STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs

IDL - International Digital Library Of
Technology & Research
Volume 1, Issue 3, Mar 2017 Available at: www.dbpublications.org
International e-Journal For Technology And Research-2017
IDL - International Digital Library 1 | P a g e Copyright@IDL-2017
STUDIES OF MICROSTRUCTURE,
MECHANICAL AND TRIBOLOGICAL
PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn
MMCs
Mohammed Talib Syed 1
, N SAI Hemanth2
, K S Prabhu3
, Avinash L4
Shiv Pratap5
UG Student, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India1, 2
Assistant Professor, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India3, 4, 5
Bangalore, India
Abstract: The aim is to study the mechanical,
tribological property and wear behavior of Al7068
alloy/alumina composite with various weight fractions
(3%, 5%, 7%) were prepared by stir casting method. In
addition, Al7068 were cast for comparison purposes.
Microstructure, hardness and tensile properties of
these composites were evaluated and compared with
as-cast alloy and the composites. In addition,
tribological properties of these composites were also
evaluated. The wear and mechanical properties of
composites improve with increasing the weight
fraction of Alumina and then decreases gradually. This
study provides an alternative way to enhance the
tribological behavior of Al7068 alloy/Alumina
composite. The study also highlights the different
contribution of different input process parameters
(like: composition of Al7068 alloy/Alumina and
particle size of reinforcement material) on wear
properties of Al7068 alloy/Alumina MMCs.
Keywords: Al 7068 alloy, matrix, Alumina,
Composite, tribological, wear
1. INTRODUCTION
Today in Modern day technology there is an ever
increasing demand in materials which achieves good
combination of strength, stiffness, toughness and
density. But the conventional monolithic materials
have limitations in achieving these combinations. To
overcome these shortcomings and to meet the ever
increasing demand of modern day technology,
composites are most promising materials of recent
interest. A broad definition for a composite is: a
combination of two components separated by a
distinct interface, thermodynamically irreversible, and
has properties which can be „engineered‟ using
composite principles.
Automotive, medical and sport equipment industries
pushed advances in materials further to introduce new
generation materials particularly having low density
and very light weight with high strength, hardness and
stiffness. Since 1960‟s there has been an ever-
increasing demand for newer, stronger, stiffer and yet
lighter-weight materials in fields such as aerospace,
transportation, automobile and construction sectors.
With the vast and rapid progress in science and
technology, modern industry has introduced a new
generation of composite materials having low density
and very light weight with high strength, hardness and
stiffness to meet the current needs of modern

technology and the challenges against liberalization
and global competitiveness in market. Particle-
reinforced aluminium alloys have the potential to be
used in a wide range of such engineering applications
due to their higher stiffness and strength when
compared with conventional aluminium alloys.
In the present investigation Al 7068 alloy was chosen
as matrix material because of its wider applications for
markets like the aerospace and automotive industries
(valve body and connecting rod applications), as well
as recreational products (bicycles) .At present very
limited information is available on the Alumina
reinforced Al 7068 alloy composites. Therefore the
present investigation makes an attempt to synthesize
the Alumina reinforced Al 7068 alloy composites by
stir casting method. Later these composites will
characterized in terms of their Optical Microscope,
SEM studies, hardness, mechanical and Tribological
properties.
2. LITERATURE SURVEY
There is abundant amount of literature available on
Metal Matrix Composites pertaining to Al7068 with
various reinforcements, Stir Casting and Hybrid
composites. This chapter gives a brief narration of the
significant research carried out on MMCs in the recent
past, conclusions drawn from them and objectives of
the present investigation.
Aluminium 7068 alloy is a heat treatable wrought
alloy with good fatigue strength, good anodizing
response, and high thermal conductivity. It was
designed as a higher strength alternative to
aluminium7075 for ordnance applications. It also
provides the highest mechanical strength of all
aluminium alloys.
2.1.Physical Properties
The physical properties of aluminium 7068 alloy are
outlined in the following table 1.
Properties Metric Imperial
Density 2.85 mg/cm³ 0.103 lb/in³
Melting Point 476-635 ºC 890-1175
ºF
2.2. Mechanical Properties
The mechanical properties of aluminium 7068 alloy
are outlined in the following table 2.
Tensile strength 641 MPa 93 ksi
Yield strength 590 MPa 85.7 ksi
Elongation 8% 8%
2.3.Thermal Properties
The thermal properties of aluminium 7068 alloy are
outlined in the following table 3.
Thermal
conductivity
190 W/mK 1317 BTU
in/hr.ft².°F
Table 4: Chemical composition of Al7068 alloy
(weight percentage).
3. OBJECTIVES
Our study can lead one to investigate the possibility of
identifying the use of these composites for commercial
applications in the in aerospace and automotive
industries (valve body and connecting rod
applications), as well as recreational products
(bicycles).Therefore the work taken up had the
following objectives:
 Fabrication of Al7068/ Alumina composites by
Stir Casting Method.
 Microstructure characterization of the composites
using optical microscopes and SEM
 Evaluation of mechanical properties of the
composites.

