| Summary: | 碩士 === 中州科技大學 === 機械與自動化工程系 === 103 === Because of the high “strength to weight” ratio and good corrosion resistance, aluminum and its alloys have been used extensively. The joint characteristics of friction-stir-welded 6061 alloys, especially concerning the improvement of mechanical properties at the weld zone, were observed with various FSW (friction stir welding) speeds and rotation. The mechanical properties of the weld zone are less inferior in comparison to that of the BM. The tensile strength of the SZ is also lightly lower and shows below 180 Mpa, i.e. at least 80%~90% that of the BM. The hardness of the weld zone shows more uniform distribution than that of the BM because some defects are remarkably reduced and the eutectic Si particles are dispersed over the SZ. The microstructures of the weld zone are composed of SZ (stir zone), TMAZ (thermo-mechanical affected zone) and BM (base metal). The microstructure of the SZ is great different from that of the BM. The eutectic Si particles are dispersed homogeneously in primary Al solid solution. TMAZ, where the original microstructure was greatly deformed, is characterized by dispersed eutectic Si particles aligned alone the rotational direction of the welding tool. These regions are mainly formed at the advancing side and the upper region of the retreating side. Therefore, the FSW is well applied to the joining of the forge Al alloys.
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