Current Trends in Friction Stir Welding (FSW) and Friction Stir Spot Welding (FSSW)

The joining technology of similar and dissimilar materials plays a crucial role in various areas, include manufacturing. Many conventional welding techniques have been used over the years to successfully join various materials. Friction stir welding (FSW) and friction stir spot welding (FSSW) are solid state welding processes. This introduction gives a brief overview of the two processes, with the focus on FSW and FSSW between copper and aluminium, which are sometimes difficult to join by using conventional joining methods because of their different melting temperatures and their high chemical affinity. Furthermore, the applications of FSW and FSSW in various industrial sectors include robotics, aerospace and automotive areas. An overview of the experimental studies conducted in joining aluminium and copper was conducted. It was observed that FSW and FSSW of aluminium to copper has not yet been fully researched; but more studies are needed for FSSW, in order to optimize the process, which could lead to its expansion.

The development of laboratory work on friction stir welding (FSW) and friction stir spot welding (FSSW) FSW of dissimilar materials should provide a good insight into their possible industrial applications; and therefore, enhance their industrial development. Many applications in various industries, especially in the manufacturing sector, have led to the development of processes, such as FSW and FSSW for similar and dissimilar materials. Aluminium and copper have different properties including melting temperatures, which make the two materials difficult to join. Choosing suitable parameters, such as rotation speed, welding speed, and tool plunge depth and dwell time is important when fabricating sound FSWelds and FSSWelds. This chapter presents the current state of FSW and FSSW of aluminium and copper. An overview of the research conducted in the field of FSW and FSSW between aluminium and copper is summarized in terms of the microstructural evolution and the mechanical properties. The quality of the fabricated welds, spot welds and explanations of various properties of the welds by various researchers is presented and summarized. This could provide an insight into the current state of the two processes; and it could also lead to the optimization of the techniques by conducting more research in the field of FSW and FSSW Al/Cu. Furthermore, future scope on the usage of the two techniques is addressed.

Friction stir welding (FSW) and friction stir spot welding are solid state joining processes employed for the joining of similar and dissimilar materials. The processes are used by many researchers; because these processes produce sound welds; and they do not have common welding problems, such as solidification and liquefaction cracking related to the fusion welding methods. FSW and FSSW of similar aluminium and copper gained ground in the development of solid state joining processes. It may be observed that for FSW and FSSW of similar copper, many research studies were carried out using pure copper as the parent material. Whereas, for similar aluminium, almost the entire aluminium alloy series is utilized. Good quality joints with enhanced properties have been produced; and more studies are required, in order to fully optimize these processes. This could be beneficial in curbing global warming; since FSW and FSSW are both labelled as being environmentally friendly joining processes. In this chapter, FSW and FSSW research studies on similar aluminium and copper are briefly summarized in terms of the process parameters, the microstructural evolution and the mechanical properties.

The Friction stir spot welding technique was used to produce lap spot welds of AA1060 and C11000. Various process parameters and tool geometries were used to fabricate the welds. The microstructures of the produced spot welds produced were examined by using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical analysis of the cross sections of the welds was investigated by using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). A good Al/Cu material mixing was observed in most of the fabricated spot welds. The presence of copper rings on both sides of the keyhole with different lengths was observed in all the spot welds. The mapping using energy dispersive spectroscopy of a region of the keyhole/copper rings and the stir zone showed the presence of copper particles in the aluminium matrix. However. Very few aluminium particles were found in the copper rings. Intermetallic compounds were found in some of the spot welds.

Friction stir spot welding (FSSW) is a solid state welding process; and it is used to overcome the difficulties of joining aluminium and copper alloys. Dissimilar joining of AA1060 and C11000 using friction stir welding was carried out. The microhardness profile analyses were carried out and the probability distribution function (PDF) of the measured microhardness values was determined. Additionally, shear tensile tests were conducted. High microhardness values were obtained in the region close to the keyhole of most of the samples, which could be linked to the presence of intermetallic compounds in the stir zone of the spot welds. For the shear tensile test, only a nugget pull out failure mode took place in all the produced spot welds. The PDF revealed that the process parameters and the tool geometries significantly have an effect on the distribution of the microhardness values.

Aluminium and copper are widely used in engineering structures, due to their unique performances, such as higher electrical conductivity, heat conductivity, corrosion resistance and mechanical properties even though they have considerable differences in their melting points. In this study, the microstructure of the friction stir spot welds of aluminium and copper produced at various parameter combinations were analyzed by using a scanning electron microscope; while the residual stresses were studied by using the X-ray diffraction technique. Furthermore, the electrical resistivities of the joints was also measured. The evolving microstructure shows a good mixing in the produced spot welds with Cu particles present in the aluminium matrix. The formation of a copper ring/hook was evident in all the spot welds; and the length thereof increased with the shoulder plunge depth variation; while the spot welds produced at 1200 rpm for the two tool geometries exhibited a decrease and a slight increment in the length of the copper ring using a flat pin/flat shoulder and conical pin/concave shoulder, respectively. The obtained residual stresses results were compressive. The maximum residual stress of −116.8 MPa was measured on the copper ring of the welds produced at 800 rpm and 0.5 mm shoulder plunge depth, when using a flat pin and a flat shoulder tool. This was due to the generation of stress, when the copper was extruded into the aluminium sheets. Furthermore, the intensity of all the peaks using different process parameters decreased in comparison to the peaks generated by the parent materials and the effect of shoulder plunge depth on the full width at half the maximum (FWHM) was observed. The values of the measured electrical resistivities of the joints were higher than those of the parent materials.