Mathematical model and optimization for underwater friction stir welding of a heat-treatable aluminum alloy

During the friction stir welding (FSW) of heat-treatable aluminum alloys, the welding thermal cycles tend to cause a local softening in the joints and thus lead to a degradation in joint properties. Underwater FSW has been demonstrated to be available for the strength improvement of normal joints. In order to obtain the optimum welding condition for underwater FSW, a 2219-T6 aluminum alloy was underwater friction stir welded and a mathematical model was developed to optimize the welding parameters for maximum tensile strength in the present study. The results indicate that a maximum tensile strength of 360 MPa can be achieved through underwater FSW, higher than the maximum tensile strength obtained in normal condition.