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Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.14, pp.1329-1335, 2011
jmmce.org Printed in the USA. All rights reserved
Wear Characteristics in Al-SiC Particulate Composites and the
Al-Si Piston Alloy
*, R. K. Pandey
*, D.K. Sehgal
Mech. Engg. Dept., JIET , Jahangirabad, Barabanki, Utter Pradesh,225203, India
Applied Mech. Dept., IIT Delhi, Hauz Khas, New Delhi, India.
* Corresponding Author : email@example.com, rkpiitd@ yahoo.com,
The Al-Si alloy with near eutectic composition has been conventionally used as a piston material for
automobile applications. It is required to possess high abrasive wear resistance for enhanced life of
the engine. The alloy is known to have fairly good wear resistance due to increased percentage of
silicon present in fine form. In the present investigation, Al-SiC particulate composites have been
studied for their wear resistance against emery paper (400 grit SiC particles) counterface and a
comparison has been made with existing piston alloy i.e. Al-Si alloy.
The Al-SiC composites have been prepared using Liquid Metallurgy technique employing 2124 Al-
alloy as the base material with 10 and 20 % SiC particulates by weight. The abrasive wear study
has been conducted on a Pin on Disc machine. The wear rate in terms of weight loss per unit sliding
distance as well as the volumetric wear rate have been obtained for the Al-SiC composites. The
characteristics of worn surface were investigated using SEM. The composites are found to possess
very high wear resistance as compared to Al-Si piston alloy. The results have been discussed and
important conclusions are outlined.
Key words: Composite Material, Wear, SEM.
There are more than 50,000 materials available for engineers to the design and manufacturing of
products for various applications. These materials range from ordinary materials (e.g., copper,
cast iron, brass), which have been available for several hundred years, to the advanced materials
e.g., composites, ceramics and high-performance steels etc.
The life of automobile depends on its engine having piston and cylinder made from suitable
alloys . The Al-based composites have found extensive applications in automobile industries due
to their increased stiffness, strength and wear resistance properties. A number of particulate
1330 Z. Hasan, R. K. Pandey Vol.10, No.14
phases have been employed in the Al-alloy matrix . For example, particulates of graphite ,
mica , zirconia, alumina, zircon, silicon-carbide, silica  etc. have been employed
in a suitable Al-alloy matrix. The introduction of the above particulate phases in the aluminium
matrix provides a good wear resistance and antifriction properties. The strength, ductility and
stiffness are the other important properties. The choice of an optimum volume fraction of the
particulate phase in the composite is therefore essential to obtain an improved combination of
The present investigation is based on the study of Al-SiC cast composites with particular
reference to the study of the effect of particulate phase on the wear characteristics of the
2. MATERIALS AND METHODS
2.1 Composite Preparation
For the present investigation four types of materials have been selected as follows
(i) Al-alloy (2124 type)
(ii) Al-alloy – 10% SiC (wt%) composite
(iii) Al-alloy – 20% SiC (wt%) composite
(iv) Al-Si piston alloy
The composites as well as Al alloy (2124 type) plates were obtained from the Regional Research
Laboratory (RRL) Thiruvananthapuram (India). The 2124 Al-alloy has been used as the base
alloy for the composite. The composition of the above alloy is given in Table 1. The composites
were prepared using liquid metallurgy technique. During the preparation of composite, addition
of 0.5 wt% Mg, 0.005 wt% Be and 0.07 wt % TiB were made along with the SiC particulates.
The SiC particles were lying in the size range of 23 - 40 µm. The TiB is used for the grain
refinement whereas Be is added for improved castability. For the improvement of interfacial
bonding of SiC particles, the surface of the latter is oxidized. This is performed by preheating of
the SiC particles in the temperature range of 700- 900
C. Proper stirring and mixing of particles
are done to ensure uniform distribution of SiC particles. The addition of Be is also known to
improve the distribution of SiC particles by minimizing the agglomerations of particles.
