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Singh, Ripandeep: Characterization of microstructure and mechanical properties of
AL6063 using FSP Multipass, Hamburg, Anchor Academic Publishing 2017
PDF-eBook-ISBN: 978-3-96067-711-6
Druck/Herstellung: Anchor Academic Publishing, Hamburg, 2017
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© Anchor Academic Publishing, Imprint der Diplomica Verlag GmbH
Hermannstal 119k, 22119 Hamburg
http://www.diplomica-verlag.de, Hamburg 2017
Printed in Germany
ABSTRACT
Need for low weight and high performance structural materials have revolutionized the
technology and had led to the emergence of new processes and methodologies. Frictions stir
processing (FSP), based on principle of friction stir welding, is an emerging solid state metal
working process. This technique causes intense plastic deformation and high strain rates in
the processed material resulting in precise control of the microstructure through material
mixing and densification. FSP process has been successfully used for achieving significant
grain refinement and enhancement of surface properties.
Present work is focused on the study of behavior of Aluminium cast alloy (Al-6063) with
processed by friction stir processing technique. Samples of FSPed aluminium were examined
and their microstructures, microhardness, Rockwell hardnesss, impact strength were studied
and compared with base metal Al-6063.
Hardness tester is employed to evaluate the interfacial bonding between the particles and
matrix by indenting the hardness with the constant load and constant time. Impact test is
employed to know the Impact Strength of samples against the Impact of Hammer.
CONTENTS
Chapter 1 Introduction
1
1.1 Friction Stir Processing
1
1.2 FSP Parameters
13
1.2.1
Tool Geometry
13
1.2.2
Processing Parameters
14
1.2.3
Tool Tilt Angle
14
1.3 Process Modelling
15
1.3.1
Metal Flow
15
1.3.2
Temperature Distribution
15
1.4 Microstructural evolution
16
1.4.1
Nugget Zone
16
1.4.2
Thermo-mechanically affected zone
18
1.4.3
Heat-affected zone
19
1.5 Applications of FSP
19
1.5.1
Superplasticity
19
1.5.2
Surface composites
19
1.5.3
Microstructural Modification
20
1.6 Need For Present Study
21
1.7 Chapter Scheme
22
Chapter 2 Literature Review
23
2.1 Review of related literature
23
2.2 Summary of related literature
36
2.3 Research gaps
37
2.4 Objective of study
37
2.5 Methodology
37
Chapter 3 Experimentation
38
3.1 Sample Preparation
38
3.1.1 Application of AL6063
39
3.1.2 Fabrication of AL6063
39
3.1.3 Supplied Forms
39
3.1.4 Properties of Aluminium AL6063
40
3.1.5 Welding of 6063 Aluminium
41
3.2 FSP Setup
41
3.2.1 Tool Geometry
42
3.2.2 Tool Specifications
42
3.2.3 CNC Vertical milling machine
42
3.2.4 Fixture
44
3.2.5 Machining Parameters
45
3.2.6 Different results after experimentation
45
3.3 Characterization and Testing
46
3.3.1 Microstructural Examination
46
3.3.2 Microhardness Measurement
48
3.3.3 Izod Impact test
49
3.3.4 Rockwell hardness test
51
Chapter 4 Results and Discussions
53
4.1 Evaluation of Mechanical Properties
53
4.1.1 Microhardness Evaluation
53
4.1.2 Rockwell hardness test
55
4.1.3 Optical Microscopy
56
4.1.4 Izod Impact result
57
Chapter 5 Conclusions and Recommendations
59
5.1 Scope for Future Work
59
References
60
LIST OF FIGURES
Figure no.
Title.
Page no.
1.1
A FSP Process
1
1.2
A FSP Machine
2
1.3
A Robotic FSP Machine
3
1.4
FSP Tool Movement
5
1.5
Impression Formed by Tool on Work piece
6
1.6
Travelling and Rotational Movement of Pin
7
1.7
The Different Tool Profiles
7
1.8
Experimental Setup
10
1.9
FSP Setup
12
1.10
FSP Laminate
13
1.11
Schematic Drawing of FSP Tool
14
1.12
Various Microstructural Zones in FSP
16
1.13
Effect of Processing Parameters on Nugget Shape
17
1.14
Microstructure of Thermo mechanically Effected Zone in FSP
18
3.1
Aluminium Alloy AL6063 Sample
40
3.2
FSP Tool
41
3.3
CNC Vertical Milling Machine
42
3.4
Fixture used for Holding the Specimen
44
3.5
Shows the used Tool
45
3.6
Experimental Parameters
45
3.7
Sample Impressions After Conducting FSP
46
3.8
Inverted Optical Microscope
47
3.9
Mounted Specimen
47
3.10
Buffing Machine
48
3.11
Microhardness Tester
49
3.12
Impact Testing Machine
49
3.13
Different Results After Impact Test
50
3.14
Rockwell Test Indenter
51
3.15
Rockwell Hardness Tester
51
3.16
Hardness Tester Specifications
52
3.17
Hardness Tested Sample
52
4.1
Graph Showing Microhardness Results
54
4.2
Graph Showing Rockwell Hardness
55
4.3
Microstructure of Samples after different passes
56
4.4
Graph Comparison Between Impact Strength
58
LIST OF TABLES
Table no.
