Improvement Of Strength And Formability Of Aluminum Alloy Sheet By Artificial Aging Treatment (Application For Car Body Panel).
IMPROVEMENT OF STRENGTH AND FORMABILITY OF ALUMINUM
ALLOY SHEET BY ARTIFICIAL AGING TREATMENT
(APPLICATION FOR CAR BODY PANEL)
SITI NURUL HAIZA BINTI MAHMUD
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
IMPROVEMENT OF STRENGTH AND FORMABILITY OF ALUMINUM
ALLOY SHEET BY ARTIFICIAL AGING TREATMENT
(APPLICATION FOR CAR BODY PANEL)
SITI NURUL HAIZA BINTI MAHMUD
Laporan ini dikemukakan sebagai
memenuhi sebahagian daripada syarat penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Rekabentuk & Inovasi)
Fakulti Kejuruteraan Mekanikal
Universiti Teknikal Malaysia Melaka
APRIL 2009
ii
‘Saya akui bahawa telah membaca karya ini dan pada pandangan saya karya ini
adalah memadai dari segi skop dan kualiti untuk tujuan penganugerahan Ijazah
Sarjana Muda Kejuruteraan Mekanikal (Rekabentuk & Inovasi)’
Tandatangan
:…………………….
Nama Penyelia I
:…………………….
Tarikh
:……………………
iii
“Saya akui laporan ini adalah hasil kerja saya sendiri kecuali ringkasan dan petikan
yang tiap-tiap satunya saya telah jelaskan sumbernya”
Tandatangan
:…………………….
Nama Penulis
:……………………
Tarikh
:…………………….
iv
To my beloved parents
v
ACKNOWLEDGEMENTS
First of all, I would like to express my sincere gratitude to my supervisor Mrs.
Rafidah bt Hassan for her constant support and motivation throughout the entire
period of this study. Mrs. Rafidah is the most important reason for my success in
accomplishment of my study. I always revere her patience and encouragement. I
would also like to thank all my friends for their full support and suggestions provided
in the realization of this research.
I would also like to express my sincere gratitude to all lab supervisors who
always give their full commitment and cooperation in finishing this study.
Last but not least, I sincerely express my acknowledgement to my parents
who always there with me and encourage me to be a better student.
vi
ABSTRACT
Nowadays, the demands for high fuel-efficiency to reduce energy
consumption and weight of vehicles become a challenge in industries especially in
automotive industry. The selection of materials used in vehicles is the most important
factors that need to be considered. This study is basically to do improvement on
formability and hardness of aluminum alloys 6061-T4 as a choice of material for
industries to fulfill the demands. The special properties or characteristics of
aluminum alloys 6061-T4 such as lightweight and high corrosion resistance have put
them among the best chosen materials to be used as automotive body sheets. Heat
treatment processes are the best ways to improve its formability and hardness as
aluminum alloys 6061-T4 are the heat-treatable wrought aluminum alloys and thus
chosen in this project. The processes were performed by re-solution heat treatment,
quenching, artificial aging and paint baking. The re-solution heat treatment was
performed at 5300C for 2 hours and followed by quenching in water at room
temperature to retain or freeze its microstructure in α-phase. While, artificial aging
treatment was carried out at 1700C for 8 hours in order to strengthen the material.
The formability and strength of aluminum alloy were determined by uniaxial tensile
test and three-point bending test respectively. The value of strain-hardening exponent
(n-value) and plastic strain ratio (r-value) indicates the formability of aluminum
alloy. The flexure stress also was observed to clearly prove the results. The results
were compared between sequences of conventional and present processes of car body
panel.
vii
ABSTRAK
Pada zaman sekarang, permintaan terhadap kenderaan yang lebih ringan dan
dapat menjimatkan penggunaan minyak telah meningkat dari semasa ke semasa dan
ia telah menjadi satu cabaran kepada mereka yang terlibat dalam industri automotif.
Dalam memenuhi permintaan ini, pengeluar perlu mengambil kira faktor pemilihan
bahan yang sesuai dalam mencipta sesebuah kenderaan. Oleh sebab itu, kajian ini
telah dijalankan ke atas satu bahan iaitu aloi aluminium 6061-T4 dalam usaha untuk
memenuhi permintaan tersebut. Ciri- ciri istimewa yang terdapat pada campuran
aluminium 6061-T4 seperti ringan dan daya tahan terhadap hakisan yang tinggi telah
meletakkan campuran aluminium 6061-T4 antara bahan yang digunakan secara
menyeluruh untuk menghasilkan badan kereta. Pemanasan ke atas bahan ini akan
dapat meningkatkan kekerasan dan kelenturannya dan dipilih sebagai proses dalam
projeck ini. Proses- proses yang dijalankan ialah rawatan haba ulangan di mana ia
dijalankan pada suhu 5300C selama dua jam. Selepas pemanasan, bahan tersebut
disejukkan secara pantas di dalam air yang sejuk untuk mengekalkan struktur di
dalam bahan tersebut. Proses seterusnya ialah penuaan buatan di mana proses ini
dijalankan pada suhu 1700C selama lapan jam untuk menambah kekuatan dan
kekerasan bahan tersebut. Kelenturan dan kekuatan campuran aluminium 6061-T4
ditentukan dengan menjalankan ujian tegangan dan ujian kelenturan tiga titik. Nilainilai n dan r bahan tersebut menunjukkan kelenturan campuran aluminium 6061-T4
tersebut. Bacaan yang didapati kemudian dibandingkan di antara proses yang
digunakan dahulu dengan proses terbaru untuk menghasilkan badan kereta.
