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Effect of Heat Treatment on Some Mechanical Properties of
7075 Aluminium Alloy
Adeyemi Dayo Isadarea, Bolaji Aremob, Mosobalaje Oyebamiji
Adeoyec,
Oluyemi John Olawalec*, Moshood Dehinde Shittuc
aPrototype Engineering Development Institute Ilesa, Nigeria
bCentre for Energy Research and Development, Obafemi
Awolowo University, Ile-Ife, Nigeria
cDepartment of Materials Science and Engineering, Obafemi
Awolowo University, Ile-Ife, Nigeria
Received: April 14, 2012; Revised: September 3, 2012
This paper reports the effects of annealing and age hardening
heat treatments on the microstructural
morphology and mechanical properties of 7075 Al alloy. The
material was cast in the form of round
cylindrical rods inside green sand mould from where some
samples were rapidly cooled by early
knockout and others gradually cooled to room temperature.
From the samples that were gradually
cooled some were annealed while others were age hardened.
Both the as-cast in each category and
heat treated samples were subjected to some mechanical tests
and the morphology of the resulting
microstructures were characterised by optical microscopy. From
the results obtained there is formation

of microsegregations of MgZn
2
during gradual solidification which was not present during
rapid
cooling. It was also found out that age hardening and annealing
heat treatment operation eliminated
these microsegregations and improve mechanical properties of
7075 Al alloy. It is concluded that
microsegregation can be eliminated by rapid solidification and
appropriate heat treatment process.
Keywords: 7075 aluminium, microsegregation, precipitation
hardening, annealing, magnesium alloy,
strength
1. Introduction
Aluminium and its alloys are used in a variety of cast and
wrought forms and conditions of heat treatment. For over
70 years, it ranks next to iron and steel in the metal market.
The demand for aluminium grows rapidly because of its
unique combination of properties which makes it becomes
one of the most versatile of engineering and construction
material1-3.
The optimum properties of aluminium are achieved by
alloying additions and heat treatments. This promotes the
formation of small hard precipitates which interfere with
the motion of dislocations and improve its mechanical
properties4-7. One of the most commonly used aluminium
alloy for structural applications is 7075 Al alloy due to its
attractive comprehensive properties such as low density, high
strength, ductility, toughness and resistance to fatigue8-11. It
has been extensively utilized in aircraft structural parts and

other highly stressed structural applications12-16.
But aluminium-zinc alloy as it is in 7075 Al alloy is
susceptible to embrittlement because of microsegregation
of MgZn
2
precipitates which may lead to catastrophic
failure of components produced from it17,18. The alloy is also
susceptibility to stress corrosion cracking19,20. This is due to
inhomogeneity of the alloy and inherent residual stresses
associated with its fabrication methods.
The formation of these microsegregations (hard
precipitates) and inherent residual stresses that are associated
with their fabrication methods have serious negative effect
on their mechanical properties18. Hence, this study is aimed
at resolving the problems of microsegregations and inherent
residual stresses that are associated with aluminium-zinc
for improved service performance. The objectives of
the work are to investigate the effects of annealing and
precipitation hardening (age hardening) heat treatment on
the microstructure, hardness, tensile strength, and impact
strength of aluminium-zinc alloy.
2. Experimental Procedure
2.1. Material preparation
The present investigation was carried out on 7075 Al
alloy composition shown in Table 1. The material was cast
in the form of round cylindrical rods of 20 mm diameter and
500 mm long. Some of the cast rods were rapidly cooled
to room temperature by knocking them out 5 minutes after

castings while the others were cooled gradually inside the
mould to room temperature. Round tensile samples and
impact test samples were machined from these categories
of rods according to British Standard BSEN 10002-1:1990
and ASTM Standard E 602-91 respectively21,22. The tensile
test samples have a gauge length of 30 mm and diameter of
5 mm. The impact test samples were V notched to a depth
of 2 mm. Samples were also sectioned from cast rods for
metallographic and hardness tests.
OI:D 10.1590/S1516-14392012005000167
Materials Research. 2013; 16(1): 190-194 © 2013
mailto:[email protected]
2.2. Heat treatment
Two types of heat treatments were carried out namely
annealing and precipitation hardening on sample machined
from castings that were gradually cooled. Annealing was
carried out by heating the already machined, metallographic
and hardness test piece samples to 470 °C, soaking them
at this temperature for 3 hours and then furnace cooled.
Precipitation hardening was carried out by first solution
treated another set of machined, metallographic and
hardness test piece samples at a temperature of 465 °C for
2 hours followed by rapid quenching in cold water. These
quenched samples were then subjected to a precipitation
hardening treatment (age hardening) by heating them to
120 °C, holding them at this temperature for 5 hours and
then followed by air cooling to room temperature.

2.3. Tensile testing
Tensile testing of all these specimens was conducted
per British Standard BSEN 10002-1:1990. Three samples
were tested from each heat-treated condition and as cast
samples. The tests were carried out at room temperature
with a crosshead speed of 1 mm/min using a computerised
Instron 3369 electromechanical testing machine.
Load – displacement plots were obtained on an X-Y recorder
and ultimate tensile strength and percentage elongation
values were calculated from this load – displacement
diagrams. The average values from three test samples are
reported here.
2.4. Impact testing
Impact testing of all these specimens was conducted
per ASTM Standard E 602-91. Three samples were tested
from each heat-treated condition and as cast samples. The
tests were carried out using Izod impact test method on
Houndsfield balance 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. The average values
from three test samples are reported here.
2.5. Hardness test
The control and the heat treated samples were
subjected to the Brinell hardness test using the Houndsfield
extensometer in compression mode. 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.

