The Effect of Ageing Time on Some Mechanical Properties of Aluminum/0.5% Glass Reinforced Particulate Composite

Paper Menu >>

Journal Menu >>

Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 919-923

Published Online September 2012 (http://www.SciRP.org/journal/jmmce)

The Effect of Ageing Time on Some Mechanical Properties

of Aluminum/0.5% Glass Reinforced

Particulate Composite

Aondona P. Ihom1*, Nyior G. Bem2, Emmanuel E. Anbua3, Joy N. Ogbodo4

1Department of M e t a l l urgy, National Metallurgical Development Center, Jos, Nigeria

2Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria, Nigeria,

3Department of Mechanical Engineering, Federal Polytechnic Bauchi, Bauchi, Nigeria

4Departmen t of Welding and Fabrication, Scientific Equipment Development Institute (SEDI), Enugu, Nigeria

Email: *[email protected]

Received June 23, 2012; revised July 31, 2012; accepted August 22, 2012

ABSTRACT

A particulate-hardened composite usually known as cermets with aluminum matrix and reinforced with ceramic parti-

cles from broken bottles was used to investigate the effect of ageing time on hard ness and tensile strength. Th e samples

used for the work were produced using stir-cast method and the samples were cast in metal moulds to improve on the

surface finish and to obtain good cooling rate. The composite composition used was Al/0.5% glass particles. The sam-

ples were treated at 500˚C and quenched in water at 65˚C. They were then aged at various temperatures ranging from

150˚C - 210˚C. The result of the hardness test showed that within the range of the ageing time selected the hardness

increased with the ageing for all the ageing temperatures used. Variations were observed but this is normal in ageing,

particularly when coherent and incoherent precipitates are formed at a point in time, or when over-ageing occurs. The

plot of the tensile strength tests and the hardness tests, with ageing time showed the trend as observed. The highest

hardness value of 37.3 HRB occurred after 5 hours of ageing likewise the highest tensile strength value of 398.36

N/mm2 occurred after 5 hours of ageing at the same ageing temperature of 190˚C. The aged composite showed im-

proved hardness and tensile strength when compared to as-cast value of 23.7 HRB for hardness and 253.12 N/mm2 for

tensile strength respectively.

Keywords: Al/0.5% Glass; Ageing Time; Particulate; Composite; Mechanical Properties

1. Introduction

Composite materials are usually classified on the basis of

the physical or chemical nature of the matrix phase e.g.

polymer matrix, metal matrix, and ceramic composites.

According to surappa [1] the term “composite” refers to a

material system which is composed of a discrete con-

stituent (the reinforcement), distributed in continuous

phase (the matrix), and which derives its distinguishing

characteristics from the properties of its con stituent, from

the geometry and architecture of the constituents and

from the properties of the boundaries (interfaces) be-

tween different constituents. A composite can also be de-

fined as a material that consists of constituents produced

via a physical combination of preexisting ingredient ma-

terials to obtain a new material with unique properties

when compared to the monolith ic material p roperties [2].

Curran [3] pointed out that there are two main types of

metal matrix composites, namely powder reinforced and

fibre reinforced. In the production of metal matrix com-

posites, one of the subjects of interest when choosing the

suitable matrix/reinforcement is the interaction in its in-

terface. For their production, oxide reinforcements have

been used in particles or whiskers morphology, like

Al2O3, ZrO2, or ThO2 in aluminum, magnesium and other

metal matrix. Metal-matrix composites provide the opp-

ortunity to combine metallic properties of the matrices

with the ceramic properties of the reinforcements, lead-

ing to greater modulus, strength, wear resistance and

thermal stability. They are a new class of materials suita-

ble for advanced structures, aerospace, automotive, elec-

trical, thermal management and wear applications [4].

The transport of solutes through the matrix of a metal

is accomplished by diffusion. Diffusion follows Fick’s

first law:

J Dcx





 (1)

where J is flux, or amount of diffusing substance that

passes through a unit cross-sectional area per unit time,

*Corresponding author.

