materials
Article
Effect of Traverse Speed Variation on Microstructural Properties
and Corrosion Behavior of Friction Stir Welded WE43 Mg
Alloy Joints
Yusra Saman Khan 1 , Mustufa Haider Abidi 2, * , Waqar Malik 1 , Nadeem Fayaz Lone 1 ,
Mohamed K. Aboudaif 2 and Muneer Khan Mohammed 2
1
2
*
Citation: Khan, Y.S.; Abidi, M.H.;
Malik, W.; Lone, N.F.; Aboudaif,
M.K.; Mohammed, M.K. Effect of
Traverse Speed Variation on
Microstructural Properties and
Department of Mechanical Engineering, Jamia Millia Islamia, New Delhi 110025, India
Raytheon Chair for Systems Engineering, Advanced Manufacturing Institute, King Saud University,
Riyadh 11421, Saudi Arabia
Correspondence: mabidi@ksu.edu.sa
Abstract: The growing demand for Magnesium in the automotive and aviation industries has enticed
the need to improve its corrosive properties. In this study, the WE43 magnesium alloys were friction
stir welded (FSW) by varying the traverse speed. FSW eliminates defects such as liquefication cracking, expulsion, and voids in joints encountered frequently in fusion welding of magnesium alloys.
The microstructural properties were scrutinized using light microscopy (LM) and scanning electron
microscopy (SEM). Additionally, the elemental makeup of precipitates was studied using electron
dispersive X-ray spectroscopy (EDS). The electrochemical behavior of specimens was evaluated by
employing potentiodynamic polarization tests and was correlated with the microstructural properties. A defect-free weldment was obtained at a traverse and rotational speed of 100 mm/min and
710 rpm, respectively. All weldments significantly improved corrosion resistance compared to the
base alloy. Moreover, a highly refined microstructure with redistribution/dissolution of precipitates
was obtained. The grain size was reduced from 256 µm to around 13 µm. The corrosion resistance of
the welded sample was enhanced by 22 times as compared to the base alloy. Hence, the reduction in
grain size and the dissolution/distribution of secondary-phase particles within the Mg matrix are the
primary factors for the enhancement of anti-corrosion properties.
Keywords: Mg WE43; friction stir welding; polarization curves; corrosion rate; rare earth elements;
precipitates
Corrosion Behavior of Friction Stir
Welded WE43 Mg Alloy Joints.
Materials 2023, 16, 4902. https://
doi.org/10.3390/ma16144902
Academic Editor: Pingping Liu
Received: 12 June 2023
Revised: 3 July 2023
Accepted: 6 July 2023
Published: 9 July 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1. Introduction
The need for weight reduction in the aviation industry has grown manifold over
recent years, driven by stringent CO2 emission regulations and the need to increase fuel
efficiency [1]. Due to its low specific weight and high strength-to-weight ratio, Magnesium
(Mg) is a potential alternative to Al alloys for aeronautical components [2]. The density of
Mg is 77% and 33% lower compared to steel and aluminium, respectively [3]. Over the last
decade, magnesium alloys have been used to account for more than 15% of the weight of
vehicles [4]. Some of the applications in the automobile sector include clutches, crankcases,
valve covers, and cylinder heads. Other applications include steering wheels, seat frames,
and alloy wheel rims. Furthermore, these materials also find applications in defense and
armor due to their shielding ability and noise-damping capacity [2,5]. Mg alloys containing
rare-earth (RE) elements have gained prominence because of their superior properties, such
as creep and corrosion resistance, ductility, and strength compared to other magnesium
alloys [2,6]. RE elements (Mg-4Y-3X-Zr, X = Gd/Nd) tend to form a safeguarding layer
over the surface, thereby inhibiting the corrosion rate [7,8]. Among RE-based Mg alloys,
the ASTM designated WE43 alloy is regarded as a high-strength alloy that can be employed
at as high as 250 ◦ C. These characteristics make it most sought after for several high-end
Materials 2023, 16, 4902. https://doi.org/10.3390/ma16144902
https://www.mdpi.com/journal/materials
Materials 2023, 16, 4902
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applications, such as transmission and power systems of military aircraft and helicopters.
Ever since Mg has been categorized as inflammable-safe, its adoption in several sectors has
increased but it mainly remained focused on AZ and AM series alloys. However, the WE43
series is superior to the AZ31, AM60, AZ91, and AM50 alloy series in terms of corrosion
resistance. Its biocompatibility also makes it popular in other exotic applications, such as
bio-absorbable implants, including screws, reinforcement/support plates, and stents [9–11].
