Thermal Properties and Microstructure Evolution of the as-cast and Annealed Al–Cu–Si Eutectic Alloy

Abstract

The Al–28%Cu–6%Si (mass%) eutectic alloy represents a possible high-temperature phase change material (PCM) for latent heat thermal energy storage (LHTES). In this paper, its microstructural characteristics and thermal properties were examined in the as-cast and annealed conditions using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), and light flash method. The microstructure of the studied alloy consists of (Al) solid solution phase, θ-Al₂Cu intermetallic phase, and (Si) phase. The annealing at 450°C for 50 h led to significant changes in the morphology of the θ-Al₂Cu and (Si) eutectic phases. The temperature dependences of thermal diffusivity and thermal conductivity were investigated within the temperature range from 25 to 400 °C. It was found that the thermal diffusivity and thermal conductivity of the annealed alloy are considerably higher than that of the as-cast alloy at temperatures lower than 300 °C. With increasing temperature, due to changes in the microstructure of the as-cast alloy, these differences decrease and finally diminish at 400 °C. The measured eutectic temperature is 522.3 °C and latent heat of melting is 358.3 Jg^-1. The findings suggest that the Al–Cu–Si eutectic alloy shows good potential for use in phase change energy storage technologies.