The plates were cast using split moulds and employing bottom pouring technique. After casting
the composite plates were obtained in the dimensions of 250 mm (length) x 225 mm (width) x 40
2.2 Processing of Composites
The cast plates of the base alloy as well as the composites were soaked in a furnace for 2 to 3 hrs
in the temperature range of 480 - 500
C. The plates were forged in the above temperature range
using hydraulic press of 3000 Ton capacity. The final reduction after forging resulted in the plate
thickness of 15-17 mm from the original 40 mm thickness.
Vol.10, No.14 Wear Characteristics in Al-SiC Particulate 1331
2.3 Aluminium –Silicon Alloy
In the present investigation an Al-Si eutectic alloy has been employed for comparison of its wear
behaviour with the wear behaviour of Al-SiC composites. The composition of the alloy is given
in Table 1. The alloy was phosphorous (P) modified by using 70-80 ppm of P. The piston had
been made by gravity die casting followed by artificial aging heat treatment. The heat treatment
involved solution treatment at 505
C for 2 ½ hours, then water quenching at 65
subsequently aging at 205
C for 5 hours. The above heat treatment was known to result in
optimum properties. After the above heat treatment following properties were obtained: Proof
stress- 205-225 MPa, Tensile Strength - 300 MPa, %Elongation - 0.3 to 1.5 %, Hardness - 65
TABLE 1. Chemical Composition of the Base Al-Alloy
Element Cu Zn Mn Fe Mg Si Ti Sn Pb Ni
1.1 - 0.2 0.3 1.1 12.5
- - - 0.9
3. WEAR EXPERIMENTATION
The wear studies were conducted using a pin on disc machine (Linear Abrasive Wear Rig) .
The maximum loading capacity was 200 N and maximum speed of 5 m/ minute. The specimens
for wear studies were cut from the base Al- alloy, composite plates and the Al-Si piston alloy in
cross section of 10 mm x 10 mm with a thickness of 8 mm. The top and bottom surfaces were
made planer by polishing against emery paper. The specimen was fixed on the specimen holder
which in turn was mounted to the machine. The disc was provided with 400 grit emery paper to
be used as the counter facing surface. For the wear test, the total travel distance covered was 100
m which was divided into 5 equal parts. The movement of specimen on the disc was continued
along the same path for the distance of 20 mm in reciprocating manner. The dry sliding wear test
was conducted in this study. After the coverage of each 20 m distance, the path was changed and
a fresh path was used. The distance of 20 m was covered by 40 cycles of travel in a reciprocating
manner as because the travel step was of 250 mm length. A travel speed of 3m/min was used
during the test.
The specimen was weighed initially using an electronic balance of 0.0001 gm accuracy and the
maximum capacity of 320 gm. After a travel distance of 20 mm on the disc, the sample was
taken out, cleaned and weighed carefully. This was continued for entire travel distance of 100 m.
The wear studies were conducted at 3 different load levels i.e. 20 N, 30 N and 50 N.
3.1 Wear Surface Study
The samples for wear surface study were sectioned carefully to appropriate sizes. They were
cleaned using ultrasonic cleaner and examined under SEM (Zeiss EVO-50) at suitable
1332 Z. Hasan, R. K. Pandey Vol.10, No.14
magnifications. The wear surface of each specimen was examined after completing its final
4.1 Effect of Load and Disc Surface on Weight Loss
The effect of load employed during wear test is presented in Fig. 1 on various materials i.e. Al
base alloy, 10% SiC Composite, 20% SiC composite and Al-Si piston alloy. In the above figure
the weight loss from the four materials is presented for loads 20 N, 30 N and 50 N in Figs. 1(a),
1(b) and 1(c) respectively for 400 grit emery paper used as the disc surface.
Following observations may be made from Fig. 1:
(a) With increasing load the weight loss increases in all the four materials.
