EFFECT OF HEAT TREATMENT OB THE MICROSTRUCTURES AND
MECHANICAL PROPERTIES OF COPPER ALLOY
MOHAMAD SYAFIQ BIN MOKHTAR
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
EFFECT OF HEAT TREATMENT ON THE MICROSTRUCTURES AND
MECHANICAL PROPERTIES OF COPPER ALLOY
MOHAMAD SYAFIQ BIN MOKHTAR
Project submitted in fulfilment of the requirements for Bachelor Degree of
Mechanical Engineering (Structure & Materials)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
MEI 2013
1
SUPERVISOR DECLARATION
“I hereby declare that I have read this thesis and in my opinion this report is
sufficient in terms of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering (Structure and Materials).”
Signature:
……………………..
Supervisor: Mr. Ridhwan Bin Jumaidin
Date:
29th May 2013
i
DECLARATION
“I hereby declare that the work in this report s my own except for summaries and
quotations which have been duly acknowledged.”
Signature:
……………………..
Author:
Mohamad Syafiq Bin Mokhtar
Date:
31st May 2013
iv
ACKNOWLEDGEMENTS
Alhamdulillah, Thanks to Allah SWT, whom with His willing give me the
opportunity to complete this Final Year Project which is title. This final year project
report was prepared for Faculty of Mechanical Engineering (FKM), Universiti
Teknikal Malaysia Melaka (UTeM), basically for student in final year to complete
the undergraduate program that leads to the degree of Bachelor of Mechanical
Engineering major in Structure and Materials.
Firstly, I would like to express my deepest thanks to, Mr. Ridhwan Bin
Jumaidin which is my supervisor who had guided me a lot to finish this final year
project.
Deepest thanks and appreciation to my parents, family, special mate of mine,
and others for their cooperation, encouragement, constructive suggestion and full of
support for the report completion, from the beginning till the end. Also thanks to all
of my friends and everyone, that has been contributed by supporting my work and
helps myself during the final year project progress till it is fully completed.
iv
ABSTRACT
Copper is an essential element for major industrial metal because of its high
ductility, malleability, thermal and electrical conductivity and resistance to corrosion.
Copper and its alloy mainly used in wiring production, piping, automotive and
architecture. Heat treatment process was applied on copper and copper alloys in order to
attain the desired properties for each application. The effect of heat treatment on the
microstructures and mechanical properties of copper alloy has been studied with
different heat treatment processes which are annealing, water quenched and aging.
Tensile test and metallurgical investigation is carried out to achieve the objective. In
term of cooling rate, the effect of annealing process and quenching process has been
investigated at different temperature. Aging process is studied with different temperature
and aging duration. Yield strength and ultimate tensile strength of annealed specimens
were decreased on 350oC to 450oC from 204.73MPa to 129.15MPa and 207.66MPa and
135.83MPa respectively. The softening of the specimens was due to the reduction of
dislocation density in the structure and the grain growth that leads to the coarsening of
the grain. Greater yield strength and ultimate tensile strength has been observed on water
quenched specimens at 450oC which record 356.34MPa and 358.89MPa. The hardening
of material was due to the finer grain structure obtained by the decreasing of grain size
after water quenched. For aging process, peak strength has been obtained by specimen
aged for 4 hours at 450oC which recorded 542.38MPa of yield strength and 559.69MPa
of ultimate tensile strength. Peak strength was achieved with an increased strain field on
the structure produced by coherent precipitates. The finer grain structure is observed on
this stage that leads to strain hardening. Lowest strength was recorded on specimen aged
for 8 hours at 450oC which recorded 441.66MPa for yield strength and 452.24MPa for
ultimate tensile strength. The reduction of strength is caused by overaging. Overaging
was occurred by the coarsening grain structure and loss of precipitate coherency. Hence,
the mechanical properties and the microstructures are altered accordingly.
iii
ABSTRAK
Tembaga adalah satu elemen penting untuk logam perindustrian utama kerana
kemuluran yang tinggi, sifat lunak dan rintangan kakisan. Tembaga dan aloi terutamanya
digunakan dalam pengeluaran pendawaian, paip, automotif dan seni bina. Proses
rawatan haba telah digunakan pada tembaga dan aloi tembaga untuk mencapai ciri-ciri
yang dikehendaki bagi setiap permohonan. Kesan rawatan haba terhadap mikrostruktur
dan sifat mekanik aloi tembaga telah dikaji dengan proses rawatan haba yang berbeza.