\
viii
TABLE OF CONTENTS
CHAPTER
SUBJECT
PAGE
NUMBER
CHAPTER I
CHAPTER II
PENGAKUAN
ii
DEDICATION
iv
ACKNOWLEDGEMENT
v
ABSRACT
vi
ABSTRAK
vii
TABLE OF CONTENTS
viii
LIST OF TABLES
xiii
LIST OF FIGURES
xiv
LIST OF SYMBOLS
xvi
LIST OF APPENDICES
xvii
INTRODUCTION
1
1.1 Overview
1
1.2 Problem Statement
2
1.3 Objective
2
1.4 Scopes
2
LITERATURE REVIEW
3
2.1
3
Aluminum Alloys
2.1.1 Types of Aluminum Alloys
6
2.1.1.1 Wrought aluminum alloys
6
2.1.1.2 Cast aluminum alloys
8
2.1.1.3 Differences between Wrought
9
ix
and Cast Aluminum Alloys
2.1.2 Aluminum Alloy 6061-T4
2.1.2.1 Applications of aluminum alloy
10
11
6061
2.1.2.2 Design Requirements for
12
Automotive Body Sheet
2.2
Heat Treatment of Aluminum Alloy
13
2.2.1 Solution Heat Treatment
15
2.2.2 Quenching (Rapid Cooling)
17
2.2.2.1 Mechanism of Quenching
18
2.2.2.2 Types of Quenchant
20
2.2.3 Age Hardening Treatment
22
2.2.3.1 Natural aging
22
2.2.3.2 Artificial aging
23
2.2.4 Paint Baking Process
25
2.2.4.1 Air drying
25
2.2.4.2 Drying in a Low-bake Oven
Spray Booth
26
2.2.4.3 Infra-red Drying
27
2.3 Mechanical Testing
27
2.3.1 Tensile Test
28
2.3.1.1 Determination of Strain
Hardening Exponent (n-values)
29
2.3.1.2 Determination of Plastic Strain
Ratio (r-values)
32
2.3.2 Bending (Flexure) Test
34
x
CHAPTER III
METHODOLOGY
36
3.1 Methodology
38
3.2 Procedures
40
3.2.1 Machining Procedures
40
3.2.2 Heat Treatment Procedures
42
3.2.3 Tensile Test Procedures
44
3.2.3.1 Tensile test to Determine nvalues
3.2.3.2 Tensile Test to Determine rvalues
3.2.4 Bending (Flexure) Test Procedures
CHAPTER IV RESULTS AND ANALYSIS
45
47
50
52
4.1 Introduction
52
4.2 Conventional Process
52
4.2.1 Re-solution Heat Treatment
55
4.2.2 Paint Baking Process
57
4.3 Present Process
58
4.3.1 Resolution Heat Treatment
58
4.3.2 Artificial Aging Treatment and Paint
63
Baking Process
4.4 Sample Calculations
CHAPTER V
67
4.4.1 Determination of n-values
67
4.4.2 Determination of r-values
70
DISCUSSIONS
72
5.1 Introduction
72
5.2 Comparison between the Results of Several
72
Conditions
5.3 Properties of Aluminum Alloy 6061-T4
81
xi
CHAPTER VI CONCLUSIONS AND RECOMMENDATIONS
82
6.1 Conclusions
82
6.2 Recommendations
84
REFERENCES
85
BIBLIOGRAPHY
88
APPENDICES
90
xii
LIST OF TABLES
No
Title
Page
2.1
Applications of Aluminum Alloys
5
2.2
General Characteristics of Wrought Aluminum Alloys Series
6
2.3
General Characteristics of Cast Aluminum Alloys Series
8
2.4
Digits Representation in Aluminum Alloy 6061-T4
10
2.5
Mechanical Properties of Aluminum Alloy 6061
11
2.6
Several Applications of Aluminum Alloy 6061 in Industries
11
2.7
Changes in Microstructure after Heat Treatments
24
3.1
Sample Distribution for Conventional Process
39
3.2
Sample Distribution for Present Process
39
4.1
Average n-values and r-values for Condition 1
53
4.2
Average Flexure Stress for Condition 1
54
4.3
Average n-values and r-values for Condition 2
54
4.4
Average Flexure Stress for Condition 2
55
4.5
Average n-values and r-values for Condition 3
56
4.6
Average Flexure Stress for Condition 3
56
4.7
Average n-values and r-values after Artificially Aged and Paint Baked
57
4.8
Average Flexure Stress after Artificially Aged and Paint Baked
58
4.9
Average n-values and r-values for Condition 1
60
4.10
Average Flexure Stress for Condition 1
60
4.11
Average n-values and r-values for Condition 2
61
4.12
Average Flexure Stress for Condition 2
61
4.13
Average n-values and r-values for Condition 3
62
4.14
Average Flexure Load for Condition 3
63
xiii
4.15
Average n-values and r-values for Condition 1
64
4.16
Average Flexure Stress for Condition 1
64
4.17
Average n-values and r-values for Condition 2
65
4.18
Average Flexure Stress for Condition 2
65
4.19
Average n-values and r-values for Condition 3
66
4.20
Average Flexure Stress for Condition 1
67
4.21
Reading 1 for Condition 1 (Resolution Heat Treatment of Present Process)
68
5.1
Average n-values, r-values and Flexure Stress for Conventional Process
73
5.2
Average n-values, r-values and Flexure Stress for Present
73
5.3
Percentage (%) of Difference of n-values, r-values and Flexure Stress of
Present Process Compared to Conventional Process
74
