Microstructure, texture and tensile properties of ultrafine/nano grained magnesium alloy processed by accumulative back extrusion

An AZ31 wrought magnesium alloy was processed by employing multipass accumulative back extrusion process. The obtained microstructure, texture and room temperature tensile properties were characterized and discussed. Ultrafine grained microstructure including nano grains were developed, where the obtained mean grain size was decreased from 8 to 0.5 µm by applying consecutive passes. The frequency of both low angle and high angle boundaries increased after processing. Strength of the experimental alloy was decreased after processing, which was attributed to the obtained texture involving the major component lying inclined to the deformation axis. Both the uniform and post uniform elongations of the processed materials were increased after processing, where a total elongation of 68 pct was obtained after six-pass deformation. The contribution of different twinning and slip mechanism was described by calculating corresponding Schmid factors. The operation of prismatic slip was considered as the major deformation contributor. The significant increase in post uniform deformation of the processed material was discussed relying on the occurrence of grain boundary sliding associated with the operation of prismatic slip.Postprint (author's final draft

Microstructure, texture and tensile properties of ultrafine/nano grained magnesium alloy processed by accumulative back extrusion

An AZ31 wrought magnesium alloy was processed by employing multipass accumulative back extrusion process. The obtained microstructure, texture and room temperature tensile properties were characterized and discussed. Ultrafine grained microstructure including nano grains were developed, where the obtained mean grain size was decreased from 8 to 0.5 µm by applying consecutive passes. The frequency of both low angle and high angle boundaries increased after processing. Strength of the experimental alloy was decreased after processing, which was attributed to the obtained texture involving the major component lying inclined to the deformation axis. Both the uniform and post uniform elongations of the processed materials were increased after processing, where a total elongation of 68 pct was obtained after six-pass deformation. The contribution of different twinning and slip mechanism was described by calculating corresponding Schmid factors. The operation of prismatic slip was considered as the major deformation contributor. The significant increase in post uniform deformation of the processed material was discussed relying on the occurrence of grain boundary sliding associated with the operation of prismatic slip

Large deviations with applications to telecommunications

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EBSD characterization of repetitive grain refinement in AZ31 magnesium alloy

A polycrystalline Mg-3Al-1Zn was subjected to high plastic strains by applying accumulative back extrusion (ABE) process. Electron back scatter diffraction analyses were used to explore the grain refinement mechanisms. A novel grain refinement trend was found at large strains, where new recrystallized grains were repetitively refined through dynamic recrystallization. The grain size was diminishing continuously up to the fourth ABE pass, after which no further grain refinement was noticed upon successive passes. (C) 2014 Elsevier B.V. All rights reserved.Peer Reviewe

Microstructure and mechanical properties of IF steel deformed during plane stress local torsion

Mechanical joints are inherently vulnerable to failure because the presence of the joint hole causes a stress concentration in the vicinity of the hole. The need for improvement of material strength around a fastener hole can be satisfied by severe plastic deformation (SPD) to produce ultrafine grains. The ultrafine grained (UFG) alloys produced by SPD processing possess higher strengths than their coarse-grained counterparts as a result of the reduced grain size. However, in some circumstances such as SPD processing of Al-Zn and Al-Mg alloys the decomposition of supersaturated solid solutions competes with the Hall-Petch effect and leads to a more pronounced softening of the material [1]. Another drawback of SPD processes is that they involve bulk deformation and large energy consumption [2]. It is therefore desirable to enhance the global behaviour of the material by limiting improvement of the material property by SPD to the location at which it is needed. Localized severe plastic deformation (LSPD) techniques, such as forward spiral extrusion [3] and friction stir processing [4], involve lower energy consumption. They modify the properties of materials locally and create a gradient of grain refinement, resulting in significant improvement in the mechanical properties of the processed samples. However, these techniques cannot be used for strengthening the material around fastener holes, and thus a method for improving the strength of material around the hole is needed. To reinforce the mechanical properties of material around a hole, the plane stress local torsion (PSLT) process, which involves a plane stress axi-symmetric torsional loading, is introduced. The PSLT takes advantage of large shearing strains induced around the intended hole position, through torsional deformation [5]. As a result, the material flows plastically within a thin annular zone around the fastener hole (AZFH). Because of the limited penetration of the flow localization zone into the material, a major proportion of deformation energy is consumed within the AZFH. The PSLT therefore consumes much less energy than do bulk grain refinement techniques

Mechanical properties and microstructure of AZ31B magnesium alloy processed by I-ECAP

Incremental equal channel angular pressing (I-ECAP) is a severe plastic deformation process used to refine grain size of metals, which allows processing very long billets. As described in the current article, an AZ31B magnesium alloy was processed for the first time by three different routes of I-ECAP, namely, A, Bc, and C, at 523 K (250 °C). The structure of the material was homogenized and refined to ~5 microns of the average grain size, irrespective of the route used. Mechanical properties of the I-ECAPed samples in tension and compression were investigated. Strong influence of the processing route on yield and fracture behavior of the material was established. It was found that texture controls the mechanical properties of AZ31B magnesium alloy subjected to I-ECAP. SEM and OM techniques were used to obtain microstructural images of the I-ECAPed samples subjected to tension and compression. Increased ductility after I-ECAP was attributed to twinning suppression and facilitation of slip on basal plane. Shear bands were revealed in the samples processed by I-ECAP and subjected to tension. Tension–compression yield stress asymmetry in the samples tested along extrusion direction was suppressed in the material processed by routes Bc and C. This effect was attributed to textural development and microstructural homogenization. Twinning activities in fine- and coarse-grained samples have also been studied