The relationship between the density and temperature in hypereutectic Al–Si alloys was measured in the temperature range from 800 K to (T _l + 30) K using the indirect Archimedean method. This method eliminates the effects of surface tension on the densities of salts and alloys and reduces the error in estimating the density and solidification shrinkage of Al–Si alloys. Eutectic LiCl–KCl salt was used as a reference liquid. The results indicate that the density vs. temperature curve has three transformation points: the liquidus temperature, eutectic transformation temperature and completely finished eutectic transformation temperature. The obtained densities of solid and liquid hypereutectic Al–Si alloys are in agreement with those reported in earlier investigations. The solidification shrinkage decreases from 2.5 % for the Al–Si alloy containing 15 % Si to −0.4 % for the alloy with 25 % Si.

The effect of pulsed magneto oscillation (PMO) on the microstructure and tensile properties of Al-25% Si alloys with and without phosphorus addition was investigated. When PMO was applied to the melt during solidification, the results show that the PMO treatment is an effective method for refining the primary Si of Al-25% Si alloy with and without phosphorus addition. The morphology of primary Si was considerably refined via coarse dendritic and polygon shape to fine and regular block under the PMO treatment, and the average size of primary Si was refined to 30.8 μm and 45.3 μm under the optimal processing conditions for the alloy with and without phosphorus addition, respectively. The tensile strength and elongation of the alloys first increased and then decreased with rise of current. Analysis shows that application of PMO decreases Gibbs free energy and critical nucleus radius of the Al-25% Si alloy during solidification. The nucleation rate first increased and then decreased with increasing PMO intensity. The variation tendency of average number of primary Si per unit area is consistent with the theory analysis.