This study examines how aluminum oxide (Al₂O₃) powder in micrometer (µm) affects the mechanical characteristics, microstructural characteristics, and slurry erosion resistance of high-density polyethylene (HDPE) composites manufactured via pipe extrusion. Al₂O₃ particles with an average size of 5 µm were added to the HDPE matrix at weight percentages of 0.5 wt.%, 0.7 wt.%, and 1 wt.%. Scanning electron microscopy (SEM) was used to analyze the compound morphology, and tensile properties and resisting erosion were assessed in accordance with ASTM recommendations. The results show that the properties of HDPE composites are dramatically changed by the addition of Al₂O₃. The composite with 0.5 wt.% Al₂O₃ had the most stable particles dispersion and strong interfacial bonding when contrasted with unfilled HDPE, resulting in a about 13% increase in tensile strength. Tensile strength decreased but material stiffness increased due to particle agglomeration brought on by an increase in filler content. The composite with 1 wt.% Al₂O₃ demonstrated a 51% reduction in erosion rate when compared to pure HDPE. Erosion resistance gradually improved with higher Al₂O₃ loadings, according to slurry erosion tests. In essence, the study demonstrates that there is a trade-off between enhancing erosion resistance and optimizing mechanical properties, depending on the filler content. These findings provide valuable insights into the erosion behavior of extruded HDPE/Al₂O₃ composite pipes and demonstrate their suitability for fluid transport and sanitary applications that demand greater durability in erosive environment.