Effect of tool rotational speed on the microstructure and mechanical properties of projection friction stir spot welding of 2024 aluminum alloy

Friction Stir Spot Welding (FSSW) is a solid state joining process which utilizes a rotating tool consisting of a shoulder and/or a probe. FSSW has a strong interest related to the welding of aluminum alloys and dissimilar materials. The main disadvantage of this technique is the keyhole which remains in the stir zone and corrosion could take place preferentially in this region. Different techniques have been used for eliminating of this keyhole. In this study, a novel technique has been successfully applied to prevent the formation of the keyhole by using a cylindrical pinless tool and a projection on the beneath anvil. The effect of tool rotational speed on the microstructure and mechanical properties of projection friction stir spot welding of 2024 aluminum alloy is studied. This process was carried out in three different tool rotational speeds (1000, 1600 and 2000 rpm). By using this new method significant improvement was observed in mechanical properties, grain size and microstructure.