 Evaluation of Tribological properties of the
composites.
 Comparing the results of mechanical and
Tribological properties of as-cast alloy with
composites.
 Drawing Conclusion based on the obtained result.
4. METHODOLOGY
Figure1: Flow Chart of Experimental Work
5. IMPLEMENTATION
Aluminium 7068 alloy is chiefly used in the following
areas:
 Aerospace and automotive industries
 Auto-sport gearbox actuators and wheel
components
 Prosthetic limbs
 Load cells
 Hydraulic valve components
 High pressure solenoids
 Flexible shaft coupling
 Snowmobile engine shafts
 Automobile shock absorbers
 Fuel pumps for racing engines
 Motorcycle gears
 Recreational products such as tents, ski and
backpack rods, bicycles and mountain
climbing equipment
 Automotive valve body and connecting rod
6. OUTCOMES
 We can expect uniform distribution of
reinforcement(Alumina) withm atrix material
(Al7068) by Stir Casting Method
 Uniform distribution may lead to good
Microstructure of As-cast as well as composites
 Further there will be a good improvement in
mechanical and tribological properties of
Composites
 Optical Microscopic Studies
Fig 2(a): As-cast 7068 Fig 2(b) As-cast 7068 +3% Alumina

Fig 2(c) As-cast 7068 +5% Alumina Fig 2(d) As-cast 7068 +7% Alumina
Figure 2: Optical Micrographs of A357 alloy
Figure 2(a), 2(b), 2(c), 2(d) shows the micro
photographs of both the matrix alloy Al7068 and its
composites system. The microstructure clearly
indicates fairly uniform distribution of reinforcement
with minimal porosity in the matrix alloy in all the
cast composite systems studied. Microstructure
consists of fine precipitates in a matrix of dendritic
Aluminium solid solution. Segregation or porosity is
not seen in the section. The majority of the Alumina
particles are located inside the matrix itself which
indicates that it has been wetted better due to the
addition of Mg as a wetting agent.
 Hardness Test Result:
Table 5: Hardness of A7068 alloy and its Composites
Fig 5: Hardness of A7068 alloy and its Composites
From Figure 5 it is found that hardness increase with
increasing Alumina content in the material. As
compared to as-cast (A7068 alloy), 3% Alumina
addition shows an increase of 7.2 BHN (10.52%). In
contrast 5% and 7% Alumina addition shows an
increase of 15.9 BHN (23.24%) and 21.7 BHN
(31.72%) respectively. The improvement in hardness
in casted composites may be attributed to uniform
distribution of reinforcement (Alumina) in the matrix
material.
 Tensile Test Result:
Table 6: Tensile strength of A7068 alloy and its
Composites
Fig 6: Tensile strength of A7068 alloy and its Composites

