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Thesis
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Studii şi cercetări referitoare la extrudarea unghiulară în canale egale (ECAE) a aliajelor de aluminiu
Şerban, Nicolae
2012-09-29
Abstract: Studies and researches regarding the equal channel angular extrusion (ECAE) of aluminium alloys Author: Eng. ȘERBAN C. NICOLAE; Scientific coordinator: Univ.prof.dr.eng ȘABAN RAMI Equal channel angular extrusion (ECAE) is an efficient method of refining grain size through severe plastic deformation (SPD) in producing ultrafine grained materials (UFG) and nanomaterials (NM). It consists mainly of pressing test samples (generally square or round) through a die containing two channels that are equal in cross section (and also identical to the workpiece cross section) and intersect at a certain angle ϕ. An additional angle of ψ defines the arc of curvature at the outer point of intersection of the two channels. Grain refinement is obtained as a result of the imposed deformation by simple shear which occurs throughout the theoretical shear plane. Despite the introduction of a very intense strain as the sample passes through the shear plane, the sample ultimately emerges from the die without experiencing any change in the cross-sectional dimensions. Since the cross-sectional area remains unchanged, the same sample may be pressed repetitively to attain exceptionally high strains and an advanced microstructure refinement. Ultrafine grained and nanostructured aluminium alloys presents a series of advantages which makes them of high interest for various structural applications, especially in the automotive, aerospace and naval industries. The main goal of this PhD thesis was to refine the microstructure of a commercial 6063 aluminium alloy up to submicrometer range and thereby to obtain ultrafine grained (UFG) or even nanocrystalline (NC) microstructures by means of severe plastic deformation using ECAE processing and consequently to obtain superior, enhanced mechanical properties for the processed material. In the same time, it was considered the influence of the particular ECAE processing conditions on the microstructural characteristics and mechanical properties of 6063 aluminium alloy and also the determination of the optimum severe plastic deformation operating mode for the case of 6063 ECAE processing. The specimens were processed for a number of passes up to nine, using three die channel angles: 90°, 100° and respectively 110°. It was determined the pass number (N) and the die channel angle (ϕ) influence on the microstructure and the mechanical properties of 6063 aluminium alloy. The investigated material was characterized from structural point of view (optical emission spectroscopy – OES, X-ray diffraction – XRD, optical microscopy – OM, scanning electron microscopy – SEM) and also in terms of mechanical behaviour (compression and microhardness tests, fracture surfaces analysis) in the as-received condition and after ECAE processing according to the PhD thesis experimental program. The experimental setting and the working tools (die-sets, punches etc.) required for 6063 aluminium alloy severe plastic deformation via ECAE processing were conceived, designed and made as a result of this present work
Keyword(s): Deformare plastică la rece -- Teză de doctorat ; Aluminiu -- Aliaje -- Extrudare la rece -- Teză de doctorat ; Materiale nanostructurate -- Teză de doctorat
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Record created 2017-02-14, last modified 2017-02-14
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