Large Thickness Of 6061-t6 Aluminum Alloy Plates Friction Stir Welding

6061-T6 aluminum alloy, a heat-treatable strengthened aluminum alloy of Al-Mg-Si alloys, with the advantages of medium strength, good plasticity and toughness, corrosion and crumpling resistance,has been widely used in the fields of aerospace, marine, railway vehicles,etc. However, due to the problems such as welding cracks and pores, large welding deformation, and low mechanical properties of welds raised in the traditional welding method for 6061-T6 aluminum alloy, the large thickness welding becomes more difficult Friction stir welding (FSW), a new solid-state welding technique,provides a new solution for thick 6061-T6 aluminum alloy plate connection.The temperature field and flow field in the FSW welding process are important factors affecting the micro-structure and mechanical properties of welded joint, hydrodynamic theory and computational fluid dynamics software FLUENT are applied to construct the flow and temperature field model of 6061-T6 friction stir welding. The numerical modeling results are in basic agreements with the experiment results.Based on numerical model, Friction-stir-weld on 6061-T6 in 22mm and 60mm thickness were separately carried out successfully by single and dual pass. Different welding speeds are used in the welding experiment of 22mm 6061-T6 plate, the results show that the welding speed plays an important role in the formation and physical property of the weld joint. In the dual pass weld experiment of 60mm 6061-T6 plate, when the rotating speed is 1000r/min and welding speed is 80mm/min, the weld's tensile strength reaches 218MPa, is 70% of the base metal. Compare the microstructure and mechanical property of the joint, the result demonstrates that the strengthening phrase's "Re-solution" and "over-aging" caused by welding thermal cycle are the main reason of the degradation of the physical property of the welding joint. The metallography and electron microscope of the microstructure of the joint with different thickness are observed, the results indicate that due to the huge different temperature distribution in the thickness direction along the welding zone, the morphology and distribution of the microstructure have undergone major changes, which was a big challenge of the aluminum alloy plate welding with large thickness.Base on 22mm and 60mm 6061-T6 aluminum alloy plates friction stir welding, we explored more sophisticated welding process parameters and laws of friction stir welding technique,extended it to the welding process of different thickness 6061-T6 aluminum alloy plate,moreover the maximum welding thickness was raised to 70mm, and successfully applied to the welding of large DC motor aluminum alloy plates.