الفهرس 
Chapter (1): IntroductionOnly 14 pages are availabe for public view
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Abstract
Friction stir welding (FSW) process is considered to be one of the most advances in solid-state welding techniques. The process offers many advantages over other fusion welding processes as it consumes less energy, experiences fewer residual stresses, and distortions, it can be used also to join dissimilar materials. Besides, to be a green technology, no fumes or sputters are emitted during the process. On the other hand, some certain limitations were encountered in FSW process, such as high welding loads, high torque needed, and low welding speeds. To overcome these limitations, as well as, extending the process capabilities and feasibilities, several modifications and advances have been applied to FSW process. One of these modifications is to use ultrasonic vibration as an auxiliary energy source to assist the process by the acoustic softening effect. In the present study, the effect of ultrasonic vibration on the microstructure, mechanical properties in terms of tensile properties and micro-hardness, weld appearance, weld formation, and defects was investigated by conducting a comparative study between conventional FSW (CFSW) and ultrasonic-assisted FSW (UAFSW). UAFSW was also optimized using the Taguchi technique to determine the optimum condition of process parameters and analyzing the effect of process parameters on the response. A thermal finite element model was developed to predict the temperature contours, temperature distribution, and thermal cycles resulting from UAFSW process. the model was then validated by comparing the simulated results to the experimentally measured data. The results have shown that ultrasonic vibration causes grain refinement at the stirring zone as well as its desirable role in enhancing the mechanical properties and eliminating some weld defects, especially at high welding speeds. Taguchi analysis has shown that a rotational speed of 800 rpm, a welding speed of 80 mm/min, and a vibration amplitude of 20 𝜇𝑚 is the optimum condition.