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Metals 2017, 7(10), 423;

Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds

Department of Mechanical Engineering, University of Canterbury, Christchurch 8140, New Zealand
Advanced Manufacturing Centre, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Durian Tunggal 76100, Melaka, Malaysia
Author to whom correspondence should be addressed.
Received: 4 September 2017 / Revised: 3 October 2017 / Accepted: 6 October 2017 / Published: 11 October 2017
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BACKGROUND—The solid-phase joining of A6082-T6 plates by bobbin friction stir welding (BFSW) is problematic. Better methods are needed to evaluate the microstructural evolution of the weld. However, conventional Al reagents (e.g., Keller’s and Kroll’s) do not elucidate the microstructure satisfactorily, specifically regarding grain size and morphology within the weld region. APPROACH—We developed innovative etchants for metallographic observations for optical microscopy. RESULTS—The macrostructure and microstructure of A6082-T6 BFSW welds were clearly demonstrated by optical microscopy analysis. The microetching results demonstrated different microstructures of the Stir Zone (S.Z) distinct from the Base Metal (B.M) and Heat Affected Zone (HAZ) & Thermo-mechanical Affected Zone (TMAZ). The micrographs showed a significant decrease in grain size from 100 μm in B.M to ultrafine 4–10 μm grains for the S.Z. Also, the grain morphology changed from directional columnar in the B.M to equiaxed in the S.Z. Furthermore, thermomechanical recrystallization was observed by the morphological flow of the grain distortion in HAZ and TMAZ. The etchants also clearly show the polycrystalline structure, microflow patterns, and the incoherent interface around inclusion defects. ORIGINALITY—Chemical compositions are identified for a suite of etchant reagents for metallographic examination of the friction-stir welded A6082-T6 alloy. The reagents have made it possible to reveal microstructures not previously evident with optical microscopy. View Full-Text
Keywords: Bobbin-FSW; stir zone; HAZ; TMAZ; A6082-T6; metallography Bobbin-FSW; stir zone; HAZ; TMAZ; A6082-T6; metallography

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Tamadon, A.; Pons, D.J.; Sued, K.; Clucas, D. Development of Metallographic Etchants for the Microstructure Evolution of A6082-T6 BFSW Welds. Metals 2017, 7, 423.

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