2.6. Optical metallography
The heat treated and as cast samples were taken
through the process of metallography: sample selection,
mounting, grinding, polishing and etching. The morphology
of the microstructures were then characterised by optical
microscopy after etching with sodium hydroxide.
3. Results and Discussions
Figures 1 to 4 show the microstructures of the specimen
in as-cast (gradually cooled), as-cast (rapidly cooled),
annealed and aged hardening condition respectively.
The microstructure of as-cast (gradually cooled) sample
(Figure 1) shows microsegeregation of MgZn
2
in aluminium
matrix while as-cast (rapidly cooled) sample (Figure 2)
shows fine grains of MgZn
2
phase which is uniformly
distributed in the aluminium matrix. The microstructure of
annealed sample (Figure 3) shows coarse grains of MgZn
2
phase which is non-uniformly distributed in the aluminium
matrix while the microstructure of age hardening sample
(Figure 4) shows the finely dispersed precipitate of MgZn

2
in
aluminium matrix. The presence of dispersed precipitate of
MgZn
2
correspond with the result of Salamci23 and Du et al.24
who discovered that aging heat treatment of Al-Zn-Mg-Cu
alloys lead to the formation of MgZn
2
intermetallic phase
in the structure.
Table 1. Chemical composition of 7075 aluminium alloy.
Element %wt.
Zn 5.6
Mg 2.5
Cu 1.6
Al Balance
Figure 1. Microstructure of gradually cooled as-cast 7075 Al
alloy
showing microsegregation of MgZn2 in Al matrix.
Figure 2. Microstructure of rapidly cooled as-cast 7075 Al alloy
showing MgZn2 Phase in Al matrix.

2013; 16(1) 191
Isadare et al.
In their study on evolution of eutectic structures in
Al-Zn-Mg-Cu alloys Fan et al.25, reported that several coarse
intermetallic phases such as MgZn
2
, Al
2
Mg
3
Zn
3
, Al
2
CuMg,
Al
2
Cu, A
l7
Cu
2
Fe, Al
13

Fe
4
and Mg
2
Si can be formed below
the solidus line during solidification of as-cast 7000 series
of aluminium alloys as a result of solute redistribution of
metals. This report supports our finding of microsegeregation
of MgZn
2
in 7075 Al alloy in gradually cooled sample. In
a rapidly cooled sample there was no room for solute
redistribution of Mg and Zn and hence microsegregation of
MgZn
2
is not formed. However, during the soaking period
of heat treatment operations the microsegregations formed
after gradual cooling are dissolved to form a homogeneous
phase and they disappeared after subsequent cooling. The
elimination of microsegregations after annealing and aging
heat treatment operations in the present investigation is
in agreement with the findings of Guo et al.26 who finds
out that solution treatment markedly reduce the degree of
microseregation in 2024 wrought aluminium alloy.
From the results of mechanical test as presented in
Table 2; the as-cast (gradually cooled) samples has the
highest ultimate tensile and yield strengths followed by age
hardened samples, as-cast (rapidly cooled) and annealed

samples. The as-cast (gradually cooled) sample has the
highest hardness and strength because of the presence of
miccrosegregations in its structure which embrittles 7075 Al
alloy. The reason for the observed trend in hardness and
strength in the remaining samples is due to the variations
in their grain size. This is in agreement with the findings of
Kenji et al.27 which indicated that solid-solution and grain
refinement contribute to the hardening of Al-Mg alloys.
Also, it is well reported in previous studies that fine-grained
materials has more grain boundaries; and are harder and
stronger than coarse grained materials that has less grain
boundaries28-30. Since age hardened sample has more grain
boundaries than as-cast (rapidly cooled) and annealed
samples there is more impediment to dislocation motion
during deformation and hence it is harder and stronger31.
For most materials the yield strength σ
y
varies with grain
size according to Hall-Petch relation:
σ
y
=
σ
o
+
k
y

d–1/2
In this expression d is the average grain diameter, σ
y
and
k
y
and are constants for a particular material.
The improvement in yield strength and ultimate tensile
strength as a result of grain size can also be explained from
the microstructures perspectives. The finer these grains are
the more the boundaries. During plastic deformation, slip
or dislocation movement must take place across these grain
boundaries. Since polycrystalline grains are of different
crystallographic orientations at the grain boundaries, a
dislocation passing from one grain to another will have to
change its direction of motion. Such changes of direction
causes impediment to dislocation movement, and increases
both the yield strength and ultimate tensile strength. Because
age hardening samples have the highest number of grain
boundaries, dislocation movement becomes more and more
difficult during plastic deformation. This is responsible for
highest yield strength and ultimate tensile strength observed
in age hardening samples. Also, 7075 Al alloy used for this
study contains about 5.6% zinc (Zn) and 2.5% magnesium
(Mg). These two alloying elements lead to increase in the
strength of this alloy through formation of MgZn
2
precipitate
within the structure as the result of aging heat treatment.
This result corresponds with Du et al.24, Li and Peng11,

