A thermal model of friction stir welding applied to Sc-modified Al-Zn-Mg-Cu alloy extrusions

A thermal model of friction stir welding is presented that proposes an energy-based formulation of the Johnson-Cook plasticity model in order to account for heat generation due to plastic deformation. The proposed formulation is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature of the alloy and the welding energy. The thermal model is applied to Sc-modified Al-Zn-Mg-Cu alloy extrusions joined by friction stir welding at 225, 250. 300 and 400 RPM (all other weld parameters held constant). With the incorporation of heat generation due to plastic deformation, the thermal model accurately predicts the maximum weld temperatures and temperature profiles at the higher energy weld conditions, i.e. 300 and 400 RPM. At the lower energy welds (i.e. 225 and 250 RPM) where plastic deformation contributes a larger portion to the total heat generation, the model under-predicts the maximum weld temperatures under the toot shoulder but shows good agreement with the remaining experimental temperature data. (C) 2008 Elsevier Ltd. All rights reserved.