Computational Analysis and Experimental Validation of the Friction-Stir Welding Behaviour of Ti-6Al-4V

A fully coupled thermomechanical finite element analysis of the friction-stir welding (FSW) process developed in the authors previous work is combined with the basic physical metallurgy of Ti 6Al 4V to predict/assess the structural response of FSW joints. A close examination of the experimental results reported in the open literature reveals that in most cases the heat-affected zone (HAZ) of the weld possesses the most inferior properties and tends to control the overall structural performance of the weld. Taking this observation into account, a microstructure evolution model is developed and parameterized for the Ti 6Al 4V material residing in the HAZ. Specifically, this model addresses the problem of temporal evolution of the globular a-phase particles located within prior b-phase grains (the dominant microstructural parameter in the HAZ) during the FSW process. Next this model is combined with the wellestablished property versus microstructure correlations in Ti 6Al 4V in order to predict the overall structural performance of the weld. The results obtained are found to be in reasonably good agreement with their experimental counterparts, suggesting that the present computational approach may be used to guide the selection of FSW process parameters in order to optimize the structural performance of FSW joints (at least while they are controlled by the HAZ-material microstructure/properties). Published in the Journal of Proc. IMechE Part B: J. Engineering Manufacture, v224 n8 p1-16, 2010. Supported in part by the US Army Grant nos. W911NF-04-2-0024 and W911NF-06-2-0042. The original document contains color images.