5.4
Properties of Aluminum Alloy 6061-T4 before Heat Treatment
81
xiv
LIST OF FIGURES
No
Title
Page
2.1
Pseudo-binary Phase Diagram for Al-Mg 2 Si
14
2.2
Heat Treatment Sequences
14
2.3
FCC (Face Centered Cubic) Structure
16
2.4
Vapor Phase in Quenching
18
2.5
Boiling Phase in Quenching
19
2.6
Convection Phase in Quenching
19
2.7
Schematic Aging Curve at a Particular Temperature for a PrecipitationHardenable Alloy
23
2.8
Typical Airflow Pattern in a Spray Booth/Low-Bake Oven
26
2.8
Gage Length for Sheet Metals
28
2.8
Two Bend Test Method: (a) Three-point Bending; (b) Four-point Bending
35
3.1
Sequential Process for Aluminum Alloy 6061-T4 Treatment
37
3.2
Tensile Test Specimens
40
3.3
Required Dimensions for Reduced Section of Specimen
41
3.4
Heat Treatment Sequences
42
3.5
Instron Machine
44
3.6
Extensometer attached to Specimen
45
3.7
Extensometer attached at the Center of Specimen
48
3.8
Specimen is pulled until Fracture
49
3.9
Instron Machine (Model 5585)
50
xv
3.10
Load Applied Vertically at the Center
51
3.11
Specimen Flexure or Bend
51
5.1
Comparison of Strain-hardening Exponent between Present and
Conventional Process after Resolution Heat Treatment
76
5.2
Comparison of Plastic Strain Ratio Between Present and Conventional
Process after Resolution Heat Treatment
77
5.3
Comparison of Flexure Stress Between Present and Conventional Process
after Resolution Heat Treatment
77
5.4
Comparison of Strain-hardening Exponent Between Present and
Conventional Process after Artificial Aging and Paint Baking Process
78
5.5
Comparison of Plastic Strain Ratio Between Present and Conventional
Process after Artificial Aging and Paint Baking Process
78
5.6
Comparison of Flexure Stress Between Present and Conventional Process
after Artificial Aging and Paint Baking Process
79
5.7
Percentage of Difference of n-values, r-values and Flexure Stress of
Present Process Compared to Conventional Process after Resolution Heat
Treatment
79
5.8
Percentage of Difference of n-values, r-values and Flexure Stress of
Present Process Compared to Conventional Process after Paint Baking
80
xvi
LIST OF SYMBOLS
n
= Strain Hardening Exponent
r
= Plastic Strain Ratio
є
= True Strain
σ
= True Stress, Pa
K
= Strength Coefficient
S
= Engineering Stress, Pa
e
= Engineering Strain
P
= Load, N
A
= Area, m2
L
= Length, m
N
= Number of Data Pairs
SD
= Standard Deviation
єw
=Width Strain
єt
= Thickness Strain
l0
= Original Gage Length, m
lf
= Final Gage Length, m
t0
= Original Thickness, m
tf
= Final Thickness, m
w0
= Original Width, m
wf
= Final Width, m
υ
= Coefficient of Variation
xvii
LIST OF APPENDICES
Appendix A
: Gantt Chart for PSM 1 and PSM 2
Appendix B
: Process Flow Chart
Appendix C
: Raw Data
Appendix D
: Raw Data from Tensile and Three Point Bending Test
1
CHAPTER I
INTRODUCTION
1.1
Overview
At the present time, technological demands for materials having high strength
to weight ratio, high specific modulus, low coefficient of thermal expansion, good
wear resistance, low density and good thermal conductivity are constantly increasing.
In automotive application, material competition has been traditionally intensive. The
increasing requirement to improve fuel economy triggered by concerns about global
warming and energy usage has a significant influence on the choice of materials.
Aluminum alloys offers one answer for the combinations of such attractive properties
which can be applied in various types of industries.
This study is basically to do an improvement on strength and formability of coldrolled aluminum alloy sheet 6XXX series (6061-T4) by artificial aging treatment,
thus investigate the tensile strain hardening exponent (n-values) and plastic strainratio (r-values) by conducting tensile test. The processes involved are re-solution
heat treatment, machining the sheets into dog-bone shape, artificial aging treatment,
paint baking and finally tensile test in order to prove the results obtained after
carrying out those treatments. This aluminum alloy 6061-T4 was chosen in this study
because of its special properties and applicable in various industries, not only limited
in automotive industry.
