PROJECT REPORT ON STUDY OF MECHANICAL PROPERTIES O.docx

PROJECT REPORT ON
STUDY OF MECHANICAL PROPERTIES
OF Al 7075 ALLOY AFTER HEAT
TREATMENT
SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENT FOR
AWARD OF DEGREE OF
MASTER OF TECHNOLOGY
Production Engineering.
Submitted by
Amandeep Singh Bhui (1539018)
Gurpreet Singh (1539020)
Under the guidance of
Dr. Sarabjeet Singh Sidhu

(Assistant Professor)
DEPARTMENT OF MECHANICAL ENGINEERING
BEANT COLLEGE OF ENGINEERING AND TECHNOLOGY,
GURDASPUR
November, 2017
ii
BEANT COLLEGE OF ENGINEERING AND TECHNOLOGY,
GURDASPUR
CANDIDATE'S DECLARATION
I hereby certify that the work which is being presented in the
project report entitled “Study of
Mechanical Properties of Al 7075 alloy after Heat treatment” by
“Amandeep Singh Bhui
(1539018) and Gurpreet Singh (1539020)” in partial fulfillment
of requirements for the award
of degree of M.Tech. (Production Engineering) submitted in the

Department of Mechanical
Engineering at BEANT COLLEGE OF ENGINEERING AND
TECHNOLOGY,
GURDASPUR under PUNJAB TECHNICAL UNIVERSITY,
JALANDHAR is an authentic
record of my own work carried out during a period from August
2017 to Nov. 2017 under the
supervision of Dr. Sarabjeet Singh Sidhu. The matter presented
in this project report has not
been submitted by me in any other University / Institute for the
award of M.Tech Degree.
Gurpreet Singh Amandeep S. Bhui
Student (s)
This is to certify that the above statement made by the candidate
is correct to the best of my/our
knowledge.
Dr. Sarabjeet Singh Sidhu
SUPERVISOR

iii
ABSTRACT
Aluminum alloys are used in a large number of applications
including automobiles,
transmission of electricity, aerospace and defense industries due
to the concepts of high
strength to low weight ratio. But aluminium-zinc alloy as in
7075 Al alloy is susceptible to
embrittlement because of micro-segregation of MgZn2
precipitates which may lead to
catastrophic failure of components produced from it. Even if Al
7075 has higher hardness,
higher strength, excellent wear resistance, and high-temperature
corrosion protection, it is in
need of further enhancement of properties for increasing its

applicability.
In this study, Aluminium alloy 7075 was selected as specimen
for analyzing the various testing
results on its mechanical properties after heat treatment. The
purpose of heat treating is to
analyze the mechanical properties of the Al 7075 alloy, i.e.
hardness, Yield strength, tensile
strength and impact resistance. In the present study, selected
samples were heat-treated by
elevating the temperature to 480°C for 2 hours and then
quenched in different mediums in
order to investigate the effect on the mechanical properties of
the Aluminium 7075 alloy. The
changes in mechanical behavior as compared to untreated
samples were investigated in terms
of changes in tensile strength, hardness and impact strength.
Results showed that the
mechanical properties of Aluminium 7075 alloy can be
improved by customized heat treatment
for a specific application.

iv
ACKNOWLEDGEMENT
“A DREAM DOESN’T BECOME REALITY THROUGH
MAGIC,
IT TAKES DETERMINATION AND HARDWORK!!”
In order to complete any project or mission, it is ensured that
the person associated with it is
patient, sincere and humble. With the absence of any one of
these attributes, errors can be
committed. At the outset, we would like to propose a word of
thanks for the people who gave
us unending support and help. Many people have been the
constant source of inspiration,

encouragement and assistance in several ways.
Firstly, we want to thanks and express my sincere gratitude to
our research based project
supervisor, Dr. Sarabjeet Singh Sidhu, for his guidance,
support, encourage and helpful
advices throughout this project. We had various interesting
discussions regarding the present
project that significantly contributed to removing all the
technical road blocks and helped in
shaping the path of achieving the goals of the present research
activity. Without his encourage
and support, this research work could not be completed and
presented to all.
We would like to extend our sincere thanks to Dr. Ranjit Singh
(HOD), Department of
Mechanical Engineering, Beant College of Engineering and
Technology for giving us this
wonderful opportunity to work in desired area of interest.
We extend our sincere thanks to all teaching staff of
Mechanical Engineering
Department, those who helped us in completing this
project successfully.
Lastly we also thanks the people who directly or
indirectly gave encouragement and

support throughout the project.
Amandeep Singh Bhui (1539018)
Gurpreet Singh (1539020)
v
LIST OF FIGURES
Page No.
Figure 1: Preparing samples for tensile test 23
Figure 2: Preparing samples for impact test 24
Figure 3: Preparing samples on lathe machine 24
Figure 4: Prepared samples for heat treatment 24
Figure 5: Muffle furnace used for experimentation 25

Figure 6: Samples inside furnace 25
Figure 7: Broken samples after tensile testing 25
Figure 8: Broken samples after impact testing 26
Figure 9: Impact testing machine 27
Figure 10: Specimen for charpy impact test 27
Figure 11: Samples after testing 27
Figure 12: Variation of tensile strength 29
Figure 13: Schematic illustration of the solid diffusion
processes 30
Figure 14: Variation of percentage elongation during tensile test
31
Figure 15: Variation of impact strength 31
Figure 16: Variation of brinell hardness 32

vi
LIST OF TABLES
Page No.
Table 1: Wrought alloys designation system 14
Table 2: Chemical composition of Al 7075 alloy 18
Table 3: Percentage variation of results compared to standard
28
Table 4: Percentage variation of elongation during tensile test
30

vii
CONTENTS
Page No.
Candidate's Declaration ii
Abstract iii
Acknowledgement iv
List of Figures v
List of Tables vi

Chapter 1: INTRODUCTION 9
1.1 Influence of alloying elements 9
1.2 Strengthening & Softening techniques 12
1.3 Wrought Alloys 14
1.4 Requirement of alloy to be treated 15
1.5 Sequences of heat treatment 16
1.6 Ageing 17
1.7 Al 7075 alloy 18
Chapter 2: LITERATURE REVIEW 19
Chapter 3: PROBLEM FORMULATION 21
Chapter 4: RESEARCH OBJECTIVE 22
Chapter 5: METHODOLOGY 23
5.1 Material Preparation 23
5.2 Heat treatment of Al 7075 alloy 24
5.3 Tensile testing 25
5.4 Hardness test 26
5.5 Impact testing 26

viii
Chapter 6: RESULTS AND DISCUSSION 28
6.1 Effect of heat treatment on mechanical properties 28
6.2 Tensile strength 29
6.3 Impact strength 31
6.4 Brinell hardness 32
Chapter 7: CONCLUSION 33
Chapter 8: REFERENCES 34

