New constitutive equation utilizing grain size for modeling of hot deformation behavior of AA1070 aluminum
(School of Mechanical Engineering, Arak University of Technology, Arak, 38135-1177, Iran)
Abstract: 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 450 μm. 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.
Key words: constitutive equation; modified Johnson-Cook model; initial grain size; flow stress; hot deformation; AA1070 aluminum