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ITMA 2016 16 T.pdfPOST-WELD HEAT TREATMENT
POST-WELD HEAT TREATMENT
FIROUZ FADAEIFARD
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfillment of the Requirements for the Degree of Doctor of Philosophy
December 2016
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COPYRIGHT
All materials contained within the thesis, including without limitation text, logos, icons, photographs, and all other works, is copyright material of universiti Putra Malaysia, otherwise stated. Use may be made of any material contained within the thesis for non- commercial purposes from the copyright holder. Commercial use of material may only on be made with the express, prior, written permission of Universiti Putra Malaysia.
Copyright© Universiti Putra Malaysia
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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirement for the degree of Doctor of Philosophy
MECHANICAL CHARACTERIZATION OF AA6061-T6 ALUMINUM ALLOY FRICTION STIR AND TUNGSTEN ARC WELDED WITH AND WITHOUT
POST-WELD HEAT TREATMENT
Chairman: Associate Prof. Khamirul Amin Matori, PhD Faculty : Institute of Advanced Technology
Friction stir welding (FSW) process is a solid-state method in which is accepted as a favorable joining method for aluminum alloys and other engineering materials. The joining of metal plates in FSW is done at below their melting point temperature and based on a thermo-mechanical action used by a non-consumable welding tool onto metal plates. Despite the fast development in solid state welding, fusing welding such as Tungsten Inert Gas welding (TIG) is still vastly applied for thick joint design. Furthermore, solid state joining such as FSW is not applicable for positions such as overhead, horizontal and vertical. On the other hand, aluminum alloys have been increasingly applied in different industries, therefore, several research works on the manufacturing processes of these alloys have been developed over the time such as joining (welding) processes. The 6061-T6 aluminum alloy is an Al-Mg-Si precipitation hardening alloy from the 6XXX series which is often employed because it presents relatively good mechanical properties in relation to its light weight. Since the microstructure of 6061-T6 aluminium alloy and chemistry as well as dimension and distribution of the intermetallic particles in the matrix of aluminium alloy may be changed owing to heat generated and severe plastic deformation during the welding process. Accordingly, mechanical properties of weldments can be changed after welding as opposed to the base metal. However, the vast part of these changing can be recovered by doing post weld heat treatment (PWHT).
Butt joints of 6061-T6 aluminum alloy were produced by FSW, and the influence of process parameters on their welds quality of weldments in terms of welding defects, microstructure, hardness distribution, and tensile properties by applying the shoulder angle and welding speed in the range of 0-10° and 63-110 mm/min, respectively, have been investigated using NDT, optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive x-ray (EDX) facilities, XRD, Electron backscatter diffraction (EBSD) and mechanical test such as microhardness test and the tensile test on the welded joints, as the first and second objective. The welding results obtained shown that among all the welding conditions, two welding parameters which is 10°– 89 mm/min and 10°-110 mm/min showed the highest tensile properties (184 MPa for UTS) and higher hardness. Consequently, one of them selected to perform post weld heat treatment (PWHT). In additional to above mentioned characterization, nanoindentation
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test was done to find local mechanical and nanomechanical properties in as-weld and PWHT of selected sample (as stated in third objective). The majority of properties were closed to the base metal condition by performing PWHT.
The TIG welding process was performed on 60061-T6 aluminum alloy using ER5356 filler. All above mentioned characterization was performed to find mechanical and nanomechanical properties in as-weld and PWHT conditions. PWHT led to microstructural recovery of the Heat Affected Zone (HAZ) in addition to the appearance of β-phase (Al3Mg2) in the grain boundaries of weld zone. The ultimate tensile stress was improved to 204 MPa, even though the improvement in FSW sample (after PWHT) was better with almost 300 MPa.
Final comparison between the effect of these two process on mechanical, metallurgical and nanomechanical properties of 6061-T6 aluminum alloy as well as the effect of PWHT in the properties studied shows better mechanical, metallurgical and metallurgical properties.