9
CHAPTER – 1
INTRODUCTION
Alloys are materials having metallic properties and are
composed of two or more elements, at
least one of which is a metal. In the case of aluminum alloys,
most of them contain 90 to 96%
aluminum. Aluminum alloys are categorized under two headings
i.e. wrought alloys and cast
alloys. Aluminum casting alloys are used in a large number of
applications including
automobiles, trucks, transmission of electricity, development of
transportation infrastructures,
and in the aerospace and defense industries. The fast growth of
aluminum alloys in industrial
applications is related to their high strength-to-weight ratio
which improves the mechanical
properties and performance of the products. Among different
foundry alloys, aluminum casting
alloys are very popular, as they have the highest cast-ability
ratings, possess good fluidity and

comparably low melting points. [4] Their light weight and high
strength-to-weight ratio are the
main reasons why cast iron and steel components are being
increa singly replaced by aluminum
alloys, particularly in the automotive industry. Choosing one
casting alloy over another tends to
be determined by the relative ability of the alloy to meet one or
more of the characteristics
required for a specific application.
In 1825 aluminium was made in laboratory, because of its high
manufacturing cost, it gain
popularity in late of 20th century. Aluminium alloy have long
been of interest in various
industries due to its increased performance in comparison with
ferrous alloys. Aluminium
alloys plays a significant role in the applications where high
strengt h to weight ratio is
necessary. Aluminium alloys are the prime candidates in the
aerospace community due to their
modest specific strength, ease of manufacture and low cost.
Uses of Titanium alloys and
composites have opened the doors for the applications in
aerospace industry [8, 10]. But dew to

their high cost and unease of manufacture and restrictions in
material handling, the extent of
application of these are quite restricted. Aluminum alloys are
commonly used in aerospace
applications such as fuselage, wing, and support structures due
to low density and good
mechanical properties. Aluminum is also used in land and
marine vehicles as well as food
containers and other structural applications [11].
1.1 Influence of alloying elements on the Aluminium cast
alloys.
There are many ways of changing properties of aluminium cast
alloys. One of them is of course
change in composition of the alloy. Although the influence of
elements that are noticeable in
the alloy is mainly considered, elements which are known as
impurities cannot be omitted, and
10
its effect are not always negative. Influence of all alloying
elements as well as impurities which
can be found in aluminium alloys are as following. [3]

Silicon
Addition of Si to the aluminium alloys has a great number of
benefit s. It is one of the elements
which do not increase the weight of the alloys and in the same
time improves it properties. The
casting ability of Al-Si alloys are on extremely high level which
lowers costs of producing Al-
Si castings. Mechanical properties of aluminium alloys depends
more on the distribution of
added silicon then on the amounts of it. In these alloys where
the Si particles are uniformly
distributed represent increase in ductility, while alloys in which
these particles are acicular,
show small increase in strength [12]. While adding silicon to
the Al alloy corrosion resistance
is only slightly affected. Generally it stays on the same level or
is slightly better than in case of
pure aluminium. With increase content of Si decrease of the
fluidity and the freezing range is
observed. Moreover silicon expands during solidification, so it
compensates the shrinkage of
the aluminium. When the content of Si in the Al-Si alloys is as
high as 25% volume shrinkage

of these alloys reaches zero level.
Copper
Changes in mechanical properties of alloy while adding copper
can be observed in its strength
and ductility. Copper has the biggest influence on high
temperature strength. These changes,
like in Al-Si alloys, do not depend on the amount of added
copper but rather on the way how it
is distributed in solid solution. Alloys in which Copper can be
found in the form of evenly
distributed sphereodised particles show biggest increase in
strength without negative effects on
ductility, while alloys with Copper present as continuous
network at grain boundaries appear to
be less ductile without noticeable increase in strength. Addition
of copper will also reduce
corrosion resistance of the alloy.
It happens because Copper disperses the oxide film which
appears on the metal surface and it
this way it prevents alloy to be electrically neutral. It leads to
the fact that Al -Cu alloys can
corrode not only by contacting another materials but also
another Al-Cu alloy.

Magnesium
Magnesium is material which is lighter then aluminium and
shows the same strength
properties. It is the main alloying element in some Al alloys,
but in the majority of them is
rather considered as impurity. The role of magnesium in
aluminium-silicon alloys is to
precipitate _‖ phase (Mg2Si). [7] Al-Mg alloys are characterized
with high strength with good
ductility. Moreover magnesium can, as one of the few elements,
increase modulus of elasticity
11
of Al alloys. Proper amount of magnesium in alloy will also
give extremely high response to
heat treatment. Another property which is very good in Al-Mg
alloys is corrosion resistance. It
is better in salt water and in mild alkalis then in pure
aluminium. The worst thing when it
comes to Al-Mg alloys is it poor castability when the content of
magnesium is small (2-4%). It
appears to be better with higher amounts of magnesium (up to

12%)
Iron
Iron added to aluminium alloys negatively influence its
corrosion resistance. As far as
mechanical properties are concerned, Fe improves strength of
the alloy and in the same time
reduces its ductility. Iron improves also resistance to hot tearing
during solidification.
Formation of beta iron needles has detrimental effect on
mechanical properties of aluminum
alloy. It happens because needle-shape like iron phases act as
stress risers and crack
propagation can start in these points.
Manganese
In wrought alloys manganese is added to obtain better results
during work hardening. In Al-Si
alloys Mn improves properties in high temperatures and
similarly to silicon reduces shrinkage
formation during solidification. Nevertheless the most important
feature of adding manganese
to the alloy is the fact that such addition result in change of iron
phases in the alloy. Iron is
changed from the needle like shape to more spherical one which

results in worse crack
propagation in the alloy.
Nickel
Nickel slightly improves both strength and ductility of the
alloys at both room and elevated
temperatures. What is more, when adding nickel together with
iron, corrosion resistance against
hot water is improved.
Chromium
Additions of chromium to the Al-Si alloys will effect in little
increase in strength of these
alloys. It will also cause slightly worst tensile properties.
Zinc
Zinc in Al-Si alloys improves its machinability but decrease
high temperatures strength. It also
increase tendency to hot tearing.
12

