Mapping the microstructure of a friction-stir welded (FSW) Al-Li-Cu alloy

The friction-stir welding (FSW) process induces both heat and deformation which lead to inhomogeneous precipitation microstructures in structural hardening alloys. A map of this microstructure can be obtained by 2D scanning SAXS in alloys where(a) a single phase is precipitating and (b) the precipitates are roughly isotropic. In Al-Li-Cu alloys, these conditions are not fullfilled. Very anisotropic precipitates are forming (T-1 and theta') with aspect ratios in the range 10 to 100. The inhomogeneity in the texture of the material (due to the deformation and recrystallisation) is a strong obstacle to the interpretation of the SAXS signal. This paper is an attempt to apply systematic simple interpretation models to characterise the precipitation microstructure across the weld area. It shows that in certain condition, it is possible to apply simple Guinier-type plot to extract the morphologies (length and thickness) of the particles.