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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Doktor Falsafah
PENCIRIAN MEKANIKAL BAGI AA6061-T6 ALUMINIUM ALOI KIMPALAN KACAU GESERAN DAN TUNGSTEN ARKA DENGAN DAN
TANPA RAWATAN HABA SELEPAS KIMPALAN
Oleh
Pengerusi: Prof. Madya Khamirul Amin Matori, PhD Fakulti: Institute Teknologi Maju
Proses kimpalan kacau geseran (FSW) adalah satu kaedah keadaan pepejal yang diterima sebagai satu kaedah yang baik untuk kaedah penyambungan bagi aluminium aloi dan bahan-bahan kejuruteraan yang lain. Penyambungan plat logam menggunakan FSW dilakukan di bawah suhu takat lebur dan berdasarkan tindakan mekanikal-haba yang dihasilkan oleh alat kimpalan ke atas plat logam. Walaupun pembangunan yang pesat dalam kimpalan keadaan pepejal, kimpalan leburan seperti kimpalan Tungsten Gas Lengai (TIG) masih banyak digunakan bagi penyambungan bereka-bentuk tebal. Tambahan pula, penyambungan keadaan pepejal seperti FSW tidak boleh digunakan untuk kedudukan seperti hujung, mendatar dan menegak. Sebaliknya, aluminium aloi semakin digunakan dalam industri yang berbeza, oleh itu, beberapa kerja penyelidikan mengenai proses pembuatan aloi ini telah dibangunkan dari masa ke masa seperti proses penyambungan (pengimpalan). Aluminium aloi 6061-T6 adalah aloi pemendakan pengerasan bagi Al-Mg-Si dari siri 6XXX yang sering digunakan, kerana ia mempunyai sifat-sifat mekanik yang baik jika dibandingkan dengan beratnya yang ringan. Disebabkan mikrostruktur 6061-T6 aluminium aloi dan sifat kimianya, serta dimensi dan pengagihan zarah antara-logam dalam matriks aluminium aloi boleh diubah kerana haba yang dihasilkan dan ubah bentuk plastik yang besar semasa proses kimpalan berlaku. Oleh itu, sifat-sifat mekanikal hasil kimpalan boleh diubah selepas kimpalan dibandingkan dengan logam asal. Walau bagaimanapun, sebahagian besar perubahan ini boleh diperolehi semula dengan melakukan rawatan haba selepas kimpalan (PWHT).
Penyambungan bahagian hujung 6061-T6 aluminium aloi telah dihasilkan menggunakan FSW, dan pengaruh proses parameter kepada kualiti kimpalan bagi hasil kimpalan dari segi kecacatan kimpalan, mikrostruktur, taburan kekerasan, dan sifat-sifat tegangan terhadap sudut bahu dan kelajuan kimpalan masing-masing dalam julat 0-10° dan 63- 110 mm/min telah dikaji dengan menggunakan NDT, mikroskop optik, imbasan mikroskop elektron (SEM) yang dilengkapi dengan kemudahan tenaga serakan x-ray (EDX), XRD, pembelauan pancaran balik elektron (EBSD) dan ujian mekanikal seperti ujian kekerasan-mikro dan ujian tegangan pada sambungan kimpalan, seperti yang dinyatakan dalam objektif pertama dan kedua. Hasil kimpalan yang diperolehi menunjukkan bahawa di antara semua keadaan kimpalan, dua parameter kimpalan iaitu
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10°-89 mm/min dan 10°-110 mm/min menunjukkan sifat tegangan yang paling tinggi (184 MPa untuk UTS) serta kekerasan yang lebih tinggi. Oleh itu, salah satu parameter telah dipilih untuk dilakukan proses rawatan haba selepas kimpalan (PWHT). Tambahan kepada pencirian yang dinyatakan di atas, ujian nano-indentasi telah dilakukan untuk mencari sifat-sifat mekanik dan nano-mekanikal setempat dalam sampel kimpalan dan PWHT yang dipilih (seperti yang dinyatakan di objektif ketiga). Majoriti ciri-ciri yang diperolehi adalah hampir kepada keadaan logam asal selepas PWHT dilakukan.
Proses kimpalan TIG telah dilakukan ke atas aluminium aloi 60061-T6 dengan menggunakan pengisi ER5356. Semua pencirian yang disebut di atas telah dilakukan untuk mencari sifat-sifat mekanik dan nano-mekanikal dalam kimpalan dan keadaan PWHT. PWHT menunjukkan kepada pemulihan mikrostruktur di zon yang terjejas haba (HAZ) sebagai tambahan kepada kemunculan β-fasa (Al3Mg2) di sempadan butiran bagi zon kimpalan. Tegasan tegangan muktamad telah meningkat kepada 204 MPa, walaupun peningkatan di dalam sampel FSW (selepas PWHT) lebih baik dengan hampir 300 MPa. Perbandingan akhir kesan di antara kedua-dua proses pada sifat-sifat mekanik, pelogaman dan nano-mekanikal 6061-T6 aluminium aloi serta kesan PWHT dalam sifat- sifat yang dikaji menunjukkan sifat mekanikal, pelogaman dan nono-mekanikal lebih baik.
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ACKNOWLEDGEMENTS
I would like to express my gratitude and sincere respect to my supervisor Associate Prof. Dr. Khamirul Amin Matori for his guidance and support throughout my research.
