Description:ALUMINIUM METAL MATRIX COMPOSITES REINFORCED WITH SIC, GRANITE AND GRAPHITE POWDER
Field of Invention
The present invention pertains to the examination of the mechanical characteristics of Aluminium Matrix Composites (AMCs) that have been fortified with Silicon Carbide (SiC), Granite and Graphite powder.
Background of the Invention
The reinforcements employed in advanced composites (AMCs) can be classified into three primary categories, namely ceramic, metallic, and organic. Ceramic reinforcements are favoured owing to their elevated strength, stiffness, and thermal stability (US4946500A). Additionally, they exhibit resistance to both corrosion and wear. Silicon carbide (SiC), aluminium oxide (Al2O3), and boron carbide (B4C) are among the frequently employed ceramic reinforcements in the fabrication of advanced metal matrix composites (AMCs). The utilisation of metallic reinforcements is a common practice in enhancing the mechanical properties of advanced metal matrix composites (AMCs), particularly in terms of their strength and ductility (US6051045A). In addition, they exhibit a lower cost compared to ceramic reinforcements. Copper, nickel, and titanium are among the frequently employed metallic reinforcements in the context of advanced metal matrix composites (AMCs). AMCs employ organic reinforcements to enhance their toughness and impact resistance. Additionally, they possess a low weight and exhibit ease of processing. Glass fibres, carbon fibers, and aramid fibres are among the frequently employed organic reinforcements in the production of AMCs. The selection of reinforcement utilised in an AMC is contingent upon the particular applications (US6284014B1). Ceramic reinforcements are frequently utilised in scenarios that necessitate elevated levels of strength and stiffness, such as in aerospace and automotive applications. Structural applications often necessitate the utilisation of metallic reinforcements due to their desirable machinability and weldability properties. Organic reinforcements are frequently employed in scenarios that necessitate toughness and impact resistance, such as marine applications and sporting goods. The utilisation of silicon carbide (SiC) as a ceramic reinforcement material in AMCs is prevalent owing to its exceptional mechanical properties and thermal stability. Silicon carbide (SiC) is a material characterised by its exceptional hardness and elevated melting temperature. Furthermore, it exhibits resistance to both corrosion and wear. The aforementioned characteristics render SiC a highly desirable reinforcement material for scenarios that demand elevated levels of strength, rigidity, and thermal endurance. The utilisation of granite powder as a reinforcement material for AMCs is a promising avenue to explore, given its cost-effectiveness, widespread availability, and distinctive characteristics such as exceptional hardness, strength, and resistance to wear. Granite is a naturally occurring rock that is comprised of a diverse range of minerals, such as quartz, feldspar, and mica. The aforementioned minerals are responsible for endowing granite with its notable attributes of elevated hardness, robustness, and capacity to withstand abrasion. The utilisation of granite powder as a reinforcement material for the enhancement of the properties of AMCs is a viable and economical approach with sustainable implications. The implementation of reinforcements in the context of advanced composite materials has resulted in the emergence of a novel category of substances that exhibit enhanced characteristics. AMCs exhibit superior properties such as reduced weight, increased strength, and enhanced durability in comparison to traditional materials. Additionally, they exhibit resistance to both corrosion and wear (US7087202B2). The aforementioned characteristics render AMCs highly suitable for a diverse array of uses, encompassing but not limited to the fields of aerospace, automotive, and construction. The stir casting technique has been considered effective in overcoming certain obstacles linked with reinforcement fillers in composites featuring an aluminium matrix. Nevertheless, it may be imperative to employ supplementary processing methodologies and surface modifications to enhance the interfacial adhesion and surmount the residual obstacles.
Summary of the Invention
In light of the above mentioned drawbacks in the prior art, the present invention aims to examine the mechanical characteristics and load transfer mechanisms of Aluminium Matrix Composites (AMCs) that have been strengthened with SiC, Granite and Graphite powder, and produced using a stir casting technique.
A further specific objective of the invention is to assesses the hardness, tensile, and shear strength of the composites through the utilisation of established ASTM test protocols.
