Under certain conditions of strain rate and temperature, the plastic flow in metallic materials can become heterogeneous at the macroscopic scale and lead to strain localization. The Portevin Le Chatelier (PLC) phenomenon is a commonly observed heterogeneous plastic flow. In Al-Mg alloys, it appears around room temperature and, consequently, can have a detrimental effect on the mechanical performances of structures. This unstable and heterogeneous behavior originates from the Dynamic Strain Aging (DSA) resulting from the dynamic interaction between mobile dislocations and solute atoms. The solute atoms diffuse to mobile dislocations during their temporary arrests at local obstacles (precipitates, forest dislocations, etc.) and increase the plastic flow stress. When the waiting time of dislocations at obstacles is of the order of the diffusion time of the solute atoms, the Strain Rate Sensitivity (SRS) of the flow stress becomes negative and leads to unstable plastic flow. In the present work, we studied jerky flow in the Al-2%Mg alloy at room temperature with a hard testing machine (i.e., constant driving velocity). Under these conditions, instability characteristics are studied in relation with dislocations structures obtained by transmission electron microscopy (TEM). A numerical study, based on the evolution of dislocations densities during plastic deformation, allowed to account for several jerky flow characteristics. These results are discussed in accordance with DSA mechanisms.
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