Demir and Gündüz32 and Kaya et al.33 who concluded that
Al-Zn-Mg alloy can get the highest strength level in natural
and artificial ageing.Figure 4. Microstructure of aged hardening
7075 Al alloy showing
precipitate of MgZn2 in Al matrix.
Table 2. Results of mechanical testing for as-cast and heat
treated Al-Zn-Mg samples.
Samples
Yield strength
(MPa)
Ultimate tensile
strength (MPa)
Percentage
elongation
Hardness number
(HB)
Impact strength
(J)
As-cast (gradually cooled) 526 603 10 201 9.2
As-cast (rapidly cooled) 467 529 17 157 17.7
Annealing 297 414 21 124 22.4
Age hardening 501 575 15 171 14.7
Figure 3. Microstructure of annealed 7075 Al alloy showing
MgZn2

phase in Al matrix.
250 µm
192 Materials Research
Annealing sample has the highest percentage elongation
followed by as-cast (rapidly cooled), age hardening
samples, and as-cast (gradually cooled). This is partly due
to increase in grain coarsening which leads to an increase
in the grain boundary area which increases the amount of
energy required for the movement of dislocations required to
cause fracture34-36. Thus, the material can withstand a higher
plastic deformation before the final fracture. However, the
percentage elongation of as-cast (gradually cooled) is very
small because of embrittlement of 7075 Al alloy as a result
of microsegregation of MgZn
2
.
As-cast (gradually cooled) sample has extremely high
hardness as a result of its brittle structure. From the remaining
three samples age hardening heat treatment samples has the
highest hardness followed by as-cast (rapidly cooled) and
annealed samples. The highest hardness values developed
by age hardening samples can be attributed to precipitation
of coherent and finely dispersed MgZn
2
phases which serves

as foreign atom or inclusion in the lattice of the host crystal
in the solid solution; this causes more lattice distortions
which makes the alloy harder. In the previous study solid
solution strengthening from elastic distortions is produced
by substitutional atoms of Mg and Zn in aluminium matrix37.
Hence, the main strengthening mechanism in these alloys is
precipitation hardening by structural precipitates of MgZn
2
formed during artificial ageing. The precipitate particles act
as obstacles to dislocation movement and thereby strengthen
the heat-treated alloys.
The impact strength followed the same trends as
percentage elongation with annealing sample been the
highest and as-cast (gradually cooled) sample been the least.
This is because impact strength is also a measure of material’s
ductility, and ductility is inversely related to strength38.
4. Conclusions
From the outcome of this study, there is formation of
microsegregations of MgZn
2
during the gradual solidification
of 7075 aluminium alloy due to solute redistribution of Mg
and Zn but this was suppressed during rapid solidification.
However, the microsegregations that were formed when it
was gradually cooled are dissolved to form a homogeneous
phase during the soaking period of heat treatment operations.
As a result of age hardening heat treatment operation there is
formation of small and finely uniform dispersed precipitate

of MgZn
2
in the aluminium matrix while coarse grains of
MgZn
2
phase was formed in aluminium matrix as a result
of annealing heat treatment operation.
It has been found that rapid solidification process and
heat treatment eliminate the formation of microsegregation,
and significantly improved some mechanical properties. Age
hardening heat treatment operation was found to improve
yield strength, ultimate tensile strength and hardness values
but lower ductility and impact strength. On the other hand
annealing heat treatment operation improves impact strength
and ductility but lower yield strength, ultimate tensile
strength and hardness values. Therefore, annealing treatment
of the alloy will be suitable for applications involving high
toughness and ductility while age hardening treatment will
be suitable for applications that require high ultimate tensile
strength, yield strength and hardness values.
Finally, it is concluded that the formation of
microsegregation embrittle 7075 aluminium alloy, and
subsequently have negative effects on its mechanical
properties and its application. This can be addressed by
rapid solidification and appropriate heat treatment process.
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COLLEGE OF ENGINEERING
DEPARTMENT OF MECHANICAL & INDUSTRIAL
ENGINEERING
BEng (Honours) in Computer Aided Mechanical Engineering
Academic Year: 2018-19 Semester: B
MHH124725: Technical Project
Final Report
Project Title: Corrosion Analysis of Aluminum Alloy 7075.
Student Name: Amani Al Ajmi
Student Number: 140150
Supervisor(s): Mr. Said Al Oraimi

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has achieved the set objectives of the project / dissertation.
Information derived from the published work of others has been
acknowledged in the text and a list of references is given at the
end of the report. I have personally checked this final report for
originality / plagiarism through the Turnitin website and, to the
best of my knowledge and belief, satisfied that the report is free
from plagiarism.
Signature of the Supervisor:
Date:
Name of the Supervisor:
Countersigned by HoD:
ACKNOWLEDGEMENT

The acknowledgement by the candidate for successfully
carrying out the project work
ABSTRACT
Aluminum plays an important role in a number of industrial
applications such as construction and electrical engineering. It
is also quite applicable in the transport industry where it is used
in the manufacturing and production of machinery used in the
aircraft building. Although aluminum and its alloys are quite
useful, they are subject to corrosion as a result of chemical
interaction with the surroundings and hence do not the best
materials for engineering applications. One of the main
significant problems faced by aluminum components used in the
aircraft is pitting corrosion. An experimental analysis of
components of aluminum in aircraft to identify corrosion will be
carried out in this project. Findings indicate severe corrosion of
nose landing component leading to its failure. Pitting corrosion
refers to the restricted high metal dissolution as a result of
depletion of the passive film on the metal surface that acts as a
protective cover. This study aims at bringing into discussion an
analysis of corrosion in the aluminum alloy (7076) mainly used
in aircraft components. Therefore, this project identifies the
details on materials, undertaking taste samples on the identified
materials, and measures are undertaken to improve corrosion
resistance. Hence, development of the two types of coating, and
testing their levels of resistance to corrosion.
This experiment identifies two types of heat treatment
experiments useful in testing samples with and without coating
condition. An examination will be carried out on the behavior of
the metal using hardness testing before and after heat treatment,
measurement of the surface roughness, corrosion test in sea
water followed with an acid test. Analysis of these results
finally will be carried out to achieve the objectives
successfully.

