Effect of Ca addition on solidification microstructure of hypoeutectic Al-Si casting alloys

The effect of Ca addition on the solidification microstructure of hypoeutectic Al-Si casting alloys was investigated using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) methods with particular aftention focused on the change of morphologies of primary alpha-Al and eutectic silicon. Meanwhile, solute distribution in solid-liquid was simulated according to Scheil-Gulliver law. Results showed that primary alpha-Al and eutectic silicon were refined as Ca content increased because of the variation of the solute concentration in liquid. The addition of Ca increased the nucleation sites like Al3Ti or Al2Cu to promote the nucleation of primary alpha-Al. Affected by modification effect of Ca, the shape of eutectic silicon changed from flake to fibrous structure. In addition, coarse plate Ca-rich phases could be found along the grain boundary with high Ca content.