I would also like to thank my co-supervisors Professor Dr. Sidek Abd Aziz, and Professor. Dr. Mohd Khairol Anuar b. Mohd Ariffin for providing useful suggestions for the completion of this research.
I would like to thank Professor Dr. Didier Chicot for his valuable support.
I would like to give my sincere thankfulness to my wife (Farzaneh) and my children (Amir Masoud and Amir Behnoud) for their patient and support.
Special thanks to my friend Ahmad Masoumzadeh for his valuable supports.
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I certify that an Examination Committee met on 4 December 2016 to conduct the final examination of Firouz Fadaeifard on his thesis entitled “Mechanical Characterization of A6061-T6 Aluminum Alloy Friction Stir and Tungsten Arc Welded with and without Post-Weld Heat Treatment” in accordance with the Universities and University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U. (A) 106] 15 march 1998. The Committee recommends that the student be awarded the Doctor of Philosophy.
Member of the Thesis Examination Committee were as follows:
Mohd Nizar Hamidon, PhD Associate professor Faculty of Enginnering Universiti Putra Malaysia (Chairman)
Shamsuddin bin Sulaiman , PhD Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)
Faizal bin Mustapha, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)
Ali Hussein Ataiwi Al Omairy, PhD Professor Materials Engineering Department Kufa University Iraq (External Examiner)
NOR AINI AB. SHUKOR, PhD Professor and Deputy Dean
School of Graduate Studies Universiti Putra Malaysia
Date: 28 February 2017
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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirements for the degree of Doctor of Philosophy. The members of the Supervisory Committee were as follows:
Khamirul Amin Matori , PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman)
Sidek Abd Aziz , PhD Professor
Faculty of Science Universiti Putra Malaysia (Member)
Mohd Khairol Anuar b. Mohd Ariffin , PhD Professor, Ir
Faculty of Engineering Universiti Putra Malaysia (Member)
ROBIAH BINTI YUNUS, PhD Professor and Dean
School of Graduate Studies Universiti Putra Malaysia
Date:
Declaration by Graduate Student
I hereby confirm that: this thesis is my original work; quotations, illustrations and citations have been duly referenced; this thesis has not been submitted previously or concurrently for any other degree at
any other institutions; intellectual property from the thesis and copyright of thesis are fully-owned by
Universiti Putra Malaysia, as according to the Universiti Putra Malaysia (Research) Rules 2012;
written permission must be obtained from supervisor and the office of Deputy Vice- Chancellor (Research and Innovation) before thesis is published (in the form of written, printed or in electronic form) including books, journals, modules, proceedings, popular writings, seminar papers, manuscripts, posters, reports, lecture notes, learning modules or any other materials as stated in the Universiti Putra Malaysia (Research) Rules 2012;
There is no plagiarism or data falsification/fabrication in the thesis, and scholarly integrity is upheld as according to the Universiti Putra Malaysia (Graduate Studies) Rules 2003 (Revision 2012-2013) and the Universiti Putra Malaysia (Research) Rules 2012. The thesis has undergone plagiarism detection software.
Signature: ------------------------------------------------ Date: --------------------------------
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Declaration by Members of Supervisory Committee
This is to confirm that: the research conducted and the writing of this thesis was under our supervision; Supervision responsibilities as stated in the Universiti Putra Malaysia (Graduate
Studies) Rules 2003 (Revision 2012-2013) are adhered to.
