Efficacy of active cooling for controlling residual stresses in friction stir welds

This paper investigates the effect of active cooling on the development of welding stresses during friction stir welding by finite element modelling. The primary aim was to see if cooling powers, corresponding to those currently obtainable using liquid CO₂ cooling systems applied in practically feasible locations could bring about a significant reduction in weld residual stress. Various cooling strategies were examined. The simulations revealed that a large reduction in residual stress can be obtained, particularly at the weld line, depending on the size, power and positioning of the cooling sinks. A heat sink placed as close as possible behind the heat source had the greatest effect on reducing the build up of tensile stresses. All the approaches tended to reduce the weld centreline stress more effectively than those at the heat affected zone/thermomechanically affected zone boundary (i.e. below the edge of the tool shoulder).