified Johnson−Cook(J−C)and the strain compensated Arrhenius-type models were developed to predict the hot flow behavior under different deformation conditions.The correlation coefficients of modified J−C model and the strain compensated Arrhenius-type models were 0.9914 and 0.9972,respectively,their average relative errors(ARE)were 6.074%and 4.465%,respectively,and their root mean square errors(RMSE)were 10.611 and 1.665 MPa,respectively,indicating that the strain compensated Arrhenius-type model can predict the hot flow stress of AA7022-T6 aluminum alloy with an appropriate accuracy.展开更多
A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA10...A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.展开更多
The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and...The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and strain rate range of 0.001–0.1 s^(-1).The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters.The critical stress and strain decreased with increasing temperature and decreasing strain rate.The investigation results of the microstructure and true strain–stress diagrams showed that dynamic recovery,dynamic recrystallization(DRX),and twinning mechanisms were caused during the hot deformation of pure copper.Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20μm whereas DRXed fine-grain took place in interior grains for samples with larger IGS.The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS.The critical strain rate and the temperature were obtained at 0.01 s^(-1) and 973 K,respectively,for the sudden change in the grain growth rate.Also,twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.展开更多
文摘The thermomechanical behavior of precipitation-hardened aluminum alloy AA7022-T6 was studied using isothermal compression at temperatures of 623−773 K and strain rates of 0.01−1 s^−1.The experimental results indicated that dynamic recrystallization(DRX)is a predominant hot deformation mechanism,especially at elevated temperatures and low strain rates.The modified Johnson−Cook(J−C)and the strain compensated Arrhenius-type models were developed to predict the hot flow behavior under different deformation conditions.The correlation coefficients of modified J−C model and the strain compensated Arrhenius-type models were 0.9914 and 0.9972,respectively,their average relative errors(ARE)were 6.074%and 4.465%,respectively,and their root mean square errors(RMSE)were 10.611 and 1.665 MPa,respectively,indicating that the strain compensated Arrhenius-type model can predict the hot flow stress of AA7022-T6 aluminum alloy with an appropriate accuracy.
文摘A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.
文摘The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and strain rate range of 0.001–0.1 s^(-1).The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters.The critical stress and strain decreased with increasing temperature and decreasing strain rate.The investigation results of the microstructure and true strain–stress diagrams showed that dynamic recovery,dynamic recrystallization(DRX),and twinning mechanisms were caused during the hot deformation of pure copper.Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20μm whereas DRXed fine-grain took place in interior grains for samples with larger IGS.The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS.The critical strain rate and the temperature were obtained at 0.01 s^(-1) and 973 K,respectively,for the sudden change in the grain growth rate.Also,twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.
