الفهرس 
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Abstract
Friction stir welding (FSW) as a promising solid-state process can avoid the formation of solidification cracking and porosity associated with fusion welding processes and significantly improve the weld properties of aluminum alloys. Meanwhile it is a thermo-mechanical approach aims at altering the microstructural and mechanical properties of material in stirred zone in order to obtain the highest performance of the weld joint. The present study addresses FSW of AA-7075 aluminum alloy in T6 temper condition. The effect of variation in the rotational (ω) and travel speeds (v) is examined on the mechanical properties and microstructure of investigated alloy. The values of rotational speed are 300 and 600 rpm while travel speed are 25, 75 and 125 mm/min. The results show that with increasing rotational speed and decreasing travel speed (i.e. increasing ω/v) the grain size of the stirred zone increasing and the hardness value in stirred zone decreasing. A post-weld heat treatment (standard T6- temper) to as-weld 7075 Al-alloy was carried out. The obtained results indicate that the hardness values across the joint significantly increased, while the toughness of the joints deteriorated. The grain size in the stirred zone slightly increased (for example from 2.44 ± 0.26 to 3.65 ± 0.54 µm) after the post weld heat treatment. These results imply that the effects of the post-weld heat treatment (PWHT) on the mechanical properties of the joints are related not only to the base material conditions, but also to the PWHT processes. The present results demonstrates the effect of the post-weld solution-ageing heat treatment on the mechanical properties of 7075 Al-alloy FSW joints. The emphasis is placed on the type and morphology of precipitates evolved and their effect on the tensile properties and fracture of the joints