| Friction stir welding (FSW) is a solid-state joining process which based on the friction welding. This new welding technique with uniqueness and superiority has been paid a great amount of attention by researchers ever since it was developed, and study of the welding performance of various materials also become one of the major fundamental researches. So far, the feasibility of FSW study has been shifted particularly from the joining of Al alloy to Cu, Ti, Mg alloys and stainless steel, steel metal. The objective of this work was to study the welding performance and parameters of FSW for joining copper, brass and dissimilar metal T2/H62, T2/A1, H62/A1 based on the previous study of FSW of experimental aluminum alloys.The study in joining homogeneous materials was focused on the characteristics of the joining, the microstructures, and mechanical properties of the FSW joints of copper, brass alloy with different thickness and parameters. The influence of varying rotational speed, traverse speed on the grain size and shapes in the nugget zone and thermo-mechanical zone during the joining of the homogeneous metal were examined and summarized, respectively. And the range of welding parameters for copper , brass alloy under experimental condition were achieved. It was also discovered that the micro-hardness of the copper or brass alloy joints by friction stir welding was low than that of base material. However, the average mechanical properties of the joint were higher than that of other conventional weld process.The investigations have been mainly carried out on the influence of different location of dissimilar metals and thickness on the quality of joint during the joining of dissimilar metals such as copper to aluminum alloy, copper to brass alloy. And the distribution of the two dissimilar metals in the joints and their components in the intersection was also analyzed from micro-point of view. The study showed that the thickness of the dissimilar metal plates (copper and aluminum alloy) was the main factor of the narrow range of welding parameters. The interfacial region was not totally uniformed blended, but constituted with grains of different shapes and mixed mode areas, meanwhile, a kind of banded transition structure with given width was formed. The intermetallic compounds generated during friction stir welding in the interfacial region were mainly Cu9Al4, Al2Cu in the joints of copper to aluminum alloy, while Cu5Zn8 in the joints of copper to brass alloy.The plastic flow in the various materials joints was also analyzed on the basis of previous studies. The study showed there were several areas with different plastic flow pattern in the cross-section of FSW joint. In this paper, the formation mechanism, structure feature and the location of onion rings were demonstrated. Furthermore, it was illustrated in particularly that the area with the welding defect generally appeared due to various influence factors and complex plastic flow.The result of the investigation proved that the joints of copper, brass alloy and copper to aluminum alloy could be successfully carried out by FSW when the optimal welding parameters were chosen. The results, which were of great practical value, not only provided a newly economical and reliable method for joining materials mentioned above, but also established foundation for the further study of FSW techniques.
|
PDF Full Text Request