A. P. IHOM ET AL.

920

D is the diffusion coefficient and δc/δx is the concentra-

tion gradient of the diffusing substance. The transport of

substance in the matrix depends on values for the diffu-

sion coefficient and the characteristics of the concentra-

tion gradient. The diffusion coefficient is in turn, a func-

tion of temperature and the solute concentration or the

particulate reinforcement in this case. At higher tem-

peratures the transport of substances within the matrix is

faster, while longer time is required for lower tempera-

ture [5]. To accomplish equilibrium in thermal ageing of

composites and alloys, lower temperatures are preferred

to avoid any negative effect on the hardness of the com-

posite [6]. Thermal ageing affects both the microstruc-

ture and the mechanical properties because it determines

the nature of precipitates and phases formed in the matrix

of the composite or alloy [7]. The work by Curran [3]

and Hassan et al. [8] have laid the foundation for this

current work, their respective works have highlighted the

effect of ageing time on mechanical properties and mi-

crostructure of metal based composites reinforced with

ceramics or oxide particulates. The morphology of phase

format i o n ha s also been explained by the autho r s.

The objective of this paper is to d etermine the effect of

ageing time on some mechanical properties of Alumi-

num/0.5% glass reinforced particulate composite.

2. Materials and Methods

2.1. Materials

The materials used for the work included; pure aluminum

from electrical cables, waste bottles, magnesium alumin-

ium alloy, and water.

2.2. Equipment

The equipment used for the work were those of the Na-

tional Metallurgical Development Centre, Jos (NMDC)

and these included, metallurgical microscope, Rockwell

hardness tester, Denison universal strength testing ma-

chine, crucible furnace, gravity metal casting mould,

hacksaw, lathe machine and ball-mill.

2.3. Methods

The samples used for the work were those produced us-

ing stir casting method. The composite was produced

using pure aluminum (99.8%) which was melted and the

temperature was raised to 700˚C. 50 g of aluminium-

magnesium (50/50) alloy frit was added to introduce

magnesium to the melt. Broken bottles which were pul-

verized using ball-mill were classified, and 90 microns

passing sizes were introduced into the molten aluminum

in various compositions. The melt was stirred at the rate

of 315 rpm after which it was poured into the metal

moulds. After the castings had cooled they were removed

and cleaned. The composition used for this study was

that of Al/0.5% glass reinforced particulate composite.

2.3.1. A geing Treatment

After the cleaning of the cast specimens they were heated

to 500˚C and held for 45 minutes before quenching in

water at 65˚C. The round bars of 20 mm diameter and

350 mm length were then aged in the oven at different

temperatures ranging from 150˚C - 210˚C. The solution

treatment was carried out to enhance the homogenization

of the reinforcement particles in the matrix of the com-

posite. After the ageing treatment the specimens were

ready for hardness testing and tensile strength testing.

2.3.2. Hardness Testi ng

The samples were tested using Rockwell hardness tester.

A minor load of 10 kg was first applied to seat the speci-

men. Then the major load of 100 kg was used on the B

Scale, with a 1.6 mm diameter steel ball. The result was

then recorded automatically on the dial gauge in terms of

arbitrary hardness numbers. This was then recorded with

the value first and HRB at the end.

2.3.3. Tensile Strength Test

The specimens for the test were produced according to

“ASTM standard” (American Society for Testing and

Materials) as specified in standard method of tension

testing of metallic materials, ASTM Designation E 8-69.

The specimen was mounted on the Denison universal

strength testing machine. It was then operated and the

progressive results and tensile strength displayed as the

materials were failed.

3. Results and Discussion

3.1. Results

The results of the work are displayed in Figures 1- 8. The

as-cast composite has a hardness value of 23.7 HRB and a

tensile strength value of 253.12 N/mm 2.

3.2. Discussion

3.2.1. Analysis of Hardness Test Results

Figures 1-4 show the variation of ageing time with

hardness values of the composite at various temperatures

(150˚C - 210˚C). Figure 1 is the variation of ageing time

with hardness values of the composite (Al/0.5% glass

reinforced) at 150˚C. The plot shows that at 1hour of

ageing the hardness value was 33.9 HRB. The hardness

value dropped gradually to 24.4 HRB after 4 hours and

then rose up to 34.2 HRB after 5 hours of ageing. This

behavior is not uncommon with ageing and is normally

linked to the nature of precipitates that have been formed

at a particular time [6-8]. The variation in hardness can

A. P. IHOM ET AL. 921

Figure 1. Effect of ageing time on the hardness of Al/0.5%

glass reinforced composite at 150˚C.

