| Summary: | 碩士 === 國立屏東科技大學 === 車輛工程系所 === 98 === Recently, the application of lightweighting materials to improve fuel efficiency and reduce pollutions has become the key issue in automotive industry. Aluminum alloy, magnesium alloy and composite, are then progressively used instead of steel for body structures. With the high strength, excellent corrosion resistance and easy recycling, aluminum alloy attracts the most attention in automotive industry. The deformation after welding significantly affects the quality of auto-body assembly. Friction stir welding (FSW) is a novel solid-state welding process. It takes the advantages of low heat input, high quality and small deformation and, is very suitable for aluminum alloy welding. But it can be problematic for thin aluminum alloy sheets. In this study, the shadow moiré technique is employed to investigate the FSW deformation characteristics for A6061-T6 aluminum alloy. Several process parameters such as tool’s rotation speed, welding speed, holding force and back plate material are investigated. A FEM model is first used to obtain the reasonable ranges of welding parameters. Then, the welding under different process parameters is performed and the warpage of the workpieces are measured. The results show that the temperature distribution is highly depends on the tool’s rotation speed and the situation of heat dissipation. In addition, the deformation is mainly affected by the longitudinal residual stress. Using a back plate with lower heat conductivity can speed the welding process and results in a smaller deformation.
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