Thermal Conductivity and Thermal Expansion of Recycled Aluminium–Graphite Composites Produced Using Recovered MnO₂–Carbon Melt Treatment
1*Babatunde, I. A., 2Durowoju M. O., 3Asafa, T. B.
1,2,3Department of Mechanical Engineering, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.
DOI: 10.36108/laujoces/6202.71.0160
Abstract
High relative density and low porosity are crucial for optimizing the thermal performance of aluminium–graphite (Al–Gr) composites for high-reliability thermal management applications in the automotive and electronics industries. This study investigated the influence of MnO2-carbon powder melt treatment on the microstructure, relative density, porosity, and thermal properties of aluminiu-graphite composites produced via stir casting method at 700 °C with a stirring time of 3 min. Despite extensive research on aluminium melt-treatment with fluoride salts (NaF, CaF2, AlF3 and MgF2) reinforced synthetic carbon fiber, little is known about the combined thermal behavior of recycled aluminum–graphite composites treated with MnO₂–carbon powder. Recovered MnO₂–carbon powder was introduced into recycled aluminum melt, treated and reinforced with 3, 6 and 9 wt.% graphite nanoparticles. Electrical conductivity of the produced composites was measured at room temperature using an FP-001 four-point probe conductivity Tester, and the thermal conductivity (TC) was estimated using the Wiedemann–Franz law, while coefficient of linear thermal expansion (CLTE) was evaluated from the change in specimen length with temperature. Scanning electron microscopy (SEM) revealed a fine and relatively homogeneous distribution of graphite nanoparticles within the aluminium matrix with reduced particle agglomeration. The highest TC of 239.50 W/m·K was obtained at Al+3 wt.% nm-Gr, representing a 27.56% improvement over the control sample of TC 173.50 W/m·K, whereas the lowest CLTE of 24.55 × 10⁻⁶ °C⁻¹ was obtained at Al+9 wt.% nm-Gr represented a 19.67% reduction relative to the control sample of CLTE 30.56 × 10⁻⁶ °C⁻¹. The composite samples exhibited lower percentage porosity values of 0.67%, 0.78% and 1.21% compared with the control sample having percentage porosity values of 1.33%. This study, therefore, demonstrated that MnO₂–carbon powder melt treatment of recycled aluminium reinforced graphite nanoparticles enhanced thermal conductivity and lowered thermal expansion of Al-Gr-based composites which have promising applications in industries especially for thermal management.
Keywords: Composite, aluminium-graphite, MnO2-carbon, Thermal conductivity, Thermal expansion.