The instable plastic flow constitutes a major inconvenient during the formability of metallic materials. The Portevin-Le Chatelier (PLC) is one of these plastic heterogeneities. It leads to heterogeneous mechanical properties, reduces the ductility of the deformed material and creates areas very sensitive to the corrosion. The strain localization zones are characterized by a dilating behavior, which can cause the material rupture and, consequently, the failure of structures. The optimization of the homogeneous material formability is based mainly on the results of characterization and modeling of the unstable plastic flow. PLC instabilities are observed in different materials with different histories and in different conditions. In Al–Mg alloys, which provide a large variety of applications due to their low weight and high mechanical strength, jerky flow appears around room temperature in a limited range of strain and strain rate.

The PLC effect is characterized by a macroscopic spatio-temporal localization of plastic flow. It appears in the form of a repeated stress drops in the stress-strain curve at imposed strain rate. The produced strain localizations on the sample surface (PLC bands) are static at low strain rates (Type C). They move by jumps at intermediate strain rates (Type B) and propagate at elevated applied strain rates (Type A). Initiation of plastic flow is generally preceded by a certain critical plastic strain ec, which is strongly dependent on the temperature and on the applied strain rate. The microscopic origin of the PLC effect is associated to the dynamic strain aging (DSA) phenomenon resulting from the interaction between mobile dislocations and the clouds of impurities. The solute atoms diffuse towards dislocations during their temporary arrests at local obstacles and increases, consequently, the plastic flow stress. The repeated breakaway of dislocations from the solute clouds reduces the strain rate sensitivity (SRS) of the flow stress, which becomes negative. Therefore, the strain localizes into narrow deformation bands and gives rise to serrated stress-strain curve at constant applied strain rate.

In the present work, we have investigated the Portevin-Le Chatelier characteristics at room temperature in cold-rolled Al-2.5%Mg alloys. Tensile tests, performed in the strain rate range 10 -6-10 -1s-1, allowed to determine the range of instability and to study PLC characteristics as a function of strain and strain rate. We show that the reduction of the strain rate sensitivity of the flow strain is accompanied by a ductility reduction in the jerky flow domain. We interpret our results in accordance with dynamic strain aging mechanisms.