Study On Microstructure And Properties Of 7A60 Aluminum Alloy By Friction Stir Processing

Friction Stirring Processing (FSP) was a novel solid state processing technology of metal surface, which was launched in 1999 by Mishra from the University of Missouri. And its processing principle was based on the stirring friction welding (FSW) in 1991 from the Institute of England Welding. According to the different depth of the processing area, the FSP was divided into the Volume FSP(VFSP) and the Surface FSP(SFSP).The machining process can realize microstructure refinement, homogenization and densification of metal workpieces using the mixing head by the severe plastic deformation, mixing, crushing effect of the mother material in the processing area. The FSP can improve strength, hardness, corrosion resistance and superplastic properties of aluminum alloy. Meanwhile, the microstructure of aluminum alloy was modified and its crystal was also refined.Combining the numerical simulation and experiment, the 7A60 high strength aluminum alloy was tested by two dimensional friction stir welding system in this paper. The distribution law of temperature field in the different processing parameters and the peak temperature occurred the processing were investigated by temperature field simulation. Then the relative processing parameters was optimized further. The different processing parameters for the performance improvement of the material microstructure were verified by some experiments, the microstructure analysis and mechanical properties test. The principle of performance change was explained via the relative measured methods from the microscopic point.The simulation results indicated that the total trend for the peak temperature became smaller with the increasing feed rate. And the peak temperature of the machining process was larger with the increasing of the rotational speed. Rotation speed had obvious influence on temperature than the feed speed. The reasonable temperature distribution was obtained and the ω/v value between 5.3 and 8. The experimental results denoted that the processing crystal particle was smaller than the mother material significantly. The reason for this change was that the special laws of thermal cycling, the dynamic recrystallized crystal particle had no longer grew up, getting the fine and the second uniform organization distribution of crystal eventually.The center hardness of 4#(600r/min×80min/min)was the highest and its size was 159.0 HV. But the the lowest center hardness was 3#(600r/min×100mm/min), the corresponding size was 137.8HV. The highest tensile strength for 4# highest hardness was 364.7MPa, exceeding 27.1% for mother material. But the tensile strength of 3# is lowest and the value is 310.9MPa, surpassing 8.3% for mother material. The research work deepened the depth and breadth of the FSP study, broadening the change process of 7A60 aluminum alloy. This can provide the research basis about the application of 7A60 aluminum alloy and also a reference for improving the overall strength of the component materials at the same time.