Journal of Alloys and Metallurgical Systems 2 (2023) 100010
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Journal of Alloys and Metallurgical Systems
journal homepage: www.journals.elsevier.com/journal-of-alloys-and-metallurgical-systems
Metallurgical and mechanical investigation on FSSWed dissimilar aluminum
alloy
K. Anton Savio Lewisea,
⁎,1
]]
]]
]]]]]]
, J. Edwin Raja Dhasb, R. Pandiyarajanc, S. Sabarishd
a
Department of Aerospace Engineering, Karunya Institute of Technology and Sciences, Coimbatore 641114, India
Department of Automobile Engineering, Noorul Islam Centre for Higher Education, Kumaracoil 629180, India
c
Department of Mechectronics Engineering, Agni College of Technology, Chennai 600130, India
d
Department of Mechanical Engineering, K.L.N. College of Engineering, Sivagangai 630612, India
b
A R T I C L E
I N F O
Keywords:
Aluminum alloys
Friction stir spot welding
AA2024-T3
AA7075-T6
Dissimilar joint
Microhardness
Fractography
A B S T R A C T
The present work is the novel examination of influence of welding process parameters and material flow on the
mechanical and microstructural characteristics during the FSSW of dissimilar AA2024/AA7075 joint were
evaluated and compared with similar AA2024/AA2024 and similar AA7075/AA7075 FSSW joints. The microstructural and physical properties of two aluminum alloy joined through friction stir spot welding (FSSW) were
examined. The aluminum alloys namely AA2024-T3 and AA7075-T6 were selected for the investigation owing to
their typical and potential applications in aeronautical industry. The input parameters were tool rotational
speed, plunge depth and dwell time (TRS 1800 rpm, 3.3 mm plunge depth and 45 s dwell time) were utilized.
The microstructure of the welded specimen was investigated by scanning electron microscope and their chemical
compositions were analyzed by energy-dispersive X-ray spectroscopy. The physical properties were investigated
by Vickers microhardness survey and the specimen strength evaluated by tensile tests. The experimental investigation revealed the influence of the tool pin penetration and frictional heat on the microstructure, distribution of the grain structure affecting the microhardness and the tensile properties of the dissimilar joint.
1. Introduction
Friction stir spot welding (FSSW) was a modified solid–state welding
process derived from friction stir welding (FSW). The process involved a
rotating tool with or without a protruding pin plunging into the weld
specimen plates that overlap each other [1,2]. The pin tool was plunged
to a predetermined depth for a set amount of dwell time and withdrawn
after leaving behind a characteristic keyhole. The frictional heat generated by the rotating tool at the region where the tool contacts the specimen surface, caused the flow of material in the stir zone [3]. The
welding input parameters such as tool geometry, tool rotation speed,
dwell time, axial force, plunge depth typically influenced the flow of the
material grains and distribution [4,5]. The flow of the material and resulting microstructure greatly influenced the possibilities of defects and
porosities. These defects typically were detrimental to the physical
properties and performance characteristics of the welded joint [6]. Several studies were carried out on the flow of material and respective
⁎
1
metallurgical behavior during FSW is described [7]. The available literature on flow of material and subsequent investigations on microstructural and physical properties of dissimilar FSSW aluminum alloy
joints was limited. The available studies presented many auxiliary insights in related approaches. The effect of FSSW process parameters of a
similar aluminum alloy joint was investigated by use of software analysis
in the weld zone [8]. The high compression force that followed the
stirring action of an FSW AND FSSW tool led to compression of the
materials in the stir zone and changes in the accumulated microstructure
[9]. The effects of FSSW on similar aluminum alloy AA7075-T6 plates
with two pin profiles were investigated to evaluate the damage the
welding tool could bear at varying input conditions [10]. The increasing
of sheet thickness at the joint region seemed to have positive effects on
the improving the fatigue life of the specimen and tool life. The effect of
refill FSSW on the aluminum alloy 5754-H22 and Ti6Al4V joint was
performed to evaluate the microstructural and mechanical properties
[11]. It was found that the refill FSSW was capable of effectively welding
Corresponding author.