Keywords: Aluminum alloy (7076)، Pitting corrosion, Hardness
testing, Heat treatment.
TABLE OF CONTENTS
The content shall follow the abstract and indicate the page
numbers of the chapters, sections, sub-sections, appendices and
references. The number and titles of all the items must be
clearly entered with page numbers against them.
LIST OF TABLES
Table Number
Description
Page No.
Table 4.1
Hardness readings before heat treatment.
Table 4.2
Hardness readings after heat treatment.
Table 4.3
Roughness measurements.
Table 4.4
Weight loss.

LIST OF FIGURES
Figure Number
Description
Page No.
Figure 1.1
Pitting Corrosion.
Figure 1.2
Aircraft Material.
Figure 3.1
Morgen Rushworth RGMS.
Figure 3.2
Aluminum Alloy Sheet Before cutting.
Figure 3.3
Aluminum Alloy Sample After cutting.
Figure 3.4
Metallic Stamp.
Figure 3.5
Hammer.
Figure 3.6
Samples After Numbering.
Figure 3.7
Aluminum Oxide and Aluminum paint.

Figure 3.8
During the Painting Step.
Figure 3.9
Sample After Applying the First layer of Coating.
Figure 3.10
Zinc Spray and the Samples Before Coating.
Figure 3.11
The Samples After Zinc Coating.
Figure 3.12
Underbody Rubber Spray.
Figure 3.13
The Samples After Rubber Coating.
Figure 3.14
Furnace during
Figure 3.15
Quenching Samples in Water.
Figure 3.16
Rockwell Hardness.
Figure 3.17
Indenter Used for Testing.

Figure 3.18
Roughness Device (Mitutoyo) connected to Computer Software.
Figure 3.19
During Roughness Measurement for Zinc Sample.
Figure 3.20
Samples immersed in Seawater.
Figure 3.21
Apparatus used for HCL Test.
Figure 3.22
HCl
Solution
.
Figure 3.23
Sample Without Coating Initial Weight.
Figure 3.24
Sample Without Coating Weight After Seawater and HCL Tests.

Figure 3.25
Zinc Sample Initial Weight.
Figure 3.26
Zinc Sample Weight After Seawater and HCL Tests.
Figure 4.1
Hardness Readings Before Heat Treatment.
Figure 4.2
Hardness Readings After Heat Treatment.
Figure 4.3
Zinc Sample Roughness Profile.
Figure 4.4
Underbody Rubber Sample Roughness Profile.
Figure 4.5
Aluminum Oxide Sample Roughness Profile.
Figure 4.6
Without Coating Sample Roughness Profile.
Figure 4.7

Rz and Rq Values of the Samples.
Figure 4.8
Weight Loss (g) of the Samples.
LIST OF SYMBOLS AND ABBREVIATIONS
NaCl – Sodium Chloride.
HCL – Hydrochloric Acid.
H2O – Water.
Al – Aluminum.
% – Percentage.
Zn – Zinc.
Al2O3 – Aluminum Oxide.
PH – Potential Hydrogen.
Chapter name & title
1
16

CHAPTER 1INTRODUCTION
1. Introduction.
Corrosion is the deterioration of materials by chemical
interaction with the surrounding environment; it is a natural
phenomenon which can be controlled by correcting the
condition when an early warning signs occurs. Airframe issues
related to corrosion have plagued the aerospace industry for
decades. The metals of aircraft components are exposed to
different forms of corrosion; there are many agents which
accelerates the corrosion process such as prolonged exposure to
corrosive factors including moisture, salts and industrial fluids.
The main source of corrosion is water vapor containing salt that
combines with the oxygen in the air. The appearance of
corrosion differs depending on the type of the metal, on the
aluminum alloy surface it shows as pitting which is combined
with white or gray powdery deposit. This project will provide
an experimental study on the corrosion analysis of aluminum
alloy where 75% of aircraft structures are made of aluminum as
shown in Figure 2.