Title.
Page no.
1.1
A summary of grain size in nugget zone
18
2.1
Summary of related literature
36
3.1
Physical composition of Al6063
38
3.2
Tempers of Al6063
40
3.3
Physical properties of AL6063
40
3.4
Specification of tool
42
3.5
Specification of CNC machine
43
CHAPTER 1
INTRODUCTION
1.1 Friction Stir Processing
FSP is manufacturing the Technique used to modify the microstructure metals. In this process
a rotating tool is penetrated in the work piece and moved in the transverse direction.
Further FSP technique is used for fabrication of surface composite on aluminium substrate
and homogenization of powder metallurgy aluminium alloy, metal matrix composites, and
the cast aluminium alloys. By this process material properties can be improved due to
enhancement of grain structure. With this technique the material have shown good corrosion
resistance, high strength and high fatigue resistance.
Fig 1.1 A FSP process (
http://en.wikipedia.org/wiki/Friction_stir_processing)
Friction stir processing is a method of changing the properties of a metal through intense,
localized deformation. This deformation is produced by forcibly inserting a non-consumable
tool into the workpiece, and revolving the tool in a stirring motion as it is pushed laterally
through the workpiece. The precursor of this technique, friction stir welding, is used to join
multiple pieces of metal without creating the heat effected zone typical of fusion
welding.When ideally implemented, this process mixes the material without changing the
phase and creates a microstructure with fine, equixed grains. This homogeneous grain
structure, separated by high-angle boundaries, allows some aluminium alloys to take on
superplastic properties. Friction stir processing also enhances the tensile strength and fatigue
strength of the metal. In tests with actively cooled magnesium-alloy work pieces, the
microhardness was almost tripled in the area of the friction stir processed seam.
(http://en.wikipedia.org/wiki/Friction stir processing)
1
It is widely used in aerospace industries and used in automobile industry for making body
panels, for cycle frames and other components, these alloys are used for boat building and
shipbuilding, It is used for architectural fabrication, particularly window frames, door frames,
roofs, and sign frames. Furthermore, the FSP technique has been used for the fabrication of a
surface composite on aluminium substrate and the homogenization of powder metallurgy
(PM) aluminium alloys, metal matrix composites, and cast aluminium alloys. Compared to
other metalworking techniques, FSP has distinct advantage
Fig 1.2 A FSP Machine
3 axis (Mishra et al., 2005)
Friction Stir Welding (FSW) is being targeted by modern industries for structurally
demanding applications providing high-performance benefits. FSW has been shown to
2
strongly decrease severe distortion and residual stresses compared to the traditional welding
processes. The Frictioned zone consists of a weld nugget, a thermo-mechanically affected
zone and a heat affected zone. The process results in obtaining a very fine and equiaxed grain
structure in the weld nugget causing a higher mechanical strength and ductility. Jata and
Semiatin showed that the microstructure in the weld nugget zone evolves through a
continuous dynamical recrystallization process, the strong grain refinement produced by the
process leads the microstructure to the fine dimensions offering the possibility to exhibit
superplastic
properties.
Fig 1.3 A Robotic FSP Machine
6 axis (Mishra et al., 2005)
3
Such technology requires a thorough understanding of the process and consequent
mechanical properties of the heavily deformed material in order to be used in the production
of components for aerospace applications and for this reason detailed research and
qualification work is required. In the FSP, a rotating tool with a specially designed rotating
probe travels down the surfaces of metal plates, and produces a highly plastically deformed
zone through the associated stirring action. The localized thermo-mechanical effected zone is
produced by friction between the tool shoulder and the plate top surface, as well as plastic
deformation of the material in contact with the tool. The probe is typically slightly shorter
than the thickness of the work piece and its diameter is typically the thickness of the work
piece. The FSP process is a solid state process and therefore a solidification structure is
absent and the problem related to the presence of brittle inter-dendritic and eutectic phases is
eliminated. In addition the strong grain refinement and the possibility to obtain a uniform
microstructure has lead researchers to investigate the possibility to employ such a process to
increase the superplastic properties of some aluminium alloys. In FSP the work piece does
not reach the melting point and the mechanical properties of the material are much higher
compared to the traditional techniques, in fact, the undesirable microstructure resulting from
melting and re-solidification, characterized by low mechanical properties, is absent leading to
improved mechanical properties such as ductility and strength in some alloys. (Cavaliere
et
al., 2005)
Friction stir processing (FSP) is a unique technique for refining and modifying the
microstructure of materials. In many aspects, the basic principles of FSP are the same as
those of FSW. Besides, FSP has been successfully used for fabricating the surface
composites, for refining the surface microstructures of various materials
as well as for
synthesizing the composite and intermetallic compounds.
