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etal matrix composites are engineered Mmaterials composed of an elemental or alloy matrix in which an insoluble second phase reinforcement is embedded and distributed to achieve some property improvement. Particulate reinforced metal matrix composites constitute a major portion of these advanced materials. Aluminium-silicon alloys, as a matrix material, are characterized by lightweight, good strength to weight ratio, ease of fabrication at reasonable cost, high strength at elevated temperature, good thermal conductivity, excellent castability, good weldability, excellent corrosion resistance and wear resistance properties. Application of particulate reinforced composites in the aerospace, automotive, transportation and construction industries depends on the choice of cost affordable factor. In this research work, particulate reinforced metal matrix composites are processed by vortex method, a melt stirring liquid metallurgy technique. Four different particulates namely, graphite, combination of tungsten carbide and aluminium silicate for hybrid composite reinforcement, quartz and titanium carbide are used as second phase reinforcers for reinforcement in the matrix. Aluminium-11.8% silicon alloy is selected as the matrix material and the particulates are mixed in different weight fraction %. Slab composite castings are made by pouring the composite mixture in permanent molds. Process parameters like pouring temperature, particulate preheating temperature, impeller blade speed and shape are optimized and composite castings containing different weight fraction % of particulate are made by permanent mold casting process. Effects on different weight fraction % addition of particulate on the particulate distribution in aluminum-11.8% silicon alloy composites are studied. The processed particulate reinforced composites are subjected to mechanical tensile testing and the properties are determined for different type of particulate reinforcements in the aluminium-11.8% silicon alloy matrix. Besides, hardness, density, impact strength, fracture toughness, electrical resistivity, electrical conductivity, thermal diffusivity, thermal conductivity, thermal expansion coefficient measurements are performed by using the appropriate equipments and machines. Besides, slab. It is found that the properties of the processed particulate reinforced aluminium-11.8% silicon alloy matrix composites are superior to the cast monolithic aluminium-11.8% silicon alloy based on the above mentioned properties studies.

FET Faculty (Engineering & Technology)MMU Multimedia University, Malaysia

Interpretation & Comparision of Properties of Different Particulate Reinforced LM6 Alloy Matrix Composite Processed by Metal Casting Technology

Emphasis of Composites in Materials Engineering

A composite material is a combination of two or more chemically different materials with a distinct interface between them. The constituent materials maintain their separate identities microscopically in the composite, yet their combination p r o d u c e s p r o p e r t i e s a n d characteristics that are different from those of the constituents. One of these constituents forms a continuous phase and it is called as the matrix. The other major constituent is the reinforcement phase available in the form of fibers or as a particulate, in general, added to the matrix to improve or alter the matrix properties. Reinforcement by a particulate forms a discontinuous phase uniformly distributed throughout the matrix. Therefore, composites have improved mechanical properties such as strength and toughness when compared with monolithic materials

Composites science and technology requires lose interaction of various disciplines such as structural design and analysis, materials science, mechanics of materials, and process engineering. The tasks of composites research are to investigate the basic characteristics of the constituents and composite materials, optimize the material for service conditions, develop effective and efficient f a b r i c a t i o n p r o c e d u r e s a n d understanding their effect on material properties and to determine material properties and predict the structural behavior by analytical procedures and h en ce t o d eve l o p e f f e c t i v e experimental methods for material characterization, stress analysis and failure analysis.

An important task is the non destructive evaluation of material integrity, structural reliability, durability assessment, flaw criticality, and life prediction. New types of carbon fibers are being introduced with higher ultimate strains. Thermoplastic matrices are used under certain circumstances because they are tough and have low sensitivity to moisture effects, and are more easily amenable to mass production and repair. The use of woven fabric and short fiber reinforcement is receiving more attention.

The design of structures and systems capable of operating at elevated temperatures has spurred intensive research in high temperature composites, such as metal/ceramic, ceramic/matrix, and carbon/carbon composites. The utilization of conventional and new composite materials is intimately related to the development of fabrication methods.

The manufacturing process is one of the most important stages in controlling the properties and ensuring the quality of the finished product. The technology of composites, although still developing has reached a state of maturity. Prospects for the future are bright for a variety of reasons. Newer high volume applications, such as in the automotive industry, will expand the use of composites greatly.

Research MethodologyIn this research work, mostly

experimental work has been carried out and the objectives of research are more focused on the determination of mechanical, thermal and electrical properties and on the metallographic studies of the composite slab castings. Therefore, this investigation is attempted to reinforce graphite par t icu la te , tungsten carb ide part iculate, a luminum si l icate par t i cu la te , t i t an ium carb ide particulate and quartz as second phase particulates in the aluminium-11.8% silicon alloy matrix. The experimental work is divided into two parts.

l Four different percentages of graphite particulate based on its weight fraction such as in the range from 1%, 2%, 3% and 4% are added to the aluminium-11.8% silicon alloy matrix to make composite slab castings by permanent metal molding process.

l Four different percentages of combined tungsten carbide particulate and aluminium silicate particulate based on its weight fractions from 2.5%, 5%, 7.5% and 10% are added to the aluminium-11.8% silicon alloy matrix to make composite slab castings by permanent metal molding process.

l Six different percentages of quartz particulate based on its weight fraction such as in the range from 5%, 10%, 15%, 20%, 25%, and 30% are added to the aluminium-11.8% silicon alloy matrix to make composite slab

castings by permanent metal molding process.

l 12% of titanium carbide particulate on its weight fraction is added to the aluminium-11.8% silicon alloy matrix to make composite slab castings by permanent metal molding process.

l Tensile tests are conducted to determine the mechanical properties

l Thermal properties and electrical properties are determined to study thermal conductivity and electrical conductivity.

l Thermal expansion studies are conducted to determine the linear thermal expansion coefficient values (CTE Values).