Tin and lead
Similarly to Zn, addition of Sn and Pb improves machinability
and decrease high temperature
strength of the alloys.
1.2 Strengthening and Softening techniques
Besides modifying Al alloys by changing its content, there are
several other methods of
modifying these alloys. That is why aluminium alloys are
almost always subjected to
strengthening or softening processes. Aluminium alloys can be
divided into two groups:
1.2.1 Work hardening and annealing
Work hardening is process in which metal is strengthening by
for example rolling or forging. It
is main technique of improving properties of alloys which
cannot be heat treated. During these
treatments number of dislocations in material increasing, and
the strength of metal improves.
This is caused because grain shape changes and microstructure
becomes more inhomogeneous

which do not allow fracture propagation in easy way. Work
hardening is method of improving
properties of these alloys which cannot be heat treated.
Nevertheless changes in structure of
alloys also affect reaction of these alloys to annealing and hot
working.
Annealing is the process during which previously work
hardening material is placed in furnace
in elevated temperatures. The great amount of commercially
used Al alloys is generally
annealed in temperature range between 300°C and 420°C. When
annealing time is too long,
recrystallization can be followed by grains growth and the
softening can occurs. [4]
1.2.2 Heat treatment
Although precipitation or ageing hardening phenomenon of
aluminium alloys was discovered,
by German metallurgist Alfred Wilm, over 100 years ago it is
still not fully known and further
experiments are still being held all over the world. There is no
exactly predicated influence of
ageing temperatures, ageing times and exact alloys composition
on the mechanical properties

on these alloys. Latest research revels for example that however
tensile strength in some alloys
decrease during first hours of ageing it starts to increase later
and reach values better than as-
cast alloys [5].
13
Heat treatment is defined as an operation or combination of
operations involving heating and
cooling of a metal or alloy for this case involving the mild steel
in the solid state in such ways
as to produce certain microstructure and desired mechanical
properties (hardness, toughness,
yield strength, ultimate tensile strength, Young‘s modulus,
percentage elongation and
percentage reduction). Annealing, normalizing, hardening and
tempering are the most
important heat treatments often used to modify the mechanical
properties of engineering
materials particularly steels. Annealing is defined as a heat
treatment that consists of heating to
and holding at a suitable temperature followed by cooling at an

appropriate rate, most
frequently applied in order to soften iron or steel materials and
refines its grains due to ferrite-
pearlite microstructure; it is used where elongations and
appreciable level of tensile strength are
required in engineering materials. Hardening is the heat
treatment processes in which increases
the hardness of a steel piece by heating it to a certain
temperature and then cooling it rapidly to
room temperature. Tempering is the process of imparting
toughness at the cost of its hardness
to an already hardened piece of steel by reheating it to a certain
temperatur e and then cooling it
rapidly. The temperature of heating depends on the toughness to
be imparted and hardness to
be reduced. In normalizing, the material is heated to the
austenitic temperature range and this is
followed by air cooling. This treatment is usually carried out to
obtain a mainly pearlite matrix,
which results into strength and hardness higher than in as
received condition. It is also used to
remove undesirable free carbide present in the as-received
sample [1]. The main objective of
heat treatment is to make the material system structurally and

physically fit for engineering
application.
1.2.3 Quenching
Quenching is the process of rapid cooling of material systems to
room temperature to preserve
the solute in solution. The cooling rate needs to be fast enough
to prevent solid -state diffusion
and precipitation of the phase. The rapid quenching creates a
saturated solution and allows for
increased hardness and mechanical properties of the material
system. In addition to this studies
have shown that the highest degree of corrosion resistance have
been obtained through the
maximum rates of quenching. To achieve supersaturated solid
solution (desired optimum
condition for precipitation hardening) process called quenching
is used. Rapid cooling of the
alloy to the room temperature evades forming type of
precipitation which has negative
influence on mechanical properties and corrosion resistance
[10]. The solid solution formed at
solution heat treating temperature is preserved.

14
Heat is dissipated from the object by movement of the
quenching medium by conduction
currents. The difference in temperature between the boiling
point of the medium and actual
temperature of the medium is the major factor influencing the
rate of heat transfer in liquid.
Very fast cooling is more effective and thus strength is higher.
Properties like Yield Strength,
Ultimate Tensile Strength and % elongation varies with
quenching mediums i.e. quenchants.
1.3 Wrought Alloys
Cast aluminium alloys are grouped into different series of
alloys, namely, 1xx.x series, 2xx.x
series, 3xx.x series, and so on. The principal alloying element
or elements in each series
characterizes that series, as shown in Table 1.1
Alloy Series Principal Alloying Element
1xx.x Aluminium (99% minimum)
2xx.x Copper

3xx.x Manganese
4xx.x Silicon
5xx.x Magnesium
6xx.x Magnesium and Silicon
7xx.x Zinc
8xx.x Other elements
Table-1: Wrought alloys designation system
The International Alloy Designation System is the most widely
accepted naming scheme for
wrought alloys. Each alloy is given a four-digit number, where
the first digit indicates the
major alloying elements, the second — if different from 0 —
indicates a variation of the alloy,
and the third and fourth digits identify the specific alloy in the
series. For exa mple, in alloy
3105, the number 3 indicates the alloy is in the manganese
series, 1 indicates the first
modification of alloy 3005, and finally 05 identifies it in the
3000 series.

15
99% aluminium content by
weight and can be work hardened.
itation
hardened to strengths comparable
to steel. Formerly referred to as duralumin, they were once the
most common aerospace
alloys, but were susceptible to stress corrosion cracking and are
increasingly replaced by
7000 series in new designs.
3000 series are alloyed with manganese, and can be work
hardened.
-
silicon alloys intended for
casting (and therefore not included in 4000 series) are also
known as silumin.
are alloyed with magnesium, and offer superb
corrosion resistance, making
them suitable for marine applications. Also, 5083 alloy has the
highest strength of not heat-
treated alloys.

easy to machine,
are weldable, and can be precipitation hardened, but not to the
high strengths that 2000 and
7000 can reach. 6061 alloy is one of the most commonly used
general-purpose aluminium
alloys.
precipitation
hardened to the highest strengths
of any aluminium alloy (ultimate tensile strength up to 700 MPa
for the 7068 alloy).
covered by other
series. Aluminium-lithium alloys are an example.
1.4 Requirements of the alloy to be heat treated
Not all aluminium alloys can be heat treated. Heat treatable
alloys are only these from groups
2XX.X, 3XX.X and 7XX.X (these in which main alloying
element is copper, magnesium and
zinc respectively). Properties of rest of aluminium alloys can be
improved only by cold
working because process of precipitation hardening do not
occurs in them.