Brief Description of Drawings
The invention will be described in detail with reference to the exemplary embodiments shown in the figures wherein:
Figure 1 Graphical representation of Rockwell hardness of AMC reinforced with SiC, Granite and Graphite Powders
Figure 2 Graphical representation of Impact Strength of of AMC reinforced with SiC, Granite and Graphite Powders
Figure 3 Graphical representation of Tensile strength results of of AMC reinforced with SiC, Granite and Graphite Powders
Figure 4 Graphical representation of Shear strength results of of AMC reinforced with SiC, Granite and Graphite Powders
Detailed Description of the Invention
The determination of hardness involves the quantification of the force exerted and its correlation with a specific geometric characteristic of the indentation, such as its surface area or depth. The baseline's hardness was determined to be 70 HRB. The investigation revealed that the Al-MMC reinforced with 2% SiC wt.% exhibited a hardness of 73 HRB, indicating a 4.5% increase compared to the baseline.The investigation determined that the addition of 2% SiC and 2% graphite by weight to the AI-MMC resulted in a hardness of 78.3 HRB, representing an increase of 11.51% compared to the baseline.The hardness of an AI-MMC specimen reinforced with 2% SiC and 2% granite powder by weight was determined to be 78 HRB, exhibiting an increase of 11.4% compared to the baseline.The hardness value of a specimen containing 4% SiC and 2% granite powder by weight has been determined to be 83 HRB. The rockwell hardness obtained for various composites is provided in Figure 1.
The fracture behaviour of Aluminium 7075 MMCs is influenced by the inclusion of graphite powder and granite powder reinforcements in the subsequent manners. The incorporation of graphite powder has the potential to enhance the impact toughness of metal matrix composites (MMCs) by virtue of its capacity to dissipate energy via the generation of numerous microcracks and delamination layers. The presence of graphite particles serves as stress concentrators, resulting in the deflection of cracks and a subsequent rise in energy absorption. The energy dissipation and consequent enhancement of fracture resistance in the MMCs are attributed to the sliding that occurs between the graphite particles and the matrix. The utilisation of granite powder as a reinforcement material. The incorporation of granite powder into metal matrix composites (MMCs) has been found to improve their initial fracture toughness due to the hard and brittle nature of the powder. The addition of granite powder has the potential to cause crack deflection and branching, resulting in a decrease in the rate of crack propagation and an increase in the energy absorption capacity of the metal matrix composites. The bonding at the interface of the granite particles and the matrix is a significant factor in both load transmission and energy dissipation. The investigation of the Charpy impact test on Aluminium 7075 Metal Matrix Composites (MMCs) that are reinforced with different proportions of graphite powder and granite powder yields significant findings regarding their fracture behaviour and impact resistance (Figure 2). The present study employed the Universal Testing Machine (UTM) - UNITEK 94100 Model to conduct a tensile test, also known as a tension test. The specimens were machined in accordance with the guidelines specified in ASTM E-8M. The Universal Testing Machine (UTM) had a maximum test load capacity of 100,000 N, a load resolution of 5 N, and a displacement resolution of 0.1mm. Additionally, the cross-head speed ranged from 0.5 to 250 mm/min. The UTM employed wedge grips of 10kN and 100kN for round specimens with diameters of 4-10mm and 0-10mm, respectively. The specimen composed of 4% SiC and 2% granite attained the maximum load of 8.735kN, concomitant with the highest displacement of 1.89 mm. The observed phenomenon can be attributed to the increase in ceramic SiC reinforcement particles in comparison to the other three samples, as evidenced by the data. The materials 2% SiC+2% Granite and 2% SiC+2% Graphite have exhibited comparable performance, with a maximum load capacity ranging from 3.75-3.9kN and a displacement of 1.05-1.1mm. The experimental results indicate a notable enhancement in the performance of the 2% SiC sample, as evidenced by the maximum load of 4.16 kN and displacement of 1.39mm (Figure 3).
