Optimisation of solution treatment of cast Al–Si–Cu alloys

The influence of solidification rate on the solution treatment response for an Al–8Si–3.1Cu alloy has been investigated. The alloy was cast using the gradient solidification technique to produce samples with three different solidification rates. The samples were solution treated at 495 °C for various times between 10 min and 10 h. The concentration of copper in the matrix was measured using the wavelength dispersive spectroscopy technique, WDS.The results show that the coarseness of the microstructure clearly affects the solution treatment time needed to dissolve particles and obtain a homogenous distribution of copper in the matrix. A short solution treatment time of 10 min is enough to achieve a high and homogenous copper concentration for a material with a fine microstructure (secondary dendrite arm spacing, SDAS of 10 μm), while more than 10 h is needed for a coarse microstructure (SDAS of 50 μm). A model was developed to describe the dissolution and homogenisation process. The model shows good agreement with the experimental results.