The growth mechanism and morphology evolution of primary Si during slow cooling solidification of high purity Al–15Si alloy with Cr additions

Abstract

The effect of Cr content (0-0.3 wt%) on the growth mechanism and morphology evolution of primary Si was investigated by slow cooling experiments. The results show that the addition of Cr increases the nucleation undercooling of the primary Si. The inhibition of macroscopic segregation is optimal in Al–15Si alloy modified with 0.3Cr. The grain size of the primary Si at the top and bottom of the sample was reduced by 18% and 75%, respectively. The CrSi2 phase was found in Al–15Si-0.3Cr alloys. The morphology of the primary Si transforms from an irregular shape with hoppers to a regular tetragonal or hexagonal shape compared to the unmodified Al–15Si alloy. The addition of Cr can inhibit the growth of primary Si in [111] direction and improve the morphology. The effect of Cr on Al–15Si alloy was mainly attributed to facilitating the heterogeneous nucleation of primary Si and the restriction growth. The optimum refinement of primary Si was achieved by the addition of 0.3 wt % Cr modifier.