A Review

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Stir Casting of Metal Matrix Composites – A Review

Article · March 2015

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Amit Pal, Sansar Swaroop Saxena, Abhishek Verma, Bhaskar Chandra Kandpal

International Journal of Computer & Mathematical Sciences IJCMS ISSN 2347 – 8527 Volume 4, Special Issue February 2015

Stir Casting of Metal Matrix Composites – A Review

Amit Pal

Department Of Mechanical Engineering Inderprastha Engineering College, UPTU

Ghaziabad, India Sansar Swaroop Saxena

Ghaziabad, India

Abhishek Verma

Ghaziabad, India Bhaskar Chandra Kandpal Department Of Mechanical Engineering Inderprastha Engineering College, UPTU

Ghaziabad, India Abstract— In the last few decades the global era

has been shifted from matrix composites to the Metal Matrix Composites. Due to their diversified properties they are being used in different sectors including majors as in automobile, aerospace and defense. Some most important properties includes good mechanical properties, its low density and better corrosion properties as compared to conventional metals and alloys. The distribution of reinforcement particulates in the matrix and the morphology of secondary matrix phase act as the most enticing part for mechanical properties of Metal matrix composites. Its low relative cost of production and beguiling mechanical properties make it a very attractive campaigner for the applications in both scientific and technological fields. Stir casting process appears a more wide and promising technique for production of metal matrix composite. This paper provides a literature review on MMCs and various effecting parameters like densities of reinforcements and metal matrices, stir speed, time of stirring, angle of stirrer and a wide range of research options which can be used and can be of vital importance for MMCs.

Index Terms— Metal Matrix Composites (MMCs), Stir casting.

I. INTRODUCTION

In last few decades the scientific approach towards the matrix composites changed significantly due to the doors unlocks in the diversified field of research for composites. The need for the search of new composites materials arises due to highly specific properties can be achieved in composites for a

specialized task and a another fact that the world is going to suffer in future due its limited resources of fuel. If talking with respect to fuel consumption now we require materials that are light in weight and withstand high strength in aerospace and automobile industry especially due to important deciding factor of fuel consumption. Since our fuel assets degrading at a significant rate in which major of them are finite resources. It’s zeal to search for composite materials. Matrix composites are composite materials in which major portion is in matrix form and reinforcement is added to it to enhance its properties. Matrix is continuous and uniform. Reinforcement is the material that is embedded in the matrix. Reinforcements can be added in the form of monofilaments or discontinuous form of short fibers, whiskers, particulates etc. Metal matrix composites are the composite materials that are composed of two phases, matrix phase and dispersed phase. The reinforcement material is embedded into the matrix.

Various techniques are developed to manufacture metal matrix composites but out of them stir casting process is most widely used because it is simple and cost effective. Stir Casting is a liquid state method of composite materials fabrication, in which a dispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal by means of mechanical stirring. The liquid composite material is then cast by conventional casting methods and may also be processed by conventional metal forming technologies.

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II. STIR CASTING

In stir casting we use stirrer to agitate the molten metal matrix. The stirrer is generally made up of a material which can withstand at a higher melting temperature than the matrix temperature. Generally graphite stirrer is used in stir casting. The stirrer is consisting of mainly two components cylindrical rod and impeller. The one end of rod is connected to impeller and other end is connected to shaft of the motor. The stirrer is generally held in vertical position and is rotated by a motor at various speeds.

The resultant molten metal is then poured in die for casting. Stir casting is suitable for manufacturing composites with up to 30% volume fractions of reinforcement.[1] A major concern in associated with the stir casting is segregation of reinforcement particles due to various process parameters and material properties result in the non-homogeneous metal distribution. The various process parameters are like wetting condition of metal particles, relative density, settling velocity etc. The distribution of particle in the molten metal matrix is also affected by the velocity of stirrer, angle of stirrer, vortices cone etc. In this method first the matrix metal is heated above its liquid temperature so that it is completely in molten state. After it is cooled down to temperature between liquid and solidus state means it is in a semi-solid state. Then preheated reinforcement particles are added to molten matrix and again heated to fully liquid state so that they mixed thoroughly each other [4].

III. FACTORS AFFECTING PROCESS

Information collected through various research papers show the following factors which affect the stir casting process the most. They are

1. Speed of stirring

2. Time duration of stirring 3. Stirring temperature A. SPEED OF STIRING

It is reported by several authors that uniform distribution of the reinforcement particles is necessary for the improvement in the properties of the particulate MMCs like hardness, toughness, tensile strength etc. The low rpm of the stirrer applies less shearing force on the matrix metal and

there is no space for the reinforcement particles (dispersed phase) to distribute uniformly throughout the matrix [2]. Moreover the dispersed phase has the tendency to agglomerate and form clusters. This happens due to the absence of the required force to resist it. At higher speeds of the stirrer the shearing force applied on the matrix metal is higher which creates the passage for the dispersed phase to move inside through the vortex created by stirring. The energy supplied by high speed rotation of the stirrer is strong enough to disperse the particles of the dispersed phase which causes uniform distribution of the dispersed phase into the matrix [2]. It was also founded out by the researchers that on increased stirrer speeds there is chance for the gas particles to move inside the matrix and increase the porosity.

B. TIME DURATION OF STIRRING

It plays a very important role in uniform distribution of dispersed phase into the matrix. Less time duration of stirring causes the clustering of the particles of reinforcement [5]. It is also seen that some portions of the matrix were found without inclusions of the reinforcement particles.

[3] Fig. 1. Microstructure of Al–10%SiCp MMC fabricated at 500 rpm: (a) 5 min stirring; (b) 10 min stirring; (c) 15 min stirring

[3] Fig. 2. Microstructure of Al–10%SiCp MMC fabricated at 600 rpm: (a) 5 min stirring; (b) 10 min stirring; (c) 15 min stirring.

As it is clear from the figure that on increasing the time of stirring, the distribution of the dispersed phase also increases which in turn improves the mechanical properties of the composite material.

C. STIRRING TEMPERATURE

It is also one of the most prominent parameters which affect the stir casting process. [3] On

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increasing the temperature of the matrix metal the viscosity decreases and the distribution of the particles is affected. The chemical reaction between reinforcement particles and metal matrix is accelerated on increasing the temperature of the melt.

IV. CONCLUSION

On increasing the speed of the stirring the properties of the composite material improves but not uniformly, this discontinuity is seen due to increase in porosity which deteriorates the mechanical properties of the composite material. On increasing the rotation speed of stirrer the shear force applied on liquid metal increases results in the more uniform distribution of reinforcement particles distribution over the molten matrix.

REFERENCES

[1] Sable, A.D., Deshmukh, S.D., “Preparation of MMCs By Stir Casting Method” IJMET, pp.3, (2012)

[2] Aqida, S.N., Ghazali, M.I., Hashim.J.,”The Effects Of Stirring Speed and Reinforcement Particles on Porosity Formation in Cast MMC” pp.

1, 2.

[3] Rajesh Kumar, Parshuram M., “Preparation Of Aluminum Matrix Composite by Using Stir Casting Method” IJEAT, Vol-3, (2013)

[4] J. Hashim, L. Looney, “Metal matrix composites:production by the stir casting method”

IJEAT (1999)

[5] Shubham Mathur, Alok Barnawal, “ Effect of Process Parameter of Stir Casting on Metal Matrix Composites” IJSR

[6] Clyne TW, Withers PJ, “An introduction to metal matrix composites”, 1st edition. Cambridge:

Cambridge University Press

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