Effect of silicon concentration and foil thickness on the structure and thermal properties of melt-quenched Al–Si alloys

Abstract

The microstructure and thermal properties of foils melt quenched from hypoeutectic, eutectic, and hypereutectic Al–Si alloys are investigated depending on their thicknesses. The maximum achievable foil thickness decreases with increasing silicon concentration. A common pattern of layered silumin microstructure formation is established for all alloys. Specifically, the number of layers increases with the foil thickness. The change in the solidification mechanism in the layers of three-layer (thick), two-layer (medium thickness), and single-layer (thin) foils at a constant component concentration is explained. Decreasing the thickness of thin single-layer foils leads to a reduction in the initial heat transfer coefficient and the formation of a microstructure with a primary phase and eutectic grains. This microstructure is characteristic of the final solidification stage of foils of medium and maximum thicknesses. Analysis of the melting thermograms of the eutectic and hypereutectic alloy reveals that the structural phase state of the layer adjacent to the freely solidified side exerts the greatest influence on the thermal properties. This layer occupies 80–100% of the foil volume.