Mechanical dissolution of copper additions in aluminium by Friction Stir Processing

Friction Stir Processing (FSP) can be used to locally modify properties in materials such as aluminium. Furthermore, the composition of the alloy can be changed by this technique. Intermixing specific micrometer-sized metal powders as well as metal foils helps to optimize both the microstructural stability during subsequent heat treatment, as well as the mechanical properties in general. Dispersing copper powder inside a matrix of AA1050 aluminium by FSP can produce homogenous solid solution of the two elements, if suitable processing parameters are used. A substantial hardening effect is shown for both effects, refinement of the grain structure and solid solution hardening. By calculating the diffusion length and using the results of investigations based on energy-dispersive X-ray spectroscopy (EDS), it can be shown that the dissolution is mainly mechanically driven and not due to diffusion. Furthermore, transmission electron microscopy (TEM) provides insights on the formation of intermetallic phases during FSP. The results may be used in future studies to evaluate the properties of such non-equilibrium alloys.