الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Friction Stir Welding (FSW) is a solid state joining process developed in 1991 by The Welding Institute (TWI). The performance of the resultant welded joint in high strength aluminum alloys sets FSW apart from traditional fusion welding. In the present investigation, dissimilar AA5754-O and AA6061-O aluminum alloy plates were joined using friction stir welding (FSW). The plates were joined at welding speeds of 50, 100 and 150 mm/min and at tool rotational speeds of 400, 600 and 800 rpm. Two tool pin profiles of cylindrical threaded (CT) and two flat sides cylindrical (TFSC) were used. The aim of this study is to evaluate the effect of the previous welding parameters on the microstructural and mechanical properties of the FS welded joints. The results revealed that all joints had a macrostructure free from defects as cavities, except a cavity of 1 mm and 0.5 mm width formed at the advancing side were detected in the joints welded at (400 rpm and 150 mm/min. having a TFSC pin profile) and (600 rpm and 50 mm/min. having a CT pin profile) respectively. The plates welded at higher tool rotational speed and/or lower welding speed had a larger grain size. For example, the joints made with CT pin profile at 800 rpm and 50 mm/min has a grain size of 14 μm which is reduced to 10.89 μm when the tool rotational speed was lowered to 400 mm/min. But as the tool rotational speed was increased the stirring action was increased and the second phase(Mg2 Si) broke down into more fine particles which affect the mechanical properties.
The hardness profiles of the welded regions increase gradually from the retreating side (i.e. AA6061-O side) toward the advancing side (i.e. AA5754-O side). However, the hardness decreases slightly when approaching the TMAZ and HAZ regions then increases in the AA5754-O base metal. The NZ
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of the joints made at 600 rpm and 100 mm/min by the two pin profiles had the highest average Vickers hardness of 59 VHN. Tensile tests showed that, the fracture of the specimen occurred in the HAZ zone of the retreating side which has less hardness. Few specimens fractured in the NZ. The joint efficiency varied from 76 to 94 % and the percent elongation was in the range from 5 to 14%. The joint made by TFSC pin profile at 800 rpm and 50 mm/min has the highest ultimate tensile strength (UTS) of 142 MPa with joint efficiency of 94% and percent elongation of 14 %.