Powder Metallurgy-Derived Cr-Reinforced Aluminium Composites with Enhanced Hardness and Alkaline Stability for Solar Thermal Systems

Despite its favorable photothermal properties and high thermal conductivity, aluminum's susceptibility to mechanical degradation and severe corrosion in aggressive environments limits its lifespan as an absorbing medium in solar thermal systems (STSs). This study addresses these durability challenges by fabricating chromium (Cr)-reinforced aluminum matrix composites via powder metallurgy, utilizing a mechanism-aware composition design ranging from 4 to 12 wt.% Cr. X-ray diffraction and electron microscopy confirmed a distinct microstructural transformation from a primary face-centered cubic (FCC) aluminum matrix to secondary body-centered cubic (BCC) structures, driven by the controlled in-situ development of localized Al₈Cr₅ and Al₂Cr intermetallic phases. These microstructural modifications altered particle morphology and grain orientation, successfully acting as the primary driver for concurrent performance gains. Mechanical and electrochemical evaluations revealed that an optimal loading of 12 wt.% Cr yields a simultaneous 81.2% increase in sintered Vickers hardness and an 80% reduction in corrosion rate within highly aggressive 0.5 M NaOH solutions. This synergistic reinforcement is further supported by stable surface passivation from native Cr₂O₃ films, which suppresses localized pit progression and environmental degradation. These findings demonstrate that precise solid-state engineering of Cr-Al composites offers a robust, low-cost material platform for manufacturing monolithic solar absorber plates, significantly extending the efficiency and operational longevity of next-generation STSs operating in harsh coastal or alkaline environments.