E-mail address: kaslewise@gmail.com (K. Anton Savio Lewise).
https://orcid.org/0000-0003-2616-3599
https://doi.org/10.1016/j.jalmes.2023.100010
Received 2 February 2023; Received in revised form 24 April 2023; Accepted 4 May 2023
Available online 5 May 2023
2949-9178/© 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/
by-nc-nd/4.0/).
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Table 1
Material composition of aluminum alloys (weight percentage).
Aluminum alloy
Cu (%)
Zn (%)
Fe (%)
Mg (%)
Ti (%)
Mn (%)
Al (%)
AA2024-T3
AA7075-T6
4.9
1.6
0.142
5.6
0.239
0.5
1.28
2.5
0.0154
0.2
0.629
0.16
balance
balance
Table 2
Physical properties of aluminum alloys.
Aluminum alloy
Yield Strength (MPa)
Tensile Strength (MPa)
Elongation (%)
Microhardness (HV)
AA2024-T3
AA7075-T6
345
480
440
540
14
11
137
175
microstructure, physical properties and subsequent analysis on fracture
of the welded specimens were not clear. It is clear that there exists a
literature gap which investigate the relation between the microstructure, joint strength and weldig parameters such as tool rotational
speed, dwell time and tool plunge depth during welding of dissimilar
aluminium 2xxx and 7xxx series alloys. In the present work, the flow of
material, microstructure, physical properties and fractography were
studied for FSSW of dissimilar aluminum alloy AA2024-T3/AA7075-T6
joint. The upper and bottom plate interaction were studied. The experimental results were evaluated to comprehend the influences of
grain dispersion and fracture crack propagation during failure.
2. Materials and methods
Fig. 1. XRD analysis of aluminum alloys AA2024-T3 and AA7075-T6.
2.1. Materials
overlap joints under optimized input conditions [12]. Reduction in heat
input can lessen the creation of joint defects, and increasing tool rotation
speed and dwell duration can increase a dissimilar joint strength and
ductility [13]. Furthermore, the development of a defect-free connection
with good mechanical characteristics can result from the right tool rotation speed and welding temperature, and the intermetallic compound
formation at the joint interface has a significant impact on the joint
strength [14]. The production of a sound dissimilar joint with good
mechanical characteristics may also be achieved by optimising the tool
geometry and process parameters, and the joint strength is determined
by the grain structure and defect development in the joint [15]. It has
also been stated that the microstructure and mechanical characteristics
of the joint may be greatly influenced by the tool pin features, such as pin
shape and pin length, and that optimising the tool pin features can result
in the development of a high-quality joint [16]. The joint strength is
determined by the dissimilar joint's microstructure and defect generation, and thus increasing welding speed can reduce joint strength while
reducing welding speed can increase joint strength [17]. The nugget
diameter was found to decrease when the tool rotating speed was increased, while the joint's hardness and ultimate tensile strength increased. when compared to other welding techniques, the FSSW is capable of generating a more homogenous microstructure [18]. The
production of a strong dissimilar FSSW joint with good mechanical
qualities necessitates optimising the tool pin profile, which can have an
impact on the joint's microstructure and mechanical properties [19]. The
ultimate tensile strength and joint elongation have been observed to
increase with increasing tool rotating speed. The nugget diameter also
decreased and the area of the heat impacted zone increased as the tool
traverse and rotational speeds were increased [20]. It was discovered
that the number of FSSW weld passes had a substantial impact on the
microstructure and mechanical characteristics of joints made of different
aluminium, with more passes producing finer grains, a more homogenous microstructure, and stronger joints [21].
The existing literature studies dealt with material flow or analysis of
weld parameters of FSSW on weld joints. The analysis behind the
The present work investigates a friction stir spot welded joint of two
aluminum alloys AA2024-T3 and AA7075-T6. The microstructure of
aluminum alloy AA2024-T3 was multifarious resulting in its elevated
tolerance to cracks and fractures. This also led to increased microhardness levels but diminishes the weldability of the alloy. With copper
being the principal alloying element of this aluminum alloy, it was
widely used in the aircraft industry where their high strength is of great
value. Aluminum alloy AA7075 in the T6 temper possessed highest
strength among all the aluminum alloys making it extremely desirable
for aircraft structural applications and high strength bracing components in performance automotive applications. Zinc was the primary
alloying element of this aluminum alloy with other elements being
copper and magnesium. The material compositions of the base aluminum alloys were evaluated by spectrochemical analysis (Table 1).