170˚C

Figure 2. Effect of ageing time on the hardness of Al/0.5%

glass reinforced composite at 170˚C.

190˚C

Figure 3. Effect of ageing time on the hardness of Al/0.5%

glass reinforced composite at 190˚C.

210˚C

Figure 4. Effect of ageing time on the hardness of Al/0.5%

glass reinforced composite at 210˚C.

150˚C

Figure 5. Effect of the ageing time on the tensile strength of

Al/0.5% glass reinforced composite at 150˚C.

170˚C

Figure 6. Effect of ageing time on the tensile strength of

Al/0.5% glass reinforced composite at 170˚C.

190˚C

Figure 7. Effect of ageing time on the tensile strength of

Al/0.5% glass reinforced composite at 190˚C.

210˚C

Figure 8. Effect of ageing time on the tensile strength of

Al/0.5% glass reinforced composite at 210˚C.

A. P. IHOM ET AL.

922

also be linked to diffusion of the reinfo rcing agent as the

ageing time progresses. This last explanation agrees with

the fact that after ageing for 5 hours the hardness values

peaked at 34 HRB. This same observation has been made

by Hassan et al. [8] in precipitation hardening character-

istics of Al-Si-Fe/SiC particulate composites. Figure 2

shows that the highest hardness value of 34.4 HRB was

attained after 3 hours of ag eing as against as against 34.2

HRB in Figure 1 attained after 5 hours. This is not sur-

prising because the ageing process is a diffusion con-

trolled pro ocess and is controll ed by thi s e q uat i on:

QRT

DDе (2)

where D is the diffusion rate, DO is the diffusion coeffi-

cient, Q is the activation energy required to move an

atom, R is the gas constant and T is the temperature in

Kelvin. At higher temperatures the movement of solute is

faster because the activation energy required is met

quickly [5,6]. Fick’s law has also explained that the

quantity of the substance passing through a unit cross-

sectional area in a unit time is proportional to the con-

centration gradient (δc/δx) along the x-direction which is

perpendicular to this cross-section as in Equation (1).

Where D stands for coefficient of diffusion and de-

pends on the type of alloy, the type of solid solution,

grain size, and so much on the temperature as in the pre-

ceding equation. Martin [6] has also predicted that the

growth of spherical precipitates should obey an equation

of the form r = α(Dt)1/2. Where, r is the particle radius

after time t, D (assumed independent of composition) is

the volume diffusion coefficient and α is a function of the

super saturation. A similar calculation made for the

growth of planar precipitates again predicted a parabolic

relationship between thickness and time [5,6]. All these

have helped in explaining the attainment of higher hard-

ness at shorter time at higher temperatures and the

growth of precipitates with time. Ageing takes place

faster at higher ageing temperature but there is a problem

of equilibrium and stability at h igh temperatures [7]. This

could result into reduced hardness as can be seen in Fig-

ures 3-4 compared. The aged composite has shown im-

proved hardness from Figures 1-4 compared with the

as-cast hardness value of 23.7 HRB. Figure 3, where

ageing took place at 190˚C, however, had the highest

hardness values with increase in ageing time [11,12].

3.2.2. Tensile Strength Test

The test has taken into consideration the ultimate strength

of the composite at various ageing temperatures and age-

ing time. Figure 1 showed that the composite at 150˚C

ageing temperature had a tensile strength of 362.05

N/mm2 after been aged for 1 hour. This gradually de-

creased to 260.59 N/mm2 and peaked again at 265.26

N/mm2 after 5 hours. The trend is in teresting and may be

interpreted in terms of the progressive dispersion of pre-

cipitates from the solid solution of the alloy with time

[7,9]. The Martin equation also explains this [6]. The

process is diffusion-controlled process and can also be

observed from Figures 2-4. Figure 3, which ageing took

place at 190˚C has high tensile strength when compared

to the others. The highest tensile strength of 398.36

N/mm2 occurred at the ageing temperature of 190˚C after

5 hours. This may be due to higher or more homogene-

ous dispersion of precipitates with time [8-12]. As the

ageing time was increased the tensile strength was also

increasing with a slight drop after 4 hours, but continued

rising to peak at 398.36 N/mm2 after 5 hours, indicating

that the tensile strength increases with the ageing time at

a constant temperature of 190˚C. This agrees with Has-

san et al. [8] in precipitation hardening characteristics of

Al-Si-Fe/SiC particulate composites. Comparing the ten-

sile strength of the age hardened composite at various

temperature and time regimes it can be seen that most

ageing times showed improved tensile streng th as against

the as-cast tensile strength [11]. The as-cast tensile

strength of the composite is 2 53.12 N/mm2 and the high-

est tensile strength of 398.36 N/mm2 of the aged hard-

ened composite occurred at 5 hours of ageing at 190˚C.

