MECHANICAL CHARACTERIZATION OF LM25/ COPPER …...Table 1 Chemical composition of LM 25 alloy, wt. % Cu Mg Si Fe Mn Ni Pb Sn Ti Zn Al 4.42 1.769 0.052 0.663 0.131 0.072 0.029 0.012

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 7, July 2018, pp. 844–851, Article ID: IJMET_09_07_091

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=7

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

MECHANICAL CHARACTERIZATION OF

LM25/ COPPER POWDER REINFORCED

METALLIC COMPOSITES

M. Naga Swapna

Assistant Professor, Dept. of Mechanical Engineering, PVPSIT, Vijayawada Guntur-INDIA

V. Chittaranjan Das

Professor, Dept. of Mechanical Engineering, RVR JC College of Engineering Guntur-INDIA

ABSTRACT

Aluminium metal-matrix composites were broadly used where high strength and

low weights are desired. To overcome the limitations with metal ceramic composite

systems metallic composite systems were developed. These systems serene of two

different metals having good solubility and may give a good, uniform and attuned

interface, when they are used as matrix and the reinforcement. The limited solubility

led to the alloy formation passing solid solution strengthening while the undissolved

particles help achieving dispersion strengthening. A356 alloy and pure copper

powders has been used as matrix and reinforcements. The composites (5 to 15 wt. %

reinforcements) were synthesized through stir casting technique by dispersing pure

copper powders of 53 microns. A decrease in reinforcement size was identified with

increasing reinforcement content, which improved the surface area to the volume ratio

of the resultant particulates. Composites exhibited improved hardness compared to

the matrix of the alloy. The specific properties of the ultimate tensile strength, yield

strength, young’s modulus and ductility have shown improved specific properties

compared to the alloy. Similarly, the specific property interms of ductility has been

proved better compared to that of alloy.

Keywords: metal-matrix composites, matrix and reinforcements and stir casting.

Cite this Article: M. Naga Swapna and V. Chittaranjan Das, Mechanical

characterization of LM25/ Copper powder Reinforced metallic composites,

International Journal of Mechanical Engineering and Technology, 9(7), 2018,

pp. 844–851.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=7

Mechanical characterization of LM25/ Copper powder Reinforced metallic composites


1. INTRODUCTION

An aluminium metal-matrix composite with ceramic particulate reinforcement enhances the

specific strength, elastic modulus. Most of the investigations and research in MMCs,

prioritized in increasing strength and hardness properties. Presence of hard and brittle

reinforcements, restrict the mobility dislocation, thus enhancing the strength properties. On

the other hand, ductility decreases to a great extent, due to lack of interfacial bonding between

the matrix and reinforcements. A. Ibrahim et al. [1] in this review author studied the

mechanical properties that can be obtained with metal matrix composites by varying

reinforcement percentage by 0, 10, 15, 20% and taking different alloy AA 6061, AA 2014,

AA 356. Conclusion of this paper is by increasing reinforcement percentage yield strength,

ultimate strength is increasing but elongation of alloy decreases. D.J. Lloyd et al. [2] White

house et al. [3] and Bretheau et al. [4] studied the effect of particle induced damage in

MMCs, with MMCs reinforced by particles with a size greater than 10 µm, the dominant

damage mechanism was cracking of particle and that the particle -matrix interface appeared to

have little effect on the overall damage fracture behaviour. Thus the properties of MMCs do

depend on the size of the particulates to a considerable extent. Song et al. [5] and Qin et al.

[6] inferred through extensive experimentations that the ductility and fracture toughness of

particle reinforced metal matrix composites (PRMMCs) are affected adversely due to the

presence of the hard and brittle ceramic reinforcement, due to discontinuous interface between

the matrix and reinforcement. The presence of the discontinuous reinforcement phase in a

continuous Aluminum alloy metal– matrix results in properties that are not attainable by other

means. However, many researchers [7-10] have commented on limitations to the wide spread

applications and use of these composites owing to their lower fracture toughness and poor

tensile ductility compared to the un reinforced counterpart. K.Chawla et al. [11] made a

detailed study of the mechanical behavior and microscopic characterization of SiC particle

reinforced aluminum matrix composites fabricated both by sinter forging and extrusion. They

observed that the extruded material exhibited higher strain to failure values while the higher

values of young’s modulus and UTS were attributed to the absence of any significant

processing- induced particle fracture, the lower strain to failure was attributed to poorer

bonding between the matrix and the reinforcing particles of the sinter forged test sample

compared to the extruded one. Varun Sethi [12] reported that incorporating ceramic particles

in A356 matrix results in weakening of the interfacial bonding and eventually resulting in the

pull-out of the SiC particle, because of the lattice straining in the surrounding areas of the

particles, there will be a reduction in the extent of plastic deformation that these areas can

undergo, which will make them more susceptible to cracking. These cracks will result in the

removal of the matrix from adjacent areas of the particles, thereby decreasing the strength of

interfacial bond. Madhusudhan et al. [13] reported that metal-metal combination system with

restricted solubility, termed as metal-metal composites were fabricated by stir casting route

