On the spatio-temporal characteristics of the Portevin-Le Chatelier effect in aluminium alloy AA5182: An experimental and numerical study

Abstract

The Portevin–Le Chatelier (PLC) effect and its spatio-temporal characteristics in the aluminium alloy AA5182 are studied experimentally and numerically in the current work. An extremely high-frequency camera (up to 1000 Hz) is utilized to capture the nucleation and propagation of the PLC bands in uniaxial tension tests with different applied strain rates. The spatio-temporal patterns and the strain accumulation are obtained from digital image correlation (DIC). A transition from continuous to discontinuous band propagation is observed with increasing strain rate. Finite element simulations are carried out using a modified Kubin-Estrin-McCormick (KEMC) model to reproduce the serration morphologies, spatio-temporal patterns and strain accumulation processes. Based on the comparison between experiments and modelling, it is revealed that the strain accumulation and strain ageing processes together decide the subsequent band nucleation. The PLC band inherently brings a strain heterogeneity to the specimen, which results in different levels of work-hardening across the specimen. The strain ageing process, which occurs both inside and outside the PLC band, is found to create another heterogeneity in terms of the solute strengthening. A unique local yield stress minimum leads to a propagating band, while multiple local yield stress minima give a jumping band behaviour. Using that equilibrium forces the work-hardening behind the propagating band to be balanced with the solute strengthening in front of the band, analytical expressions for the band strain and band velocity are derived and verified by the experimental data.