The main requirement for an alloy system to respond to heat
treatment is a significant decrease
in solid solubility of one or more of the alloying elements with
decreasing temperature [4].
What is more, alloys which are cast using high-pressure die-
casting method are not suitable for
heat treatment. During high pressure die casting gas bubbles are
trapped inside the casting and
create so called porosity. During heat treatment process these
gas pores expand and distort the
casting which makes component unusable.
https://en.wikipedia.org/wiki/Silumin
https://en.wikipedia.org/wiki/Welding
16
1.5 Sequences of heat treatment
There are many different sequences of heat treatment which
improves properties of aluminium
alloys. Its designation consists of one letter T means ‗heat
treated‘ and a number showing how

the sequence looks like. The most common sequences are as
following:
eat treated

Most common sequences of heat treatment of aluminium alloys
are T5 and T6. To specify heat
treatment more precisely one or more digits could be added to
T1 -T9. For example T351 means
that the parts were solution heat treated, then stress were
relieved by controlled amount of
stretching. Aluminium receives no further straightening after
stretching. This process can be
applied to plate, rolled or cold finished rods and bars.
1.6 Ageing
Ageing is divided for natural ageing, when keeping samples in
room temperature and artificial
ageing conducted in elevated temperatures. Most of the
properties like hardness and electrical
conductivity are influence by ageing, depending on time and
temperature [11].
While ageing, supersaturated solution is decomposing to
disperse precipitates. Ageing is a key
factor in all heat treatment processes because it allows to obtain
mechanical properties even

two times better than in as-cast state.
Natural ageing
Hardening process starts at room temperature after quenching
(quenching keeps alloying
elements in supersaturated solid solution). During natural
ageing clusters are formed. This
effect can negatively affect properties of the alloy because when
clusters are not stable and
critical radius is not attained; fewer coarse precipitates are
formed [10]. Nevertheless natural
ageing cannot be omitted during production process and that is
why it is generally taken into
consideration while performing research in the field of heat
treatment of aluminium alloys.
Artificial ageing
Artificial ageing causes precipitation hardening which is a
process where properties of material
can be changed by mean of heat treatment. During precipitation
hardening allotrope
transformation does not occur [9]. Artificial ageing process is
based on phase separation which
happens in supersaturated solid solution in room temperature or
in slightly elevated

temperature.
18
Heat-treatable alloys like 7xxx series (primary alloying
elements: zinc, magnesium, and
copper) are particularly desirable for aerospace applications as
they develop high specific
strength. These aluminum alloys generally undergo thermo
mechanical processing in their
production.
In this study, the hardness, tensile properties, impact strength
and microstructure of Al 7075
alloy was investigated. This alloy was selected for study based
on its promising potential for
use in aerospace, marine and automotive applications.
1.7 Alloy 7075
Aluminum alloys fall into two general categories: heat-treatable
and non-heat treatable. Series
7xxx alloys are considered the high strength aircraft alloy
family, are heat treatable by solution
and aging. Al alloy 7075 was introduced in 1943 by Alcoa and

is primarily an aircraft and
aerospace alloy. 7075 is typically used in applications requiring
a combination of high strength
and moderate toughness and corrosion resistance, including
aircraft structures, gears and sha fts,
missile parts and various defense equipment. The chemical
composition of 7075 is given in
Table 1.2
Concentration [wt%]
Cr Cu Fe Mg Mn Si Ti Zn Al
0.18-0.28 1.2-2.0 0.50 2.1-2.9 0.30 0.40 0.20 5.1-6.1 Balance
Table-2: Chemical Composition of Al 7075 Alloy
7075 Al alloy due to its attractive comprehensive properties
such as low density, high strength,
ductility, toughness and resistance to fatigue. It has been
extensively utilized in aircraft
structural parts and other highly stressed structural applications.

19
CHAPTER – 2
LITERATURE REVIEW
Patricia Mariane Kavalco et. al. (2009) overviewed the inter-
granular corrosion (IGC)
process and contrasted it to pitting corrosion. It was shown that
the propensity for IGC of heat
treatable aluminum alloys was cooling rate dependent. If an
aluminum alloy was slowly cooled
from an elevated temperature, alloying elements precipitate and
diffuse from solid solution to
concentrate at the grain boundaries, small voids, on un-
dissolved particles, at dislocations, and

other imperfections in the aluminum lattice. For optimal
properties, it was desirable to retard
this diffusion process and maintain the alloying elements in
solid solution. This was done by
quenching from the solution temperature [1].
Adeyemi Dayo Isadare et. al. (2013) investigated the effects of
annealing and age hardening
heat treatments on the micro-structural morphology and
mechanical properties of 7075 Al
alloy. It was also found out that age hardening and annealing
heat treatment operation
eliminated micro-segregations and improved mechanical
properties of 7075 Al alloy. It was
concluded that micro-segregation can be eliminated by rapid
solidification and appropriate heat
treatment process [2].
Jasim M. Salman et. al. (2013) studied to improve properties of
7075-T6 such as impact
toughness, thermal age hardening behaviour and corrosion
resistance in 3.5% NaCl solution by
using quenching in 30% polyethylene glycol and addition
alloying elements, i.e. boron (B) to
this alloy. Results showed improved impact toughness by (30%)
when quenching in water, and

by (50 %) when quenching in 30% PAG corresponding to the
base alloy at aging temperature
150ºC [3].
Paul A. Rometsch et. al. (2014) described the effects of
homogenisation, solution treatment,
quenching and ageing treatments on the evolution of the
microstructure and properties of 7xxx
alloys. it was demonstrated how improvements in the
microstructure and properties can be
obtained by, 1) dissolving unwanted coarse constituent particles
such as the S-phase through
well-controlled high temperature treatments, and 2) controlling
the quench rate and factors that
influence the quench sensitivity [4].
Tolga Dursun et. al. (2014) reviewed important recent advances
in aluminium aircraft alloys
that can effectively compete with modern composite materials.
Recent developments in high
strength Al–Zn and Al–Li alloys, damage tolerant Al–Cu and
Al–Li alloys, has been successful
20

in improving the static strength, fracture toughness, fatigue and
corrosion resistance through
the design and control of chemical composition, and/or through
the development of more
effective heat treatments [5].
Guo Lianggang et. al. (2015) developed true stress–strain
curves at temperatures of 300 –
500°C and strain rates of 0.01–10 s
-1
by the isothermal compression tests, providing a data
basis for the establishment of hot processing map of as-cast
7075 aluminum alloy. The stable
area with homogeneous grain resulted from dynamic recovery,
namely the temperatures at
425–465 °C and the strain rates at 0.01–1 s
-1
, was suggested to be the suitable processing
window for the as-cast 7075 aluminum alloy [6].
Ankitkumar K. Shriwas et. al. (2016) reviewed the
microstructure of aluminium alloys series
and their emphasis on the mechanical properties were discussed.
It was observed that 7075 -T6

