Microstructural, Hardness, and Abrasive Wear Properties of Functionally Graded Al/ZrB2 Composites Produced by In Situ Centrifugal Casting

Functionally graded aluminum matrix composites are of interest for applications requiring region-dependent mechanical and tribological performance. In this study, the micro-structure, hardness, and abrasive wear properties of functionally graded Al/ZrB2 compo-site materials produced by an in situ centrifugal casting method were investigated. The ZrB2 reinforcement phase was synthesized in situ within the molten aluminum matrix, and functional grading was achieved through the action of centrifugal force during solidification. Samples taken from cylindrical castings were characterized using optical microscopy, scanning electron microscopy (SEM), X-Ray diffraction (XRD), density measurements, Brinell hardness testing, and abrasive wear experiments. Phase analyses con-firmed the successful in situ formation of ZrB2 and verified that the phase distribution in-creased toward the direction of centrifugal force. Hardness increased with reinforcement content, rising from approximately 28 HB in the matrix-rich region to 68 HB and 72 HB in regions reinforced with 12% and 15% ZrB2, respectively. Abrasive wear behavior was evaluated using the pin-on-disk method, and a Taguchi L (35) orthogonal array was employed for experimental design. Statistical analyses showed that the composite region was the most influential parameter affecting wear performance, followed by abrasive particle size and applied load, while sliding distance and sliding speed were not statistically significant. These findings demonstrate that in situ centrifugal casting is an effective approach for producing functionally graded Al/ZrB2 composites with improved hardness and wear resistance.