Ujian tegangan dan penyiasatan logam dijalankan untuk mencapai matlamat tersebut.
Dari segi kadar penyejukan, kesan proses penyepuhlindapan dan proses pelindapkejutan
telah disiasat pada suhu yang berbeza. Proses penuaan dikaji dengan suhu yang berbeza
dan tempoh penuaan. Kekuatan alah dan kekuatan tegangan muktamad spesimen anil
telah menurun pada 450oC dari 204.73MPa untuk 129.15MPa dan 207.66MPa dan
masing-masing 135.83MPa. Penurunan spesimen adalah disebabkan oleh pengurangan
ketumpatan kehelan dalam struktur dan pertumbuhan bijian yang membawa kepada
pengasaran bijirin. Kekuatan alah yang lebih besar dan kekuatan tegangan muktamad
telah diperhatikan pada spesimen direndam air pada 450oC yang mencatakan 356.34MPa
dan 358.89MPa. Pengerasan bahan adalah disebabkan oleh struktur bijian yang lebih
halus yang diperolehi oleh penurunan saiz butiran selepas air dipadamkan. Untuk proses
penuaan, kekuatan puncak telah diperolehi oleh spesimen berusia 4 jam pada 450oC
yang mencatatkan 542.38MPa kekuatan alah dan 559.69MPa kekuatan tegangan
muktamad. Kekuatan puncak telah dicapai dengan medan tekanan meningkat ke atas
struktur yang dihasilkan oleh mendakan koheren. Struktur bijirin halus diperhatikan
pada peringkat ini yang membawa kepada ketegangan pengerasan. Kekuatan terendah
dicatatkan pada spesimen berusia 8 jam pada 450oC yang mencatatkan 441.66MPa
untuk kekuatan hasil dan 452.24MPa untuk kekuatan tegangan muktamad. Pengurangan
kekuatan disebabkan oleh overaging yang berlaku oleh struktur bijian pengasaran dan
kehilangan pertalian mendakan. Oleh itu, sifat-sifat mekanikal dan mikrostruktur diubah
sewajarnya.
v
TABLE OF CONTENT
CHAPTER
CHAPTER 1
CHAPTER 2
TITLE
PAGE
DECLARATION
ii
ABSTRAK
iii
ABSTRACT
iv
TABLE OF CONTENT
v
INTRODUCTION
1
1.1 Objectives
3
1.2 Problem Statement
3
1.3 Scope of study
3
LITERATURE REVIEW
4
2.1 Background of copper
4
2.1.1 Properties of copper
5
2.1.1.1 Physical properties
5
2.1.1.2 Mechanical properties
6
2.1.2 Application of copper
6
2.1.3 Phase Diagram and Microstructure
7
2.2 Heat Treatment
2.2.1
Cooling Stage
7
8
vi
2.2.1.1 Effect of cooling rate on the
microstructure
8
and
microhardness on copper alloy
2.2.2
Annealing
2.2.2.1 Effect of annealing process on the
11
12
microstructures and hardness of
pure copper
2.2.3
Quenching Normalizing
13
2.2.3.1 Water quench
14
2.2.4
Normalizing
14
2.2.5
Age-hardening
15
2.2.5.1 Effect of aging process to the
16
hardness and microstructure of
Cu-3Ti-1Cd
2.2.5.2 Age hardening in a Cu-4.5Ti-
18
0.5Co alloy
CHAPTER 3
2.3 Tensile Test
22
2.4 Summary of literature review
23
RESEARCH METHODOLOGY
21
3.1 Specimen preparation
26
3.2 Heat treatment
28
3.2.1 Annealing
29
3.2.2 Quenching
29
3.2.3 Age-hardening
30
3.3 Cooling rate
31
3.4 Mechanical test
32
3.4.1 Tensile Test
33
3.5 Metallurgical investigation
33
3.6 Preliminary work
34
vii
CHAPTER 4
RESULTS AND DISCUSSION
35
4.0 Introduction
35
4.1 Composition of copper alloy
36
4.2 Tensile properties of heat treated copper
38
alloy
4.2.1 Effect of cooling rate
38
4.2.2 Effect of aging process
41
4.3 Metallurgical investigation on heat
44
treated copper alloy
4.3.1 Microstructure observation
44
4.3.1.1 Annealed specimen
45
4.3.1.2 Quenched specimen
46
4.3.1.3 Aged specimen
47
4.3.1.4 Analysis
49
4.3.2 Grain size measurement
50
4.3.2.1 Sample calculation
51
4.3.2.2 Collected data
55
4.3.2.2.1 Effect of cooling
55
rate
4.3.2.2.2 Effect of aging
4.3.2.3 Grain size analysis
CHAPTER 5
CONCLUSION AND
56
57
59
RECOMMENDATION
5.1 Conclusion
59
5.2 Recommendation
60
REFERENCES
61
APPENDICES
66
LIST OF TABLES
TABLE
TITLE
PAGE
2.1
Physical properties of copper
5
2.2
Mechanical properties of copper
6
2.3
Properties of Cu–3Ti alloy before aging and
6
after aging
3.1
Specimen preparation details
3.2
Variation
of
hardness
with
26
annealing
28
temperature of 8-pass ECARed copper.
