Abstract
The work addresses the effects of nanosize particles and grain refinement on the patterns of stress serrations and kinematics of deformation bands associated with the Portevin–Le Chatelier instability of plastic flow. Ultra-fine-grained microstructure was obtained using equal-channel angular pressing of the initial coarse-grained alloy. Tensile tests were carried out on flat specimens at strain rates in the range from 3 × 10−5 to 1.4 × 10−2 s−1. Using local extensometry techniques, it was found that the presence of nanoscale precipitates promotes quasi-continuous propagation of deformation bands in the entire strain-rate range. The grain refinement leads to a transition to relay-race propagation at high strain rates and static strain localization at low rates. The results are discussed from the viewpoint of competition between various dynamical modes of plastic deformation associated with collective dynamics of dislocations.
Highlights
The elaboration of new alloys sustains strong interest to the phenomenon of unstable plastic flow, or the Portevin–Le Chatelier (PLC) effect [1], caused by interaction of dislocations with solute atoms
equal-channel angular pressing (ECAP) resulted in the formation of a fully recrystallized structure composed of equiaxed grains with the size reduced to less than 1 μm
CG condition is that the quasi-continuous mode of deformation plastic instability, instability, whereas whereas the the well-known behavior behavior suggests suggests aa transition transition to to relay-race relay-race propagation propagation band propagation persists over the entire strain-rate domain of plastic instability, whereas the well-known behavior suggests a transition to relay-race propagation and to static deformation bands when the imposed strain rate is decreased
Summary
The elaboration of new alloys sustains strong interest to the phenomenon of unstable plastic flow, or the Portevin–Le Chatelier (PLC) effect [1], caused by interaction of dislocations with solute atoms. The plastic instability manifests itself as strain localization in deformation bands giving rise to serrations on the stress-strain curves [2]. Such localization can have detrimental consequences on the production and utilization of industrial pieces, in particular, because of the formation of traces on the surface of the product and a reduced ductility. Plastic deformation of Al-based alloys is prone to instability in a wide range of experimental conditions [10]. Binary Al-based alloys, especially 5000 series with Mg as the main impurity, Metals 2017, 7, 325; doi:10.3390/met7090325 www.mdpi.com/journal/metals
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