Figure 1.1 Pitting Corrosion
Figure 1.2 Aircraft material
1.1 Problem statement:
Pitting corrosion is one of the most common problems faced by
aluminum components used in aircraft, as the name implies this
type of corrosion means the formation of small holes in the
surface of the material. Due to the high-speed landing of
aircraft on the dusty runway, the protective coating is removed
which lead to the exposure of the metals surface to the corrosive
factors.
1.2 The aim of the project:
To perform an experimental study about corrosion analysis of
aluminum alloy material used in aircraft component. 1.3 The
main objectives:
· Identify the causes of corrosion.
· Carry out the corrosion resistance process experimentally.
· Analyze the obtained result.1.4 Scope of studies:
· Literature review about corrosion in aluminum alloy material.
· Investigate and understand the working principle of the metal

coating and heat treatment to reduce the corrosion in aluminum
alloy.
· Implement roughness measurement of the coated samples
followed by corrosion test with sea water and acid.1.5
Importance of the research:
Understanding and analyzing the corrosion behavior is
important, there are many factors regarding the significance of
corrosion study including economic, by implement corrosion
control process, the useful life of aircraft can be extended,
therefore the maintenance cost will be reduced. Also, the best
insurance against corrosion associated failures is studying and
testing the metals used in the design of the planes in order to
select the proper ways to control the problem to increase the
safety of public.
CHAPTER SUMMARY
Corrosion is considered to be a natural phenomenon which can
be controlled through changing or altering the conditions
immediately after early warning signs are detected. Corrosion
has been a major concern within the Aerospace industry where
it has been leading to issues related to Airframe. In Aerospace
industry, metals of aircraft are becoming exposed to corrosion
and this activity is accelerated by prolonged exposure to
corrosive agents like moisture, salts, and industrial fluids.
Water vapor is considered to be the primary source of corrosion
and it is composed of salts which combine with oxygen in air.

One of the metals affected as a result of pitting corrosion is
aluminum components used in aircraft leading to the formation
of small holes in the surface of the material. This study aims at
identifying the causes of corrosion; carrying out the corrosion
resistance process experimentally; and analyzing the obtained
result. The scope of this study is to investigate and understand
the working principle of the metal coating and heat treatment to
reduce the corrosion in aluminum alloy; and implement
roughness measurement of the coated samples followed by
corrosion test with sea water and acid. There are a number of
advantages associated with this study. Through implementation
of corrosion control process, it is possible to extend the life of
aircraft can be extended thus helping in reducing the
maintenance cost.
CHAPTER 2:LITERATURE REVIEW
2. Introduction.
Corrosion refers to the process of material degradation as a
result of interaction with the environment. Corrosion occurs in
metals, polymers, and ceramics. The research on corrosion and
its alloys is an enormous area of research since it involves a

broad range of applications in areas such as marine, aerospace,
industrial and family environments. The main reason for its
usage is due to the good machinability, weldability, and good
corrosion resistance. Corrosion resistance of alloys is attributed
to the fact that they are naturally developing to an oxide film on
their surface as a result of environmental condition. However,
pitting corrosion is the main corrosion phenomenon which is
common and occurring due to the breakage in the oxide film.
Resistance to pitting of the metals is influenced by the physical,
electrical, and mechanical features of the passive layer. As a
result of perfect passivity with greater uniform corrosion
resistance to seawater, pitting remains the primary concern for
Aluminium Alloys in the environment with seawater.
This chapter includes some literature reviews which have been
referred to regarding corrosion analysis of Aluminum alloy.
2.1 Effect of heat treatment on some mechanical properties of
7075 aluminium alloy.
Adeyemi Dayo Isadare, Bolaji Aremo, Mosobalaje Oyebamiji
Adeoye, Oluyemi John Olawale, Moshood Dehinde Shittu,
(2013) work entails a detailed explanation of their experiment
which involved an examination of annealing on micro-structural
morphology as well as mechanical properties of 7075 Al alloy.
Additionally, the experiment evaluated the relationship between
age hardening on microstructural characteristics of 7075 alloy.

The researchers concluded from the experiment results that
annealing heat treatment had the power to do away with micro-
segregation. Age hardening heat treatment was also observed to
bring an improvement on mechanical characteristics of the
Alloy (Isadare, Aremo, Adeoye, Olawale & Shittu, 2013). This
work perfectly fits the topic since it shed light on how the
project topic can be handled. This stem from the fact that the
work reveals that age hardening heat treatment can improve the
mechanical property of the aluminum alloy. One such
characteristic is resistance to corrosion. To make the allow
resistant to corrosion by other elements or acids using the
results from Adeyemi Dayo Isadare, Bolaji Aremo, Mosobalaje
Oyebamiji Adeoye, Oluyemi John Olawale, Moshood Dehinde
Shittu (2013) work it’s hence recommendable to do age
hardening heat treatment.
2.2 Quenching of aluminum alloys: cooling rate, strength, and
inter-granular corrosion‖.
Patricia Kavalco, Canale Lauralice and George Totten (2009)
research entails the study of intergranular corrosion. The
researchers investigated how intergranular corrosion could be
used to reduce corrosion. In the study, it was found out that the
cooling rate of any aluminum alloy determined the rate of
pitting corrosion. The slower the rate of cooling the fewer

chances an aluminum allow being affected by corrosion. On the
other hand, if an alloy was quickly cooled the impact would be
that the alloy would be easily corroded by corrosive reagents or
chemicals (Kavalco, Lauralice & Totten, 2009). On that note,
the authors recommend that while making any aluminum allow
it was crucial to give attention to the cooling rate. In the event
that the alloy will be exposed to highly corrosive agents, it is
advisable to have the cooling rate very slow and vice versa.
This work is useful in informing the topic that is corrosion in
Aluminum alloy. With the findings from the source, one can
state that corrosion in aluminum alloys is dependent on the rate
of cooling of the alloy during its making.
2.3 Improvement Properties of 7075-T6 Aluminum Alloy by
Quenching in 30% Polyethylene Glycol and Addition 0.1%B‖.
Jasim Salman, Shaymaa Alsada and Khadim Al-Sultani (2013)
work discusses the results of their experiment. The experiment
was set up to investigate the impact of sodium chloride,
polyethylene glycol and boron on aluminum alloy. The authors
wanted to know whether the combination of these solutions or
elements could improve the feature of the 7075-T6 alloy. The
target features were corrosion resistance, toughness as well as
thermal aging behavior. The researchers took 3.5% NaCl, 30%
polyethylene glycol and Boron solution and treated 7075- T6

