Aluminum matrix composites (AMCs) have received great attention in the market of modern engineering materials which mainly focus on cost, quality and durability, styling and performance, emission and fuel economy, and recyclability [
1]. Aluminum matrix composites with appropriate reinforcements offers several advantages such as high specific strength, hardness, stiffness, high-thermal and electrical conductivity, low coefficient of thermal expansion, good corrosion and wear resistance, etc. [
2]. The reinforcement in AMCs may be monofilaments, continuous or discontinuous fibers, short fibers or whiskers, and fiber preforms and particulates [
3,
4]. A literature review indicates the dominance of particulate reinforced AMCs due to their ease of manufacturing and process competitiveness. This type of composite is produced by (i) solid-state processing such as powder metallurgy techniques, physical vapor deposition, diffusion bonding, etc. [
5]; (ii) liquid-state processing such as stir casting, squeeze casting, melt-infiltration, spray deposition, etc. [
6]; and (iii) in situ processing such as directional solidification of eutectics and formation of intermetallic phases [
7]. Hard ceramic particulates such as carbides, oxides, nitrides, and borides have been widely used as reinforcements in AMCs. Generally used reinforcement constituents in aluminum alloy matrices are non-metallic phases such as SiC, Al
2O
3, MgO, TiC, TiB
2, B
4C, BN, AlN, or dissimilar metallic phases (Pb, Be, Mo, Ti, W, etc.) [
8,
9]. The addition of these particulates have been found to improve the properties of commonly used matrix alloys of series 2xxx, 5xxx, 6xxx and 7xxx (wrought alloys) through various strengthening mechanisms. However, to improve the tribological performance of the AMCs, researchers have used soft-phase solid lubricating agents such as graphite and MoS
2 [
10,
11,
12]. A few proven applications of AMCs include pistons, connecting rods, brake drums and rotors, braking systems of trains and cars, and recreational products such as golf club shafts and heads, ice-skating shoes, baseball shafts, horseshoes, bicycle frames, etc. [
13,
14,
15]. Also, particulate reinforced composites have been successfully used in fan exit guide vanes in gas turbine engines as ventral fins and fuel access cover doors, flight control hydraulic manifolds in military aircrafts, and as rotating blade sleeves in helicopters [
16,
17,
18]. Growing engineering and technology needs demand newer materials of superior performance. Hybrid composite materials, another class of composite materials which uses multiple reinforcements, are promising solutions for future material requirements to replace heavier materials and which suit a wide range of engineering components. However, making these components an exact shape and size from bulk composite materials has been a challenge over the years. Other challenges in the development of hybrid aluminum matrix composites (HAMCs) include inferior ductility, low fracture toughness, and precise control of the distribution of the different micro-constituents during processing. Many of the traditional metallurgical methods may be conveniently used to produce HAMCs. For example, the stir casting process may be followed by cost-effective casting methods such as gravity die casting (GDC), permanent mold casting (PMC), or squeeze die casting (SDC) to obtain HAMC components. In the present work, HAMCs are developed using A390 alloy as the matrix and silicon carbide, graphite (Gr), and molybdenum di sulphide (MoS
2) as the particulate constituents using a stir casting process followed by a squeeze casting technique.
Tribological products are finding significance in industries and provide means to conserve energy and materials. An understanding of various friction and wear properties is necessary to make the right selection of materials and operating conditions for a given engineering application. Friction is a serious cause of energy dissipation, and wear is the main cause of material wastage in any system with mating bodies. Appropriate selection of materials for mating bodies and solid/liquid lubrication may be used to control friction and wear to an acceptable level. Mostly, monolithic materials are either incapable of satisfying the desired design requirements or are too expensive to meet superior tribological performance whereas HAMCs may be designed to meet this desired performance.
This investigation is focused on the study of composites using A390 aluminum cast alloy, as this alloy has wide acceptance in tribological applications such as cylinder blocks, transmission pump and air compressor housings, small engine crankcases, and air conditioner pistons [
19]. This work includes the designing of a composite materials system (by varying both hard and soft particulate constituents wt %) at a compatible processing condition. There is no doubt that for the development of an appropriate HAMC, a number of experiments which quantifies the various properties such as mechanical and wear properties are required. Characterization studies mainly include metallurgical analysis to understand different phases and measurements of important properties such as tensile, compressive, impact strength, hardness, and wear. Further, the experimental observations in the production and characterization of HAMCs is expected to serve as a qualitative and quantitative guide to understand the effect of particulates in rendering various properties.