Published in International Journal of Advanced Engineering & Application, Jan 2011 Issue 71

Studies on Mechanical Properties of Al6063-SiC

Composites

1G.R.C. Pradeep,

2A. Ramesh,

3G.B. Veeresh Kumar

1Associate Professor, Dept of Mech Engg, Sri Venkateswara Institute of Technology,Rapthudu Bypass, Anantapur – 515 001, India

2Principal, Gates Institute of Technology,Gootyanantapuram (Vill), Gooty, Anantapur, A.P., India 3Assistant Professor, Dept of Mech Engg, S B M Jain College of Engineering, Jain University, Kanakapura Tq,

Abstract – In recent times the application of Aluminium Metal Matrix Composites (MMCs) as engineering materials has

exceedingly increased in almost all industrial sectors. Aluminum MMCs are preferred to other conventional materials in

the fields of aerospace, automotive and marine applications owing to their improved properties like high strength to weight

ratio, good wear resistance etc. These materials are of much interest to the researchers from past few decades. In this

paper it is aimed to present the research findings of Al6063–SiC particulate metal matrix composites prepared by liquid

metallurgy route (stir casting technique). The amount of reinforcement is varied from 0 to 9 wt. %. The SiC particulates

were dispersed the in steps of 3 into the Al6063 alloy. The prepared composites are subjected to the mechanical testing as

per the ASTM standards. The Brinell‘s hardness of the composite was found to increase with increase in filler content in

the composite. The tensile strength of the composites was also found to increase confirming the enhancement of the

mechanical properties.

Key words – Al6063, SiC, composites, hardness, tensile strength, mechanical properties

I. INTRODUCTION

Metal matrix composites are of wide interest owing

to their high strength, fracture toughness and stiffness.

Among the various MMCs used in industry, the

composite consisting of Al6061 matrix alloy reinforced

with SiC has found wide application [1]. In the

investigation of wear behaviour of Al6061 alloy filled

with short fiber (Saffil) it was concluded that Saffil

reinforcement are significant in improving wear

resistance of the composites[2]. Self-lubricating graphite

was incorporated in Al6061 alloy to prepare composites

[3]. Al2O3, B4C, Ti3Al, and B2Ti in Al6061, were used to

show that Mechanically Mixed Layers (MML) are

generated during sliding wear condition [4].

Transition from mild to severe wear was noticed

when the surface temperature reaches about 0.4 times

the melting temperature of Al6061 alloy [5]. In pin-on-

disc test a mechanically mixed layer (MML) six times

harder than the bulk material is produced. This layer is

responsible for reduction in wear rate of MMCs [6].

Friction coefficient value of the composite was also

found to increase due to the presence of hard MML layer

and plastic deformation of the steel disc during sliding

[7]. The light metals such as Al and its alloys form

superior composites suitable for elevated temperature

applications when reinforced with ceramic particulates

[8]. It was found that the matrix hardness has a strong

influence on the dry sliding wear behaviour of Al2O3

particulate Al6061 MMC [9].

In the investigation on the tribological behavior on

Al6061 reinforced with Al2O3 particles it was concluded

that a characteristic physical mechanism exists during

the wear process [10]. When a sufficiently high load is

applied on the contact, the matrix phase is plastically

deformed, and the strain is partially transferred to the

particulates, which are brittle with small failure strains.

It was clearly demonstrated that the effects of applied

load and temperature on the dry sliding wear behavior of

Al6061 alloy matrix composites reinforced with SiC

whiskers or SiC particulates and concluded that, the

wear rate decreased as the applied load is increased [11].

At higher normal loads (60N), severe wear and

silicon carbide particles (SiC) cracking and seizure of

the composite was observed in pin-on-disc test during

dry sliding wear of Al2219 alloy MMCs [12]. MMCs

having SiC of 3.5, 10 and 20 μm size with 15 vol. %,

produced by P/M route displayed good wear resistance

with increasing particle size in sliding wear [13]. Sliding

distance has the highest effect on the dry sliding wear of

MMCs compared to load and sliding speed [14].

Addition of 20% reinforcements increases the wear

resistance of the composites, but beyond that no

improvement was observed [15].

The above literature reveals that very little

information is available regarding the mechanical

behaviour of the composites with MMCs of Al6063

reinforced with SiC particulates. Hence the present paper

describes the mechanical behavior of SiC filled Al6063

metal matrix composites.

II. EXPERIMENTAL DETAILS

The following section highlights the material, its

properties and methods of composite preparation and

testing.

A. Materials used

The matrix material for the present study is Al6063.

Table I gives the chemical composition of Al6063. Table

II gives the details of the physical and mechanical

properties of Al6063. The reinforcing material selected

was SiC of particle size of 15 μm. Table III gives the

details of the physical and mechanical properties of SiC.