3.3
Tensile properties of copper alloy before
34
heat treatment process
4.1
Composition of copper alloy
36
4.2
Tensile properties of heat treated copper
38
alloy based on the effect of cooling rate
4.3
Tensile properties of heat treated copper
41
alloy based on the effect of aging treatment
4.4
Grain size number of copper alloy based on
55
effect of cooling rate
4.5
Grain size number of copper alloy based on
the effect of aging duration
56
LIST OF FIGURES
FIGURE
TITLE
PAGE
2.1
Application of copper in wire cables and
5
roofing
2.2
Phase diagram of pure copper
6
2.3
Authentic microstructure of pure copper
6
2.4
Schematic view of the microstructure of the
9
Cu40Zr44Ag8Al8
alloy
for
different
cooling rates
2.5
Microhardness measurements from the
10
periphery to the center of a BMG slice with
a diameter of 9 mm.
2.6
Variation of hardness with annealing
12
temperature of 8-pass ECARed copper.
2.7
Effect of prior cold work on hardness
17
during aging of Cu-3Ti alloy at a) 400oC b)
450oC and c) 500oC
2.8
Light optical micrograph of solution treated
18
of Cu-3Ti at a) peak aged at 450oC for 4h
b) overaged at 450oC for 14h
2.9
Effect of prior cold work on age hardening
19
at 400°C in Cu–4.5Ti–0.5Co alloy
2.10
Effect of prior cold work on age hardening
20
at 450°C in Cu–4.5Ti–0.5Co alloy.
2.11
Effect of prior cold work on age hardening
20
at 500°C inCu–4.5Ti–0.5Co alloy.
2.12
Optical microstructures of Cu–4.5Ti–0.5Co
21
alloy
2.13
Elongation of the specimen after fracture
22
3.1
Flow process of heat treatment of pure
23
copper
3.2
Specimen dimensions
26
3.3
Dog bone dimensions
26
3.4
Specimen preparation process
30
3.5
Age-hardening process
31
3.6
Cooling rate pattern of various cooling
32
methods
3.7
Universal Testing Machine (INSTRON-
33
Model 8802)
3.8
Inverted Optical Microscope
34
3.9
Microstructure of copper alloy before heat
35
treatment
4.1
Tested area of copper alloy specimen that
36
have been spotted by SEM
4.2
EDX results for copper alloy
37
4.3
Effect of cooling method on ultimate
39
tensile strength
4.4
Effect of cooling method on yield strength
39
4.5
Effect of aging process on yield strength
42
4.6
Effect of aging process on ultimate tensile
42
strength
4.7
Microstructure of annealed copper alloy at
350oC
45
4.8
Microstructure of annealed copper alloy at
45
400oC
4.9
Microstructure of annealed copper alloy at
45
450oC
4.10
Microstructure of quenched copper alloy at
46
o
350 C
4.11
Microstructure of quenched copper alloy at
46
400oC
4.12
Microstructure of quenched copper alloy at
46
450oC
4.13
Microstructure of aged copper alloy at
47
o
400 C and 2h
4.14
Microstructure of aged copper alloy at
47
400oC and 4h
4.15
Microstructure of aged copper alloy at
47
400oC and 6h
4.16
Microstructure of aged copper alloy at
48
400oC and 8h
4.17
Microstructure of aged copper alloy at
48
450oC and 2h
4.18
Microstructure of aged copper alloy at
48
400oC and 4h
4.19
Microstructure of aged copper alloy at
49
400oC and 6h
4.20
Microstructure of aged copper alloy at
49
400oC and 8h
4.21
1st position
51
4.22
2nd position
52
rd
4.23
3 position
53
4.24
Table 4 of ASTM E112
54
4.25
Effect of cooling rate to the grain size
55
number
4.26
Effect of aging on grain size number
57
LIST OF APPPENDIX
APPENDIX
TITLE
PAGE
A
Properties and Average Cooling Abilities of
66
Quenching Media
B
ASTM E112 Table 4: Grain Size Relationship
66
Details
C
D
ASTM E8 Dog Bone Dimensions
Quenched Dog Bone Specimen after Tensile Test
67
67
E
Annealed Dog Bone Specimen after Tensile Test
68
F
Aged Dog Bone Specimen after Tensile Test
68
1
CHAPTER 1
INTRODUCTION
Heat treatment is described as the controlled heating and cooling methods
performed on a material in a solid state in order to alter the characteristic of
microstructure and its properties. Heat treatment can be applied to ingots, castings, semifinished products, welded joints and various elements of machines and instruments.
