Material constitutive behaviour and microstructure study on aluminium alloys for friction stir welding

The material constitutive behaviour and microstructure of Aluminium alloys 6082 and 7449 were studied with the Gleeble hot compression test. The novel aspect of the work is that the testing was done at high strain-rates and at temperatures within 5 K of the solidus. The results indicated that the strength was maintained up to near solidus temperatures, with no dramatic strength reduction being observed. There was however, a distinct change in the slope observed with the 7449 results around 720 K. The experimental results were then fit to the Zener-Holloman equation, which describes the relationship between the material flow stress, temperature and strain-rates. The material microstructure of the hot compression test samples was analysed, and the averaged grain size was calculated to compare with friction stir weld nuggets. This will be used to infer the processing conditions that exist in the dynamically recrystallized weld nugget. Finally, a simple model was used to understand how processing conditions affected the deformation behaviour.