To have good compatibility between the matrix and the reinforcement, an established alloy

system with proven application (Al-Cu system), where the solvent acts as the matrix and the

solute as the reinforcement. Strengthening of the resultant composite can be achieved by a

combination of reinforcement and alloying.

M. Naga Swapna and V. Chittaranjan Das


2. EXPERIMENTAL WORK

2.1. Materials

2.1.1. Matrix Material

LM25 alloy was wsed as matrix material for the fabrication of composites and the

composition have been showed below

Table 1 Chemical composition of LM 25 alloy, wt. %

Cu Mg Si Fe Mn Ni Pb Sn Ti Zn Al

4.42 1.769 0.052 0.663 0.131 0.072 0.029 0.012 0.013 0.11 balance

2.1.2. Reinforcement Material

Pure copper powder of EC grade has been used as the reinforcement material in the present

investigation, powders were procured from NICE metal industries, an average particle size of

53 μm was used.

2.2. Fabrication of Composites

All the composites were produced through stir casting technique, which is a proven and well

established method for composite (AMMC) making. A356 alloy was melted in an electric

resistance furnace. A temperature of 740 0

C, was maintained throughout the process. The melt

(1 kg) was thoroughly degassed using Argon, and gas jacket on melt was maintained

throughout the process. A vortex was created at an rpm between 750 and 800 using a graphite

impeller, preheated (300 0

C) Pure copper powder were added quickly (5-15 wt.%) and

continuously to the vortex, through a screen. At the end the particulate addition, composite

was cast into a Grey Cast Iron mould. Hot ingot was transferred to a furnace at 100 0C, and

homogenized for 24 hrs.

Vickers hardness studies were carried out for the investigated alloys and composites using

Vickers hardness tester (Leco Vickers hardness tester, Model: LV 700, USA) with 1 kg load.

An average of six readings was taken for each hardness value. Tensile strength of composites

at room temperature was determined using INSTRON 500kN UTM 8803 J 5353, UK with an

electronic extensometer as per ASTM E-8 standards. Scanning electron microscopy (SEM)

and Energy Dispersive X-ray Spectroscopy (EDS) were carried out using SEM-Hitachi S-

3400N– Japan and SEM–ZEISS SUPRA 55VP operated at 20 kV, in order to evaluate the

morphological and chemical compositions. The X-ray diffraction (XRD) pattern of

reinforcement material was carried out using RGAKU, ULTIMA-IV H-12-JAPAN for

identification of phases

3. RESULTS AND DISCUSSION

3.1. Microstructural Behaviour

It is evident from the microstructures that with increasing reinforcement content, the particle

size is decreasing. An average of 40 readings was considered in each image, with over 15

SEM images for each composite. Few selected particles have been shown with magnified

letters. Table 2 shows the average particle size of the reinforcement with increasing weight

fraction. Since addition time for particulate material increases with increasing weight fraction,

the particulates present in the molten metal for larger periods. Hence, there is surface

disbanding in the matrix and correspondingly particulate size reduction is observed.



Table 2

Reinforcement percentage Particle size

5 9.619 ±0.42

10 5.825 ±0.33

15 4.300 ±0.33

The decrease in particle size with increasing reinforcement content enhances the surface

area to the volume ratio of the resultant particulates. This further enhances the bonding

between the matrix and the reinforcement. These microstructures have been shown in figure

1.

Figure (a) Figure (b)

Figure (c) Figure (b)

Figure 1 Microstructures of composites, showing reduction in particulate sizes a) Copper particulates

b) 5% c) Copper particulate d) uniform distribution

The EDS spectrum of the composite shows the presence of Al, Si and Cu in the matrix

phase, figure 2, and Al, Cu and Mg constituents on the reinforcement, figure 3. The matrix

doesn’t show any increment in Cu and Mg concentration reveals that the dissolution of the

reinforcement is restricted to its vicinity. Similarly, the reinforcement phase shows only the

constituents, such that no contamination of silicon has occurred. Since, perfect shielding of

argon gas is maintained, traces of oxygen is not seen either with the matrix or the

reinforcement. An average of six readings was taken on the matrix, free from particulates.



