Small additions of scandium to Al-Zn-Mg-Cu 7000 series alloys can significantly improve mechanical properties and augment the strength retention at low and elevated temperatures. This research program evaluates the residual properties of Sc-modified Al-Zn-Mg-Cu alloy extrusions joined through friction stir welding (FSW). Mechanical and corrosion testing were performed on the baseline material and on panels friction stir welded at 175, 225, 250, 300, 350 and 400 RPM (all other weld parameters held constant). A thermal model of friction stir welding is developed that utilizes an energy-based scaling factor to account for tool slip. The proposed slip factor is derived from an observed, empirical relationship between the ratio of the maximum welding temperature to the solidus temperature and energy per unit length of weld. The thermal model successfully predicts the maximum welding temperatures over a range of energy levels, and the mechanical and corrosion behavior is correlated to the temperature distribution predicted by the model.

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