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Materials 2019, 12(2), 227; https://doi.org/10.3390/ma12020227

Embrittlement Due to Excess Heat Input into Friction Stir Processed 7075 Alloy

Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan
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Received: 12 December 2018 / Revised: 28 December 2018 / Accepted: 8 January 2019 / Published: 10 January 2019
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
PDF [4543 KB, uploaded 10 January 2019]   |   Review Reports

Abstract

The grain size of high strength 7075 hot-rolled aluminum plates was refined by a friction stir process (FSP) to improve their mechanical properties. The results of the tensile ductility tests, which were conducted at various tool rotational speeds, in the friction stir zone indicate significant tensile ductility loss, which even resulted in a ductile-to-brittle transition (DBT). DBT depends on the tool rotational speed. Our 1450 rpm specimens showed large data fluctuation in the tensile ductility and the location of the fracture controlled the formation of friction stir induced bands (FSIB). The crack initiation site located at FSIB was due to the tool rotational speed (1670 rpm). A higher heat-input causes the formation of FSIB, which is accompanied with micro-voids. This contributes significantly to tensile cracking within the stir zone after the application of the aging treatment. This investigation aimed to determine the dominant factor causing tensile ductility loss at the stir zone, which is the major restriction preventing further applications.
Keywords: 7075 aluminum alloy; friction stir process (FSP); tool rotational speed; tensile ductility; ductile-to-brittle transition (DBT) 7075 aluminum alloy; friction stir process (FSP); tool rotational speed; tensile ductility; ductile-to-brittle transition (DBT)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Ku, M.-H.; Hung, F.-Y.; Lui, T.-S. Embrittlement Due to Excess Heat Input into Friction Stir Processed 7075 Alloy. Materials 2019, 12, 227.

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