Basically, heat treatment can be operated with various methods. Common heat treatment
is including annealing, normalizing, stress relief treating, hardening, quenching, and
tempering. The cold treatment for each treatment is different based on the heating
methods used. (Kakani, 2004)
Heat treatment are done on material to achieve different results such as softening
the material for improved workability, increase the strength or hardness of material,
increase the toughness or resistance to fracture of the material, stabilize mechanical or
physical properties against changes that might occur during exposure to service
environments, to insure part dimensional stability, to harden non-ferrous metals and
alloys like copper and aluminum and relieve undesirable residual stresses induced during
part fabrication. (Kakani, 2004)
Based on the characteristic of material, each metal has a specific chemical
composition. Thus, the changes in physical and structural properties take place at
different critical temperatures. As a result of heat treatment, the microstructure of a
metal will change due to movement of dislocations, changes in the solubility of atoms,
2
increasing of grain size, new grains formation at same phase or different phase, a change
in crystal structure and others mechanisms.
When an alloy or pure metal is heated, the molecules in the metal will become
mobile and subjected to vibrating. Once the metal is allowed to cool, the molecules in the
metal will reform into a solid mass and will crystallize into distinct structures. Hardness is
directly linked to the crystalline structure. (Trophe.M, 2003)
In this study, copper alloy will be to undergone various type of heat treatment in
order to identify the effects on microstructure and mechanical properties. Copper alloy is
chosen in order because the effect of heat treatment on its mechanical properties.
3
1.1
Objective
i.
To identify the effect of heat treatment process on copper alloy.
ii.
To observe the change of microstructure before and after heat treatment process.
iii.
To compare tensile strength of copper alloy before and after heat treatment.
1.2
Problem Statement
Copper is an essential element for major industrial metal because of its high
ductility, malleability, thermal and electrical conductivity and resistance to
corrosion. Copper and its alloy mainly used in wiring production, piping,
automotive and architecture. Unfortunately, some copper and copper alloys
needs to undergone heat treatment process in order to attain the desired
properties for each application.
1.3
Scope of Study
The main scope of the study is:
i.
To conduct heat treatment process on copper alloy.
ii.
To conduct tensile test of copper alloy before and after heat treatment.
iii.
Metallurgical investigation and material characterization before and after heat
treatment on copper alloy.
4
CHAPTER 2
LITERATURE REVIEW
Based on previous study, the researchers were mainly focused on the heat
treatment of pure copper and copper alloy by using certain methods. As a result of heat
treatment, the microstructure features are modified and the mechanical properties like
hardness and tensile strength is altered. Thus, the findings can be used as a guidance and
reference for this study.
2.1
Background of copper
Copper is known as non-ferrous metal. Copper also is one of basic chemical
elements which have atomic number of 29 and atomic weight of 63.55. It consists of two
stable isotopes, of mass number 63 and 65. Copper is located in group 11 of the periodic
table. The symbol for copper is Cu. (Kakani, 2004)
In its nearly pure state, copper is reddish-orange metal known for its high
thermal and electrical conductivity. Basically, pure copper is usually combined with
other chemicals in the form of copper ores that are obtained from the mines as sulfides
which contain zinc, lead and other sulfur. Others are known as oxide ores, carbonate
ores, or mixed ores depending on the chemical presents. Most of copper ores also
5
contain significant quantities of commercially useless material. Contains of the copper
ores mined in the pure copper is only about 1.2-1.6% of copper weight. (Kakani, 2004)
Recently, copper is mainly used in industry. The capability of copper to be made
into alloys makes the copper become popular in industry. This means copper can be
combined with other metals to make new alloys. There are variable types of metals are
used to produce copper alloys such as brass, nickel, lead, magnesium and others. The
alloying elements make the parents or base copper become stronger in variable aspects
like become harder, tougher and more corrosion resistant than pure copper. (S.