(b) With increasing travel distance the weight loss increases in all the materials at a given
(c) For a given load and distance travelled the, weight loss is found to be maximum in the
Al-Si piston alloy and minimum in the Al- 20% SiC composite. The Al-base alloy shows
greater weight loss as compared to both the composites for a given load and travel
Fig.1 Weight loss as a function of sliding distance for 400 emery paper
(a) 20 N (b) 30 N (c) 50N
020 4060 80100
Weight Loss (g)
Weight Loss (g)
020 40 60 80100
Weight Loss (g)
Vol.10, No.14 Wear Characteristics in Al-SiC Particulate 1333
4.2. Effect of Load and Disc Surface on the Wear Volume
The wear volume was calculated as follows.
Cumulative weight loss
The calculated wear volumes were plotted against the sliding distance for the materials
investigated at different loads. Fig. 2 presents the wear volume vs sliding distance diagrams for
400 grit emery paper at 20 N, 30 N and 50 N of loads.
From the above diagrams following observations may be made.
a) The wear volume in all the situations is the minimum for the Al-20% SiC composite.
b) The maximum wear volume is noticed either for the Al-Si piston alloy or the Al-base
c) The performance of Al-10% SiC composite almost lies in between the maximum and
the minimum wear volume.
d) With increasing load there is consistent increase in the wear volume.
Fig.2 Wear volume as a function of sliding distance for 400 emery paper
(a) 20 N (b) 30 N (c) 50N
020 4060 80100
Wear volume (mm3)
Wear volume (mm
020 4060 80100
Wear volume (mm
1334 Z. Hasan, R. K. Pandey Vol.10, No.14
5. WEAR SURFACE STUDIES USING SEM
For the wear study following wear test specimens were selected
(a) Al-10% SiC composite at 50 N load
(b) Al-20% SiC composite at 50 N load
Representative SEM diagrams from the wear surfaces of Al-10% SiC composite against 400
emery paper are presented in Fig. 3. The Fig.3 (a) provides overall view of wear pattern at 2000
X. Fig. 3(b) provides an enlarged view of material removal from the surface at 4500 X. The
wear surface features from Al-20% SiC composite are shown in Figs 4 (a) and (b). Fig 4(b)
provides details of wear track and process of materials removal.
6. DISCUSSION AND CONCLUSIONS
1. The dry sliding wear behavior in the base alloy and composites were investigated against
emery papers of 400 grit. The SiC particulate phase is found to reduce the wear rate
(expressed in terms of gm/m, mm
/m etc) significantly in the composites. The volumetric
wear rate (mm
/m) in 20 % SiC composite is reduced by 62-66% for 400 emery sliding with
respect to the base alloy. In case of 10% SiC composite the corresponding reduction in the
wear rate is 15-25%.
Vol.10, No.14 Wear Characteristics in Al-SiC Particulate 1335
2. The wear rate is found to increase with load in all the materials studied. The increase in wear
rate with load is steeper in the base alloy as compared to that of the composites. The
increasing load is known to produce heating effect leading to thermal softening and seizure.
Also it brings more area into sliding contact and thereby causes enhanced wear.
3. With increasing size of the abrasive particles (in the emery paper) the wear rate of the
materials investigated has been increased. The effect of increasing abrasive particle size from
15 µm to 38 µm has been studied. The increase in wear rate of the base alloy is more
significant due to cutting and plowing action by large abrasive particles. In case of
composites (especially 20 % SiC composite) the effect of abrasive particles size on the wear
rate is less significant as reported by other investigates also . However at higher load the
effect of abrasive particle size on the wear rate of composites is more significant.
4. The micromechanism of wear against the coarse abrasive emery paper was found to be
characterized by deep wear tracks along with fragmented SiC particulates in the 10 % SiC
composite. Fine cracks were also noticed. In 20 % SiC composite wear was followed by
limited extent of cutting and plowing marks keeping the overall surface smooth.
5. The wear rate in the Al-Si piston alloy is found to be significantly higher than that of the
composites. The volumetric wear rate in this alloy is closer to the same as in the Al- base
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