Figure 2 EDS of A356 Matrix

Figure 3 EDS of composite

3.2. Hardness Studies

Hardness values of the composites were found to be increasing with increasing reinforcement

contents. This can be attributed primarily to the refined grain structure of matrix, presence of

harder reinforcement and harder CuMgAl2 phase in the matrix. Also the increase may be due

to increase in interfacial area between the matrix and the reinforcement leading to increase in

strength appreciably. Composites exhibit improved hardness values compared to the matrix of

the alloy, figure 4, hardness found to be increasing with increasing reinforcement content

from 55 to 98 VHN i.e. 70 %.

Figure 4 Hardness variations of composites

Similar behaviour of increase in hardness with increasing silicon carbide between 5 and

15 wt %, as reinforcement in A356 alloy [15]. Presence of SiC particles which are very hard

dispersoids contribute positively to the hardness of the composite. The increased hardness is

also attributable to the hard SiC particles acting as barriers to the movement of dislocations

within the matrix.

Howell et al. [16] and Vencl et al. [17] reasoned the improvement of the hardness of the

composites to the increased particle volume fraction. Wu [18] and Deuis [19] attributed this

increase in hardness to the decreased particle size and increased specific surface of the



reinforcement for a given volume fraction. J.B Rao et al. [20] reported the improvement in

hardness in aluminum alloys by reinforcing with flyash as between 5 and 15 wt%. Particulates

with major formation of alumina and silica are hard in nature. With increase in volume

fraction of the reinforcements, more load is transferred to the reinforcements, resulting in

higher strength values.

3.3. Tensile Behavior of Composites

Figure 5 shows the fracture behavior of alloy and the composites under tension. Compared to

the alloy, the composites show higher strength values and the strength increases with

increasing reinforcement contents. Figure 6 shows the fractured tensile samples of

composites.

Figure 5 Fractured tensile samples

The modulus of elasticity increased from 9 to 25% with the addition of 5 to 15%

reinforcements. Presence of reinforcement restrict the mobility of the dislocation enhance the

modulus to higher values. Similar behaviour was identified by many researchers. The ductility

of the A356/fly ash reinforced composite decreased with the increase in weight fraction of the

fly ash [21]. This is due to the hardness of the fly ash particles or clustering of the particles.

The various factors including particle size, weight percent of reinforcement affect the percent

elongation of the composites even in defect free composites. The ultimate tensile strength

increased by 28 to 37% and yield strength increased by 10 to 15% with addition of 5 to 15%

reinforcements, transfer of stress from the matrix to the reinforcement may be one of the

reasons. Similar behavior was observed by many researchers. The ductility found to be more

with alloy compared to the composite, as the percentage of the reinforcement content

increases.

M. Vanarotti [22] reported a marginal increase in ultimate tensile strength with increase of

silicon carbide content in the matrix. The increase in strength was not commensurate with

corresponding increase in hardness. This perhaps can be attributed to insufficient

homogeneity obtained on account of improper stirring during the casting of the composite.

The % elongation of the composite decreased as the percentage of the reinforcement content

increases in the composite and this appears to be quite obvious from the enhanced hardness

associated with higher SiC content. Basavarajappa et al. [23] reported that the hard fly ash

particles obstruct the advancing dislocation front, thereby strengthening the matrix. However,

as the size of the fly ash particles increased, there was decrease in tensile strength. Good

bonding of smaller size fly ash particles with the matrix is the reason for this behavior. The

observed improvement in tensile strength of the composite is attributed to the fact that the

filler fly ash possess higher strength, also they concluded the decrease in the tensile strength

of the samples with fly ash weight fraction beyond 15 % is due to the poor wettability of

the reinforcement with the matrix.



4. CONCLUSIONS

1. Composites were fabricated by reinforcing pure copper Particulates in LM25 matrix.

2. Resultant composites were secondary processed by direct hot extrusion.

3. The decrease in particle size with increasing reinforcement content was due to

increased casting time during processing.

4. Presence of reinforcement decreased the resistivity of the resultant composite

5. Composites exhibited improved hardness values compared to that of the alloy.

6. Increased reinforcement content enhanced the strength properties in terms of yield

strength, ultimate tensile strength and modulus of elasticity.