TABLE I CHEMICAL COMPOSITION OF AL6063 BY WT%

Si Fe Cu Mn Mg

0.6 0.3 0.1 0.1 0.8

Cr Zn Ti Al

0.1 0.1 0.1 Bal

Published in International Journal of Advanced Engineering & Application, Jan 2011 Issue 72

Variation in Hardness

25

30

35

40

45

50

55

0 1 2 3 4 5

% SiC in Al6063

Hard

ness B

HN

TABLE II PHYSICAL AND MECHANICAL PROPERTIES OF

AL6063 AND SIC

Elastic

Modulus

(Gpa)

Density

(g/cc)

Hardness

(HV)

Tensile

Strength

(Mpa)

69.5 2.7 25 100

TABLE III PHYSICAL AND MECHANICAL PROPERTIES OF SIC

Elastic

Modulus

(Gpa)

Density

(g/cc)

Hardness

(HB500)

Compressive

Strength

(Mpa)

410 3.1 2800 3900

B. Preparation of composites

The liquid metallurgy route (stir casting technique)

has been adopted to prepare the cast composites as

described below. Preheated SiC powder of laboratory

grade purity of particle size 15 μm was introduced into

the vortex of the molten alloy after effective degassing.

Mechanical stirring of the molten alloy for duration of

10 min was achieved by using ceramic-coated steel

impeller. A speed of 400 rpm was maintained. A pouring

temperature of 7300C was adopted and the molten

composite was poured into cast iron moulds. The extent

of incorporation of SiC in the matrix alloy was varied

from 0 to 9 wt% in the steps of 3. Thus composites

containing particles 0 to 9 wt % were obtained in the

form of cylinders of diameter 22mm and length 210mm.

C. Testing of composites

The cast composites were machined and the

specimens for the measurement of hardness as well as

for mechanical behavior were prepared as per ASTM

standards. Brinell’s hardness tester was used to measure

the Hardness of the composites. The mechanical

properties were evaluated using Akash make

computerized universal testing machine of 40-ton

capacity.

III. RESULTS AND DISCUSSIONS

The test results of Al6063 and its composites

containing SiC at various weight percentages are

presented in these sections.

A. Effect of SiC on the mechanical properties

The mechanical properties such as hardness, tensile

strength, elongation and compressive strength property

test results of Al6063 and its composites containing SiC

at various weight percentages are presented in these

sections.

B. Hardness

The change in the hardness of composites with

increased content of reinforcement shown in Fig. 1

represents the variation in hardness evaluated at a load

of 500kg with increasing percentage of SiC in Al6063. It

is observed that the hardness of Al6063 composites

increases with increased content of the SiC

reinforcement. Improved hardness results in decrease in

wear rate [16]. Finer the grain size better is the hardness

and strength of composites leading to lowering of wear

rates. This increase in hardness of the composite may be

due to the reason the reinforcement material is much

harder than that of the matrix material and it is also due

to the good bonding between the matrix and

reinforcement materials [17].

C. Tensile Strength

From the study of Fig. 2 it can be seen that the

tensile strength increases with increasing percentage of

SiC. From the figure, it can be observed that the tensile

strength of the composites is higher than that of the

matrix alloy. Further, from the graph, the trends of the

tensile strength can be found to be increased with

increase in SiC content in the composites. This

improvement in tensile strength of the composites may

be attributed to the fact that the filler SiC possesses

higher strength and also may be due to the better

bonding strength due lower fineness of dispersed

particulates. The similar results were obtained when the

Aluminium alloy was reinforced with ceramic

particulates [4, 16, and 18].

D. Percentage elongation

Further it can be seen from fig. 3 that the

percentage elongation is decreasesing with the

increasing percentage of SiC content. This is due to the

higher brittleness of the reinforcing material. Hence

from the fig 3 it is clear that the composite material is

becoming more and more brittle as the SiC content is

increasing in the matrix material, in other words the

matrix material is losing its ductility due to the influence

of the reinforcement material.

E. Compressive Strength

From the study of Fig. 4 it can be seen that the

compressive strength increases with increasing

percentage of SiC. From the figure, it can be observed

that the compressive strength of the composites is higher

than that of the matrix alloy. Further, from the graph, the

trends of the compressive strength can be found to be

increased with increase in SiC content in the composites.

Fig. 1. Variation in the hardness with different wt% of SiC

Published in International Journal of Advanced Engineering & Application, Jan 2011 Issue 73

Variation in Tensile Strength

50

60

70

80

90

100

110

0 1 2 3 4 5

% SiC in Al6063

Ten

sile S

tren

gth

(N

/mm

2)

Decrease in % Elongation

6

7

8

9

10

11

12

13

14

0 1 2 3 4 5

% SiC in Al6063

% E

lon

gati

on

Variation in Compressive Strength

700

800

900

1000

1100

0 1 2 3 4 5

% SiC in Al6063

Co

mp

ressiv

e S

tren

gth

(MP

a)

Fig. 2. Variation in tensile strength of Al6063 with increasing wt% of

SiC

Fig. 3. Variation in the % elongation with different wt% of SiC

Fig. 4. Variation in the compressive strength with different wt% of SiC

IV. CONCLUSIONS

The significant conclusions of the studies carried

out on Al6063 - SiC composites are as follows.

Cast Al6063 - SiC composites were prepared

successfully using liquid metallurgy techniques.

Hardness of the composites found increased with

increased SiC content. Finer the grain size better is the

hardness and strength of composites leading to lowering

of wear rates.

The tensile strength of the composites found

increasing with increased reinforcements in the

composites.

The percentage elongation of the composite material

is found decreasing with the increase in the percentage

SiC content.

The compressive strength of the composites found

increasing with increased reinforcements in the

composites.

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