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InfluenceofGraphiteReinforcementonMechanicalPropertiesofAluminum-BoronCarbideCompositesARTICLEJANUARY2013DOI:10.4028/www.scientific.net/AMR.845.398

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Influence of Graphite Reinforcement on Mechanical Properties of

Aluminum-Boron Carbide Composites

C.Muthazhagan1,a, A.Gnanavel babu2,b, G.B.Bhaskar3,c, K. Rajkumar4,d 1Department of Mechanical Engineering, S.K.P Engineering College, Tiruvannamalai, Tamil Nadu

- 606 611, India

2Department of Automobile Engineering, Karpaga vinayaga College of Engineering and

Technology, Chennai, TamilNadu - 603 308, India

3Department of Mechanical Engineering, Tagore Engineering College, Chennai, TamilNadu - 600

127, India.

4Department of Mechanical Engineering, SSN College of Engineering, Chennai, TamilNadu - 603

110, India.

a jeevamudhan@yahoo.co.in,

bdr.agbabu@gmail.com,

cbhaskaran01@yahoo.com,

drajkumark@ssn.edu.in

Keywords: Al-B4C, Two-Step Stir Casting method, Conventional Heat Treatment, Solid lubricant Graphite.

Abstract. This paper deals with the mechanical properties in conventional heat treatment of Al

(6061)-B4C-Graphite. Aluminium Metal Matrix Composites (MMC) is fabricated through two step

stir casting method. The composites were fabricated with various volume percentage levels as

Aluminium reinforced with (5, 10 &15%) Boron Carbide and (5,10 & 15%) of Graphite. Fabricated

composites were subjected to conventional heat treatment for enhancing the mechanical properties.

Influences of Graphite reinforcement on mechanical properties of Aluminum-Boron carbide

composites were analyzed. The microstructure studies were also carried out. It is observed that

increasing the graphite content within the aluminum matrix results in significant decrease in

ductility, hardness, ultimate tensile strength. The addition of boron carbide conversely increased the

hardness of the composites.

Introduction

Metal matrix composite can be fabricated by using several techniques including powder

metallurgy, molten metal and spray deposition [1].Metal matrix composites , combine the metallic

properties such as high ductility with ceramic properties such as high strength [13]. Generally,

casting or molten metal technique is always used to manufacture aluminium composite with

particulate or continuous fibre reinforcement. Powder metallurgy method was employed to produce

aluminium composites reinforce with non continuous fibre such as SiC, Al2O3 etc. Among modern

composites materials, particulate reinforced metal matrix composites (MMCs) are finding increased

applications due to their favourable mechanical properties such as improved strength, stiffness and

increased wear resistance compared to unreinforced alloys. Combining high specific strength with

good corrosion resistance, metal matrix composites (MMCs) are materials that are attractive for a

large range of engineering applications [12].Metal Matrix Composite shows enhanced properties

compared to unreinforced alloys. Al-MMCs have become the necessary materials in various

engineering applications such as aerospace, marine and automobile products applications such as

engine piston, cylinder liner, brake disc/drum etc [1]. Aluminium metal matrix reinforced with

Boron Carbide (B4C) is a novel composite, which is used in automotive industries (ex. brake pads

and brake rotor) due to high wear resistance [15], high strength to weight ratio, elevated temperature

toughness and high stiffness. B4C is also used in the nuclear industry [2] as radioactivity

containment vessels and control rods fixture, since B4C is a neutron absorber, high-temperature

thermoelectricity conversion [3, 4] and ballistic protections [5].

Advanced Materials Research Vol. 845 (2014) pp 398-402Online available since 2013/Dec/04 at www.scientific.net (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.845.398

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 101.222.246.59, Karpaga Vinayaga College of Engineering and Technology, TamilNadu, India-05/07/14,05:51:01)

These characteristics have made this composite as a very potential material in engineering field.

The usage of aluminium reinforced with boron carbide composite becomes especially in neutron

application due to its ability to absorb neutron very well. This composite is used as shielding

materials to absorb free neutron released during the reaction in the nuclear reactor and to avoid any

radiation escape to the surrounding environment. A clear interfacial reaction product was found at

AlSiC interface for composites processed for long period, while no reaction product was observed

at AlB4C [6]. Heat treatment is a process used to change certain characteristics of metals and

alloys in order to make them more suitable for a particular application. It can greatly influence

physical and mechanical properties such as strength, hardness, ductility, toughness and wear

resistance of the alloys [7]. It is often associated with increasing the strength of material, but

increase in hardness also make machinablility difficult using conventional machinery[14] , so it can

also be used to alter certain manufacturability objectives such as improve machining, improve

formability. Conventionally processed or casted products exhibited higher porosity and coarser

microstructure [8].

Self lubricant reinforcement like graphite improves antifriction properties due to its lamellar

structure [9]. The self lubricating effect of graphite is necessary for the lead free Aluminium-Boron

Carbide contact materials. The addition of graphite improves the machinablility [16]. This paper

deals with effect of the boron carbide and graphite reinforcement on mechanical properties of

aluminum matrix.