aluminium alloy provides good yield strength, ductility and
fracture toughness. It was observed
that in 7075 -T6 aluminium alloys energy required for crack
propagation is larger than crack
formation. There is large scope for research in the
microstructure analysis for 7075 -T6
aluminium alloy [7].
P. Rambabu et. al. (2017) overview of the historical
development of aerospace aluminium
alloys, followed by a listing of a range of current alloys with a
descriptio n of the alloy
classification system and the wide range of tempers in which Al
alloys are used. A description
was given of the alloying and precipitation hardening
behaviour, which is the principal
strengthening mechanism for Al alloys. Various aerospace
applications of Al alloys were
enlisted. The Indian scenario with respect to production of
primary aluminium and some
aerospace alloys, and the type certification process of Al alloys
for aerospace applications were
described. Finally there was a critical review of some of the
gaps in existing aerospace Al alloy

technologies [9].
21
CHAPTER – 3
PROBLEM FORMULATION
From the literature it is observed that heat treatable aluminum
alloys are widely used in aircraft
structural, marine, automotive parts applications and are
susceptible to localized corrosion in
chloride environments, such as pitting, crevice corrosion,
intergranular corrosion and stress
corrosion cracking (SCC). Pitting is the most common corrosion
process encountered with
aluminum alloys, and is a major cause in variations in the grain
structure between adjacent

areas on the metal surfaces in contact with a corrosive
environment. Intergranular
(intercrystalline) corrosion occurs most commonly in the
following aluminum alloys: -
Al-Cu-Mg (2xxx); Al-Mg (5xxx), which is similar to the Al-Cu-
Mg alloys; Al-Mg-Si (6xxx);
and Al-Zn-Mg-Cu (7xxx) [10].
During normal operation aircraft and marine ships are subjected
to natural corrosive
environments due to humidity, rain, temperature, oil, hydraulic
fluids and salt water [11].
High strength aluminium alloys such as the 7075-T6 are widely
used in aircraft and marine
structures due to their high strength-to-weight ratio,
machinability and relatively low cost.
However, due to their compositions, these alloys are susceptible
to corrosion. Fatigue life and
strength properties are always important design data for such
structures; therefore an approach
is made for enhancing the strength and corrosive properties of
Al 7075 with heat treatment
method using different quench mediums.
Titanium powder and CNTs were chosen as quenchants in

addition with oil because of their
high corrosion resistance, optimal mechanical properties in load
bearing applications and weak
response to magnetism [12].
22
CHAPTER – 4
RESEARCH OBJECTIVES AND OUTLINE
The goal of this research is to examine the effects of modified
solution heat treatment on the
microstructure, mechanical properties, and SCC resistance of
Aluminium alloy 7075. This is
done through an experimental program which included heat
treating specimens of the alloy to

various metallurgical conditions, a two part testing program
with one phase designed to
evaluate the resulting mechanical and physical properties and
the other phase to assess the
microstructure and SCC susceptibility under various conditions.
This was accomplished by the following objectives: -
of different quenching mediums.
quenchants.
ress Corrosion Cracking (SCC)
during the heat treatment of
Aluminium alloy 7075.
treatment parameters on the
Ultimate Tensile Strength, Yield Strength and %Elongation
values, employing mathematical
analysis.
mediums.

23
CHAPTER – 5
METHODOLGY
5.1 Material Preparation
The present investigation was carried out on Al 7075 alloy. The
material was purchased from
Bharat Aerospace Metals, Mumbai in extruded rod shape having
diameter 20 mm and length
915 mm (2 lengths). From the raw material, six samples were
prepared for tensile test
according to ASTM E8M standard (dia. 12 mm and gauge length
60mm). Lathe machine was

used to make the dumble shape for the tensile test. Similarly,
six samples were prepared for
impact test according to ASTM standard E23. Firstly, square
shape of 14 mm was made on
lathe machine and then square of 14 mm reduced to 10 mm
using grinder according to ASTM
standard followed by v – notch for the final test.
Fig.-1: Preparing samples for Tensile test on lathe machine
24
Fig.-2: Converting rod bar to square for Fig.-3: Preparing
samples on Lathe machine.
impact sample on lathe machine.
Fig.-4: Prepared Samples for Heat Treatment
5.2 Heat Treatment of Al 7075 alloy
The prepared samples of aluminium 7075 alloy were subjected
to solutionizing treatment at a

temperature of 480°
C for a period of 2 hours using muffle furnace, followed by
quenching in
five different quenchants viz; Water, Brine
Solution
, Oil, Oil + TiO2 , and Oil + CNTs and one
sample was furnace cooled.
25
The Heat treatment was conducted according to the ASTM
standard B918 – 01 i.e. the standard
for the heat treatment of aluminium alloys.

Fig.-5: Muffle Furnace used for Experimentation. Fig.-6:
Samples placed inside furnace for heating.
5.3 Tensile testing
Tensile testing of all these specimens was conducted per ASTM
standards. Six samples were
tested; five were quenched and one was annealed i.e. furnace
cooled. The tests were carried out
at room temperature using FIE make Universal Testing
Machine, UTE – 20 electromechanical
testing machine. Load – displacement plots were obtained and
ultimate tensile strength and
percentage elongation values were calculated from this load –
displacement diagrams.
Fig.-7: Broken Samples after Tensile Testing.

26
5.4 Hardness test
The control and the heat treated samples were subjected to the
Brinell hardness test. The
specimens were polished to 600 microns and mounted on the
machine using a dwell time of 15
seconds. The diameter of the impression left by the ball was
then measured using the Brinell
calibrated hand lens and the corresponding Brinell hardness
number was determined.
5.5 Impact testing
Impact testing of all these specimens was conducted per ASTM
Standard E 23. The tests were
carried out using Charpy impact test method on En Kay

Enterprises impact-testing machine.
The amount of impact energy absorbed by the specimen before
yielding was read off on the
calibrated scale attached to the machine as a measure of impact
strength in Joules.
Fig.-8: Broken Samples after Impact Testing.
27
Fig.-9: Impact Testing Machine. Fig.-10:
Specimen for Charpy Impact Test.

