A Precipitation Model for Simulation of Mechanical Properties of Al–Si–Mg–Cu Foundry Alloys

A precipitation model has been developed for Al–Si–Mg–Cu foundry alloys. The aging response of these alloys is strongly influenced by the prior processing conditions, including casting parameters and any subsequent solution heat treatment (SHT). The model first predicts the as-cast microstructure, in particular the volume fraction and size of the primary particles, and the solid solution levels of Mg and Si when no SHT is applied. When an SHT is included, the model simulates the evolution of key microstructure parameters and the associated changes in Mg and Si concentrations in solid solution throughout the SHT process. These predictions define the microstructure conditions entering the final aging heat treatment. The precipitation during the aging heat treatment is simulated by a model previously developed for wrought alloys with a few modifications, adapted to represent the characteristics of cast alloy systems. Model predictions were compared with measured tensile properties obtained at various aging times at 170 °C for samples aged directly after casting under water-cooled or air-cooled conditions, as well as for samples subjected to an intermediate SHT prior to aging. The simulations showed good agreement with the experimental data. In particular, the model successfully reproduced the increase in yield stress observed after SHT relative to samples aged directly after casting, an effect attributed to the dissolution of Mg-containing particles during SHT and the resulting increase in Mg available in solid solution.