Microstructure, thermal and fretting wear of a region-specific graded Al–Si heat sink fabricated using laser additive manufacturing

High-silicon aluminum alloys are widely used in heat dissipation devices due to their favorable thermophysical properties. In this study, 2 wt.% boron nitride (BN) whiskers have been incorporated in an Al-36Si-3Cu-5Mg alloy, and a region-specific graded Al-based heat sink composed of 36Si-2BN, 36Si, and 42Si regions was fabricated using laser additive manufacturing. The microstructure, thermophysical properties, and fretting wear of the graded structure have been systematically investigated. The results indicate that the addition of BN whiskers significantly refines the grain structure and results in the formation of AlN and AlB 2 ceramic phases. When compared with the 36Si region, the thermal conductivity of the 36Si-2BN region increases from approximately 150 W·m -1 ·K -1 to 170 W·m -1 ·K -1 at room temperature, corresponding to an improvement of ∼13%, and is higher over the temperature range from room temperature to 300 °C that was tested. In contrast, the 42Si region exhibits a relatively invariant thermal response, providing a suitable complement in the three zones of the proposed heat exchanger. In terms of fretting, the steady-state coefficient of friction of the 36Si-2BN area is lowered from approximately 0.33 to 0.26, representing a drop of 20% and a more stable degree of friction. The application of BN whiskers enables an integrated improvement of thermal conductivity and interfacial fretting, facilitating an enhanced thermal management of high-thermal conductivity graded Al alloys.