The physical properties of these aluminum alloys were obtained from
existing literature (Table 2).
The microstructures of the aluminum alloys AA2024-T3 and
AA7075-T6 were investigated X-ray diffraction (XRD) analysis. The
XRD spectrometer used was X-Pert PRO by Panalytical systems with Cu
target with fixed tube. The XRD analysis showed three dominant peaks
for aluminum alloy AA2024-T3 at with the highest peak at 400 followed
by two small peaks at 66.70, and 79.70 respectively (Fig. 1).
The analysis presents a single peak observed at 400, for aluminum
alloy AA7075-T6. The chemical composition of the base AA2024-T3
and AA7075-T6 alloys were analyzed by spectrochemical analysis and
the highest composition elements of the alloys were analyzed for peak
intensities by XRD analysis. The JCPDS database was inferred to determine the composition substances based on the X-Ray diffraction
data. The variations of the microstructures were also exemplified by the
respective peaks seen in Fig. 1.
2.2. Friction stir spot welding (FSSW)
In the present study, the two-aluminum alloy AA2024-T3 and
AA7075-T6 were used to fabricate lap joints by FSSW as schematically
2
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Fig. 2. (a) Working schematic representation of FSSW process; (b) Experimental setup of FSW AND FSSW machine.
represented by Fig. 2(a). This was accomplished by customized vertical
milling machine with a specialized fixture designed to hold the working
specimens linearly. This modified machine was also capable of accommodating FSW (Fig. 2(b)). The friction stir spot weld was performed by a
pin tool fabricated from D3 tool steel known for its high abrasion resistance and superior dimensional properties. The tool possessed a pin
length of 2.5 mm with 3 mm diameter, while the tool shoulder had a
diameter of 10 mm. FSSW experimental trials were performed with varied
input process conditions such as tool rotational speed (800–2400 rpm),
plunge depth (3–3.6 mm) and dwell time (30–60 s). The present experimental study yielded process parameters of tool rotational speed
1800 rpm, plunge depth of 3.3 mm and a dwell time of 45 s
The FSSW process was essentially a three-stage process as the schematic shown in Fig. 2(a) [22]. The first stage started with the contact of
rotating tool pin over the top surface of the aluminum alloy AA2024-T3
upper plate until when the tool pin contacted the top surface of the
AA7075-T6 bottom plate. This stage resulted in plastic flow or stirring of
the material facilitated by frictional heat generated by the tool pin. The
next stage involved the plunging of the pin onto the bottom sheet
resulting in active mixing of the materials in the upper and bottom
plates. The downward motion of the tool aided in increasing the volume
of the stirred material. During the next stage the tool shoulder met the
upper plate thereby greatly increasing the stir zone and frictional heat
generation. Majority of the material flow during the entire FSSW process
had occurred at this stage where the steady downward motion of the tool
pin forced the material in the stir zone upwards around the pin. The tool
pin was retracted when the weld joint obtained was satisfactory. A total
of nine welded specimens were fabricated. They included three specimens each with the combination of similar AA2024 welded joints, similar AA7075 welded joints and dissimilar AA2024/AA7075 welded
joints. The different specimens were subsequently tested for their mechanical and microstructural characteristics. The mean values obtained
for each set of the similar AA2024, AA7075 and dissimilar AA2024/
AA7075 specimens are discussed in Figs. 6 and 7, while the microstructures of the specimens with highest values among each specimen set
are recorded in Figs. 5 and 9. The friction stir spot welded dissimilar
aluminum alloy AA2024-T3/AA7075-T6 was evaluated for microstructural and physical characteristics.
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K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Fig. 3. (a) Micrograph of the top aluminum alloy AA2024-T3 plate after weld; (b) micrograph of the bottom aluminum alloy AA7075-T6 plate after weld; (c)
micrograph of the FSSW weld zone.
