Claims:The scope of the invention is defined by the following claims:

Claim:
1. A metal matrix composite comprising:
a) A magnesium matrix; and
b) A reinforcement includes Zirconium, Garnet and Graphite dispersed in the magnesium matrix.
c) The reinforcement has an average particle size ranging from 10 µm - 20 µm in diameter.
2. The composite recited in claim 1, wherein the amount of Zirconium 1 wt %; Garnet and Graphite ranges from 0.3 wt % - 0.9 wt % based on net weight of the metal matrix composite material.
3. The composite recited in claim 1, wherein the amount of reinforcement (Zirconium, Garnet, and Graphite) 0.6 wt % on net weight of the metal matrix composite material shows excellent tensile properties.
4. The composite of claim 1, whereas decrease in ductility was occurred with the increase in garnet particulate addition beyond 0.6 wt % on net weight of the metal matrix composite material shows
5. The composite of claim 1, wherein the particulate reinforcement (0.6 wt %) was uniformly distributed within the metal matrix pool which acted as a barrier to dislocation and augments the tensile property of the composite material.
6. The composite recited in claim 1, wherein increase in tensile strength is attributed to the formation of high dislocation density and strengthening of alloy followed with increase in volume fraction of the graphite and garnet particles. , Description:Field of Invention
The present invention pertains to improve the tensile properties of magnesium matrix composites reinforced with Zirconium, Graphite and Garnet.
Background of the Invention
Magnesium matrix composites gained significant attention by the aerospace and automotive industries for lower cost of production and reduced fuel consumption. Modern applications demand energy conservation and refined performance. Because of lower density, and higher specific strength compared with other structural metals, magnesium matrix alloys are considered for aerospace and automobile applications in order to minimize greenhouse emission and fuel consumption [S. Nimityongskul et al., Mater. Sci. Eng. A 527 (2010) 2104, B.L. Mordike et al., Mater. Sci. Eng. A 302 (2004) 37 and M. Habibnejad-Korayem et al., Mater. Sci. Eng. A 519 (2009) 198]]. However, lower rate of wear, poor resistance to creep at higher temperatures, lower strength and modulus restricts the applications of these alloys for fabricating major load bearing members in structural applications [Q.C. Jiang et al., Scripta Mater 48 (2003) 713 and P. Poddar et al., Mater. Sci. Eng. A (2007) 357]. Reinforcing with industrial grade particle reinforcements impart better physical and mechanical properties. Such composites is being considered as a better alternative for Al MMCs as a lightest metal structural material and possess several advantages over monolithic magnesium such as high strength, high elastic modulus, superior creep and wear resistances at elevated temperatures [M.Y. Zheng et al., J. Mater. Sci. 38 (2003) 2647 and V. Viswanathan et al., Mater. Sci. Eng. R 54(2006) 121]. The properties of Mg MMCs can be tailored through judicious selection of reinforcement particles. The reinforcement is selected based on the working temperature and ambience. Some of the commonly used particle reinforcements are Aluminium Oxide (Al2O3), Titanium Carbide (TiC), and Silicon Carbide (SiC). It is reported that addition of carbides as reinforcement improves the ultimate tensile strength, yield strength, hardness, ductility and wear resistance of Mg and its alloys [W.L.E. Wong et al., Comp. Sci. Technol. 67 (2007) 1541]. In our invention, Magnesium is reinforced with particulate Zirconium, Garnet and Graphite and proved its significance in improving the tensile properties of the composites.
In the area of matrix, many metallic systems were considered as matrix material including Al, Ag, Be, Co, Fe, Ti, Ni, and Mg. By far, aluminum matrix composites are considered to be the most suitable candidate for structural applications in aerospace and automobile applications. However, recent studies claimed that magnesium could be considered to be a better alternative as matrix material as it offers lower density and better mechanical properties compared with Aluminum. Magnesium is approximately two thirds lighter than that of aluminum, one fifth of steel and one quarter of zinc [M. Pekguleryuz et al., International Materials Reviews 55 (2010) 197]. Because of this, magnesium and its composites offer higher specific strength. The increase in demand for high performance and lightweight materials increases the need for magnesium matrix composites [M. Yu, Sci. 287 (2000) 63]. The magnesium matrix reinforced with thermally stable reinforcements makes them suitable for high temperature applications [S.C. Sharma at al., Wear 241 (2000) 33]. For magnesium matrix composites, ceramic powders are considered to be the most widely used reinforcement. High-temperature stability and structural properties of ceramic materials make them favorable reinforcement candidates desirable for reinforcements. These properties include lower density and high levels of strength, thermal stability, hardness, and elastic modulus [Q.C. Jiang et al., J Alloys Compd 386 (2005) 177]. However, lower wettability, compatibility and reduced ductility are some of the problems associated with ceramic reinforcements to be used along with magnesium matrix. The most commonly used reinforcements are Aluminium Oxide, Silicon Carbide (SiC), and Titanium Carbide (TiC). The microstructure and mechanical properties of SiC reinforced with magnesium matrix composites were reported in the earlier study [K.B. Nie et al., Materials Science and Engineering A 528 (2011) 5278]. TiC particulates reinforced with magnesium matrix composites shows excellent damping behaviour and mechanical properties [Zhang Xiuqing et al., Composites: Part A 37 (2006) 2011]. Bhingole et al. prepared and studied AZ91 alloy matrix composites reinforced with MgO and Al2O3 particles, formation of hard oxides improves the strain hardening exponent, hardness and ultimate strength of the composites [P.P. Bhingole et al., Composites: Part A 66 (2014) 209]. The major problem encountered by researchers in magnesium based composite material is decrement in tensile properties which is rectified in our invention.