2
1.2
Problem Statement
a) The increased in oil price has caused the economical problems to car users.
b) The alternative solution to replace the present material is important to reduce
weight of vehicles and energy consumption.
c) Aluminum alloys are the best choice because of its lightweight properties, but
its formability and hardness need to be improved to make it suitable to be
applied in industries especially in automotive industry.
1.3
Objective
To investigate the tensile strain-hardening exponents (n-values) and plastic strainratio (r-values) of product rolled from aluminum alloy sheet produced by sequences
of conventional and present processes.
1.4
Scopes
This project is more to material and design engineering. The scopes of this project
are:
a) Material: Aluminum alloy 6061-T4
b) Standard: American Standard for Testing Method (ASTM)
c) Mechanical testing:
i.
Tensile test
ii.
Bending (Flexure) test
d) Variables: Time duration from re-solution heat treatment to artificial aging
treatment
e) Modified heat treatment from ASTM B918-01
3
CHAPTER II
LITERATURE REVIEW
2.1
Aluminum Alloys
Aluminum is categorized as a light metal besides magnesium, titanium and
beryllium and its lightweight characteristic positions aluminum among the most
widely used materials in industries. Currently, the needs for light metals have been
the predominant consideration by manufacturers in choosing materials especially in
automotive field and for this reason, aluminum offers the best answer compared to
other metals such as iron, copper and nickel.
Basically, pure aluminum is soft, ductile, corrosion resistance and high
electrical conductivity and these properties are most suitable to be applied for coil
and conductor cable. However, aluminum is identified to have a low tensile strength
of about 90 MPa and this constraint has limited its usage in industries
(nonferrous.keytometals.com). By working the aluminum, as by cold rolling will
give improvement in tensile strength for approximately doubled. To gain higher or
marked increases in mechanical properties, the best way to be taken is by alloying the
aluminum with small percentages of one or more other elements for example
magnesium, silicon, copper, zinc and manganese. For aluminum alloys, they are also
made stronger by cold working. Some alloys can be further hardened and
strengthened by performing heat treatments to give a very large increase in tensile
strength for almost 700MPa (nonferrous.keytometals.com). Generally, aluminum and
4
its alloys have a self-protecting characteristic in which they are capable in forming a
thin visible oxide skin immediately whenever its surfaces are exposed to atmosphere.
This special characteristic gives aluminum and its alloys their high resistance to
corrosion as well as to many acids. Alkalis are among the few substances that attack
the oxide skin and therefore are corrosive to aluminum.
Aluminum alloys also can be cast into any form and provides good surface
finish. It can be rolled, stamped, drawn, spun, roll-formed, hammered and forged.
Beside that, it can be riveted, welded, brazed or resin-bonded. In automotive
industry, the demands to produce the lightweight components and enhance the fuel
efficiency have increased and the best solutions to meet the needs are aluminum
alloys.
For manufacturers, the needs to produce lightweight vehicles for improving
fuel economy are significant in order to compute in today’s market and for
customers’ satisfaction. Current research (Smerd et al. 2005), claims that aluminum
intensive space frame that reduce body weight up to 40% has been employed
successfully and the advantage of aluminum lying in its strength-to-weight ratio.
Previous research (Miller et al. 2000) shows that the usage of aluminum in
automotive applications has grown more than 80% in the past 5 years. The usage of
aluminum is predicted to be used in hoods, trunk lids and doors hanging on a steel
frame.
Among the characteristics of aluminum alloys that make it suitable for a
variety of automotive applications are (Source: www.autoaluminum.org):
(a) Strong: the entire vehicle body can be aluminum
(b) Durable: good resistance to corrosion and fatigue
(c) Conductive: both thermal and electrical-for efficient engine and electrical
components
(d) Nonmagnetic: useful in electronics
(e) Nontoxic: important in any material used in cars
(f) Abundant: adequate supply worldwide
(g) Recyclable: saves energy, benefits the environment
5
(h) Workable: uses well understood metalworking process
(i) Available: aluminum’s many product forms offer design flexibility
Table 2.1 below is the applications of several types of aluminum alloys:
Table 2.1: Applications of Aluminum Alloys
(Source: www.autoaluminum.org)
Types/Designations
Applications
1100
Trim, nameplates, appliqués
2008
Outer and inner body panels
(also suitable for structural
applications)
3004
Interior panels and components
4004
Cladding for brazing sheet
5052
Interior panels and components,
truck bumpers and
body panels
6010
Outer and inner body panels,
seat shells and tracks
7003
Seat tracks, bumper reinforcements
6
2.1.1
Types of Aluminum Alloys
There are two types of aluminum alloys available in industries and can be
identified according to their designations. Those types are:
2.1.1.1
Wrought Aluminum Alloys
Wrought aluminum alloys are used in the shaping processes such rolling,
shaping, extrusion, pressing and stamping. The examples of wrought products are
rolled plate (>6 mm thickness), sheet (0.15 mm- 6 mm), foil (
ALLOY SHEET BY ARTIFICIAL AGING TREATMENT
(APPLICATION FOR CAR BODY PANEL)
SITI NURUL HAIZA BINTI MAHMUD
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
IMPROVEMENT OF STRENGTH AND FORMABILITY OF ALUMINUM
ALLOY SHEET BY ARTIFICIAL AGING TREATMENT
(APPLICATION FOR CAR BODY PANEL)
SITI NURUL HAIZA BINTI MAHMUD
Laporan ini dikemukakan sebagai
memenuhi sebahagian daripada syarat penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Rekabentuk & Inovasi)
Fakulti Kejuruteraan Mekanikal
Universiti Teknikal Malaysia Melaka
APRIL 2009
ii
‘Saya akui bahawa telah membaca karya ini dan pada pandangan saya karya ini
adalah memadai dari segi skop dan kualiti untuk tujuan penganugerahan Ijazah
Sarjana Muda Kejuruteraan Mekanikal (Rekabentuk & Inovasi)’
Tandatangan
:…………………….
