Multiscale Modelling of Back-Stress during Equal-Channel Angular Pressing

摘要

Equal-channel angular pressing (ECAP) is a well known process to produce ultrafine-grained materials. The mechanical properties of these materials, including a compression-tension asymmetry and a transient hardening saturation in the beginning of the flow curve, largely depend on the evolution of the microstructure during ECAP. Consequently, the back-stress induced by the dislocation microstructure exhibits kinematic hardening at the macroscopic scale. In this paper, commercial purity aluminium AA1050 is processed by ECAP route C. Tensile and compression specimens are machined from the post-ECAP samples. The back-stress level is estimated from the different yielding strengths of tensile tests and compression tests. Then two different models, a macroscopic phenomenological Teodosiu-type model and a microscopic dislocation-based multi-layer model, are used to predict the back-stress values. A set of parameters for Teodosiu's model is identified from simple shear tests, Bauschinger tests and orthogonal tests. The dislocation-based multi-layer model is based on the Estrin-Tóth dislocation model and Sauzay's intragranular back-stress model. The predicted and experimental back-stresses due to ECAP are compared and critically evaluated.