From Figure 6 it is found that Tensile strength increase
with increasing Alumina content in the material. As
compared to as-cast (A7068 alloy), 3% Alumina
addition shows an increase of 30.5 UTS (17.77%). In
contrast 5% and 7% Alumina addition shows an
increase of 53.1 UTS (30.94%) and 61.7 UTS
(35.95%) respectively. The improvement in UCS in
casted composites may be attributed to uniform
material. The superior tensile properties of the
composite over the alloy should be attributed to the
existence of the Alumina reinforcing particles to
strengthen the α‑ Al phase.
 Compression Test Result :
Table 7: Tensile strength of A7068 alloy and its
Composites
From Figure 7 it is found that compression strength
increase with increasing Alumina content in the
material. As compared to as-cast (A7068 alloy), 3%
Alumina addition shows an increase of 16.05 UCS
(12.87%). In contrast 5% and 7% Alumina addition
shows an increase of 22.86 UCS (18.33%) and 30.18
UCS (24.20%) respectively. The improvement in UCS
in casted composites may be attributed to uniform
material.
 Tribological Studies
Dry sliding wear tests were conducted as per ASTM-
G99 norms. The wear rate was based on the average
value of 3 tests. Two loads of 10N and 30N at a
sliding velocity of 3.5m/sec and sliding distance of
2100m. During the test the following specifications
were used:
Table 8: Specifications used in wear studies
Calculations:

Table 9: Wear behaviour of A7068 alloy and Composites
Fig 9: Effect of load on wear (µm) of the A7068 alloy and
its Alumina composites
(Sliding Velocity: 3.5m/s, Sliding distance: 2100m, load:
10 and 30N)
From the fig 9 it can be see that as the load increases
the wear rate increases. Maximum wear rate can be
observed in A7068 alloy and least wear rate is
observed in As-cast alloy with 7% alumina. The
decrease in wear rate may be attributed to the alumina
particles which act as load bearing in the A7068
matrix and resist wear. Due to the absence of ceramic
particle as reinforcement in as-cast alloy it has a
maximum wear rate.
 Wear Surface Morphology
As-Cast 7068 Alloy As-Cast 7068 Alloy +3%
Alumina
As-Cast 7068 Alloy +3% As-Cast 7068 Alloy +3%
Alumina Alumina
Fig 10: Wear Surface Morphology of A7068 alloy and its
Alumina reinforced composites at a Sliding velocity of
2.5m/sec and Sliding distance of 1500meters.
The worn-out surface of some selected /typical
specimens after the wear test are observed under
optical microscope Figs. 13 , (a-d) shows the surface
morphology of A7068 alloy reinforced alumina
composite, tested under two different load and speed
conditions .it appears that cavities are formed in the
composite matrix and have aligned parallel to the
direction of sliding. Some particles also have chopped
off during sliding. The amount of cavitations is less
than that of the previous case. In some regions, the
substructures are aligned parallel to the sliding
direction. In some area smaller particulate have come
out from the composite matrix.
7. CONCLUSION
The following conclusions were drawn from the
present study:
From the tests conducted in order to determine the
mechanical and Tribological properties of Alumina

