| Friction stir welding (FSW) is a novel solid-state joining technique. As compared to the conventional fusion welding methods, FSW has many prominence benefits, such as low distortion of workpiece, absence of cracking, gas cavity. In this paper, the friction stir welding is used to weld thick aluminium alloy plate, and the designing of friction stir welding tools, the mechanical properties of the joints, the formation of weld, and the microstructures of the FSW joints are studied to explain the feasibility of FSW thick aluminous alloy plate and lay a foundation for further application of FSW technology.Friction stir welding of a 10mm thick LF6 Al alloy plate has been successfully performed. The technological parameters have an very important effect on weld formation. The results show that thick plate should be welded at lower rotation speed and welding velocity. The highest strength of joints is equal to that of base metal, and can be obtained at a welding velocity of 50mm/ min and rotational speed of 150rpm, which are regarded as the most optimum parameters under experimental conditions. A formation process model of plain arch is successfully established to explain the formation process of plain arch.The micro analysis demonstrate that the cross section of FSW joint can be divided into weld nugget zone, thermal mechanically affected zone, heat affected zone and base metal. The microstructure of horizontal section is different at different location. In the middle section of weld, the flow lines of weld nugget on the advacing side are similar to that of plain arch plain arch on the weld surface. The flow lines like"S"under the tool shouder in the longitudinal section of the weld are observed and they have uniform distance.During the friction stir welding, the interface reaction occurs in the contact surfaces of welding tool to aluminium alloy, and chemical compound layers are produced. The chemical compound layers coud affect heat production and materials flow in the weld.
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