Signature: Name of Chairman of Supervisory Committee: Associate Prof. Dr. Khamirul Amin Matori
Signature: Name of Member of Supervisory Committee: Professor Dr. Sidek Abd Aziz
Signature: Name of Member of Supervisory Committee: Professor Dr. Mohd Khairol Anuar b. Mohd
Ariffin
TABLE OF CONTENTS
Page ABSTRACT i ABSTRAK iii ACKNOWLEDGEMENT iv APPROVAL vi DECLARATION vii LIST OF TABLES xiii LIST OF FIGURES xiv LIST OF ABBREVIATIONS xix
CHAPTER 1 INTRODUCTION 1
1.1 Background 1 1.2 problem statement 1 1.3 Objectives 3 1.4 Research Scope and Significance 3 1.5 Thesis Layout 4
2 LITERATURE REVIEW 5 2.1 Aluminum and Its Alloys: An Overview 5
2.1.1 Introduction 5 2.1.2 Alloy Designation System 5 2.1.3 Temper Designation System 6 2.1.4 Microstructural and Metallurgical Properties 6 2.1.5 Effect of Alloy Elements 9 2.1.6 Weldability of Aluminum Alloys 10 2.1.7 AA6061 Aluminum Alloys 10
2.2 Friction Stir Welding (FSW) 16 2.2.1 Background 16 2.2.2 Principle of Operation 18 2.2.3 Friction Stir Welding parameters and related Variables 19 2.2.4 Tool 24
2.2.4.1 Shoulder (diameter and surface) 25 2.2.4.2 Pin (probe) geometry 28
2.2.5 Welding speed 31 2.2.6 Post weld heat treatment (PWHT) 31 2.2.7 Flaws and Failures in FSW 31
2.3 TIG welding of aluminium alloys 33 2.4 A comparison; TIG and FSW 35 2.5 Indentation 38
2.5.1 Background 38 2.5.2 Origin of indentation for measuring the hardness 39 2.5.3 Comparison of techniques and born of different
indenters and methods 41
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2.5.8 Pile up and Sink in (Swell) 51 2.5.9 Nanoindentation in welding joints 53
2.6 Summary 55
3 METHODOLOGY 56 3.1 Introduction 56 3.2 Material Selection 58 3.3 Welding Preparation for FSW samples 58
3.3.1 Plate Preparation 58 3.3.2 FSW Machine and Clamping System 59 3.3.3 Welding Tool Preparation 61 3.3.4 Selection of Welding Conditions 63
3.4 Welding Preparation for TIG samples 64 3.5 Post Weld Heat Treatment (PWHT) 65 3.6 Inspection and Non-Destructive Test (NDT) 66 3.7 Macro- Structure Evaluation 66
3.7.1 Sample Preparation 66 3.8 Micro- Structure Evaluation 67
3.8.1 Sample Preparation for Optical Microscopy, SEM and FESEM
67
3.8.2 Sample Preparation for EBSD 67 3.8.3 Grain Size Measurements 67
3.9 Mechanical Properties Evaluation 68 3.9.1 Micro-Hardness Testing 68 3.9.2 Tensile Testing 69 3.6.3 Fracture Behavior Evaluation of Weldments 70
3.10 XRD 70 3.11 Nanoindentation 70
3.11.1 Equipment 70 3.11.2 Method 71
4 RESULT AND DISCUSSION 73 4.1 Friction Stir Welding (FSW) 73
4.1.1 Non-destructive Inspection 73 4.1.2 Macrostructure study 76 4.1.3 Microstructure evaluation 83 4.1.4 Precipitations 95 4.1.5 Hardness Evaluation 99 4.1.6 Tensile properties and fractography 101 4.1.7 The highlights of FSW of AA6061-T6 in different welding speeds and different shoulder angles
105
4.2 PWHT of FSW sample 106 4.2.1 Macro and Microstructure analysis 106 4.2.2 Tensile test and fractography 112 4.2.3 Indentation: Hardness and elastic modulus 115 4.2.4 The highlights of PWHT of FSW 121
4.3 TIG welding (as-weld and PWHT) 122 4.3.1 Macrostructure 122 4.3.2 Microhardness 123 4.3.3 Microstructure study 125 4.3.4 Tensile test and fractography 131
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4.3.5 Nanoindentation 133 4.3.6 The highlights of TIG welding in as-weld and PWHT 138
5 CONCLUSIONS AND RECOMMENDATIONS 139 5.1 Friction stir welding of 6061-T6 aluminum alloy 139 5.2 PWHT of FSW join of 6061-T6 aluminum alloy 139 5.3 TIG welding of 6061-T6 (as-weld and PWHT) 140 5.4 Comparison of FSW and TIG welding of AA6061-T6 141 5.5 Recommendations and Future Study 141
REFERENCES 142 APPENDICES 158 BIO DATA OF STUDENT 164 LIST OF PUBLICATIONS 165
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[5]. 7
11
2.4 Overview over some selected temper designations [47]. 12 2.5 Properties of AA6XXX alloys in annealed condition [51]. 15 2.6 Properties of AA6XXX alloys in T6 condition [51]. 15 2.7 Applications of AA6XXX Aluminum Alloys [54]. 16 2.8 Mechanical properties of investigated materials [113]. 36 3.1 Nominal composition of parent alloy used in the welding test. 58 3.2 Mechanical properties of the 6061-T6 aluminum alloy. 58 3.3 Summary of material types and workpiece dimensions. 58 3.4 Summary of dimensions of the tools used in FSW experiments. 61 3.5 Process Parameters for fabricating FSW joints at constant
rotation speed (1480rpm). 64
3.6 Chemical composition of the filler metal (wt.%). 64 4.1 γ and β deviations for different welds. 78 4.2 Grain size of NZs and HAZs. 90 4.3 Average hardness of NZs and HAZs. 100 4.4 Mechanical properties obtained by tensile tests for machined
(RS-LHZ) and As-weld (Kissing bond). 102
4.5 Mechanical properties obtained by tensile tests. 103 4.6 Average grain size in the different zones of weld joint in as-
weld and PWHT samples. 111
4.7 Mechanical properties obtained by tensile tests. 113 4.8 The results of tensile tests. 131
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LIST OF FIGURES
Figure Page 2.1 Equilibrium Binary Solid Solubility As A Function of
Temperature For Alloying Elements Most Frequently Added to Aluminium [3].
