Abstract
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.

Key words
FSW, aluminium alloy, mechanical properties, micro defects, microstructure

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