Rheology and microstructural development of a Al–4wt%Cu alloy in the semi-solid state

Rheological and microstructural studies were performed on a Al–4wt%Cu alloy in the semi-solid state employing two different experimental techniques: the indentation test and the simple compression test. Results showed that recrystallized microstructures exhibit lower viscosities than dendritic microstructures and that the rheological behavior can be described by the Power Law. The viscosity values were analyzed in terms of solid volume fraction and deformation rate and the pseudoplasticity of the Al–4wt%Cu alloy was thus ascertained. As for the solid particle size and shape evolution within the semi-solid temperature range, the experimental growth kinetics obeyed the classic D3=Kct relation, which indicates a Ostwald Ripening type of growth, but the particles size distribution was wider than the one predicted by the LSW theory. Also, comparison of the experimental and the theoretical growth rate constants suggested that coarsening due to hard impingement of the solid particles was the main growth mechanism.