Fig.-11: Samples after Testing.
28
CHAPTER – 6
RESULTS AND DISCUSSION
Mechanical properties (hardness, tensile strength, yield
strength, elongation and percentage of
elongation) of the treated and untreated samples are determined
using standard methods. For
hardness testing, oxide layers formed during heat treatment
were removed by stage-wise

grinding and then polished. Average Brinell Hardness Number
(BHN) readings were
determined by taking two hardness readings at different
positions on the samples and tensile
test using universal testing machine. Impact energy was
recorded using the Charpy impact
tester.
6.1 Effect of heat treatment on mechanical properties
The effect of heat treatment (annealing, quenching) on the
mechanical properties (ultimate
tensile strength, hardness, percentage elongation, and impact
strength) of the treated and
untreated samples is shown in Table 3. The function of
annealing is to restore ductility and also
removes internal stresses but its Brinell Hardness Number is
less than hardening because here

carbon get more time to react with oxygen in the atmosphere for
slow cooling rate. The
function of quenching is to increase the hardness of the
specimen and so its Brinell hardness
number is larger than annealing because here carbon cannot get
more time to react with oxygen
(for quick cooling rate), so carbon is trapped with the specimen
and formed martensite.
Sample Type
Tensile
Strength
(MPa)
%age
change

Brinell
Hardness
(BHN)
%age
change
Impact
Strength
(Joule)
%age
change
Standard 510 --- 150 --- 27 ---
Water
Quenched

515 1% 161 7% 68 152%
Brine solution
Quenched
541 6% 172 15% 91 237%
Oil Quenched 543 6% 165 10% 83 207%
(Oil + TiO2)
Quenched
535 5% 156 4% 52 93%
(Oil + CNT)
Quenched
471 -8% 145 -3% 80 196%
Annealed 220 -57% 71 -53% 8 -70%
Table-3: Percentage Variation of Tensile strength, Brinell
hardness, and Impact strength as compared

to the standard Al-7075-T6 alloy.
29
Comparing the mechanical properties of annealed sample with
the untreated sample, annealed
sample showed that lower tensile strength (220 MPa), impact
strength (8 Joule) and hardness
(71 BHN). The decrease in tensile strength and hardness can be
associated with the formation
of soft ferrite matrix in the microstructure of the annealed
sample by cooling.
The mechanical properties of the brine quenched sample
revealed that it had the highest value
of hardness (172 BHN), impact strength (91 Joule) and tensile
strength of 541 MPa were

obtained. The specimen was in muffle furnace at 480°C for 2
hours and then brine quenched.
This treatment increased the tensile strength and hardness but
there was massive reduction in
elongation and reduction in area respectively.
6.2 Tensile strength
Fig.-12: Variation of tensile strength of standard specimen
compared to the different heat treatments.
From Table-3 and Fig.-1 it can be inferred that, there is only 1%
increase in tensile strength
with water quenching, and the maximum value of tensile
strength (543 MPa) was achieved by
oil quenching. Drastic decrease in tensile strength (-57%) can
be seen in the case of annealing,
this is due to inter-granular corrosion in which upon slow

cooling from the solutionizing
temperature, alloying elements precipitate and diffuse from
solid solution to concentrate at the
grain boundaries, small voids, on un-dissolved particles, at
dislocations, and other
30
imperfections in the aluminium lattice occur as shown in Fig. 2
[1]. Hence annealing is not the
preferred heat treatment process for aluminium alloys.
Fig.-13: Schematic illustration of the solid diffusion processes
that may occur during solution heat
treatment of aluminium alloy.

Elongation during tensile testing
From the load vs displacement graphs provided by the testing
lab, the percentage elongation of
each specimen was calculated. The length of dumble prepared
for testing was 220 mm.
Sr. No. Sample type Elongation in length
(mm)
%age Elongation
1 Water Quenched 9.6 4.36%
2 Brine solution
Quenched
12.3 5.61%
3 Oil Quenched 14.75 6.70%
4 (Oil + TiO2)
Quenched

14.3 6.5%
5 (Oil + CNT)
Quenched
12.84 5.83%
6 Annealed 18.9 8.6%
Table-4: Percentage Variation of Elongation during Tensile test
of Al-7075-T6 alloy.
31
Fig.-14: Variation of elongation during tensile test in the
different heat treatments.

From the table-4 and fig.-3, it was observed that the minimum
elongation was in the case of
water quenched sample (4.36%), and the maximum elongation
was in the case of annealed
sample (8.6%). In the case of oil quenched sample the
percentage elongation was highest
among the quenched samples with 6.7% elongation. It is
obvious from the results that the
percentage elongation is not that high because quenching makes
the material brittle and for
brittle materials the necking phase is diminished.
6.3 Impact strength
Fig.-15: Variation of impact strength of standard specimen

32
From table-3 and fig.-4 it was observed that maximum increase
of 237% in impact strength in
the case of quenching with brine water, and minimum of 52%
increase in impact strength in the
case of quenching with a solution of oil+TiO2. Again a drastic
decrease in impact strength was
observed when the sample was annealed.
6.4 Brinell Hardness
Fig.-16: Variation of brinell hardness of standard specimen
From table-1 and fig.-4 it was observed that maximum increase
in brinell hardness of 15% was
in the case of quenching in brine solution and minimum ( -8%)

in the case of quenching in
oil+CNT solution. Annealing of aluminium alloy again results
in drastic decrease in hardness
as annealing makes the alloy soft and moreover as discussed
earlier that, alloying elements
precipitate and diffuse from solid solution to concentrate at the
grain boundaries and small
voids.
33

CHAPTER – 7
CONCLUSION
From the results, it was concluded that mechanical properties of
aluminium 7075 alloy can be
customize according to different applications. In our work, we
had used five samples for
different quenching mediums i.e. water, brine solution, oil, oil
mixed TiO2, oil mixed CNTs
and one sample was annealed. Following points are concluded
on the behalf of results:
and decrease drastic to 220
MPa during annealed due to slow cooling.
ng the hardness of the
specimen.

with the hardness of 172
BHN.
because quenching makes
the material brittle and for brittle materials the necking phase is
diminished.

34
CHAPTER – 8
REFERENCES
1. Patricia Mariane Kavalco, Lauralice C. F. Canale, George E.
Totten, ―Quenching of
aluminium alloys: cooling rate, strength, and inter-granular
corrosion‖, Heat treating
progress, Nov-Dec, 2009.
2. Adeyemi Dayo Isadare, Bolaji Aremo, Mosobalaje Oyebamiji
Adeoye, Oluyemi John

Olawale, Moshood Dehinde Shittu, ― Effect of Heat Treatment
on Some Mechanical
Properties of 7075 Aluminium Alloy‖, Materials research, 2013.
3. Jasim M. Salman, Shaymaa Abbas Abd Alsada, Khadim F.
Al-Sultani, ―Improvement
Properties of 7075-T6 Aluminum Alloy by Quenching in 30%
Polyethylene Glycol and
Addition 0.1%B‖, Research Journal of Material Sciences, 2013.
4. Paul A. ROMETSCH, Yong ZHANG, Steven KNIGHT,
―Heat treatment of 7xxx series
aluminium alloys—Some recent developments‖, Transactions of
non-ferrous metals
society of china, 2014.
5. Tolga Dursun, Costas Soutis, ―Recent developments in
advanced aircraft aluminium
alloys‖, Materials and design, 2014.