Nama Penyelia I
:…………………….
Tarikh
:……………………
iii
“Saya akui laporan ini adalah hasil kerja saya sendiri kecuali ringkasan dan petikan
yang tiap-tiap satunya saya telah jelaskan sumbernya”
Tandatangan
:…………………….
Nama Penulis
:……………………
Tarikh
:…………………….
iv
To my beloved parents
v
ACKNOWLEDGEMENTS
First of all, I would like to express my sincere gratitude to my supervisor Mrs.
Rafidah bt Hassan for her constant support and motivation throughout the entire
period of this study. Mrs. Rafidah is the most important reason for my success in
accomplishment of my study. I always revere her patience and encouragement. I
would also like to thank all my friends for their full support and suggestions provided
in the realization of this research.
I would also like to express my sincere gratitude to all lab supervisors who
always give their full commitment and cooperation in finishing this study.
Last but not least, I sincerely express my acknowledgement to my parents
who always there with me and encourage me to be a better student.
vi
ABSTRACT
Nowadays, the demands for high fuel-efficiency to reduce energy
consumption and weight of vehicles become a challenge in industries especially in
automotive industry. The selection of materials used in vehicles is the most important
factors that need to be considered. This study is basically to do improvement on
formability and hardness of aluminum alloys 6061-T4 as a choice of material for
industries to fulfill the demands. The special properties or characteristics of
aluminum alloys 6061-T4 such as lightweight and high corrosion resistance have put
them among the best chosen materials to be used as automotive body sheets. Heat
treatment processes are the best ways to improve its formability and hardness as
aluminum alloys 6061-T4 are the heat-treatable wrought aluminum alloys and thus
chosen in this project. The processes were performed by re-solution heat treatment,
quenching, artificial aging and paint baking. The re-solution heat treatment was
performed at 5300C for 2 hours and followed by quenching in water at room
temperature to retain or freeze its microstructure in α-phase. While, artificial aging
treatment was carried out at 1700C for 8 hours in order to strengthen the material.
The formability and strength of aluminum alloy were determined by uniaxial tensile
test and three-point bending test respectively. The value of strain-hardening exponent
(n-value) and plastic strain ratio (r-value) indicates the formability of aluminum
alloy. The flexure stress also was observed to clearly prove the results. The results
were compared between sequences of conventional and present processes of car body
panel.
vii
ABSTRAK
Pada zaman sekarang, permintaan terhadap kenderaan yang lebih ringan dan
dapat menjimatkan penggunaan minyak telah meningkat dari semasa ke semasa dan
ia telah menjadi satu cabaran kepada mereka yang terlibat dalam industri automotif.
Dalam memenuhi permintaan ini, pengeluar perlu mengambil kira faktor pemilihan
bahan yang sesuai dalam mencipta sesebuah kenderaan. Oleh sebab itu, kajian ini
telah dijalankan ke atas satu bahan iaitu aloi aluminium 6061-T4 dalam usaha untuk
memenuhi permintaan tersebut. Ciri- ciri istimewa yang terdapat pada campuran
aluminium 6061-T4 seperti ringan dan daya tahan terhadap hakisan yang tinggi telah
meletakkan campuran aluminium 6061-T4 antara bahan yang digunakan secara
menyeluruh untuk menghasilkan badan kereta. Pemanasan ke atas bahan ini akan
dapat meningkatkan kekerasan dan kelenturannya dan dipilih sebagai proses dalam
projeck ini. Proses- proses yang dijalankan ialah rawatan haba ulangan di mana ia
dijalankan pada suhu 5300C selama dua jam. Selepas pemanasan, bahan tersebut
disejukkan secara pantas di dalam air yang sejuk untuk mengekalkan struktur di
dalam bahan tersebut. Proses seterusnya ialah penuaan buatan di mana proses ini
dijalankan pada suhu 1700C selama lapan jam untuk menambah kekuatan dan
kekerasan bahan tersebut. Kelenturan dan kekuatan campuran aluminium 6061-T4
ditentukan dengan menjalankan ujian tegangan dan ujian kelenturan tiga titik. Nilainilai n dan r bahan tersebut menunjukkan kelenturan campuran aluminium 6061-T4
tersebut. Bacaan yang didapati kemudian dibandingkan di antara proses yang
digunakan dahulu dengan proses terbaru untuk menghasilkan badan kereta.