alloy with. The results indicated that the solution improved the
toughness feature of the alloy by 50%. However, the corrosion
property was not significantly influenced by the solution. This
indicates that the solution cannot be used to improve the
corrosion resistance of the alloy (Salman, Alsada& Al-Sultani,
2013). Generalizing the case to other types of aluminum alloys
one can draw an insight that a mixture of boron, sodium
chloride and polyethylene glycol have no properties in
improving the corrosive resistance feature of an aluminum
alloy. On that note, the work is significant in this topic since it
gives direction on elements and solution which should not be
used while improving the resistance features of an aluminum
alloy.
2.4 Recent developments in advanced aircraft aluminum alloys.
Tolga Dursun and Costas Soutis (2014) work is about their
review on the recent aluminum technology employed in aircraft
industry which is one area aluminum alloys are industrially

exploited. The authors learned that the technology has led to
having damage tolerant, strong, tough and corrosion resistant
alloys. The review shows that a combination of Aluminum and
zinc leads to a very strong alloy. Mixing Aluminum and copper
results to a high damage resistant alloy. Of key importance in
this context is mixing aluminum and lithium that is AL-Li. The
outcome is an alloy with improved properties such that the alloy
is has higher fracture toughness and is corrosion resistant
(Dursun& Soutis, 2014). This work is essential in the study of
this topic from the angle that it shows the right chemical
composition that can be used to have a high corrosion resistant
alloy.
2.5 Aluminum Alloys for Aerospace Applications‖, Aerospace
Materials, and Material Technologies.
The work entails a history of aerospace technology with
aluminum alloys in focus. Also, entails classification of
aluminum alloys. The classification is based on temperatures
used to heat and cool the alloys. This is because the
temperatures are a significant determinant of the strength
property as well as other features (Rambabu, Prasad& Wanhill,
2017). Additionally, the work entails weaknesses or gaps in the
current aluminum technology used in aerospace. These gaps are
crucial in handling the topic given that they will show areas that
require more research in improving the corrosion resistance

feature of aluminum alloys.
2.6 Aluminium alloy corrosion of aircraft structures: modelling
and simulation.
To prevent corrosion occurrences, Aluminum and its alloys
were properly handled using various protection methods that
prevent corrosion of the aircraft. These methods include:
waxing, painting, zinc-chromate priming, coating using thin
layer of Alclad, anodizing and coating with a liquid protective
solution (DeRose, 2013 pg. 23-29).
Barrier coating using materials such as paint, plastic, wax or
powder was applied and left out for some time for later
observations. Aluminum was also coated using a thin layer of
pure aluminum. Pure aluminum was successfully sprayed on the
aluminum flat and round coupons at low temperatures. Hardness
test was then carried out before and after the heat treatment
Demo, (Steiner, Friedersdorf, and Putic, 2010 pg. 1-9).
Aluminum specimen was heated at 500 Celsius and then
quenched in cold oil. Hardness of the heat-treated specimen and
those without heat treated specimen was measured in and
recorded. Resistance to corrosion of the samples was evaluated
in 3.5 % sodium chloride solution by weight loss method.
Corrosion test was also conducted in wet conditions which
included seawater and hydrochloric water conditions.
Roughness measurements were also conducted on the final

product.
2.7 Milestone case histories in aircraft structural integrity.
We found out that epoxy, nylon and urethane which are types of
powders, which were heated and placed on the aluminum
surface to form a thin film layer offered protection from
corrosion. Plastic and waxes which were sprayed onto the
aluminum surfaces acted as a coating to offer protection to
aluminum surface from mixing with other corrosive elements
that lead to corrosion (Wanhill, Molent, Barter and Amsterdam,
2015 pg. 346) People have come up with current painting
systems in the aircraft components that combine different
painting layers which have been designed to serve different
functions. They are usually applied in three layers. The first
spray paint acts as the inhibitor which decreases the activity of
the aluminum and its alloys or blocks it from combining or
reacting with other corrosive elements. The second and
intermediate layers of paint coats are applied to add to the
overall thickness of the paint and to make sure that no
aluminum surface is left exposed (Kiyak, 2012 pg. 9-16) The
last and finish coat is primarily designed to offer resistance to
the environmental factors such as humidity, pH concentration
and alkaline concentration of the surrounding.We also found out
that pure aluminum coating component insulates and protects
aluminum from corroding. This helped in reducing the extent of

corrosion.
2.8 Can pitting corrosion change the location of fatigue failures
in aircraft?
Regarding hardness test, it was found out that after heat
treatment at 500 °C and subsequent quenching in oil of
aluminum component the hardness and corrosion resistance of
pure aluminum improved whereas before heat treatment, the
hardness and corrosion resistance of the material was low.
Concerning corrosion in wet areas, we found out that aluminum
corrodes faster or quicker when placed in wet areas. This is
because the water component acts as a catalyst in the process of
corrosion (Crawford, Loader, Liu, Harrison, and Sharp, 2014
pg. 304-314). When Aluminum, which is the material used to
make aircrafts, is left unprotected in certain areas such as salty
areas near the ocean or sea waters, it will form an oxide layer
and corrodes almost immediately. Because of the corrosive
action of this strongest of acids like hydrochloric acid on metals
like aluminum, normally, non-metal materials are preferred,
when possible (Jaya, Tiong, and Clark, 2012 pg. 64-73).
Aluminum have useful corrosion resistance in low
concentrations of HCl. The corrosivity increases dramatically as
the concentration of HCl and temperature increase. This led to
an increased rate and extent of corrosion. Therefore, the extent
of destruction was higher in wet areas as compared to that one
in dry areas.

