الفهرس 
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Abstract
Friction stir welding is a modernistic solid-state welding technique which
characterized by an environmentally friendly process. FSW finds increasing use in fabricating components of aluminum alloys in sectors such as automotive, aerospace, and railways. Four tool rotational speeds vary from 230 to 470 rpm and three welding speeds 160,200, and 250 mm/min with kept the other parameters constant, to fabricating twelve FSW butt joints of similar AA6063-O aluminum alloys to investigate the effect rotational and welding speeds on impact
strength of joints at different test temperature room, -20°C, -40°C, and -60°C. The effect tool rotational and welding speeds on Surface roughness of joint and also on hardness distributions of different weld zones were investigated. The macrostructure and microstructure of the weld joints zones were evaluated to detect defects. For impact test temperature of room temperature, -20℃, -40℃ and-60℃, the maximum impact strength(J) was obtained at weld joint code (D), (H), (H), and (F) which recorded (92.69 J), (103.03 J), (114.79 J), and (109.25 J)
respectively. Impact strength increases as the tool rotational speed decreases and welding speed increases. the impact absorbed energy increases as the impact test sample temperature decreases to a certain level then return to decreases. At highest welding speed of 250 mm/min and lowest rotational speed of 230 rpm,
the maximum average hardness was obtained. The hardness of weld zone
increases as the welding speed increases and rotational speed decreases. At high tool rotational speed 470 rpm and low welding speed 160mm/min, the best surface roughness was obtained Ra=7.990 μm. onion ring patterns was observed in NZ of weld region, also kissing bond, lack of penetration and void defects were
obviously observed, which in turn weakens the weld zone.