\
viii
TABLE OF CONTENTS
CHAPTER
SUBJECT
PAGE
NUMBER
CHAPTER I
CHAPTER II
PENGAKUAN
ii
DEDICATION
iv
ACKNOWLEDGEMENT
v
ABSRACT
vi
ABSTRAK
vii
TABLE OF CONTENTS
viii
LIST OF TABLES
xiii
LIST OF FIGURES
xiv
LIST OF SYMBOLS
xvi
LIST OF APPENDICES
xvii
INTRODUCTION
1
1.1 Overview
1
1.2 Problem Statement
2
1.3 Objective
2
1.4 Scopes
2
LITERATURE REVIEW
3
2.1
3
Aluminum Alloys
2.1.1 Types of Aluminum Alloys
6
2.1.1.1 Wrought aluminum alloys
6
2.1.1.2 Cast aluminum alloys
8
2.1.1.3 Differences between Wrought
9
ix
and Cast Aluminum Alloys
2.1.2 Aluminum Alloy 6061-T4
2.1.2.1 Applications of aluminum alloy
10
11
6061
2.1.2.2 Design Requirements for
12
Automotive Body Sheet
2.2
Heat Treatment of Aluminum Alloy
13
2.2.1 Solution Heat Treatment
15
2.2.2 Quenching (Rapid Cooling)
17
2.2.2.1 Mechanism of Quenching
18
2.2.2.2 Types of Quenchant
20
2.2.3 Age Hardening Treatment
22
2.2.3.1 Natural aging
22
2.2.3.2 Artificial aging
23
2.2.4 Paint Baking Process
25
2.2.4.1 Air drying
25
2.2.4.2 Drying in a Low-bake Oven
Spray Booth
26
2.2.4.3 Infra-red Drying
27
2.3 Mechanical Testing
27
2.3.1 Tensile Test
28
2.3.1.1 Determination of Strain
Hardening Exponent (n-values)
29
2.3.1.2 Determination of Plastic Strain
Ratio (r-values)
32
2.3.2 Bending (Flexure) Test
34
x
CHAPTER III
METHODOLOGY
36
3.1 Methodology
38
3.2 Procedures
40
3.2.1 Machining Procedures
40
3.2.2 Heat Treatment Procedures
42
3.2.3 Tensile Test Procedures
44
3.2.3.1 Tensile test to Determine nvalues
3.2.3.2 Tensile Test to Determine rvalues
3.2.4 Bending (Flexure) Test Procedures
CHAPTER IV RESULTS AND ANALYSIS
45
47
50
52
4.1 Introduction
52
4.2 Conventional Process
52
4.2.1 Re-solution Heat Treatment
55
4.2.2 Paint Baking Process
57
4.3 Present Process
58
4.3.1 Resolution Heat Treatment
58
4.3.2 Artificial Aging Treatment and Paint
63
Baking Process
4.4 Sample Calculations
CHAPTER V
67
4.4.1 Determination of n-values
67
4.4.2 Determination of r-values
70
DISCUSSIONS
72
5.1 Introduction
72
5.2 Comparison between the Results of Several
72
Conditions
5.3 Properties of Aluminum Alloy 6061-T4
81
xi
CHAPTER VI CONCLUSIONS AND RECOMMENDATIONS
82
6.1 Conclusions
82
6.2 Recommendations
84
REFERENCES
85
BIBLIOGRAPHY
88
APPENDICES
90
xii
LIST OF TABLES
No
Title
Page
2.1
Applications of Aluminum Alloys
5
2.2
General Characteristics of Wrought Aluminum Alloys Series
6
2.3
General Characteristics of Cast Aluminum Alloys Series
8
2.4
Digits Representation in Aluminum Alloy 6061-T4
10
2.5
Mechanical Properties of Aluminum Alloy 6061
11
2.6
Several Applications of Aluminum Alloy 6061 in Industries
11
2.7
Changes in Microstructure after Heat Treatments
24
3.1
Sample Distribution for Conventional Process
39
3.2
Sample Distribution for Present Process
39
4.1
Average n-values and r-values for Condition 1
53
4.2
Average Flexure Stress for Condition 1
54
4.3
Average n-values and r-values for Condition 2
54
4.4
Average Flexure Stress for Condition 2
55
4.5
Average n-values and r-values for Condition 3
56
4.6
Average Flexure Stress for Condition 3
56
4.7
Average n-values and r-values after Artificially Aged and Paint Baked
57
4.8
Average Flexure Stress after Artificially Aged and Paint Baked
58
4.9
Average n-values and r-values for Condition 1
60
4.10
Average Flexure Stress for Condition 1
60
4.11
Average n-values and r-values for Condition 2
61
4.12
Average Flexure Stress for Condition 2
61
4.13
Average n-values and r-values for Condition 3
62
4.14
Average Flexure Load for Condition 3
63
xiii
4.15
Average n-values and r-values for Condition 1
64
4.16
Average Flexure Stress for Condition 1
64
4.17
Average n-values and r-values for Condition 2
65
4.18
Average Flexure Stress for Condition 2
65
4.19
Average n-values and r-values for Condition 3
66
4.20
Average Flexure Stress for Condition 1
67
4.21
Reading 1 for Condition 1 (Resolution Heat Treatment of Present Process)
68
5.1
Average n-values, r-values and Flexure Stress for Conventional Process
73
5.2
Average n-values, r-values and Flexure Stress for Present
73
5.3
Percentage (%) of Difference of n-values, r-values and Flexure Stress of
Present Process Compared to Conventional Process
74
