| Summary: | 碩士 === 國立虎尾科技大學 === 材料科學與綠色能源工程研究所 === 102 === Friction stir welding is a fairly recent welding technique that utilizes a rotating cylindrical pin tool is forced to plunge into the plates to be welded and moved relative to each other along the joint line. During this operation heat is produced by friction between tool and workpiece. The highest temperature is lower than the melting temperature of the material, which means that welds can be produced without the need for melting or fusion, therefore are free of many of the defect formation issues associated with fusion welding, especially applies with high strength “difficult to weld” aluminum alloys. In the present work, a piece of copper foil was inserted along the faying surface of the weld. Friction stir welding were carried out to make dissimilar butt joints of 6082 and 6066 aluminum alloy plates with various tool rotational speeds. Microstructures of welds were examined through optical microscope, scanning electron microscope equipped with an energy dispersive spectroscopy system, and X-ray diffraction analysis. In addition, tensile tests and microhardness measurements were performed to evaluate mechanical properties. The results of the experiment revealed that the hardness of welds increased with increase rotation speed and a maximum value of 100Hv was achieved. Besides, the yield strength and ultimate tensile strength could be improved at high rotational speed, but the weldments were produced without a copper foil showed a significant inversely trends. The welds experienced the severe plastic deformation, the X-ray diffraction analysis on crystal orientation show that the diffraction intensity of (200) plane was significantly decreased, while accompanied by the increase in (111) plane intensity.
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