Nagarjuna, 2000)
2.1.1
Properties of copper
2.1.1.1 Physical properties
Table 2.1: Physical properties of copper (T J. Miller, 2000)
Physical properties
Boiling point
Value
o
2567 C
Density@ 20oC
8.96 g/cm3
Melting point
1081.9oC
6
2.1.1.2 Mechanical properties
Table 2.2: Mechanical properties of copper (T J. Miller, 2000)
Properties
Material Condition
Soft
Hard
Polycrystalline
Hardness-Vickers
49
87
137.8
Tensile Strength (MPa)
224
314
-
2.1.2
Application of copper
Main uses of copper can be seen in electrical applications, construction,
transports, and architecture. Approximately 65% of copper produced is used for
electrical applications due to the highest electrical conductivity of any metal. This is
leading for applications in power generation and transmission like generators,
transformers and cables. For electrical equipment, the copper is provided for circuitry,
wiring and contacts for electronic devices. Copper has a key role to play in energy
efficiency. Besides that, 25% of all copper produced is used in buildings especially in
plumbing, roofing and cladding. For application of copper on transports, the high purity
copper wire harness system carries the current from battery throughout the vehicle to
equipment such as lights, central locking and satellite navigation system. Copper also is
used in production of coins, musical instruments and cookware.
Figure 2.1: Application of copper in wire and cables and roofing for construction
7
2.1.3
Phase Diagram and Microstructure of copper
Figure 2.2: Phase diagram of copper alloy, CuAl [Source: Hosford, 2005]
Figure 2.3: Austenite microstructure of copper alloy
[Source: Hosford, 2005]
2.2
Heat treatment
Heat treatment is defined as physical process which entails the controlled heating
and cooling of material which is metal or alloy to obtain desired properties. Heat
treatment also is considered as a sequence of heating and cooling designed of steel after
heat treatment are due to the phase transformations and structural changes that occur
during heat treatment. The factors which determine and control the structural changes
are called the principles of heat treatment.
The important principles of heat treatment are as follows;
i.
Phase transformation during heating.
ii.
Effect of cooling rate on structural changes during cooling.
8
iii.
Effect of carbon content and alloying elements.
For copper alloy, the heat treatment processes available are annealing, quenching,
and age-hardening.
2.2.1
Cooling Stage
After a metal has been soaked, it must be returned to room temperature to
complete the heat-treating process. To cool the metal, you can place it in direct contact
with a cooling medium composed of a gas, liquid, solid, or combination of these. The
rate at which the metal is cooled depends on the metal and the properties desired. The
rate of cooling depends on the medium. Therefore, the choice of a cooling medium has
an important influence on the properties desired. (Zhang, 2002)
Quenching is the procedure used for cooling metal rapidly in oil, water, brine, or
some other medium. Because most metals are cooled rapidly during the hardening
process, quenching is usually associated with hardening; however, quenching does not
always result in an increase in hardness. For example, to anneal copper, usually quench
it in water. Other metals, such as air-hardened steels, are cooled at a relatively slow rate
for hardening. Some metals crack easily or warp during quenching, and others suffer no
ill effects. Therefore, the quenching medium must be chosen to fit the metal. Brine or
water is used for metals that require a rapid cooling rate, and oil mixtures are more
suitable for metals need a slower rate of cooling. (Zhang, 2002)
2.2.1.1 Effect of cooling rate on the microstructure and microhardness on copper
alloy
Regarding to the study on the effect of microstructure and microhardness of
CuZrAgAl alloy by Liu (2012), an alloy with a composition of Cu40Zr44Ag8Al8 (at.%)
was prepared by casting in copper moulds and were melted in a cold crucible in an argon
atmosphere and injected under pressure into water-cooled copper mold. The alloy was
solidified under various shapes to be use as sample which are: