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Microstructure and mechanical properties of the AA7075 tube fabricated using shear assisted processing and extrusion (ShAPE)

Nazari Tiji Sobhan A., Asgharzadeh Amir, Park Taejoon, Whalen Scott A., Reza-E-Rabby Md, Eller Michael, Pourboghrat Farhang

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

85--94

EN

Shear-assisted processing and extrusion (ShAPE) experimental setup and tooling were adopted for extruding thin-walled AA7075 aluminum tube from as-cast non-homogenized billet material in a single run. The mechanical and microstructural characterizations were performed on the as-extruded tube through tensile, hardness, electron backscatter diffraction (EBSD), and energy dispersive spectroscopy (EDS) tests. The results showed that the ShAPE process developed a significantly refined microstructure with uniform and almost equiaxed grain structure on both hoop and axial cross-sections of the extrudate as well as through the thickness of the material. The pole figures and inverse pole figures of the EBSD data showed a strong shear texture development, and it was found out that axial shear is the dominant deformation mechanism in the regions near the inner surface of the tube, while combined axial and torsional shears are the two dominant modes of deformation near the outer surface of the extrudate. As for the mechanical properties, there was an increase of 150 and 73% in the yield and ultimate strengths of the tube produced using ShAPE process, respectively, and an 18% decrease in maximum uniform plastic elongation compared to the conventionally extruded AA7075-O tube.

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Effect of shoulder features during friction spot extrusion welding of 2024-T3 to 6061-T6 aluminium alloys

Han Jinzhen, Paidar M., Vignesh R. Vaira, Mehta Kush P., Heidarzadeh A., Ojo O. O.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

292--308

EN

Friction spot extrusion welding process is successfully performed on dissimilar aluminum alloys of AA2024-T3 and AA6061-T6 under the influence of shoulder features. The joints were analysed by microstructural features and mechanical properties using conventional and advanced tools of visual inspection, optical microscopy, scanning electron microscopy, transmission electron microscopy, electron back scattered diffractions, tensile testing and hardness testing. The results revealed that the joining was obtained by combination of mechanical locking from extruded material of top surface to predrilled bottom surface and diffusion in solid state. The stir zone and plastically deformed metal flow zone were influenced by scroll shoulder and smooth shoulder features. The tensile specimen of scroll shoulder was resulted to higher fracture load of 6381 N whereas the same was 4916 N in case of smooth shoulder. The interface of between plastically deformed metal flow zone and base material of AA6061-T6 can be considered as critical/weakest zone in case of friction spot extrusion. The variations of hardness were observed in stir zone, plastically deformed metal flow zone and thermo-mechanically affected zone in case of friction spot extrusion welding process.

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Development of a repair process for manmade structures in space by using aluminium brazing and friction stir spot welding

Koehler Tobias, Yu Cheng-Nien, Schmidt Kiril, Graetzel Michael, Wu Yangyang, Bergmann Jean Pierre, Sekulic Dusan P.

Welding Technology Review

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2019

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R. 91, nr 9

39--49

EN

Small-sized parts and micrometeoroids’ impacts represent an increasing threat to artificial components/structures. The damages caused by them can be fixed using e.g., mechanical fixture with epoxy adhesive. However, the repair process is costly and only intended for a temporary fixing the penetration. In order to increase the life time of the repair, an approach for a more reliable process using similar materials is needed. The objective of this work is to develop a process for repairing manmade structures in space by generating joint properties similar to the base material. In this work, two approaches for repairing complex structures were considered. The first approach aims to fill a hole using liquid aluminium phases by brazing, and the second approach aims to fill the holes by a solid-state process (friction stir spot welding). In this study, different binding mechanisms of these two approaches were analyzed preliminarily by means of mechanical and/or metallographic characterization under terrestrial, controlled atmosphere conditions. Both concepts are proven feasible under these conditions. It has been shown that it is possible to realize a good filling of the hole with the investigated materials and under selected process conditions with both presented concepts.

PL

Uderzenia małych części i mikrometeorytów stanowią rosnące zagrożenie dla sztucznych komponentów/struktur. Uszkodzenia przez nie spowodowane można naprawić np. za pomocą mechanicznego osprzętu z klejem epoksydowym. Proces naprawy jest jednak kosztowny i służy jedynie do tymczasowego zatrzymania penetracji. W celu zwiększenia żywotności naprawy potrzebne jest podejście do bardziej niezawodnego procesu z wykorzystaniem podobnych materiałów. Celem tej pracy jest opracowanie procesu naprawy sztucznych konstrukcji w przestrzeni kosmicznej poprzez generowanie właściwości połączeń podobnych do materiału podstawowego. W pracy tej rozważono dwa podejścia do naprawy złożonych konstrukcji. Pierwsze podejście ma na celu wypełnienie otworu za pomocą faz ciekłego aluminium przez lutowanie, a drugie podejście ma na celu wypełnienie otworów metodą półprzewodnikową (zgrzewanie tarciowe punktowe z przemieszaniem). W tym badaniu wstępnie przeanalizowano różne mechanizmy wiązania tych dwóch podejść za pomocą mechanicznej i/lub metalograficznej charakterystyki w warunkach kontrolowanej atmosfery ziemskiej. Obie koncepcje okazały się wykonalne w tych warunkach. Wykazano, że możliwe jest prawidłowe wypełnienie otworu badanymi materiałami oraz w wybranych warunkach procesu przy obu przedstawionych koncepcjach.

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Friction Stir Radial Backward Extrusion (FSRBE) as a new grain refining technique

Jafarzadeh H., Babaei A., Esmaeili-Goldarag F.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1374--1385

EN

A new method entitled Friction Stir Radial Backward Extrusion (FSRBE) is presented for processing fine-grained tubes. In FSRBE technique, an initial pure copper billet is placed inside a cylindrical chamber. The billet is pushed toward a rotating tool which results in radial and backward flow of the material while is frictionally stirred. The microstructure evolution during FSRBE was investigated through experimental observations and cellular automaton (CA) modeling. The observations reveal that the microstructure with initial grain size of 75 μm was refined to a fine-grained structure with an average grain size of 12 μm. The results of tensile tests demonstrate slight improvement in the value of yield and ultimate strength, elongation and microhardness. The microstructural evolution during FSRBE processing in the micro-level was studied using a coupled cellular automaton algorithm and finite element model. First, the macroscopic plastic flow behavior of material during FSRBE was calculated using FEM simulation method. Next, by tracing the plastic strain, the strain rate and temperature, in the deformation domain of cellular automaton, the DRX kinetics of pure copper is obtained in a devised post-processing step. The microstructure observations showed that the proposed model predictions were in reasonably good agreement with the experimentally obtained results.