Process–structure–property relationships for nugget and heat affected zone regions of AA2524–T351 friction stir welds

The effects of weld tool rotational speed ω, welding speed v and z-axis force F_Z during friction stir welding of the aluminium alloy 2524-T351 on the resulting process response variables, nugget microstructure, nugget tensile properties and heat affected zone hardness variations were investigated. For the range of conditions examined, the results indicate that ω has the dominant effect on nugget properties and structure, that optimum nugget tensile properties can be obtained by increasing ω to obtain a peak temperature that is just below the incipient local melting temperature, and that excessive values of ω result in low nugget ductility because of localised embrittlement near the weld crown. The study has also shown that the peak weld temperature is inversely related to the measured torque T₀. The T₀–ω relationship appears to be a useful guide for weld modification, as it is indicative of conditions leading to overheating in the nugget region.