reinforced Al7068 composites of different weight
fractions of the reinforcement, it was found that:
 Microstructure indicates uniform distribution of
ceramics in the matrix resulting in good bonding
of the particulates and showed primary dendrite
 -Dendrite phase rich in aluminium.
 The composite with 7% Alumina has highest
hardness, UTS and wear resistance. The Alumina
particles help in matrix strengthening acting as
barriers to the dislocations moments when load is
applied.
 The wear rate is maximum for A7068 alloy and
least for A7068 with 7% Alumina.
 The temperature due to friction at the interface
increased with sliding velocity and increased load.
The increase in sliding velocity resulted in increased
strain rate leading to increased hardness which in turn
leads to reduced area of contact resulting in reduced
wear rate.
8. FUTURE SCOPE
In the present study, the analysis of as-cast and
composite (A7068/Al2O3) were made to determine the
mechanical properties and tribological behaviour.
Research can be further extended to study the
following:
 The study of the mechanical properties,
tribological behaviour with different heat
treatment tempers such as T4, T5 can be made
and compared with alloys and its composite.
 Sliding wear tests may be conducted for the alloys
and composites with further variation of
parameters such as sliding distance, load.
 A study on heat treatment by varying different
Solutioning and ageing temperature may be
carried out and tested for strength and wear
resistance.
9. REFERENCES
[1] Tamer Ozben, Erol Kilickap, “Investigation of
mechanical and machinability properties of SiC
particle reinforced Al-MMC”, Dicle University,
Turkey, June 2007.
[2] Arun Kumar .M.B. And R.P. Swamy, „Evaluation
of Mechanical Properties of Al7068, Fly Ash and E-
Glass Fiber Reinforced Hybrid Metal Matrix
Composites‟, ARPN journal of engineering and
applied science vol. 6 No.5 2011.
[3] R.D.Rawlings and F.L.Mathews, “Composite
material: Engineering and science”, Text Book,
London, 1994.
[4] M.Sreenivasa Reddy, Soma V. Chetty, Sudheer
Premkumar, (2012)“Effect of reinforcements and heat
treatment on tensile strength of Al-Si-Mg based hybrid
composite” ARPN journal of engineering and applied
science vol. 6 No.5
[5] T. Sasimurugan, K. Palanikumar, (2011) “Analysis
of the Machining Characteristics on Surface
Roughness of a Hybrid Aluminium Metal Matrix
Composite (Al7068-SiC-Al2O3)”, IJIRSET Vol.3 N0.5
[6] R. Karthigeyan, G. Ranganath and S.
Sankaranarayanan, (2012) “Mechanical properties and
microstructure studies of Aluminium (7075) alloy
matrix composite reinforced with short Basalt Fibre”,
European Journal of Scientific Research, Vol. 68. No.
4, pp. 606-615,
[7] Deepak Singla and S.R. Mediratta, (2013)“Effect
of load and speed on wear properties of Al7075-Fly
Ash composite material”, International Journal of
Innovative Research in Science, Engineering and
Technology, Vol. 2, Issue. 5, pp. 1-9.
[8] EzhilVannan and S. Paul Vizhian, (2014)
“Microstructure and mechanical properties of as case
aluminium alloy 7075/Basalt dispersed Metal Matrix
Composites”, Journal of Minerals and Materials
Characterization and Engineering No. 2, pp. 182-193.
[9] L Avinash, T RamPrabhu, Adithya Parthasarathy,
KN Varun Kumar, Basavaraj Sajjan, (2016)“Wear and

mechanical behaviour of Hypo-eutectic Al-7%Si-
0.5%Mg alloy (A357) reinforced with Al2O3
particles”, Applied Mechanics and Materials, Trans
Tech Publications,829 pp 66-72
[10] C. Garcia-Cordovilla, J. Narciso, E. Louis,(1996)
“Abrasive wear resistance of aluminium alloy /ceramic
particulate Composites”, Wear 192 pp170-177
[11] Mohan Vanarotti, SA Kori, B.R. Sridhar,
B.Shrishail Padasalgi,(2012)” Synthesis and
Characterization of Aluminium Alloy A356 and
Silicon Carbide Metal Matrix Composite”,
International Conference on Industrial Technology and
Management , 49 pp.11-15
[12] Rajeshkumar Gangaram Bhandare, Parshuram M.
Sonawane, (2013) “Preparation of Aluminium Matrix
Composite by Using Stir Casting Method”,
International Journal of Engineering and Advanced
Technology (IJEAT), Pune University.
[13] Jasim Hahim, PhD thesis, (2000) “The Production
of MMC using the Stir Casting Technique”, Dublin
City University.
[14] Aleksandar Vencl, A.Rac, (2004) “Tribological
Behaviour of Al-Based MMCs and .their Application
in Automotive Industries”, University of Belgrade.
[15] Devaraju A, Kumar A, Kotiveerachari B. (2013)
“Influence of addition of Grp/Al2O3p with SiCp on
wear properties of aluminum alloy 6061-T6 hybrid
composites via friction stir processing.Trans
Nonferrous Met Soc China; 23(5):1275–80.
[16] Devaraju A, Kumar A, Kotiveerachari B.(2013)
“Influence of rotational speed and reinforcements on
wear and mechanical properties of aluminum hybrid
composites via friction stir processing”. Mater Des,
45:576–85.

STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs

Similar to STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs (20)

Recently uploaded

Recently uploaded (20)

STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs