Optimization of friction stir welding process for joining of aluminum to steel

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Background****Friction stir welding (FSW) is a solid-state welding process, which can produce high quality welds of several materials difficult to weld. Due to the low energy input used, FSW creates high strength joints with reduced distortion. Being capable of handling variations inherent to high volume production, advantages of FSW also include improved process robustness and reduced production costs. FSW has rapidly gained acceptance for the manufacturing of lightweight structures. The rising demands for improved fuel economy have driven the efforts for the development of innovative aluminum products for transportation vehicles. However, the majority of the structures used in vehicle involve steel and the employment of lightweight materials in steel structures is of great interest. The use of the combination of steel and aluminum alloys has been increasing in fabrication and many efforts to weld steel to aluminum alloy have been invested.*******Problem statement****Although the benefits of FSW to join aluminum to steel are clear, the applications of FSW to alloys with high melting temperature have been limited due to stringent demands on the tool.*The FSW tool is exposed to severe stress and high temperatures particularly for the welding of hard alloys such as steels, which promotes tool degradation. For these alloys, the commercial application of FSW is limited by the high cost and short life of FSW tools. Wear has a huge influence on tool life of FSW of steel. Therefore, it is important to identify and understand the wear mechanisms present. Tool wear is influenced by many factors, which include the composition of the tool and the workpiece material, the nature of the welding operation, the welding conditions and machine setup and the tool geometry.*******Methodology proposal and expected results****In FSW, only limited work has been done on tool wear mechanisms. The goal of the proposed project is to identify the primary wear modes of tools used to produce aluminum to steel FSW joints and to explain the mechanisms contributing to tool wear and failure. With the help of existing wear models, critical factors that influence the behavior of tool wear in FSW will be identified. This knowledge will be applied to optimize welding conditions and tool performance. The identification of dominant wear mechanisms for this type of dissimilar welding will have a significant impact on the Canadian industry, because of its potential for the automotive and other industrial sectors. For the automotive industry, replacing steel with aluminum will decrease the weight of vehicle resulting in reduced fuel consumption and greenhouse gas emissions.******