Effect of Pin Length and Rotation Rate on the Tensile Strength of a Friction Stir Spot-Welded Al Alloy: A Contribution to Automated Production

Friction stir spot welding (FSSW) is performed on thin plates of an aluminum alloy in a lap joint configuration with tools of different pin lengths and various rotation rates. The effects these process parameters have on the joint properties of the welds are investigated. The tensile strength of the welds decreased when the rotation rate was increased. The tensile strength of welds made with a pinless tool is on average 90% the strength of the full penetration spot welds. Intermediate pin lengths were tested between these two extremes. It was found that the tensile strength decreases as the pin length increases from pinless to 10% bottom plate penetration. Three distinct failure modes were identified when the welds were placed under tensile loading: shear mode, mixed mode, and nugget-pullout mode. The dependence of static joint strength on these process parameters is discussed.