Corrosion Behaviour of Al6061-Frit Particulate Metal Matrix Composites in Sodium Chloride Solution

doi:10.4236/jmmce.2013.11003

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Journal of Minerals and Materials Characterization and Engineering, 2013, 1, 15-19

http://dx.doi.org/10.4236/jmmce.2013.11003 Published Online January 2013 (http://www.scirp.org/journal/jmmce)

Corrosion Behaviour of Al6061-Frit Particulate Metal

Matrix Composites in Sodium Chloride Solution

Dasappa Ramesh1*, Ragera Parameshwarappa Swamy2, Tumkur Krishnamurthy Chandrashekar3

1Sri Siddhartha Institute of Technology, Kamataka, India

2Department of Studies in Mechanical E ngineering , University B.D.T. College of Engineering, Kamataka, India

3Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Kamataka, India

Email: *[email protected]

Received July 5, 2012; revised September 5, 2012; accepted September 20, 2012

ABSTRACT

In this investigation, an attempt has been made to develop Al6061-Frit particulate metal matrix composites through stir

casting technique using metal molds and to study the corrosion behaviour. Pre heated frit particles were added to matrix

as reinforcement. Al6061 containing 2 wt% to 8 wt% in steps of 2 wt% of frit particulate composites were prepared.

Corrosion tests were conducted by using Potentiostat model SEP238C where 3.5% NaCl solution was used as corrodent.

The corrosion rate of metal matrix composites was lower than that of matrix material Al6061 under the corrosive at-

mosphere for both un-heat treated and heat treated conditions.

Keywords: Al6061 Alloy; Frit; Stir Casting; Potentiostat; Corrosion Rate (mmpy)

1. Introduction

The literature survey on metal matrix composites indicate

that much published information is not available on de-

velopment, and corrosion behaviour of Al6061-Frit par-

ticulate metal matrix composites. From the literature sur-

vey, it is reported by many researchers have reported that

melting and casting technique is the most economical

way of producing Discontinuous Reinforced Metal Matrix

Composite (DRMMCs) [1-5].

Al alloy based particulate reinforced composites have

a large potential for a wide number of engineering appli-

cations. Attraction in reinforcing of ceramic particles in

Al alloy matrix materials is mainly due to low density,

low co-efficient of thermal expansion and high strength

of reinforcements and also their availability. Among

available various useful aluminium alloys, Al6061 is ty-

pically characterized by several advantages and proper-

ties such as excellent casting properties, reasonable

strength, fluidity, corrosion resistance, high strength to

weight ratio and heat treatable. Al6061 has been com-

monly used as base metal for aluminium metal matrix

composites (AMCs) reinforced with a variety of rein-

forcements [6-8].

Corrosion is the disintegration of an engineered material

into its constituent atoms due to chemical reactions with

its surroundings. Corrosion means in common elec-

trochemical oxidation of metals in reaction with an oxi-

dant such as oxygen. Formation of an oxide of iron due

to oxidation of the iron atoms in solid solution is a well-

known example of electrochemical corrosion (rusting).

This type of damage typically produces oxides and/or

salts of the original metal. Corrosion can also occur in

materials other than metals and alloys, such as ceramics

or polymers.

S. Samala et al. studied the corrosion behaviour in

3.4% NaCl-solution, which is similar to marine environ-

ment and stated that both the yield strength and tensile

strength decreases with increasing corrosion rate. In acidic

environment yield is directly proportional to corrosion

rate and tensile strength inversely proportional corrosion

rate [9].

An aggressive marine environment was simulated by

preparing 3.5 wt% NaCl, NaOH and H2SO4 solution by K.

K. Alaneme et al. [10] and studied the corrosion be-

havior of AA6063/Al2O3p composite in NaCl, NaOH and

H2SO4 was investigated. They observed that Al(6063)—

Al2O3 composites exhibited excellent corrosion resistance

in NaCl medium than in the NaOH and H2SO4 med ia.

M. A. Bodude et al., in their research work they have

identified austempering heat-treatment is an effective

technique for improving the corrosive wear resistance of

ST60Mn steel in cassava juice [11].

The aim of this present research is to study the corro-

sion behaviour of Al6061 alloy reinforced with frit par-

ticulates. Acid medium was selected to study the corro-

sion behaviour of this alloy and Al6061-Frit particulate

*Corresponding author.