6. Guo Lianggang, Yang Shuang, Yang He, Zhang Jun,
―Processing map of as-cast 7075
aluminum alloy for hot working‖, Chin J Aeronaut 2015.
7. Ankitkumar K. Shriwas, Vidyadhar C. Kale, ―Impact of
Aluminum Alloys and
microstructures on Engineering Properties - Review‖, IOSR
Journal of Mechanical and
Civil Engineering, 2016.
8. Singh, Lakhwant & Singh, Gurpreet & Bhui, Amandeep.
(2017). Optimization of
process parameters for MRR, Kerf Width, Surface Roughness of
Ti-6Al-4V after heat
treatment using WEDM.
9. P. Rambabu, N. Eswara Prasad, V.V. Kutumbarao, R.J.H.
Wanhill, ―Aluminium Alloys

for Aerospace Applications‖, Aerospace Materials and Material
Technologies, Indian
Institute of Metals Series, 2017
10. Quenching of aluminum alloys: heat treating progress •
November/December 2009.
35
11. Tolga Dursun
[a],
Costas Soutis
[b],
―Recent developments in advanced aircraft aluminium
alloys‖ Materials and Design 56 (2014) 862–871.
12. G.E. Totten and D.S. MacKenzie (Eds.), Handbook of

Aluminum, Vol. 1: Physical
Metallurgy and Process, Marcel Dekker Inc., New York, 2003,
pp. 114-168.
13. Yuping Zhang, Hongzheng Zhu, Chen Zhuang, Shougang
Chen, Longqiang Wang,
Lihua Dong, TiO2 coated multi-wall carbon nanotube as a
corrosion inhibitor for
improving the corrosion resistance of BTESPT coatings,
Materials Chemistry and
Physics Volume 179, 15 August 2016.
http://www.sciencedirect.com/science/article/pii/S02540584163
03285#!
03285#!
03285#!

03285#!
03285#!
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http://www.sciencedirect.com/science/journal/02540584/179/su
pp/C
Running head: BARRIER TO ECONOMIC STABILITY1
Taiyuan Mei
Caitlin Kirkley
English 1A
November 19，2018
Inequality as Barrier to U.S Economic Stability
Inequality has become a pressing concern since many people
including economists feel that it causes economic harm. The gap
between the rich and the poor is ever increasing and becoming
even greater over the years. It affects economic stability and
growth by undermining education opportunities to those from
poor backgrounds, hindering skills development and lowering
social mobility. It obstructs productive investment and limits an

economy’s productive and consumptive capacity. The poor
people tend to spend more of their income to meet their basic
needs. Lower income means lower consumption resulting to a
weaker economy. Also, too much spending means there is little
left to be saved by such persons yet we know savings are the
base for economic growth in the long term. Too much spending
among low-income earners obstructs investments that play a
significant role in economic growth. Economic growth is
hindered by inequality that causes gaps between the poor and
the rich. In fact, inequality plays a crucial role in economic
growth and stability. Inequality is the biggest barrier to
economic stability in the U.S because it leads to higher
spending hampering investment.
Inequality, in particular, income inequality seems to have
worsened significantly in the U.S since 1980s. It has led to
“secular stagnation” meaning that the economy is decreasing in
value that it may not easily recover from (Hiltzik). The U.S
economic growth and projected future growth seems to be
getting worse over time. In fact, the U.S economic growth
averaged 2% only since 2013. The situation worsened because
there was meager growth in the pre-recession period. Secular
stagnation exists though people have different perspectives on
its causes and remedies. Some argue that it is caused by an
increase in income inequality, slowdown of technological
advances that facilitate productivity and lack of investment in

infrastructure. Others feel that slow rates of innovation and
invention essential for facilitating human productivity
contribute to the stagnation being witnessed for centuries. Some
recommendations to improve the situation include the
government increasing public investment and reducing
structural barrier to private investment. This will show its
commitment to maintain spending power and reducing
inequality thus redistribute income to lower and middle income
households (Hiltzik).
The rising income inequality continues to exist both in good and
bad times in the U.S. It is considered a historical norm since it
has been experienced from the past and is likely to continue in
the future. The U.S government fails to take adequate measures
such as increase incomes for the poor and middle class to alter
inequality like it has done in making childbirth safe for women.
The incomes and assets of the rich continue to rise rapidly
compared to those of the middle and low class. The rich spend
some of their incomes and focus on more investment while the
poor have little to spend and lack investments. For instance,
larger farmers will make more money than small farmers. They
will earn more profit and buy more capital that in return bring
them more profits. On the hand, the small farmer might find it
difficult to expand his farm because of small profits some of
which he could be using to pay debts (Leonhardt 544). This will
hinder him from investing slowing down economic growth.

The rich earn enough allowing them to save and make
investments. Investments whether small are associated with
positive return. This positive return facilitates economic
growth. This trend continues over years with the few rich
persons contributing to economic development. There could be
faster economic development if the low- and middle-income
earners had something to save and invest. If the current
economic development is facilitated by the few rich, what could
it be at if the middle- and low-income earners were also at a
position to contribute to it? Unfortunately, they continue to
struggle with the income inequality that exists. They continue to
spend most if not all they earn to meet their basic needs. This
hinders them from investing and enjoying the positive returns
from their investments. This hinders them from facilitating
economic development through investments. This trend can be
stopped by emulating policies that have helped other counties
have their middle-class earners earn better incomes in the recent
years. The U.S can attack inequality by looking at tax wealth,
taxation of the poor and middle-income earners, financing of
schools and infrastructure such as roads and transit systems
(Leonhardt 546). This should help improve on economic growth.
Rising inequality tends to reduce income growth and in return
slow economic growth. Crises too like the Great Recession also
contributed to the slow economic growth. The historic recession
in the late 2007 significantly affected the U.S economy. An

approximate doubling of the household debt income ratio from
the 1980 preceded the crisis. If the group consumption income
ratio had declined, it could have been possible to maintain the
ratio of stable debt to income. Unfortunately, this did not
happen in 2006 and the debt income ratio dramatically
increased. It led to increased household debt-income ratio that
led to collapse of household spending. The bottom 95%
consumption income ratio took the fall, concurrently with
borrowing constraints even tighter while the top 5% ratio rose.
Their rising was accompanied consistently with consumption
smoothing. .The rise in inequality seems to have dragged
expenditure growth since the Great Recession holding back
recovery (Cynamon & Fazzari). Since expenditure is among the
major drivers of economic growth, dragging expenditure growth
means dragging economic growth.
There is no visible sign that inequality has reversed since the
beginning of the recession. From 2006 to 2009, there was a
pause in income share increase of the top 5% and it has risen
once again steeply. The demand drag caused by rising inequality
that was postponed for decades by bottom 95% borrowing is
causing a drag in consumption growth and predictably will
continue doing so for a few more years (Cynamon & Fazzari).
There is a large demand gap caused by slower PCE growth
relative to the recession trends that were before. This is
evidence of the sluggish recovery of consumption in the Great

