True Fracture Stress of UFG Samples of Al-6101 Alloy

The results of the study on determining the true fracture stresses of cylindrical samples with an ultrafine-grained structure of alloy 6001 obtained by the ECAP-C method are presented. These results are compared with similar data for a coarse-grained structure of the same alloy produced through standard heat treatment. This work was conducted to accurately describe the mechanical behavior of the material in both the coarse-grained (CG) and ultrafine-grained (UFG) states. The analysis revealed that the true strain to failure in the artificial aging (AA) state and the UFG state of alloy 6101, taking measurement errors into account, is the same. However, the true fracture stress of samples with a UFG structure is significantly higher than that of samples with an AA structure. The increase in strength and yield point resulting from ECAP-C processing is determined by the reduction in grain size according to the Hall–Petch relationship. An explanation for the increase in true fracture stress of samples during grain refinement is proposed on the basis of a compilation of the Hall–Petch relationship and the Zener–Stroh model, which involves a criterion for pore formation in particles when the stresses at the matrix/particle interface reach critical values.