The enhancement in the tensile strength of Aluminium 7075 metal matrix composites (MMCs) that are reinforced with different proportions of graphite powder and granite powder can be attributed to multiple mechanisms. The present study focuses on the phenomenon of load transfer and reinforcement distribution. As the concentration of graphite powder and granite powder is augmented in the Metal Matrix Composite (MMC), the reinforcements establish an interconnected structure within the aluminium matrix. Under tensile loading conditions, the stress applied is transmitted from the matrix to the reinforcing particles, resulting in efficient load distribution. The manner in which reinforcements are distributed and dispersed is of paramount importance in facilitating load transfer. The implementation of appropriate mixing and processing methodologies is crucial in achieving a consistent distribution of graphite and granite powders, thereby reducing the likelihood of stress concentrations and facilitating load transfer throughout the composite.
The Orowan strengthening mechanism refers to the increase in strength of a material due to the presence of dislocations that interact with obstacles such as precipitates or grain boundaries. The Orowan strengthening mechanism is a significant contributor to the enhancement of the tensile strength of metal matrix composites (MMCs).
The impediment of dislocation movement within the aluminium matrix is caused by the existence of rigid reinforcement particles, such as graphite and granite.
The investigation into the shear strength of Aluminium 7075, which has been reinforced with SiC, Granite, and Graphite Powders, can contribute to the advancement of knowledge regarding the variables that influence this particular property. The aforementioned data can be utilised to devise novel materials and processing techniques that have the potential to enhance the shear strength of the material. The aforementioned circumstances may result in the emergence of novel material applications, particularly in structural domains that necessitate elevated shear strength. The sample consisting of 2% SiC and 2% Granite exhibited the maximum load of 43.38kN, accompanied by a displacement of 1.89mm. The specimen comprising 2% SiC and 2% graphite exhibited a maximum load of 34.415 kN, accompanied by a displacement of 1.7mm (Figure 4). The enhancement of shear strength observed in Aluminium 7075 metal matrix composites (MMCs) that are reinforced with different proportions of graphite powder and granite powder can be attributed to several mechanisms. The incorporation of graphite powder and granite powder reinforcements facilitates the transfer of externally applied loads between the matrix and the particles. Upon application of a shear force onto the composite material, the resultant load is distributed between the matrix and the reinforcement particles. Graphite and granite powders possess high shear modulus and strength, which endow them with the ability to effectively withstand the load. This, in turn, leads to a reduction in stress concentration and an overall enhancement of the composite's shear strength. The enhancement of the shear strength of a composite material is significantly influenced by the interfacial bonding quality between the matrix and the reinforcement. Efficient load transfer and reduced debonding or particle pull-out can be achieved through appropriate interfacial bonding between the matrix and the graphite and granite particles.
The process of altering the microstructure of Aluminium 7075 metal matrix composites (MMCs) through the incorporation of graphite powder and granite powder in varying proportions entails multiple mechanisms that impact the dispersion, interplay, and performance of the reinforcements within the matrix. The concepts of dispersion and distribution are frequently discussed in academic literature. The initial stage of microstructure modification involves the dispersion and distribution of graphite and granite powders within the aluminium matrix. In the fabrication process, it is customary to introduce powder particles into the molten aluminium, which facilitates their dispersion and uniform distribution. The spatial arrangement of the reinforcement particles is contingent upon various factors, including the processing technique employed, the degree of mixing, and the inherent characteristics of the powder particles. Achieving a uniform microstructure, preventing agglomeration, and facilitating effective load transfer between the matrix and reinforcements are critical aspects that necessitate appropriate dispersion and distribution. The phenomena of wetting and interfacial bonding are of significant interest in the field of materials science. The phenomenon of wetting pertains to the capacity of the matrix material to disperse and attach itself to the surface of the reinforcement particles. The attainment of satisfactory wetting in graphite powder, characterised by its non-metallic properties, can pose a formidable challenge due to the incongruity in surface energies between graphite and aluminium. The enhancement of wetting and interfacial bonding between the matrix and graphite particles can be achieved through the utilisation of surface treatments and suitable additives. In contrast, granite powder is composed of mineral particles that exhibit a greater attraction to aluminium, thereby facilitating wetting and interfacial bonding. The present discourse concerns the topics of mechanical interlocking and load transfer. Incorporating reinforcements, particularly granite powder, can induce mechanical interlocking mechanisms in the microstructure of the composite.