Summary of the Invention
The tensile stress increases with particulate addition up to 0.6 wt% and it declined afterwards. A significant variation was observed in the fracture micro-mechanism with variation in volume fraction of the reinforcement particles. The presence of undulations was more for composites containing higher garnet particulate content. This was attributed through the higher cohesive strength between the reinforcement particulate with the matrix material. The reinforced particles remained intact, which is attributed through the good bonding between the matrix material and the reinforcement particles. The fractured surface exhibited the presence of uniform voids across the SEM micrograph. This was attributed through the uniform distribution of the reinforcement across the matrix material.
Brief Description of Drawings
The invention will be described in detail with reference to the exemplary embodiments shown in the figures wherein:
Figure 1 Weight percentage of particle reinforcement.
Figure 2 (2a) – Tensile strength and (2b) Percentage elongation of MG MMCs
Figure 3 Fractograph of Mg-MMCs (a) MGG 1 (b) MGG 2(c) MGG 3 (d) MGG 4 (e) MGG 5 (f) MGG 6 (g) MGG 7 (h) MGG 8 (i) MGG 9
Detailed description of the drawing
Figure 1 gives the varying weight percentage of reinforcement particles used to prepare the composites. The weights of the particles are varied in 9 different levels to find the optimized combination.

Figure 2 gives the variation in tensile strength and percentage elongation of the prepared composites. The presence of reinforcement particles imparts higher strength to the softer Mg matrix and imparts higher resistance to the applied tensile load. The uniformly distributed hard particles restricted the plastic flow and impart improved mechanical strength.
Figure 3 gives the fractography of the fractured composites. Close examining fractured surface revealed that fracture is often macroscopically brittle in nature. This was attributed through the low fracture strain.
Detailed Description of the Invention
The Magnesium MMCs is reinforced with Zirconium, Graphite and Garnet particles having a particle size of approximately 10-20µm in diameter. The tensile stress increases with particulate addition up to 0.6 wt% and it declined afterwards. Also, a decrease in the ductility was observed with the increase in garnet particulate addition. This infers that the deformation of composites is significantly influenced by these particulates. The load from the matrix material will get transferred to the reinforcement because of the strong interface bonding. The uniformly distributed reinforcement acted as a barrier to the dislocation and increased the tensile strength of the composites. The increase in tensile strength is also attributed to the formation of high dislocation density and strengthening of the alloy followed with increase in the volume fraction of the graphite and garnet particles. The dislocation density is associated to the difference in thermal expansion between the reinforcement and metal matrix. The volume fraction of reinforcement has significant influence in improving the strength of the particle-reinforced composites. The presence of reinforcement particles imparts higher strength to the softer Mg matrix and imparts higher resistance to the applied tensile load. The uniformly distributed hard particles restricted the plastic flow and impart improved mechanical strength.
The fractography of the fractured composites are given in Figure 3. Close examining the fractured surface revealed that the fracture is often macroscopically brittle in nature. This was attributed through the low fracture strain. The SEM micrograph of fractured surface revealed the presence of micro voids having submicron size. The dimple structure observed over the fractured surfaces were attributed through decohesion or fracture of the graphite particles. During tensile loading, micro-voids present along the reinforcement-matrix interface acts as crack nucleation sites. The induced cracks propagate along the grain boundaries with progressive loading. A significant variation was observed in the fracture micro mechanism with variation in volume fraction of the reinforcement particles. The macroscopic entities present over the fractured surface preclude an investigation over the damage accumulation mechanism. Despite the similar mechanism for fracture, presence of undulations was more for composites containing higher garnet particulate content. This was attributed through the higher cohesive strength between the reinforcement particulate with the matrix material. This increase in cohesive strength imparted higher tensile strength to the prepared composites. Surface cracks were present over the fractured surfaces. The percentage of cracks got reduced with higher volume fraction of graphite. The propagation of cracks along the soft matrix material was restricted by the harder reinforcement particles.
The importance of uniformly distributed reinforced materials can be observed from the microstructure of the fractured surfaces performed over the hybrid composites. All composite specimens exhibited brittle fracture. It was observed that higher volume fraction of hardened reinforcement particles imparts higher degree of brittleness into the softer ductile-matrix material. The reinforcement particles void the crack nucleation. The size of the reinforcement particles and their distribution inside the matrix material significantly control the brittleness of the prepared composites. The fractured surfaces were characterized with micro-voids whereas the fractographs of the hybrid composites containing garnet particles above 0.6wt% exhibited comparatively larger voids. The local volume fraction of reinforcement is considered to be more important than the average volume fraction in determining the tensile strength of the composites containing larger volume fraction of reinforcement. Increase in the percentage of reinforcement results in the clustering of reinforcement particles. The micrographs for composites containing higher percentage of reinforcement were free from clusters. However, the dendrites were closely packed with reduced primary arm spacing. This attributed to the formation of larger voids in the fractured surfaces of the prepared composite containing larger volume fraction of reinforcement. The micro-mechanism of the fracture was greatly influenced by the details in the matrix microstructure. The reinforced particles remained intact, which is attributed through the good bonding between the matrix material and the reinforcement particles. The fractured surface exhibited the presence of uniform voids across the SEM micrograph. This was attributed through the uniform distribution of the reinforcement across the matrix material. This emphasizes the relationship between the reinforcement particle size and their distribution characteristic over the fracture mechanism leading to the composite failure.