This still confirms that ageing time has effect on this

mechanical property of the composite. The general trend

in Figures 1-4 is that the tensile strength increased with

the ageing time of the composite at different tempera-

tures covering the range 150˚C to 210˚C. This can be

linked to the precipitation of a second phase during age-

ing of the composite giving rise to increased tensile

strength [8]. The strength is due to solid solution metal-

ceramic bond formed at the interface leading to increased

tensile strength.

4. Conclusions

The study has been conducted and the following conclu-

sions were drawn from the study:

1) The mechanical properties of the composite (Al/

0.5% glass reinforced) are higher in the age-hardened

samples than in the as-cast samples, most likely due to

the precipitation of a second phase during ageing which

cover the surface at the particles-matrix interfaces.

2) The hardness increased with ageing time.

3) The tensile strength of the composite also increased

with ageing time.

4) The study has established that this grade of com-

posite responded to ageing as shown in the improved

mechanical properties tested.

5) The composite is a cermet composite with the in-

creased strength arising from solid solution bonding at

A. P. IHOM ET AL.

923

the interface.

5. Acknowledgements

The authors are seriously indeb ted to the management of

the National Metallurgical Development Centre, Jos for

providing their facilities for this research work.

REFERENCES

[1] M. K. Suprappa, “Aluminum Matrix Composites: Chal-

lenges and Opportunities,” Sadhana, Vol. 28, No. 1-2,

2003, pp. 319-334. doi:10.1007/BF02717141

[2] Http:/umewww.epf/ch/people/cayron/Fichiers/thesebook-

hap.2pdf

[3] G. Curran, “MMCs, the Future,” Materials World, Vol. 6,

No. 1, 1998, pp. 21-22.

[4] M. Gupta, “Recycling of Aluminum Based Composite

Using Disintegrated Melt Deposition Technique,” Na-

tional University of Singapore, Engineering Research,

Vol. 23, No. 1, 2008.

[5] ASM Committee on Gas Carburizing, “Carburizing and

Carbonitriding,” American Society for Metals, 1977, pp.

6-20.

[6] J. W. Martin, “Precipitation Hardening,” 2nd Edition,

Butterworth Heinemann, 1998.

[7] R. A. Higgins, “Properties of Engineering Ma terials,” 5th

Edition, Hodder and Stoughton, London, 1983.

[8] S. B. Hassan, O. Aponbiede and V. S. Aigbodion, “Pre-

cipitation Hardening Characteristics of Al-Si-Fe/SiC Par-

ticulate Composite,” Journal of Alloys and Compounds,

Vol. 466, No. 1-2, 2008, pp. 268-272.

doi:10.1016/j.jallcom.2007.11.023

[9] S. B. Hassan and V. S. Aigbodion, “The Effect of Ther-

mal Ageing on Microstructure and Mechanical Properties

of Al-Si-Fe/Mg Alloys,” Journal of Alloys and Com-

pounds, Vol. 486, No. 1-2, 2009, pp. 309-314.

doi:10.1016/j.jallcom.2009.06.131

[10] G. E. Dieter, “Mechanical Metallurgy,” 3rd Edition,

MCgraw-Hill Book Company, London, 1988.

[11] M. H. Mohammad, T. M. Ahmad, M. H. Adel and T. H.

Mohammad, “The Effect of Time, Percent of Copper and

Nickel on Naturally Aged Al-Cu-Ni Cast Alloys,” Jour-

nal of Minerals and Materials Characterization and En-

gineering, Vol. 11, No. 2, 2012, pp. 117-131.

[12] O. A. Alo, L. E. Umoru, J. A. Ajao and K. M. Oluwase-

gun, “Thermal, Hardness, and Microstructural Charac-

terization of Al-Si-SiCp Composites,” Journal of Miner-

als and Materials Characterization and Engineering, Vol.

11, No. 2, 2012, pp. 159-168.