2.9 Recent developments in advanced aircraft aluminium
alloys. Materials & Design.
The main disadvantage of using coating as a method of
preventing corrosion is that the coating components need to be
reapplied over and over again which is tiring and expensive.
Poorly applied coatings always fail and can lead to increased
rate and increased extent of corrosion (Dursun and Soutis, 2014
pg. 862-871). Sometimes, there might exist some volatile
organic components in certain coatings which make them
vulnerable to corrosion.
2.10 Role of chemical composition in corrosion of Aluminum
Alloy.
The current political environment in industrial application
demands the use of light structural materials for several reasons
including lower gas emissions, better fuel economy and reduced
energy consumption. Furthermore, taking into consideration
several proprieties, Aluminum alloy is the favourable material
for crafting many components for aerospace and automotive
applications due to its strong corrosion resistance, low density,
excellent formability and high weight to stiffness ratio.

The study was to establish the mechanical, physical and
chemical properties of alloys of Aluminum. This would be used
to identify the best alloy for the aerospace and automobile
industries. The literature review was done sufficiently and
highlighted that Aluminum alloys have become the most used
metals in the automobile and aerospace manufacturing
industries in the world.The alloys are used in aerospace and
automobile industries because of its physical properties and
durability. From the literature, it was established that important
properties that make Aluminum metal useful in various
manufacturing plants include its low density, excellent
formability property, high strength stiffness in relation to
weight and good corrosion resistance.
I will attach two more literature, analyze them same way as
seen in literatures above.

Chapter Summary.
This section provides some past researches and works related to
corrosion; each author studied the topic from different areas
including the relationship between age hardening on
microstructural characteristics of Al 7075 alloy which
concluded from the experiment results that annealing heat
treatment had the power to do away with micro-segregation.
Also, investigation on how intergranular corrosion could be
used to reduce corrosion where the authors recommend that
while making any aluminum allows it was crucial to give
attention to the cooling rate. Moreover, another author
discussed the impact of sodium chloride, polyethylene glycol
and boron on aluminum allow. In addition, another review
shows that a combination of Aluminum and zinc leads to a very
strong alloy. As well as the classification of aluminum alloy
were studied, and the author concluded that the classification is
based on temperatures used to heat and cool the alloys. This is
because the temperatures are a significant determinant of the
strength property as well as other features. Also, barrier coating
is one of the easiest and cheapest methods in preventing
corrosion in aircraft components made of aluminum. It was very
effective in preventing corrosion but only if proper procedures
were carried out carefully. Coating, therefore, insulates,

beautifies and increases the aircraft’s life expectancy. It is also
easy to apply and reflects 80% of ultraviolet rays. Though it
faces certain challenges, it is very effective in preventing
corrosion in aluminum, an aircraft component.
CHAPTER 3EXPERIMENTAL SETUP
3. Introduction.
This chapter includes the steps followed in order to achieve the
project objectives. First, samples preparation step which
involves two parts, cutting the Aluminum alloy sheet and
Numbering the samples. Then, the main step which is coating
the sample using three types of coating:
· Aluminum Oxide.
· Zinc.
· Underbody Rubber coating.
After the coating step, some investigations and tests were
carried out such as: Hardness test using Rockwell hardness test
before and after heat treatment. Also, Roughness measurements
using Mitutoyo device connected to computer software. In
addition to corrosion test in sea water for 192 hours followed
with a Hydrochloric test for 10 minutes in order to monitor the
weight loss of the samples.

3.1 Samples Preparation.
For an accurate and fast cutting of the Aluminum alloy sheet, a
mechanical guillotine called Morgan Rushworth RGMS is used.
Figure 3.1 Morgen Rushworth RGMS
Figure 3.2 Aluminum alloy sheet before cutting
The following is the procedure of cutting the Aluminum Alloy
sheet using Morgen Rushworth RGMS.
1. Place the Aluminum sheet on the support table as shown in
Figure 3.2.
2. Switch on machine.

3. Press SET write the desired position to the display.
4. Press START, machinery moves to the desired position.
5. Cutting operation will carried out.
6. Switch off machine.
Figure 3.3 Aluminum Alloy Sample After cutting.
Then, using metal stamps and hammer the numbering step is
done by applying the following procedure:
1. Place the desired number stamp on the sample.
2. Strike twice on the stamp using the hammer.
3. The number will appear on the sample.
4. Repeat the steps using different numbers for different
samples.

