Grain boundary properties and microstructure evolution in an Al-Cu alloy

Grain boundary (GB) properties in an Al-5 wt % Cu alloy have been extracted from diffraction contrast tomography images after 10 sequential annealing steps for 15 min at 630°C. At the annealing temperature, a copper-rich liquid was present at the GBs. The growth and shrinkage of the grains are strongly correlated with the grain size, and the velocity of individual boundaries is strongly correlated with boundary mean curvature, as expected from the classical theory of coarsening. The experimental results compare well to a threshold dynamics grain growth simulation of the process assuming uniform grain boundary energies. The correlation of the interface velocity and curvature is observed both for the data on average and for certain commonly occurring grain boundary disorientations. It is also found that the curvatures and relative areas of GBs depend on the five grain boundary parameters, even though the GBs are formed in conditions of low energy anisotropy. The observations are compared to results from grain growth in the solid state, where strong correlations between interface velocity and curvature are not observed.