7. The decrease in particle size caused

a. Enriched matrix concentration with alloy contents.

b. Enriched interfacial bond between the particulates and the matrix.

c. Fine grained structure due to increased nucleation phenomenon.

d. Enriched intermetallics contents.

e. Increased surface are to volume ratio of the particulates/reinforcement for

cumulative effect of above.

REFERENCES

[1] I.A. Ibrahim, Particulate reinforced metal matrix composites-a review, Journal of

materials science, 26, 1991, 1137-1156

[2] D.J. Lloyd, Particle reinforced aluminum and magnesium matrix composites, International

Materials Reviews 1994 Vol.39 No.1.

[3] Whitehouse, A.F. Clyne and T.W. Acta Metallurgy & Material Sci, 1993; 41:1701.

[4] Ribes, H., Da Silva, R., Suery and M., Bretheau, T., Mater Sci Technol, 1990, 6:pp.621

[5] Song, S.G., Ghi, N., Gray III, G.T. and Roberts, J.A. Metallurgy & Material Sci Mater.

Trans. A27, 1996, pp.3739

[6] Qin, S., Chen, C., Zhang, G. Material Sci. Eng., A272, 1999, pp.363

[7] Sugimura, Y, Suresh, S., Effects of SiC content on fatigue crack growth in aluminium

alloys reinforced with SiC particles. Metall Trans, 1992; 23A.

[8] Liaw, P.K., Logsdon, WA. Engineering. Fracture. Mech., 1986

[9] Davidson, D.L. Engineering. Fracture Mech., 1989; 33:965-77

[10] Manoharam, M., Lewandowski, J.J., Acta Metal, 1990; 38(3): 489-99

[11] Chawla, N., Williams, J and Saha, R., Journal of light metals, 2, 2002, 215-227

[12] V. Sethi, Effect of aging on abrasive wear resistance of silicon carbide particulate

reinforced aluminum matrix composite, M.S Thesis 2007

[13] S.Madhusudan, Fabrication and characterization of aluminium-copper composites,

International journal of alloys and compounds, 2009, pp.116-118

[14] Biljana Zlaticanin, Charectrization of structure and properties of As-cast AlCuMg alloys,

Met Trans, Vol 45, No. 2(2004) pp. 440 - 446

[15] M. Vanarotti, Synthesis and characterization of aluminium Alloy A356 and SiC Metal

Matrix Composite, 2nd International conference on industrial technology and

management, Singapore DOI: 10.7763/IPCSIT.2012.V49.3

[16] G.J. Howell, Dry sliding wear of particulate-reinforced aluminium alloys against

automobile friction materials, wear 181-183 (1995) pp.379-390.



[17] A. Vencl, and I. Bobi, Effect of thixocasting and heat treatment on the tribological

properties of hypoeutectic Al–Si alloy, Wear, 2008, pp.616-623

[18] J.M. Wu, Contributions of the particulate reinforcement to dry sliding wear resistance of

rapidly solidified Al-Ti alloys, wear 244 (2000) pp.147–153

[19] R.L. Deuis, C. Subramanian and J.M. Yellup, Abrasive wear of aluminium composites-A

review, wear, 1996, pp.132–144

[20] J.B. Rao, Mechanical properties and corrosion behaviour of fly ash particles reinforced

AA 356 composites, Journal of composite materials, June 2012, vol46, pp. 1393-1404

[21] M.K. Surappa, Synthesis of flyash particle reinforced A356 Al composites and their

characterization, Materials Science and Engineering (A) 480, (2008), pp.117–124

[22] M. Vanarotti, Synthesis and characterization of aluminium alloy A356 and SiC Metal

Matrix Composite, ICITM Singapore, IPCSIT.2012.V49.3

[23] K Praveen Kumar, M Gopi Krishna, J BabuRao, and NRMR Bhargava “Fabrication and

Characterization of 2024 Aluminum - High Entropy Alloy Composites”, Journal of Alloys

and Compounds, 640 (2015) 421–427.

http://www.sciencedirect.com/science/article/pii/S0925838815008063

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MECHANICAL CHARACTERIZATION OF LM25/ COPPER …...Table 1 Chemical composition of LM 25 alloy, wt. % Cu Mg Si Fe Mn Ni Pb Sn Ti Zn Al 4.42 1.769 0.052 0.663 0.131 0.072 0.029 0.012