5.4
Properties of Aluminum Alloy 6061-T4 before Heat Treatment
81
xiv
LIST OF FIGURES
No
Title
Page
2.1
Pseudo-binary Phase Diagram for Al-Mg 2 Si
14
2.2
Heat Treatment Sequences
14
2.3
FCC (Face Centered Cubic) Structure
16
2.4
Vapor Phase in Quenching
18
2.5
Boiling Phase in Quenching
19
2.6
Convection Phase in Quenching
19
2.7
Schematic Aging Curve at a Particular Temperature for a PrecipitationHardenable Alloy
23
2.8
Typical Airflow Pattern in a Spray Booth/Low-Bake Oven
26
2.8
Gage Length for Sheet Metals
28
2.8
Two Bend Test Method: (a) Three-point Bending; (b) Four-point Bending
35
3.1
Sequential Process for Aluminum Alloy 6061-T4 Treatment
37
3.2
Tensile Test Specimens
40
3.3
Required Dimensions for Reduced Section of Specimen
41
3.4
Heat Treatment Sequences
42
3.5
Instron Machine
44
3.6
Extensometer attached to Specimen
45
3.7
Extensometer attached at the Center of Specimen
48
3.8
Specimen is pulled until Fracture
49
3.9
Instron Machine (Model 5585)
50
xv
3.10
Load Applied Vertically at the Center
51
3.11
Specimen Flexure or Bend
51
5.1
Comparison of Strain-hardening Exponent between Present and
Conventional Process after Resolution Heat Treatment
76
5.2
Comparison of Plastic Strain Ratio Between Present and Conventional
Process after Resolution Heat Treatment
77
5.3
Comparison of Flexure Stress Between Present and Conventional Process
after Resolution Heat Treatment
77
5.4
Comparison of Strain-hardening Exponent Between Present and
Conventional Process after Artificial Aging and Paint Baking Process
78
5.5
Comparison of Plastic Strain Ratio Between Present and Conventional
Process after Artificial Aging and Paint Baking Process
78
5.6
Comparison of Flexure Stress Between Present and Conventional Process
after Artificial Aging and Paint Baking Process
79
5.7
Percentage of Difference of n-values, r-values and Flexure Stress of
Present Process Compared to Conventional Process after Resolution Heat
Treatment
79
5.8
Percentage of Difference of n-values, r-values and Flexure Stress of
Present Process Compared to Conventional Process after Paint Baking
80
xvi
LIST OF SYMBOLS
n
= Strain Hardening Exponent
r
= Plastic Strain Ratio
є
= True Strain
σ
= True Stress, Pa
K
= Strength Coefficient
S
= Engineering Stress, Pa
e
= Engineering Strain
P
= Load, N
A
= Area, m2
L
= Length, m
N
= Number of Data Pairs
SD
= Standard Deviation
єw
=Width Strain
єt
= Thickness Strain
l0
= Original Gage Length, m
lf
= Final Gage Length, m
t0
= Original Thickness, m
tf
= Final Thickness, m
w0
= Original Width, m
wf
= Final Width, m
υ
= Coefficient of Variation
xvii
LIST OF APPENDICES
Appendix A
: Gantt Chart for PSM 1 and PSM 2
Appendix B
: Process Flow Chart
Appendix C
: Raw Data
Appendix D
: Raw Data from Tensile and Three Point Bending Test
1
CHAPTER I
INTRODUCTION
1.1
Overview
At the present time, technological demands for materials having high strength
to weight ratio, high specific modulus, low coefficient of thermal expansion, good
wear resistance, low density and good thermal conductivity are constantly increasing.
In automotive application, material competition has been traditionally intensive. The
increasing requirement to improve fuel economy triggered by concerns about global
warming and energy usage has a significant influence on the choice of materials.
Aluminum alloys offers one answer for the combinations of such attractive properties
which can be applied in various types of industries.
This study is basically to do an improvement on strength and formability of coldrolled aluminum alloy sheet 6XXX series (6061-T4) by artificial aging treatment,
thus investigate the tensile strain hardening exponent (n-values) and plastic strainratio (r-values) by conducting tensile test. The processes involved are re-solution
heat treatment, machining the sheets into dog-bone shape, artificial aging treatment,
paint baking and finally tensile test in order to prove the results obtained after
carrying out those treatments. This aluminum alloy 6061-T4 was chosen in this study
because of its special properties and applicable in various industries, not only limited
in automotive industry.
