Microstructure and mechanical properties of joints welded by friction-stir welding in aluminum alloy 7075-T6 plates for aerospace application

This paper focuses on the effect of welding parameters on microstructure and tensile strength of joints welded by friction-stir welding (FSW). The effects of pin profile (threaded conical, non-threaded conical and triangular pin), tool rotational speed (800, 1000, 1250 and 1600 r·min⁻¹) and welding speed (63, 80, 100 and 125 mm·min⁻¹) on the mechanical and microstructural properties of joints welded in 5-mm 7075-T6 were investigated. The results depict that the pin profile has a major role in the shape and grain size of the weld nugget zone (WNZ). In other words, a wider weld nugget and a finer grain size by threaded conical pin are obtained in WNZ. The attained data of tensile tests show that the maximum ultimate tensile strength (UTS) belongs to the threaded conical pin which is attributed to a finer grain size generated in the weld nugget zone. Additionally, it is found that the tensile strength increases with the welding speed increasing, whereas rotational speed has a bilateral effect on the tensile strength. The microhardness tests show that the minimum hardness is obtained in the heat-affected zone (HAZ).