8
2.2 Phase Diagram of A Hypothetical Alloy System Showing the Β Solvus And GP Zone Solvus. For Composition (A). ΔT1 is the Temperature Range for Solution Heat Treatment, and ΔT2
is the Temperature Range for Precipitation Heat Treatment [5].
8
2.3 Contributions from dissolved alloying elements in solid solution (A) and particles from precipitation hardening (B, C)[48].
13
2.4 Effect of artificial ageing and naturally ageing on the strength evolution in Al/Mg/Si alloys. Naturally ageing only allows GP-zones to form [50].
14
2.5 Friction Stir Weld in the butt configuration with important Friction Stir Welding terminology identified [62].
18
2.6 Schematic of a typical FSW Cross-Section (A) Parent Material.(B) Heat Affected Zone. (C) Thermal Mechanically Affected Zone. (D) Weld Nugget [13].
19
2.7 Metal flow zone developed during friction stir joining [83]. 24 2.8 Material flow during FSW a) horizontal b) vertical [86]. 25 2.9 The effect of shoulder diameter to the peak temperature [88]. 26
2.10 Different shoulder features a) scrolled b) knurled c) ridged d) grooved e) concentric circle [87].
27
2.11 A cross section of a concave shoulder. 27 2.12 Changing in temperature distribution influenced by shoulder
angle [90]. Temperature distribution at t = 2.7 s: a) α = 0° , b) α = 2° , c) α = 4° , d) α = 6°.
28
2.13 Cylindrical tool design [82, 84]. 29 2.14 Basic variants on the Whorl™ type probes [86]. 29 2.15 Triflute™ tool with frustum shaped probe with three flutes
[86]. 29
2.16 Schematic diagrams of tool pin-tip profiles: a-thread taper, b- triangular, c-square, d-three grooves, and e-conical platform [92].
30
2.17 Cross section of weld zone (appearance of wormhole in advancing side like void) [93].
31
2.18 Metallographic analysis of the weld zones and size evaluation of a kissing bond (KB). (a) Overview image of a weld nugget with adjacent zones. (b) Detail of the large KB flaw with a clear zig-zag shape revealed by etching in AA7475 [95].
32
2.19 Schematic diagram of Newton’s cradle arrangement used by Hodgkinson in the 1830s to investigate relative dynamic hardness of range of materials [121].
38
2.20 Indentation machine developed by Calvert and Johnson in 1850s [124].
39
xv
2.21 Schematic diagram of Middelberg’s knife indentation. technique for studying hardness of railway tyres [125].
40
2.22 Indentation hardness machine reported by Unwin in 1896 [126].
40
2.23 Schematic drawing of Knoop indentation [139]. 42 2.24 Comparison of Knoop (leftmost), Vickers (middle) and Brinell
(rightmost) indentations [139]. 43
43
2.26 Diagrams of two diamond indenters, Vickers and Knoop [143].
45
2.27 Schematic Diagrams of nanoindentation [150]. 46 2.28 (a) A typical load–displacement curve and (b) the deformation
pattern of an elastic –plastic sample during and after indentation [152].
47
2.29 SEM images of the tips of (a) Berkovich, (b) Knoop, and (c) cube-corner indenters used for nanoindentation testing. The tip radius of a typical diamond pyramidal indenter is in the order of 100 nm [152].
49
2.30 Indentation parameters for (a) Spherical, (b) Conical, (c) Vickers, and (d) Berkovich indenters (not to scale) [152].
49
2.31 AFM image of the plastic impressions [155] remaining in the BCB material after indentation (height scale is 0 to 20 nm from black to white) [155].
50
2.32 Matlab-mesh surface plot of 40 mN indent in 750 nm Cu film [156].
51
52
3.1 Methodology flow chart. 57 3.2 A vertical milling machine used for FSW experiments. 59 3.3 Schematic of joint configuration utilized in this research. 60 3.4 The real shape of fixture (clamping) used to restrain the plates
during FSW. 60
3.5 The real shape of welding tool designed in this work. 62 3.6 Shoulder of…