2.3. Microstructure analysis
welded specimen shown in Fig. 3(a) illustrates the regions that were
characterized by EDAX analysis. The region near the stir zone and the heat
affected zone of the aluminum alloy AA2024-T3 top plate was observed
under with SEM-EDAX apparatus as seen in Fig. 3(b). The heat affected
zone below the keyhole of bottom plate AA7075-T6 was also characterized
as seen in Fig. 3(c) while the stir zone in the interfacial layer between the
two plates were also observed in Fig. 3(b). The chemical compositions and
the material information observed are presented in Table 3.
The graphical representation of the EDAX data in Figs. 4(a), (b) and
(c) illustrated the material composition of the base aluminum alloys
AA2024-T3, AA7075-T6 and the FSSW specimen respectively. From the
inference of Fig. 4, after the FSSW process, the material had undergone
significant changes in element within the vicinity of the stir zone
(Figs. 4(a), (b)). The interfacial layer between the base alloys exhibited
material fusion and the joint exhibited elemental distribution changes
(Fig. 4(c)). The distribution of the constituent elements of the weld joint
post FSSW in Fig. 4(b) illustrated the flow of material greatly. The weld
nugget zone of the joint possessed the redistributed elements due to the
material flow which greatly enhanced the joint structure and impacted
the properties of the welded specimen.
Subsequent to the analysis of material composition of the welded
specimen, the grain structure of specimen in interfacial region was
The microstructural characteristics of the dissimilar aluminum alloy
welded specimen were determined by scanning electron microscopy
(SEM) (Thermo Scientific Apreo S) and subsequent Energy dispersive Xray analysis was performed to examine the intermetallic composition of
the joint. The flow of the material and grain structure in the stir zone
was evaluated for the weld specimens. The welded specimens had both
length and width of 15 mm with 10 mm thickness. The surfaces of the
welded specimens were prepared per ASTM E3 standard for the microscope analysis. Abrasive papers with differing grit size were utilized
in initial surface preparation followed by polishing of the surface by
alumina solution. The surfaces were subsequently subjected to etching
by Keller’s reagent (ASTM E407).
3. Result and discussion
3.1. Metallurgical characterization of FSSW joints
The metallurgical properties and composition of the base aluminum
alloys AA2024-T3 and AA7075-T6 were evaluated by Energy-dispersive Xray spectroscopy at 15 kV for duration of 200 s. The macrograph of the
4
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Fig. 4. Material composition of (a) top aluminum alloy AA2024-T3 plate after FSSW; (b) bottom aluminum alloy AA7075-T6 plate after FSSW; (c) FSSW weld zone.
Fig. 5. SEM analysis FSSW joints (a) interfacial zone; (b) WNZ; (c) region between HAZ and TMAZ; (d) TMAZ.
studied by SEM analysis. The weld interface zone shown in Fig. 5(a)
illustrates the friction stir zone in the region. Within the stir zone (SZ),
fine grain structure was observed (Fig. 5(b)). This fine grain structure
was attributed to the material flow caused by the FSSW process during
the initial stage. The fine grain structure was also observed near the
weld nugget zone (WNZ) [23,26,27]]. The heat affected zone (HAZ) of
the interfacial joint was seen as the boundary that separated the coarse
grain structure seen in the thermo mechanically affected zone (SZ in
Fig. 5(c) and the TMAZ in Fig. 5(d)). The lower levels of weld joint
microhardness observed in HAZ on both AA2024 and AA7075 base
alloys, was a characteristic behavior observed in aluminium alloys
welded by FSW and FSSW processes.
5
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Fig. 6. Weld specimen macrostructure and microhardness survey.
The was due to the conflicting behavior of material over-ageing and
work-hardening that lead to decreased strength with respect to the stir
zone and the base alloys [16,24]. The welded specimens were heat
treated by cold water cooling and artificially aged for 8 h at a temperature of 90 °C. The appearance of coarse grain structure was due to
the lack of power dissipation during the welding caused by the higher
innate microhardness level of the bottom AA7075-T6 aluminum alloy.
