Combined powder metallurgy routes to improve thermal and mechanical response of Al-Sn composite phase change materials
(Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156 Milan, Italy)
Abstract: Powder metallurgy processes are suitable to produce form-stable solid-liquid phase change materials from miscibility gap alloys. They allow to obtain a composite metallic material with good dispersion of low-melting active phase particles in a high-melting passive matrix, preventing leakage of the particles during phase transition and, therefore, increasing the stability of thermal response. Also, the matrix provides structural properties. The aim of this work is to combine conventional powder mixing techniques (simple mixing and ball milling) to improve active phase isolation and mechanical properties of an Al-Sn alloy. As matter of fact, ball milling of Sn powder allows to reduce hardness difference with Al powder; moreover, ball milling of the two powders together results in fine microstructure with improved mechanical properties. In addition, different routes applied showed that thermal response depends on the microstructure and, in particular, on the particle size of the active phase. In more detail, coarse active phase particles provide a fast heat release with small undercooling, while small particles solidify more slowly in a wide range of temperature. On the other hand, melting and, consequently, heat storage are independent of the particle size of the active phase. This potentially allows to “tailor” the thermal response by producing alloys with suitable microstructure.
Key words: metallic phase change materials; powder metallurgy; thermal stability; mechanical properties; miscibility gap alloys