Comparison of Precipitate Structure, Modeling and Characterization in an Aluminum Alloy 7050 Friction Stir Weld

Microhardness, DSC, and TEM are used to characterize the precipitate structure and mechanical behavior as a function of position in an aluminum alloy 7050 friction stir weld that received a stabilization treatment after welding followed by natural aging for 13 years. DSC scans at the outer regions of the weld show a region of precipitate dissolution, with increasing dissolution as the weld center is approached. Precipitate coarsening increases rapidly near the TMAZ/HAZ boundary. The DSC scans also provide evidence of natural aging near the hardness minimum that were stabilized with a 2nd stabilization heat treatment. These results were compared with predictions of existing microstructural and thermal models to predict the temperature history, hardness and microstructural evolution during welding. Comparison of the models and test results show good agreement between experiment and models.