The top plate AA2024-T3 had lower innate microhardness making it
capable of facilitating better tool pin penetration. The grain structure
distribution observed in the TMAZ was notably sparser than the
neighboring HAZ and this was due to the obstructed material flow by
the harder AA7075-T6.
of the WNZ, HAZ and TMAZ of the welded specimen. The observed
microhardness levels top AA2024-T3 and bottom AA7075-T6 plates
were shown in Fig. 6. As the graph illustrated, the peak microhardness
observed at the top AA2024-T3 plate was 132 HV in the HAZ near the
WNZ and followed by another peak at 130 HV about 20 mm further
from the stir zone beyond the HAZ. The peak microhardness observed
for the bottom AA7075-T6 plate was 213 HV in the HAZ near the WNZ
of the specimen. The microhardness observed in the WNZ for the weld
specimen was 138 HV. The average microhardness values of the top and
bottom plate showed variations to their original microhardness levels
expressed in Table 2. This was the resultant effect of the influence of the
frictional heat transfer in the plunge depth of the pin tool effectively
stirring the material into dispersing the grains between the layers
[22,25]. This resulted in AA2024-T3 gaining some improved microhardness and AA7075-T6 losing some microhardness level as the mixture of the materials in the WNZ becomes homogenous. Initially the
smoother AA2024-T3 had allowed the pin tool to penetrate the specimen towards the bottom plate which had higher innate microhardness. This effect led the welded specimen to exhibit increased cohesive
microhardness levels [19,21,24].(Table 4).
3.2. Microhardness analysis
The microhardness levels were evaluated at various points on the
surfaces of the welded specimens to determine the average microhardness level. Vickers microhardness test was conducted on the specimen on the surfaces of the top plate with intervals of 1 mm by a
diamond indenter. The test load applied was 0.5 kgf for dwell time of
10 s at each survey point. The weld specimens were of the same dimensions as prepared for the microscopic analysis. The average microhardness distribution of the welded specimens is indicated in Fig. 7.
The microhardness survey was conducted to establish the relationship
between the strength distribution and the fracture of the weld specimen. The Vickers microhardness survey was conducted on the regions
3.3. Tensile analysis
The tensile properties of the welded specimens were measured by
subjecting to tensile test (ASTM E8 standard) by universal testing machine. The specimens were prepared by wire-cut process to obtain the
6
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Fig. 7. Tensile properties of welded specimen.
Fig. 8. Tensile tested FSSW specimens (a) AA2024-T3/ AA2024-T3 joint; (b) AA7075-T6/ AA7075-T6 joint; (c) AA2024/AA7075 joint.
standard test specimen geometry and were subsequently loaded until
fracture of the specimen. The ultimate tensile strength, elongation and
elastic modulus of the welded specimen were evaluated and compared
with those of the base aluminum alloys AA2024-T3 and AA7075-T6
(Figs. 7a, b and c). The resulting fractured specimens were studied for
their microstructure by fractographic analysis on various zones of the
fractured material (Fig. 8). The fracture analysis was performed at
scanning electron microscope using secondary electron mode. The Load
vs Displacement curve in Fig. 7(d) illustrates the relation between the
load applied and the deformation of the test specimens. The curve of the
dissimilar AA2024/AA7075 FSSW specimen indicates the reduced level
of displacement during loading that corresponds to the lowered elongation of the dissimilar specimens compared to the similar AA2024/
AA2024, AA7075/AA7075 FSSW specimens. This was observed to be in
accordance to the inferences from Figs. 7(a), (b) and (c). The observed
values are listed in Table.
As represented by the illustration, the UTS of the welded specimen
were seen to be improved up to 15%. The yield strength of the specimen
has also gained improvement albeit it being minor. The percentage of
elongation of the welded specimen was observed to be lower than the
7
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Fig. 9. Fractography of the welded joint (a) top surface; (b) bottom surface; (c) interfacial zone; (d) crack propagation; (e) WNZ of AA2024-T3; (f) WNZ of AA7075T6.
Table 3
Material composition of the FSSW specimen.
Specimen
C (%)
O (%)
Na (%)
Mg (%)
Al (%)
Mn (%)
Cu (%)
Cr (%)
Zn (%)
AA2024-T3
AA7075-T6
Welded specimen
6.20
5.30
3.36
16.21
15.45
2.60
–
1.75
–
2.14
1.45
1.95
69.65
72.10
83.78
–
0.34
–
1.27
3.60
1.73
0.20
–
4.33
0.90
base aluminum alloys because of the improved overall microhardness
has reduced the ductility of the specimen [14–16].
