In the present investigation the mechanical behaviour of AA7075T651 and AA6061T6 aluminium alloys plates joined by friction stir welding (FSW) were evaluated. The effects of weld process parameter like tool rotation speed 650-1000 rpm and weld speed 30-40mm/min with square trapezoidal pin profile on mechanical properties were investigated. The welded joints were tested by means of by X-ray radiography, tensile, hardness and optical microscopy testing. The radiography revealed the presence of internal in FS welds and observed that increasing transverse speed increases the occurrence of weld defects. The hardness was found to be mixed effect with respect to tool rotations and transverse speed for similar FSW joints. But in dissimilar FSW joints, hardness decreases with increasing tool speed and weld speed and it was strongly affected by precipitate distribution. Difference in grain size and distribution was observed for different ranges of rotation and weld speed. پرونده مقاله