Friction stir processing is based on the friction stir welding (FSW) technique which was
invented by The Welding Institute (TWI) in 1991. On observing the advantages associated
with FSW, mainly grain refinement, the phenomenon has been extended to processing of
commercial alloys. Friction stir processing (FSP) is a solid-state process in which a specially
designed rotating cylindrical tool, consisting of a pin and a shoulder, is plunged into the
sheet. The tool is then traversed in the desired direction. The rubbing of the rotating shoulder
generates heat which softens the material (below the melting temperature of the sheet) and
with the mechanical stirring caused by the pin, the material within the processed zone
4
undergoes intense plastic deformation yielding a dynamically recrystallized fine grain
structure. Despite the large number of studies that are being conducted to advance FSP
technology, the effects of FSP on various mechanical and microstructural properties are still
in need for further investigations. In addition, correlations between FSP parameters,
mechanical properties and microstructural characteristics are not yet well understood.
Accurate correlations are needed for successful modeling and process optimization. Most of
the work that has been done in the field of friction stir processing focuses on aluminium
alloys. (Darras
et al., 2007)
Friction stir processing (FSP), developed based on the basic principles of friction stir welding
(FSW), a solid-state joining process originally developed for aluminium alloys, is an
emerging metal working technique that can provide localized modification and control of
microstructures in near-surface layers of processed metallic components. The FSP causes
intense plastic deformation, material mixing, and thermal exposure, resulting in significant
microstructural refinement, densification, and homogeneity of the processed zone. The FSP
technique has been successfully used for producing the fine-grained structure and surface
composite, modifying the microstructure of materials, and synthesizing the composite and
intermetallic compound in situ. In this review article, the current state of the understanding
and development of FSP is addressed. (Ma
et al., 2008)
Fig 1.4 FSP Tool movement
Friction stir welding (FSW) is a relatively new solid state joining process. It requires no local
melting in order to join pieces together. This joining technique is energy efficient,
environment friendly, and versatile. The basic concept of FSW is remarkably simple. A non-
consumable rotating tool with a specially designed pin and shoulder is inserted into the
5
abutting edges of sheets or plates to be joined and traversed along the line of joint. The tool
serves two primary functions: (a) heating of work piece, and (b) movement of material to
produce the joint. The heating is accomplished by friction between the tool and the work
piece and plastic deformation of work piece. During FSW process, the material undergoes
intense plastic deformation at elevated temperature, resulting in generation of fine and
equiaxed recrystallized grains. The fine microstructure in friction stir welds produces good
mechanical properties. Recently friction stir processing (FSP) was developed by Mishra and
Mahoney as a generic tool for microstructural modification based on the basic principles of
FSW. In this case, a rotating tool is inserted in a monolithic work piece which provides
frictional heating and mechanical mixing in the area covered by the tool. The large
processing strain involved, resulted in microstructural refinement and homogenization. FSP
has developed into a broad field covering microforming, casting modification, powder
processing. Another area in which FSP shows a lot of promise is in the creation of
superplastic materials. FSP creates
a region called the ``stir zone" (SZ) or ``nugget", where
the microstructural refinement occurs with equiaxed ultra-fine grains with high angle grain
boundaries. The resultant microstructure in the nugget region can present the ideal conditions
for superplasticity in some materials. (Ehab
et al., 2010)
FSP is a solid state processing based on friction stir welding (FSW). FSW is innovation of
The Welding Institute (TWI) of UK in 1991. FSP is defined as a severe plastic deformation
technique used in order to improve surface properties. Fine microstructure and absence of
casting defects are the main advantages of FSP. During FSP, rotational tool (non-
consumable) with a specially designed pin and shoulder is plunged into the plate and
traversed in desired direction. (Akramifard
et al., 2014)
Fig 1.5 Impression formed on workpiece after FSP mutipass
6
Multipass FSP can be performed in two ways, continuously or after cooldown of first pass.
multipass in which material was allowed to cool back down to room temperature and after
that second pass was employed and second method is all subsequent passes were employed
continuously without alloying the material to cool down.
Fig 1.6 Travelling and rotational movement of pin and fabrication of Cu/Sic
Friction stir welding (FSW) technique was first invented by The Welding Institute (TWI),
widely used in welding of aluminium, magnesium and copper alloys. This technique not only
being limited to welding, friction stir processing (FSP) has found various applications: grain
refinement of wrought and casting parts, super plasticity improvement, formation of
intermetallics and composite fabrication. FSP offers a low energy consumption route to
introduce reinforcing phases into the metal matrix and to form bulk composites. Grain
refinement is also enhanced by dynamic recrystallization and grain boundary pinning during
FSP.
Fig 1.7 shows the different FSP tool profiles (Elangovan
et al., 2008)
7
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