الفهرس 
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Abstract
Friction Stir Welding (FSW) is a solid state welding process which is used for welding similar and dissimilar materials. The process is widely used because of its production of sound welds and does not have common problems such as solidification and liquidation cracking associated with the fusion welding techniques. The FSW of Aluminum and Aluminum alloys have been used commercially; and recent attention is focused on joining dissimilar materials such as aluminum alloys. The aim of this study is to explore the boundaries of the so-called welding window, within which a good quality welds can be produced, for the friction stir welding of AA5083 - AA5754 and AA5083 -AA7020 using a systematic set of rotation and traverse speeds. In this work, the microstructurally related characteristics have been examined in details, including hardness and grain size. In addition, the tensile properties have been studied. The observed variations were correlated and contrasted with the observed and predicted thermal distributions. Experiments were done at rotational speeds of 300, 400, 500 and 600 rpm. Four travel speeds of 20, 40, 60 and 80 mm/min were applied and the position of dissimilar alloys from advancing and retreating sides has been changed. All other process parameters were kept constant; i.e., tilt angle 30 , plunge rate 0.1 mm/sec, tool rotation clockwise. Joints were obtained by positioning the tool probe between the two alloys sheets with 0 mm offset, and employing selected processing parameters. After FSW, macrostructure and microstructure analyses were done using optical microscopy and electron back scattered diffraction on specimens that sectioned transverse to the welding direction. To have an insight into the mechanical properties, Vickers macrohardness measurements were carried out. Furthermore, fracture surface of the tensile specimens were investigated using scanning electron microscopy. The results have shown that a good mixing of the alloys is accomplished and a strong weld was formed, with a uniform distribution in the stir zone due to the low heat input in comparison with fusion welding. The strength of the joint was comparable with the strength of base materials for both joints. A joint strength of 96.5% of the base alloy was reached at the welding conditions: pin rotation of 400 rpm and travel speed of 60mm/min for the joint AA5754 - AA5083, while and strength 97.5% of the base alloy was reached at tool rotation of 500 rpm, and travel speed of 20mm/min for the joint AA5083 - AA7020.