NEW FINDING IN FRICTION STIR WELDING (FSW): JOINING CLAD MATERIAL, LIQUID-REPELLED UNDERSEA FSW, AND ADHESIVE ASSISTED COMPOSITE MANUFACTURING

Abstract

With significant demand for greenhouse gas reduction through energy-efficient manufacturing technology, Friction stir welding (FSW), a solid-state joining technology, has been promoted in several aspects of its application. This includes joining advanced light-weight materials, demonstrating its feasibility as an underwater wet welding technique for sub-sea industries, and the ability to produce lightweight metal matrix composites cost-effectively. In the case of joining advanced material systems, like bi-layer thin clad sheet material, welding is challenging as they are composed of different material layers in a single material system. Fusion welding processes for clad materials often lead to multi-layer delamination and introduce cast microstructures with possible solidification defects. Therefore, the application of FSW to the clad material system will be beneficial to have efficient joint fabrication for advanced vehicles in the automotive industry. Further, material intermixing of the surface cladding layer into the core and the strengthening mechanism of the joint are discussed based on microstructural observation. Likewise, using FSW as underwater wet welding technique is necessary to avoid the common solidification defects caused by fusion welding processes. However, the most notable of subsequent developments with FSW would be finding a way to divert seawater from the welded region while operating amid the sea. Thus, the newly developed gas pocket-assisted friction stir spot welding (GAFSSW) technique was developed, leading to new ways of reducing or eliminating the absorption of corrosive species (like chlorine) from seawater into the welded area. Furthermore, the quality of the processed region is studied and compared with conventional underwater friction stir spot welding (UFSSW) and FSSW in the air. The current results are consistent with the perspective for the development of UWW technology. This newly developed GAFSSW technique addresses most of the key challenges associated with focused area seawater drainage and solidification defects form in fusion processes. Producing low-cost light metal matrix composites (MMC) can also be another area of choice where FSW can be applied to improve the efficient green manufacturing of these composites. Several iii manufacturing processes have been employed to produce MMC, mainly casting, sintering, powder metallurgy, and other melt-based techniques. However, poor interfacial bonding, reinforcing particle agglomeration, and other common melt defects could be common issues with these traditional processing methods. Hence, friction stir processing (FSP), a solid-state material processing technology developed from the mechanism of FSW, can be an efficient method to produce composite materials. In FSP, tool stirring enables uniform distribution of reinforcements and controls other possible reactions between the matrix and reinforcements to achieve excellent synergy between strength and ductility. Consequently, a detailed study involving the correlation of microstructure and mechanical properties of GO-reinforced AMC prepared by single-pass FSP is much needed to establish this method as an alternative to the existing method.