The relationship between thermal conductivity and phase formation of cast Al–Cu–Li alloys

Abstract

Thermal conductivity directly affects the temperature gradient, cooling rate, microstructural evolution, and thermal stress distribution during alloy solidification, particularly for the Al alloys with complex thermal conduction behavior (e.g. AA2195 and AA7085 Al alloys). Accurate modeling of thermal conductivity is therefore crucial for optimizing casting processes and improving ingot quality. This study develops and validates the accurate mathematical models for thermal conductivity of ternary Al–Cu–Li alloy systems across a broad temperature range (25–700 ℃). The Thermo-Calc software was employed to compute phase formation, phase constituents, and solidification paths along with different temperatures. Then, the Scheil–Gulliver model was applied to calculate the dynamic variation of solid/liquid phase fractions during solidification. Then, thermal conductivity as a new model of temperatures, compositions, and secondary phases for different Al–Cu–Li alloys were derived, based on the Kopp’s law and the differential effective medium (DEM) theory. For experimental validation, the materials density, thermal diffusivity, and specific heat capacity of six representative alloys with various chemical compositions were experimentally determined using thermal dilatometer, differential scanning calorimetry, and laser flash analysis. Comparative analysis between theoretical calculation and experimental data indicates a relatively small deviation of only 7%. Meanwhile, the dynamic variation of thermal conductivity were reliably predicted throughout solidification. These models would provide some fundamental insights in casting of high-performance Al alloy components via controlling solidification.

Graphical abstract