Architecture-Controlled WC Distribution in Aluminum Composites via Stacked-Disc Hot Extrusion

Aluminum matrix composites (AMCs) are attractive materials for lightweight structural and tribological applications due to their low density and improved mechanical and wear properties compared with monolithic aluminum alloys, making them suitable for automotive and aerospace components where weight reduction is critical. Their high strength-to-weight ratio, stiffness, and thermal stability have driven extensive research on ceramic-reinforced AMCs in recent years [1-3]. Among ceramic reinforcements, tungsten carbide (WC) is particularly appealing because of its high hardness, excellent wear resistance, and thermal stability, especially for tribological applications. WC-reinforced aluminum composites have demonstrated significant improvements in hardness and wear resistance; however, their fabrication remains challenging due to poor wettability, particle agglomeration, and limited control over reinforcement distribution when using conventional processing routes [4]. Traditional fabrication methods for WC-reinforced AMCs, such as stir casting and powder metallurgy, typically result in random particle dispersion and heterogeneous microstructures, which restrict the ability to tailor interfacial characteristics and reinforcement architectures [2]. Recent studies show that controlled, non-random reinforcement architectures can significantly enhance the mechanical and tribological performance of metal matrix composites. [5]. Nevertheless, most reported approaches to achieve such architectures involve complex processing steps or limited scalability. Hot extrusion is an industrially established process capable of imposing large plastic deformation, thereby promoting consolidation and interfacial bonding in aluminum-based materials. Despite its widespread use, its potential to transform pre-designed layered reinforcement configurations into interconnected microstructural architectures has not been fully explored. Therefore, there remains a need for simple, scalable, and reproducible fabrication routes that enable controlled reinforcement placement prior to consolidation. In this work, a novel fabrication route for WC-reinforced aluminum matrix composites is proposed, based on the sequential stacking of WC-coated aluminum discs followed by indirect hot extrusion. This layer-stacking approach enables the controlled placement of WC at predefined aluminum–aluminum interfaces, which is subsequently redistributed and interconnected during extrusion by the imposed metal flow, giving rise to a distinctive microstructural architecture characterized by scanning electron microscopy (SEM). Figure 1 schematically illustrates the experimental fabrication procedure. Commercially pure aluminum (AA1050) was machined into discs with a diameter of 25.4 mm and a thickness of 1.5 mm and ultrasonically cleaned in acetone for 5 min. WC powder (Alfa Aesar, 99.9% purity) with an average particle size of 0.8 µm was dispersed in acetone to form a stable suspension, which was applied onto the disc surfaces and subsequently dried. Discs were sequentially stacked to form a billet, enabling controlled WC introduction at each interface and a reproducible concentric-layer architecture prior to consolidation. The stacked billet was placed in a steel container, preheated, and indirectly hot extruded at 485 °C using an extrusion ratio of 16:1. Microstructural characterization was performed on cross-sectional and longitudinal specimens prepared by standard metallographic procedures. Samples were ground using SiC papers (#400–#2000) and polished to a mirror finish with a 1 µm diamond suspension. SEM observations were conducted using a Hitachi SU3500 microscope operated at 15 kV. Backscattered electron (BSE) imaging was used to distinguish WC particles from the aluminum matrix, while energy-dispersive spectroscopy (EDS) mapping was employed to confirm elemental distribution. Figure 2 shows SEM-BSE micrographs of the extruded composite in (a) cross-sectional and (b) longitudinal views, together with (c–d) corresponding EDS elemental maps. The micrographs reveal a distinctive concentric WC architecture within the aluminum matrix, characterized by radially distributed WC-rich rings extending from the center toward the periphery of the extruded rod. The spacing between adjacent rings progressively decreases toward the outer regions, indicating a radial gradient in reinforcement density. This architecture originates from the initial stacked-disc configuration combined with the non-uniform plastic flow imposed during indirect hot extrusion, where higher shear strains near the billet–die interface promote increased distortion and compression of WC-containing interfaces. EDS mapping confirms that the concentric bands correspond to WC-rich regions, demonstrating that the extrusion process redistributes the reinforcement while preserving the pre-designed spatial architecture. These results show that the proposed stacked-disc extrusion route enables deliberate microstructural architecture control in aluminum matrix composites rather than relying on conventional random particle dispersion. The concentric WC arrangement may influence tribological behavior by increasing local WC availability near the surface, although further evaluation is required. Schematic representation of the experimental fabrication procedure for WC-reinforced aluminum matrix composites. SEM–BSE micrographs and corresponding EDS elemental maps of the extruded composite: (a,c) cross-sectional and (b,d) longitudinal views, confirming the distribution of WC particles in the aluminum matrix.