2
1.2
Problem Statement
a) The increased in oil price has caused the economical problems to car users.
b) The alternative solution to replace the present material is important to reduce
weight of vehicles and energy consumption.
c) Aluminum alloys are the best choice because of its lightweight properties, but
its formability and hardness need to be improved to make it suitable to be
applied in industries especially in automotive industry.
1.3
Objective
To investigate the tensile strain-hardening exponents (n-values) and plastic strainratio (r-values) of product rolled from aluminum alloy sheet produced by sequences
of conventional and present processes.
1.4
Scopes
This project is more to material and design engineering. The scopes of this project
are:
a) Material: Aluminum alloy 6061-T4
b) Standard: American Standard for Testing Method (ASTM)
c) Mechanical testing:
i.
Tensile test
ii.
Bending (Flexure) test
d) Variables: Time duration from re-solution heat treatment to artificial aging
treatment
e) Modified heat treatment from ASTM B918-01
3
CHAPTER II
LITERATURE REVIEW
2.1
Aluminum Alloys
Aluminum is categorized as a light metal besides magnesium, titanium and
beryllium and its lightweight characteristic positions aluminum among the most
widely used materials in industries. Currently, the needs for light metals have been
the predominant consideration by manufacturers in choosing materials especially in
automotive field and for this reason, aluminum offers the best answer compared to
other metals such as iron, copper and nickel.
Basically, pure aluminum is soft, ductile, corrosion resistance and high
electrical conductivity and these properties are most suitable to be applied for coil
and conductor cable. However, aluminum is identified to have a low tensile strength
of about 90 MPa and this constraint has limited its usage in industries
(nonferrous.keytometals.com). By working the aluminum, as by cold rolling will
give improvement in tensile strength for approximately doubled. To gain higher or
marked increases in mechanical properties, the best way to be taken is by alloying the
aluminum with small percentages of one or more other elements for example
magnesium, silicon, copper, zinc and manganese. For aluminum alloys, they are also
made stronger by cold working. Some alloys can be further hardened and
strengthened by performing heat treatments to give a very large increase in tensile
strength for almost 700MPa (nonferrous.keytometals.com). Generally, aluminum and
4
its alloys have a self-protecting characteristic in which they are capable in forming a
thin visible oxide skin immediately whenever its surfaces are exposed to atmosphere.
This special characteristic gives aluminum and its alloys their high resistance to
corrosion as well as to many acids. Alkalis are among the few substances that attack
the oxide skin and therefore are corrosive to aluminum.
Aluminum alloys also can be cast into any form and provides good surface
finish. It can be rolled, stamped, drawn, spun, roll-formed, hammered and forged.
Beside that, it can be riveted, welded, brazed or resin-bonded. In automotive
industry, the demands to produce the lightweight components and enhance the fuel
efficiency have increased and the best solutions to meet the needs are aluminum
alloys.
For manufacturers, the needs to produce lightweight vehicles for improving
fuel economy are significant in order to compute in today’s market and for
customers’ satisfaction. Current research (Smerd et al. 2005), claims that aluminum
intensive space frame that reduce body weight up to 40% has been employed
successfully and the advantage of aluminum lying in its strength-to-weight ratio.
Previous research (Miller et al. 2000) shows that the usage of aluminum in
automotive applications has grown more than 80% in the past 5 years. The usage of
aluminum is predicted to be used in hoods, trunk lids and doors hanging on a steel
frame.
Among the characteristics of aluminum alloys that make it suitable for a
variety of automotive applications are (Source: www.autoaluminum.org):
(a) Strong: the entire vehicle body can be aluminum
(b) Durable: good resistance to corrosion and fatigue
(c) Conductive: both thermal and electrical-for efficient engine and electrical
components
(d) Nonmagnetic: useful in electronics
(e) Nontoxic: important in any material used in cars
(f) Abundant: adequate supply worldwide
(g) Recyclable: saves energy, benefits the environment
5
(h) Workable: uses well understood metalworking process
(i) Available: aluminum’s many product forms offer design flexibility
Table 2.1 below is the applications of several types of aluminum alloys:
Table 2.1: Applications of Aluminum Alloys
(Source: www.autoaluminum.org)
Types/Designations
Applications
1100
Trim, nameplates, appliqués
2008
Outer and inner body panels
(also suitable for structural
applications)
3004
Interior panels and components
4004
Cladding for brazing sheet
5052
Interior panels and components,
truck bumpers and
body panels
6010
Outer and inner body panels,
seat shells and tracks
7003
Seat tracks, bumper reinforcements
6
2.1.1
Types of Aluminum Alloys
There are two types of aluminum alloys available in industries and can be
identified according to their designations. Those types are:
2.1.1.1
Wrought Aluminum Alloys
Wrought aluminum alloys are used in the shaping processes such rolling,
shaping, extrusion, pressing and stamping. The examples of wrought products are
rolled plate (>6 mm thickness), sheet (0.15 mm- 6 mm), foil (