The aluminum alloy AA2024-T3 top surface of the welded specimen
is observed in Fig. 9(a) which showed the stirred surface. The broken
bottom plate was observed in Fig. 9(b) which showed its coarse microstructure in contrast with its finer counterpart seen in Fig. 9(a). The
interfacial region of the fractured specimen was observed in Fig. 9(c)
which showed the cracks formed within the region during fracture. The
cracks observed in the interface region were not as profound as observed in Fig. 9(d) which showed the crack propagated in the HAZ of
3.4. Fractography
The tensile tested specimens were illustrated in Fig. 8. The fractography of the weld specimen was evaluated by scanning electron microscope.
8
K. Anton Savio Lewise, J. Edwin Raja Dhas, R. Pandiyarajan et al.
Journal of Alloys and Metallurgical Systems 2 (2023) 100010
Table 4
Tensile properties of the tested specimens.
Ultimate Tensile Strength
(MPa)
Std. Dev.
Mean (MPa)
Elastic Modulus
(GPa)
Std. Dev.
Mean
(MPa)
Elongation (%)
Std. Dev.
Mean
(MPa)
14.65
14.75
15
16.7
17
16.35
18.25
18.15
18.45
0.180278
14.8
0.1
11.6
7.867
16.6833
0.104083
11.83
0.05
7.75
0.152753
18.2833
0.125831
12.13
7.8
7.9
7.9
7.8
7.7
7.75
6.9
6.95
6.95
0.057735
0.32532
11.5
11.7
11.6
11.8
11.95
11.75
12
12.25
12.15
0.028868
6.933
the weld specimen. The interfacial region possessed higher levels of
microhardness and the WNZ possesses improved tensile properties
thereby leading to reduced crack formation in that region [25,26]. The
HAZ and the TMAZ were most affected by the tensile stress and were
subsequently fractured as evidenced in Fig. 9(d).
The WNZ of AA2024-T3 and AA7075-T6 can be observed in
Figs. 9(e) and (f) showed the fractured surfaces on either plate’s side.
The cohesive distribution of the material in the AA2024-T3 was in
contrast to the observation in the WNZ of the AA7075-T6 of the weld
specimen [13,23].
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[19] R.M. Mohd Jani, N.A. Ariffin, M.Z. Omar, M.Z. Abdullah, M.Z. Nuawi, Effect of tool
pin profile on mechanical properties and microstructure of FSSW of dissimilar
aluminum alloys, J. Mech. Eng. Res. Dev. 43 (1) (2020) 14–23.
[20] A.M.A. Hussein, A.M.M. Ali, M.S.A. Serry, A.A.M. Alaskari, Influence of tool traverse speed and rotational speed on the mechanical properties and microstructure
of dissimilar AA6061-T6 and AA7075-T6 friction stir spot welded joints, J. Mater.
Res. Technol. 9 (5) (2020) 9781–9791.
[21] S. Vidyasagar, A. Balaji, S.M. Sharif, R. Uthayakumar, Influence of multi-pass
friction stir spot welding on microstructure and mechanical properties of dissimilar
aluminum alloy joints, J. Mater. Res. Technol. 10 (2) (2021) 449–459.
4. Conclusion
The dissimilar aluminum alloy AA2024-T3/AA7075-T6 joint was
successfully welded by friction stir spot welding process with the process parameters. The welded specimens were subjected to microstructural characterization and analysis of physical properties and
fractography.
• The dissimilar alloy joint was welded devoid of macroscopic por•
•
•
osities and superficial defects. Satisfactory interfacial bonding was
obtained due to better tool pin penetration.
The material flow within the specimen resulted in redistribution of
grain structure and improved particle homogeneity. This was the
resultant effect of softer aluminum alloy AA2024-T3 enabling better
distribution of friction heat within the interfacial layer.
The improved average microhardness of the specimen was attributed to AA7075-T6 possessing higher innate microhardness and
during the material stirring greatly affecting the stir zone. This effect
reduced the percentage of elongation of the welded specimen due to
reduced ductility of the weld specimen. The UTS of the welded
specimen however was improved due to the frictional heat tempering the material mixture within the interfacial layer of the weld
specimen.
An improvement of 7.1% was observed between the microhardness
observed in AA2024-T3 and the WNZ of the dissimilar weld specimen.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence the work reported in this paper.
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