Microstructural features and thermal response of granulated Al and A356 alloy with relevant Sn additions

The aim of the work was to explore the possibility of producing Sn-bearing composite phase change materials (C-PCMs) intended to be used as Latent Heat Thermal Energy Storage (LH-TES) systems. To this purpose, pure Al and A356 Al alloy, with 40%mass Sn, were produced by granulating process. They were composed by an Al (and other phases) matrix and a low melting Sn-rich phase that can store/release latent heat by its melting/solidification. Pure Al and A356 were produced as reference materials. Finite Element Analyses was used to estimate the cooling rate experienced by the alloys during granulation. Microstructural features of the produced materials were discussed as for C-PCM. Granules thermal characterization was performed with Differential Scanning Calorimetry and dilatometry tests. Results show that Sn addition delays the solidification and increase microstructural refinement. Phase transition of the Sn-rich phase occurs at about 230 °C in Al-Sn alloy and in the 200–230 °C range for A356-Sn alloy, as also assessed by CALPHAD modelling. The stability of the thermal response for all the systems, as well as the form stability, is achieved after the first cycle. Moreover, A356-Sn exhibits suitable microstructure for limiting the exudation of the Sn-rich phase, making this alloy very attractive for C-PCMs.