During the solidification process of the aluminium matrix, the irregular shape and surface roughness of the granite particles lead to mechanical interlocking between the reinforcement particles and the matrix. The interlocking mechanism facilitates the transfer of load between the matrix and reinforcements, thereby augmenting the mechanical characteristics of the composite material, encompassing strength and stiffness. The process of grain refinement is a technique used to reduce the size of grains in a material, typically a metal or alloy, through various methods such as mechanical deformation, thermal treatment, or the addition of grain-refining agents. This can result in improved mechanical properties, such as increased strength and ductility, as well as enhanced surface finish and better resistance to fatigue and corrosion. Grain refinement is an important area of research in materials science and engineering, with applications in industries such as aerospace, automotive, and biomedical. Incorporating graphite and granite powders into the aluminium matrix has the potential to refine its grain structure. Graphite powder has the ability to function as a nucleating agent, thereby facilitating the development of small grains during the process of solidification. The incorporation of fine grains into the composite material has been observed to enhance its mechanical characteristics, including but not limited to its strength, toughness, and fatigue resistance. Solid solution strengthening is a method of strengthening materials by adding one or more elements to a base metal. This process involves the formation of a solid solution, which is a homogeneous mixture of two or more elements in a single phase. The added elements occupy the interstitial or substitutional sites in the crystal lattice of the base metal, which increases the strength and hardness of the material. Solid solution strengthening is commonly used in the manufacturing of alloys, which are materials composed of two or more metals. The precipitation-hardened Aluminium 7075 is renowned for its exceptional strength. The incorporation of graphite and granite powders results in an additional improvement in strength via the mechanism of solid solution strengthening. The reinforcing particles serve as hindrances to the movement of dislocations within the matrix, thereby obstructing plastic deformation and augmenting the strength of the material. It is noteworthy that the alterations in microstructure and corresponding mechanisms are contingent upon the processing parameters, proportion of reinforcement, and characteristics of the reinforcement materials employed.
4 Claims & 4 Figures , Claims:The scope of the invention is defined by the following claims:

Claim:
1. Reinforcing SiC, Granite and Graphite powders exhibited following characteristics:
a) Incorporating SiC at a weight percentage of 2% yielded a hardness value of 73 HRB, signifying a rise of 4.5% in comparison to the reference value.
b) Incorporating 2% weight of SiC and 2% weight of granite powder led to a hardness value of 78 HRB, indicating an elevation of 11.4% in comparison to the reference value.
c) The hardness value of a sample with a weight composition of 4% SiC and 2% granite powder was determined to be 83 HRB.
d) The sample consisting of 4% SiC and 2% granite demonstrated the greatest ultimate load of 8.735 kN and displacement of 1.89 mm.
e) The experimental results indicate that the specimens containing 2% SiC and 2% Granite, as well as those containing 2% SiC and 2% Graphite, exhibited similar performance. The maximum load capacities of these specimens ranged from 3.75 to 3.9 kN, with corresponding displacements of 1.05 to 1.1 mm.
f) The sample containing 2% SiC exhibited significant enhancements, attaining a maximum load of 4.16 kN and displacement of 1.39 mm.
2. As mentioned in claim 1, the presence of graphite particles serves as stress concentrators, thereby deflecting cracks and augmenting energy dissipation through inter-particle sliding with the matrix.
3. As mentioned in claim 1, the inclusion of granite powder in Metal Matrix Composites (MMCs) enhances the initial fracture toughness owing to its inherent characteristics of being hard and brittle.
4. As mentioned in claim 1, the superior performance of this specimen, in comparison to the other three samples, can be attributed to the heightened presence of ceramic SiC reinforcement particles.