Mechanism of Implementation of High Ductility in Ultrafine-Grained Aluminum after Annealing and Subsequent Deformation

Enhanced Ductility of High-Strength Ultrafine-Grained Aluminum Alloys at Ambient Temperature (Review)

“…According to Refs. [19,72], this approach is based on modification of the GB network structure. However, a number of questions remain unanswered:…”

“…Recently, a new approach (also based on grain boundary engineering) has been proposed to achieve high strength and high plasticity in UFG Al and some UFG Albased alloys structured by SPD, which consists in a special deformation-heat treatment (DHT) of the material after SPD processing. Such deformation-heat treatment includes low-temperature short-term annealing and subsequent small additional HPT deformation of UFG or NC alloys structured by HPT method [3,18,19,[72][73][74]. It has been demonstrated that the ductility of commercially pure (CP) aluminum processed by HPT can be significantly increased by short-term annealing at 150 °C and subsequent additional deformation by HPT to 0.25 turns at RT [3].…”

“…To explain the plastification effect, a theoretical model was proposed [19,72]. According to the model, the plastic deformation in UFG Al occurs through emission of lattice dislocations (LDs) from triple junctions of GBs containing pile-ups of GBDs, glide of the LDs across neighboring grains, their accumulation at and climb along the opposite GBs (Fig.…”

“…Thus, according to Refs. [19,72], the nature of the increase in plasticity due to deformation is associated with a change in the dislocation structure of the GBs (the degree of nonequilibrium of the GBs), which facilitates the emission of dislocations from triple junctions.…”

“…[18], the authors explain the effect of AIH in ARB Al by a decrease in the dislocation density in grain interior during annealing, which leads to a decrease in the sources of dislocations in the grains and, consequently, to an increase in the yield strength. Within the framework of the model [19,72], the AIH effect and a dramatic decrease in plasticity after annealing in HPTprocessed Al are due to relaxation of non-equilibrium HAGBs during annealing, which is accompanied by annihilation of extrinsic dislocations at GBs, which leads to depletion of the dislocation pile-ups, which are formed at triple junctions under external stresses (Fig. 8).…”