Experimental Details

Preparation of composites. Boron Carbide particles of 25 m size were used in this study. Two

step stir casting method was used to fabricate the Al-B4C-Graphite. Aluminium alloy was melted

up to C. aryin olume 5 5 of reinforcement B4C and graphite) was added

with this molten Al-6061 alloy. It is allowed to cool to solidus temperature and stirred at 120 rpm

using steel impeller. In this way 100% of the B4C particles were transferred to the metal.

Simultaneously, graphite was added with Al-B4C. Then stirred composite material is transferred to

metal mould. Composites were cast into a cylindrical rod in required diameter and length.

Heat Treatment. The mechanical properties of Al 6061 in T6 condition are better than the same

of wrought Al 6061 [10]. Hence heat Treatment (T6) was carried out for the different composition

samples in using a heat treatment furnace. 1500W muffle furnace was used to heat treat the Al

6061-B4C-Graphite. In order to obtain T6 property of Al-6061 alloy, solution heat treatment was

carried out over the material and it was heated up-to 520oC in muffle furnace. After reaching

required temperature, the composite material was maintained for definite holding time at 520oC.

With this procedure, all the samples were heat treated.

Microscopic Examination. The heat treated composites were polished according to standard

metallo raphic procedures etched with Kellers reagent [11] and observed in Scanning Electron

Microscope.

Mechanical Properties. The hardness of the Al-B4C(5,10 & 15%)-Graphite(5,10 & 15%) was

carried out using Brinell Hardness machine at load of 1500kgf.In order to find Tensile strength of

the material, UTM machine was used. As per the ASTM B557M-10 for the Alumnium alloys, the

material was sized and tested for the tensile strength. The obtained results were compared for

various volume percentages of B4C and graphite.

Results & Discussion

Microstructure. The microstructure of the Al-B4C-Graphite is shown in Fig.1 (a,b). A typical

micrograph of Al6061-B4C-graphite composites shows a reasonably even distribution of graphite

particles and boron carbide. It is to be noted that the B4C & graphite particles were simply

entrapped by the primary aluminium 6061 during the solidification of the composite melt. It is also

observed that porous sites were minimal.

Advanced Materials Research Vol. 845 399

a b

Fig.1 (a) Al-B4C(5%)-Graphite(5%) (b) Al-B4C(5%)-Graphite(15%)

Mechanical Characteristics. Fig.2 shows the hardness of heat treated composites of Al in 5, 10

& 15% B4C with constant 5 &10% of graphite. It can be seen that the addition of B4C particles

improves the mechanical properties of the resulting composite. It is observed that increasing the

percentage of B4C in Al matrix, hardness of the composite is increased due to pinning down the

dislocations.

Fig.2. Hardness of Al in 5,10 &15% of B4C Fig.3. Tensile Strength of Al in 5,10 &15% of

with constant 5&10% of Graphite B4C with constant 5&10% of Graphite

Fig.3 shows the tensile results of Al-B4C (5, 10 & 15%) with constant 5&10% of graphite. The

tensile strength of MMC is mainly depending on reinforcement strength and interfacial strength

between matrix and reinforcement. Tensile strength of hybrid MMC is 378 MPa in stir casting

method. It is observed that decrease in tensile strength of produced composite material with

increasing in boron carbide particles. This is due to inadequate interface bond between particulates

and matrix.Fig.4 shows the hardness of Al composites with varying % level of graphite for constant

(5,10 &15%) of B4C particles. It is understood from the results, addition of graphite paricles

decreases the hardness of the composite. The reason for decreasing hardness while adding graphite

is soft nature of the graphite.

400 Materials, Industrial, and Manufacturing Engineering Research Advances 1.1

Fig.4 Hardness of Al in constant (5, 10 & 15%) Fig.5 Tensile Strength of Al in constant

of B4C with varying (5,10 & 15%) of Graphite (5,10 & 15%) of B4C with varying (5,10 &

15%) of Graphite

Fig.5 shows the tensile strength of the Al in constant (5, 10 &15%) of B4C with varying % level

of graphite. It is observed from the graph, increasing the graphite volume fraction is decreased the

tensile strength of the composites. The reason is that interfacial bond between graphite particles and

aluminium matrix is poor. As well, boron carbide increased the hardness of the aluminium, mean

while decreased the tensile strength of the composites. The addition of graphite particles greatly

reduced the elongation of the composites.

Conclusion

Hybrid metal matrix composites were successfully fabricated using stir casting method.

Reinforcement particles such as boron carbide and graphite were uniformly distributed in Al matrix.

The hardness of the composite is increased with increasing of boron carbide particles in Aluminium

matrix. The hardness of the composite is decreased with increasing of graphite particles in

Aluminium matrix. Addition of boron carbide and graphite greatly influences the tensile properties.

Acknowledgements

The author would like to thank the previous researchers for their contributions in the area of

graphite reinforcements and their valuable references.

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