The first part explains the selected fabrication process of the composite castings in the form of slabs. The second par t dea l s w i th t he experimental work done throughout the study.

Particulate reinforced metal matrix composite casting fabrication by vortex liquid slurry mixing technique

In this work, four different types of particulates are added in the alloy matrix by varying the weight fraction % addition to the aluminium-11.8% silicon alloy matrix to process four types of particulate reinforced composite castings. The weight fraction percentage addition of each type of particulate to the alloy matrix varies from one type of particulate to another particulate and priorly a few calculations are required to determine the weight fraction % to be added to the selected alloy matrix material.

Composite Casting Process in Action

In fact, the processing of particulate reinforced composite castings is not an easy task to perform in a common foundry research laboratory. This whole process requires a sequential set of equipments and particulate chemicals in powder form of particular size and shape. Since the particulate is very small and its size is in microns (micrometer), careful handling is required and it is expensive too. Necessary safety measures and precautionary steps should be taken during the entire processing. The real composite casting technology is shown in Figure-1 to Figure-9.

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Fig. 2 : Ready to Start the Composite Casting Process

Fig. 3 : Melting of Aluminium - 11.8% Silicon Alloy is Starting

Fig. 4 : Full View of the Composite Casting Process before Starting

Fig. 5 : Permanent Metallic Molds are Numbered as 1, 2 and 3 for Identification

Fig. 6 : Mixing of Particulate in the Metal Well Crucible of the Induction-Melting Furnace

Fig. 7 : Mixing in Action by the Vortex Machine Impeller Blade

Fig. 8 : Pouring the Composite Slurry Mixture in Grey Cast Iron Mold

Fig. 9 : Processed Composite Castings

Interpretation and comparison of properties of different type of particulate reinforced LM6 alloy matrix composite

Interpretation and comparison is an important analytical technique often used in engineering analysis to predict the optimum properties and hence to choose a particular material type for a specific application. It is very useful to avoid unnecessary cost factors, to improve the durability and hence to increase the service life of the components made from the chosen material. Particularly, it is more applicable in the new composite materials development research. This concept is applied here to predict the optimum properties of a particular type of particulate reinforcement phase in the LM6 alloy matrix and it is illustrated in the graph G-K respectively.

Indicators Used : Series Used in the Interpreted Graphs

Series 1 : For Graphite particulate reinforced LM6 alloy matrix composite

Series 2 : For Combined tungsten carbide and aluminium silicate particulate reinforced LM6 alloy matrix composite

Series 3 : For Quartz particulate reinforced LM6 alloy matrix composite

Series 4 : For Titanium carbide particulate reinforced LM6 alloy matrix composite

The above-interpreted graphs are used to choose a particular type of particulate reinforced LM6 alloy matrix material for a specific application. In the graphs shown above, series 1 indicates the graphite particulate reinforcement, series 2 indicates the combined tungsten carbide and aluminium si l icate part iculate reinforcement, series 3 indicates the quartz particulate reinforcement, and series 4 represents the titanium carbide particulate reinforcement in

the LM6 alloy matrix. An interpretation is made on some of the selected properties with the weight fraction % addition of a particular type of particulate reinforcement phase in the alloy matrix. . For a selected property of a particulate type from the above plotted graphs, a suitable weight fraction addition is found and it is always chosen well below the optimum limit of the four different particulates reinforced in the LM6 alloy matrix. The plotted curves are extrapolated for the convenience to predict the required value of a suitable weight fraction percentage of a particulate type corresponds to a particular property.

ConclusionsThis research work on different particulate

reinforced metal matrix composite processed by liquid metallurgical technique concludes the following:

l Sufficient amount of turbulence during the mixing of the particulate and the liquid matrix alloy is necessary to get uniform particulate distribution during its solidification processing.

l The thermal conductivity of the metallic molds, used to make composite castings influences largely apart from the vortex generation.

l It is strongly recommended to pursue research on different types of hybrid composites by this liquid metallurgy route based on the properties requirement and application.

l The impeller blade type and its rotational speed have not shown any effect on the distribution uniformity. But, faster pouring of the composite slurry mixture into the mold immediately after the mixing by vortex method has played a significant role in the distribution of the particulates used in this project.

l The temperature drops while mixing the mixture by the impeller blade is a serious problem. Sometimes the mixture sticks with the blade and the process is ceased.

l The speed of the blade should be controlled properly to avoid this.

l An extensive study on process parameters optimization of the process is strongly recommended.

l Different types of metallic molds are used for pouring the composite mixture and no significant variation in properties.

l Particulate preheating has shown an important parameter in this process. Preheating of particulate has

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improved the wettability and produced good bonding and distribution uniformity in the composites.

l The optimum particulate preheating temperature is 450 degree centigrade and immediate transfer of the same for mixing with the liquid alloy is very strongly recommended.

l The processed four types of particulate reinforced aluminium-11.8 % silicon alloy matrix composites properties and microstructural features are superior to cast aluminium-11.8% silicon alloy castings with or without grain refining process.

AcknowledgementThe author of this research paper

expresses his thanks to the Faculty of Engineering and Technology, FET, MMU, Multimedia University, Melaka Campus, Bukit Beruang, 75450, Melaka, Malaysia.

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