Figure 3.4 Metallic Stamp
Figure 3.5 Hammer
Figure 3.6 Samples After Numbering

3.2 Coating Step.
In this step I used three types of coating: Al2O3 (Aluminum
Oxide), Zinc and Underbody Rubber coating.
3.2.1 Aluminum Oxide Coating:
To achieve this type of coating an Aluminum Oxide powder,
Aluminum paint and a brush are required. The procedure is:
1. Prepare a mixture of 25 ml of Aluminum paint with 250 g of
Al2O3.
2. Place the mixture in the rotary shaker for one hour in order to
mix properly.
3. Apply the Aluminum oxide mixture on the sample using a
brush.
4. Put the coated sample in a place to be exposed to air for three
hours in order to dry then apply an extra layer if needed.

Figure 3.7 Aluminum Oxide and Aluminum paint.
Figure 3.8 During the Painting Step.
Figure 3.9 Sample After Applying the First layer of Coating.
3.2.2 Zinc Coating:
Zinc spray provides along-lasting cathodic corrosion protection
to all metal surfaces. Zinc spray is forming a fast-drying,
adherent protective layer of microfine zinc flakes. Zinc flakes
are forming a resistant protective layer even under extreme

weather and environmental conditions.
The following is the procedure for Zinc coating:
1. Shake the can well before using.
2. Spray evenly on the samples about 20 cm distance from the
surface.
hours in order to dry.
4. Repeat the second step until the desired thickness is obtained.
Figure 3.10 Zinc Spray and the samples Before Coating.
Figure 3.11 The Samples After Zinc Coating.

3.2.3 Underbody Rubber Coating:
This type of coating is mostly used on cars to protect them from
damage, rusts, and decay. It is used in rust prevention and are
applied when the car is brand and new. The manufactures are
using thick paints as well as sealants for the Underbody and this
is made better by the addition of the Underbody coats.
Underbody coating is providing a long-lasting protection from
corrosion to the car’s Underbody. It also protects parts such as
the internal body panels, the frame rails, and other inner
cavities which are physically accessible but are more exposed to
corrosion.
The following is the procedure for underbody rubber coating:
1. Shake the can well before using.
2. Spray evenly on the samples about 20 cm distance from the
surface.
hours in order to dry.
4. Repeat the second step until the desired thickness is obtained.

Figure 3.13 The Samples After Rubber Coating.
Figure 3.12 Underbody Rubber Spray.
3.3 Heat Treatment.
Heat treatment is a group of industrial as well as metalworking
processes that are utilized in altering the physical, chemical,
and properties of a material. Heat treatment is also used in
manufacturing of many other materials.
3.3.1 Annealing.
Annealing process is carried out through heating of a sample
which has been machined, undertaken through hardness testing,
and metallographic to a temperature of 4700C. Soaking such
samples at a temperature of 4700C for about 2 hours is then

followed by cooling process using furnace.
3.3.2 Precipitation Hardening.
This procedure is performed by using a solution to treat another
set of test piece of sample which has been machined, undertaken
through metallographic and hardness test at 465 °C for 2 hours.
This process is then followed by quenching the samples rapidly
in cold water. The quenched samples then undergo precipitation
hardening, a process which is also referred to as age hardening
through a heating process of the samples to 120 °C for 3 hours.
The final step is the cooling process using the air within the
room.

3.4 Hardness Test.
Using Rockwell hardness test which is a hardness scale based
on the indentation hardness of material. Rockwell test is
determining the hardness through measurement of the
penetration depth of an indenter under a huger load in
comparison to the penetration which has been made by the
minor load.
The working principle of this device as following:
1. Select the proper indenter depending on the type of the alloy
to be measured, for Aluminum Alloy 1/8 ball is used.
2. Turn the device on.
3. Place the sample to be measured on top of the anvil.
4. Rotate the anvil adjustment clock wise in order to rise the
anvil till it touch the surface of the sample.
5. The reading will appear on the screen, write it down and
repeat the steps using different coating samples.

Figure 3.16 Rockwell Hardness.
Figure 3.17 Indenter Used for Testing.
3.5 Roughness Measurements.
Roughness is the component of the surface texture. Its
quantification is based on the deviations towards the direction
of the normal vector of a real surface from the one which is
considered to be ideal form. In case the deviation is large, then
the surface is considered to be rough whereas if the deviations
are smaller, then the surface is smooth.
The following are the steps to measure the roughness of the
samples:
1. This device is connected to the computer software, first turn
on the computer and the device.
2. Place the sample to be measured as shown on Figure 3.17,
notice the movement of the tip on the surface of the sample for

about 5 seconds.
3. The surface roughness measurements will show on the
computer screen.
4. Repeat the steps using different coating samples.
Figure 3.18 Roughness device (Mitutoyo) connected to
computer software.

Figure 3.19 During Roughness Measurement for Zinc sample.
3.6 Corrosion Test in Seawater.
Sea water is also known as salt water and is water from the sea
or ocean. Sea water is considered to be playing a key role
towards increasing the rate of corrosion. Corrosion by sea water
is an electrochemical process and when it comes into contact
with all metals and alloys, it makes them have specific
electrical potential or corrosion potential at specific pH.
The corrosion test was carried out in Seawater In this test the
samples with and without coating were immersed in sea water
for 192 hours and the weight was measured before and after the
test.
3.7 Corrosion Test in Hydrochloric Acid (HCl).
In this test, a solution of 100ml of HCl and 900ml of H2O was

prepared and the samples with and without coating were treated
with the solution for 10 minutes and the weight of the sample
before and after the test were measured in order to monitor the
weight loss.
Figure 3.21 Apparatus used for HCL Test.
Figure 3.22 HCl

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