D. RAMESH ET AL.

composites. NaCl of unit normality was selected as cor-

rodent.

2. Materials and Methods

Al6061 was choosen as matrix material owing to its many

advantages like excellent casting properties, strength,

formability, and heat treatable. Table 1 shows the chemi-

cal composition of Al6061 matrix material used in this

present study.

Frit particles sizes of around 50 µm were used as rein-

forcement material in Al6061 matrix material. Table 2

shows the chemical co mposition of frit particle reinforce-

ment used in this present study. The frit used was deve-

loped in ceramic glass system. It has a density of 2.52

gm/cc, with hardness of 6.0 on the Mohr’s scale.

2.1. Composite Production

Al6061-Frit particulate composites were prepared using

liquid metallurgy route (VORTEX). Particulate MMC’s

are most commonly manufactured either by melt incur-

poration and casting technique or by powder blending and

consolidation [12].

AMC’s are synthesized via variety of manufacturing

routes. These techniques include stir casting [13-15], li-

quid metal infiltration [16], Squeeze casting [17] and

spray co-deposition [18]. Stir casting route is generally

practiced commercially [19-21]. Its advantage lies in its

simplicity, flexibility and applicability to large quantity

of production. Al6061 matrix material was melted using

6 KW electrical resistance furnace. Pre heated frit parti-

cles were slowly added into the molten matrix alloy ma-

terial and mixed thoroughly by means of mechanical stir-

rer. The melt was degassed using hexachlroetane tablet.

Thoroughly mixed composite melt maintained at a tem-

perature of 710˚C was poured into the preheated metal-

lic mold. The proportion of frit particles was varied from

Table 1. Chemical composition of Al6061 (wt %).

Si Cu Fe Mn Mg

0.809 0.355 0.155 0.027 0.8

Zn Pb Ti Sn Al

0.008 0.023 0.010 0.010 Bal

Table 2. Chemical composition of frit (wt%).

SiO2 Al2O3 Fe2O3 CaO

68.90 9.41 0.40 15.22

MgO Na2O K2O B2O3

4.30 0.75 0.42 <0.05

2 wt% to 8 wt% in steps of 2 wt%. However Al6061 ma-

trix material was also casted for comparison. Castings

were produced in permanent molds in the form of rec-

tangular block. Cast Al6061 matrix materia l and Al6061-

Frit particulate composites were machined to test stan-

dards.

2.2. Specimen Preparation

The cast Al6061 matrix alloy material and Al6061-Frit

particulate composites were successively ground using

grit emery papers and polished to metallographic stan-

dards cleaned with acetone. Rectangular specimens of 20

mm length, 10 mm breadth and 1 mm thickness were

prepared by adopting standard metallographic procedure.

2.3. Heat Treatment

Al6061 matrix alloy and Al6061-Frit particulate compo-

sites were subjected to thermal treatment by solu tionizing

at a temperature of 530˚C followed by ice quenching.

Artificial ageing was performed at a temperature of

175˚C for duration of 6 h.

2.4. Corrosion Test

All corrosion is an electrochemical process of oxidation

and reduction reactions. As corrosion occurs, electrons

are released by metal (oxidation) and gained by elements

(reduction) in the corroding solution. Because there is a

flow of electrons (current) in the corrosion reaction, it

can be measured and controlled electronically. Controlled

electrochemical experimental methods can be used to

characterize the corrosion properties of metals and metal

components in combination with various electrolyte so-

lutions. Potentiostat model SEP238C was used to con-

duct the corrosion test. The electrodes are connected to

an electronic instrument called Potentiostat. The electrodes

used are;

1) The working electrode.

2) The reference electrode.

3) The counter electrode.

The working, reference, and counter electrodes are

placed in the electrolyte solution. The experiments were

conducted in 3.5% Solution of Sodium chloride (NaCl).

Rectangular specimens of 20 mm length, 10 mm breadth

and 1 mm thickness were prepared by adopting standard

metallographic procedure [22]. They were polished and

washed with liquid soap and dried in acetone. The spe-

cimens were fixed to working electrode and corrosion tests

were conducted.

The Figure 1 shows the set up of electrochemical test

rig which is used for corrosion test. In the present re-

search work corrosion rates in terms of mmpy for the

Al6061 matrix alloy and developed Al6061-Frit particu-

late composites have been measured.

