Work hardening in heterogeneous alloys - A microstructural approach based on three internal state variables

A new work-hardening model for homogeneous and heterogeneous cell-forming a lloys is introduced. It distinguishes three internal state variables in ter ms of three categories of dislocations: mobile dislocations, immobile dislo cations in the cell interiors and immobile dislocations in the cell walls. For each dislocation population an evolution law is derived taking into acc ount dislocation generation, annihilation and storage by dipole and lock fo rmation. In particular, these rate equations take into account the number o f active glide systems and, thus, introduce texture in the model in additio n to the Taylor factor. Microstructure is represented by the dislocation ce ll structure as well as second-phase particles, which may undergo changes b y precipitation and Ostwald ripening. Interaction of mobile dislocations wi th the microstructure is taken into account through an effective slip lengt h of the mobile dislocations. For the same set of parameters, the predictions are in excellent agreement with measured stress-strain curves of both a precipitation-hardened alumini um alloy (Al-4.16 wt% Cu-1.37 wt% Mg, AlCuMg2) and a precipitation-free mod el alloy (Al-0.35 wt% Cu-0.25 wt% Mg), the composition of which corresponds to the matrix of the two-phase alloy. (C) 2000 Acta Metallurgica Inc. Publ ished by Elsevier Science Ltd. All rights reserved.