Recession. To help this out, the group that took the debt in the
first place should deleverage. This is the same group that lost
out to inequality rising. Consumption must be reduced to re
align it to income and pay its debts. Inequality is thorn in the
US economy’s flesh that must be confronted even as debt
burdens return to more sustainable levels. It would be vital to
get a clear understanding that rising inequality is way beyond
social justice as an issue. Inequality also compromises the
demand engine that was important and necessary for good and
hopeful macroeconomics results in the USA before the Great
Recession. Greater inequality threatens growth of demand and
even unemployment.
Economic growth is influenced by income inequality.
Investigating the relationship between income inequality and
economic growth changes over time helps illustrate the impact
income inequality has on economic growth from the past. It
illustrates a negative effect on inequality on economic growth.
However, analysis and comparison of time periods 1970-1985
and 1985-1999 fails to illustrate a statistically significant
relationship between income inequality and economic growth.
There exists a negative association between income inequality
and growth though the effect is not adverse (Binatli).
By the mid-nineties, empirical research suggested that there
existed a negative effect of income inequality on economic
growth. Some researchers like MacDonald and Majeed

illustrated that there existed a robust association between
income inequality and economic growth on their analysis on
GDP from 1970 to 2008. They argued that the poor lack the
opportunity to exploit returns on growth that is essential for
continued economic growth. However, a quality test performed
on available data investigating growth income inequality failed
to illustrate a significant relationship on income inequality and
economic growth (Binatli). This does not mean that inequality
does not affect economic growth, only that their research
findings suggest that the association is weak.
According to (Samimi & Jenatabadi) income level of a country
could be affecting growth of the country. The authors identify
economic globalization as a factor significantly impacting
economic growth of Organization of Islamic Cooperation (OIC)
countries. High and middle-income countries benefit from
globalization that directly promotes growth and through
complementary reforms. Globalization affects growth through
diffusion of technology, effective allocation of resources and
improvement in factor productivity. The U.S is one country with
good technology that facilitates production. It embraces
globalization that promotes economic growth. However, unequal
allocation of resources and income distribution are some factors
hindering it from economic stability and growth.
As much as inequality contributes significantly to economic
growth, it is not the biggest factor influencing economic

growth. Factors like education, infrastructure and innovation
contribute significantly to economic stability and growth
(Samimi & Jenatabadi). Lack of progress in these areas hinders
economic growth. Looking back at Europe and the US in
comparison, Europe has grown at a slower rate. Researchers
argue that the slow growth may have been due to the European
Union’s relatively meager investment of 1.1 % of its gross
domestic product in higher education. This is in comparison to
the 3% of the U.S. More instances of how education affects
growth is in the thirty years after World War 2, Europe
presented a faster growth than the U.S. despite having invested
mainly in primary and secondary education. Moreover, the
Asian miracle, that is high productivity growth in the Asian
countries is attributed more with their investments in primary
and secondary education other than tertiary and higher
education (Samimi & Jenatabadi). This clearly shows
importance of different levels of education and their impact to
growth. Lack of innovation could hinder maximum productivity
in companies negatively affecting economic growth. Poor
infrastructure in some areas could hinder flow of goods and
development hindering economic growth. These are some
factors that should be analyzed into depth since they tend to
influence economic growth. However, the U.S is an innovative
country with good infrastructure meaning that these are some
major but not the biggest factors influencing economic growth.

The U.S should focus on strategies like income redistribution
and establishing stricter income-equalizing policies to promote
growth.
Uneven distribution of resources in the U.S is a major challenge
to economic growth. In fact, inequality that exists in the country
seems to be the biggest barrier to economic stability because it
leads to higher spending hampering investment. The middle and
low income earners who have a significant percentage in the
country’s total population have little to save. Their low salaries
and wages are mostly used to satisfy needs leaving them with
nothing or little to save. They may lack money to investment
and earn profits like the rich persons. Since they constitute a
significant percentage of the U.S total population, lack on
investment from them is impactful on economic development of
the country. They spend much and invest too little if any.
Inequality can be addressed through policies to ensure that
people from all classes positively contribute to economic
development.
Works Cited
Binatli, Ayla Ogus. "Growth and Income Inequality: A
Comparative Analysis." Economics

Research International (2012): doi.org/10.1155/2012/569890.
Cynamon, Barry, Z., & Steven M. Fazzari. "Inequality, the
Great Recession and slow recovery."
Cambridge Journal of Economics (2015): 40(2): 373–399.
Hiltzik, Michael. "Is U.S. stuck in secular slump?" 05
November 2014. Los Angeles Times.
<https://search-proquest-
com.ezp.pasadena.edu/docview/1619820387?accountid=28371>.
Leonhardt, David. "Inequality Has Been Going On Forever ...
but That Doesn’t Mean It’s
Inevitable." They Say / I Say: the Moves That Matter in
Academic Writing with Readings. W. W. Norton & Company,
2018..
Samimi, Parisa & Hashima Salarzadeh Jenatabadi.
"Globalization and Economic Growth:
Empirical Evidence on the Role of Complementarities." PLOS
ONE (2014): doi.org/10.1371/journal.pone.0087824.
Literature review.
The students are expected to critically evaluate minimum of five
previous literatures pertaining to their project topic that contain
key finding of previous authors such as methodology adopted,

parameters used, results obtained and important conclusions
along with shortcomings / gap areas. In text citation must be
made without fail. The in text citation and referencing should be
in CCE Harvard referencing style. This chapter should precisely
link the present study to the collected literature with gap areas
identified.
Dear Sir: Only analyze the Aluminum alloy parts in each paper
because the project about the corrosion in Aluminum alloy.

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