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The microstructural changes, mechanical properties and residual stress distribution of 7075-T651 Al alloy joined using friction stir welding were investigated in this study. Welding was performed at 900, 1 250, and 1 600 rev/min and 20, 40, and 60 mm/min welding speeds. Mechanical tests were carried out on the welded joints in addition to microstructural examinations performed using a scanning electron microscope. Furthermore, residual stress distribution of the joints was determined by the hole drilling method. Generally, higher tensile strength was obtained at medium rotational and welding speeds. Tunnel defects were formed in the root of the weld seam. At high welding speeds, insufficient filling in the joints led to microvoids and large grain bands on the retreating side of the weld seam. The tensile strength of the welded specimens decreased at the rate of 26 – 45 % compared to the reference material. Lower residual stresses were determined in the specimens joined at a high rotational speed.

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In this study, 7075-T651 Al alloys were joined by friction stir welding (FSW) at a fixed rotational speed and different welding speeds. The stirring tool used in the welding processes was comprised of a shoulder of 20 mm in diameter and modified M6 × 1 HSS hand taps used as pins. The FSW was performed at a rotational speed of 1600 rpm and at welding speeds of 20, 40, and 60 mm min −1 . Mechanical and metallographic tests were carried out on the welded joints and the effects of the welding speed on the mechanical and metallurgical properties of the welded specimens were investigated. Welding speed significantly affected the microstructure and mechanical properties of the joining. Results showed that the average grain size of the weld nugget was reduced as welding speed was increased. In addition, it was found that high welding speed negatively affected the mechanical properties of the weld nugget.K e y w o r d s : FSW, aluminium alloy, mechanical properties, micro defects, microstructure

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