D. RAMESH ET AL. 17

2.5. Scanning Electron Micrographs (SEM)

Studies

To gain more insight on the corrosion products formed

on the electrode surface were examined by Scanning

Electron Microscope (SEM). The SEM micrographs of

composite were obtained using the scanning electron

microscope Microscopic studies to examine the mor-

phology, particle size and micro structure were done by a

JEOL 6380 LA Scanning Electron Microscope (SEM)

equipped with an Energy Dispersive X-ray (EDX) detec-

tor of Oxford data reference system. Micrographs are

taken at suitable accelerating voltages for the best possi-

ble resolution.

3. Results and Discussion

The scanning electron micrograph images of the cor-

roded samples of Al 6061-Frit particulate composite is

shown in Figure 2. From the scanning electron micro-

graph it is clear that uniform dispersion of particles in the

matrix material. The scanning electron micrograph of

corroded samples reveals pitting corrosion development .

Figure 1. Shows the set up of electrochemical corrosion test

rig.

Figure 2. Scanning electron micrograph of Al6061-Frit par-

ticulate composite.

The SEM micrographs show a complete deterioration

of the smoothness of the surface of matrix material [23],

suggesting the penetration of chloride ions into the ma-

terial surface forming corrosion spots [24].

The corrosion rate in mmpy measurement is shown in

Figure 3. The trend observed in all specimens indicates

decrease in corrosion rate. The phenomenon of gradually

decreasing corrosion rate indicates the possible passiva-

tion of the matrix alloy is due formation of permanent

layer, which affects the corrosion process. According to

De Salazar [25] the protective black film consists of hy-

drogen hydroxyl chloride slows the forward reaction.

Castle, et al. [26], reported that the black film consist of

aluminium hydroxide compound, which protects further

corrosion in acid media. Protective black film chemical

nature is not determined still.

Figure 3 clearly indicates for both Al6061 matrix ma-

terial and Al6061-Frit particulate composites the corro-

sion rate decreases as the weight percentage of frit par-

ticulate increases. Hard and inert ceramic frit is not ex-

pected to affect the corrosion mechanism of composites

in acidic media during the test duration. The corrosion

result indicates an improvement in corrosion resistance

as the weight percentage of frit particulates increases,

which shows the influence of frit particulates on the cor-

rosion property. Similar result trend was reported by B.

M. Girish et al. [27], in glass short fiber reinforced Al7075

composites. Research work by Wu Jinaxin et al. [28],

reported that the corrosion is not affected significantly in

aluminium based SiC particulate reinforced MMCs, but

the inclusion of SiC particulate plays a secondary role as

a physical barrier in MMCs corrosion characteristics.

The result trend is in line with the result reported by A.

Jameel et al. [29] found that corrosion behavior of

Al6061/Zirc on MMC s te sted by O CP me thod , th e Zi rcon

content plays a significant role in corrosion resistance of

the material. Increase in wt% of Zircon reduces the cor-

1.8

1.85

1.9

1.95

2.05

2.1

0% 2%4% 6% 8%

Wt . % o f Rein forcement

Corrosion Rate in mmpy

Unheat Treated

Heat Treated

Sol utionizi n g temp.:530

Qu enchi ng m edia: IC E

Ageing tem p.: 17 5

Figure 3. Shows the variations of corrosion rates Al6061

alloy and developed Al6061-Frit particulate composites.

D. RAMESH ET AL.

rosion rate from 0 wt% to 7 wt% in Al6061/Zircon MMCs.

In the present study, corrosion rate decreases as the wt%

of reinforcement increases for both un-heat treated and

heat treated composites. Further, heat treatment has im-

proved the corrosion resistance for both matrix material

and its composites in 3.5 % NaCl solution.

4. Conclusion

Based on the results of this research, the following con-

clusions have been drawn. The Al6061-Frit particulate

reinforced composites are successfully developed using

liquid metallurgy method. The frit inclusion in Al6061

matrix material plays a significant role in the corrosion

resistance of the material. Increase in the weight per-

centage of frit increases the corrosion resistance signifi-

cantly. The corrosion rate of the composites was lower

than that of the corresp onding matrix material in b o th un-

heat treated and heat treated conditions.

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