The expanse of application domains is directly coupled with the welding of alloys. A
critical review of the literature carried [2,12,13] out as part of this work reveals that despite
far better properties of WE43 compared to common Mg alloys of the AM/AZ series, WE43
has not been extensively used.
Despite the improved anti-corrosion properties of the WE43 Mg alloy, it is still susceptible to corrosion due to precipitates, secondary phase particles (SPPs), and grain size.
The main concern is the higher gain boundary energy and galvanic cell formation around
the precipitates and SPPs. Several strategies have been used to improve Magnesium’s
corrosion resistance. The use of protective coatings is an effective method against the external environment [10]. Alloying with high-purity elements has also been used to enhance
corrosion resistance [14]. Other strategies deployed to enhance corrosion resistance include
surface modification by ion implementation, laser annealing, and grain refinement [15].
The growth of Mg alloys in aviation, automobiles, and other key sectors necessitates
its joining with self and other interfaced materials in comparable volume to its use. Fusion
welding of Mg alloys frequently results in expulsion, voids in weldment, and liquefication cracking [16,17]. Friction stir welding (FSW), a solid-state process, eliminates the
aforementioned solidification-related problems; it is energy efficient and regarded as a
green welding technique [18,19]. FSW is a promising welding technique to join similar
as well as dissimilar materials [20–23]. FSW also refines and modifies the grain structure,
often leading to the redistribution and dissolution of SPPs [24]. The grain morphology
modification improves several mechanical properties, including tensile strength, hardness,
ductility, and corrosion resistance [25]. The stirring action under frictional heat is known to
modify basal texture and may result in the dissolution or redistribution of SPPs depending
on the prevailing temperature. The stirring action during FSW and friction stir processing
(FSP) refines and redistributes the SPPs and helps improve corrosion resistance [26–28].
FSP has been used to modify the microstructure of FSW materials. For instance, Mehdi
and Mishra [29] successfully performed the FSP on dissimilar aluminium joints welded
by Tungsten inert gas welding and reported that, at higher tool rotational speed, tensile
strength and hardness can be increased. Charandabi et al. [30] also utilized the FSP to
modify the mechanical and microstructural properties of an Al-Si alloy. The results showed
enhancement in mechanical properties and the microstructure was modified by eliminating
the porosity, dendritic structure, and segregation of particles. Moreover, the SPPs were
redistributed uniformly. The effect of refinement and microstructural morphology on
corrosion behavior is presently attracting colossal interest [31].
Some works related to the corrosion behavior of the WE43 series have been reported.
For instance, Pereira et al. [8] studied the corrosion rate of Mg-WE43 and pure Mg alloy
by immersing the specimens in 0.6 M brine solution. They observed that the corrosion
rate of pure Magnesium was much higher compared to WE43. The enhanced corrosion
resistance in WE43 was attributed to the development of a protective layer over the surface.
Additionally, in their study, Chu and Marquis [32] investigated how the heat-treated
microstructure of WE43 affects the corrosion rate and found that age hardening can lead to
increased corrosion resistance. Yang et al. [33] also compared the corrosion rate of WE43
alloy in both as-cast and heat-treated conditions and demonstrated that the eutectic phase
in the as-cast structure damages the protective layer, thereby accelerating the corrosion
rate. The property evolution, apart from process parameters, is also greatly affected by
the thickness of the cross-section being welded. The thickness adds to the microstructural
and thermal profile heterogeneity, significantly affecting the properties of and around the
joint [34]. Whereas high-end industrial applications, e.g., space/aerospace and aircraft, call
Materials 2023, 16, 4902
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for thick sections, the reported literature is mainly focused on relatively thin sections [35].
The microstructural, corrosion property evolution, and their correlation for thick section
welding prove to be more useful but, unfortunately, very acutely reported. To the best
knowledge of the authors, the effect of grain size modification and redistribution of SPPs
attained by FSW on the corrosion rate is not yet reported in the literature. Importantly,
while Mg alloys are marked for poor corrosion resistance, the WE series Mg alloys are
the recent class of materials which are developed for improved corrosion behavior. The
welding modifies the corrosion behavior and, in the case of welding of the thick WE series,
which is acutely reported, the investigation on corrosion behavior is valuable in better
understanding the weld characteristics of this recent class of material. This maiden work
investigates the effect of traverse speed in a through-thickness FSW WE43 Mg alloy with
11.5 mm thick plates and simultaneously evaluates the effect of microstructure evolution
on the corrosion rate of the welded specimens and the base alloy using potentiodynamic
polarization tests.
2. Materials and Methods
The as-cast Mg-WE43 alloy plates, having a thickness of 11.5 mm, were butt welded
by carrying out FSW. The FSW setup, experimental tool design, and bottom view of the
tool probe are shown in Figure 1. Before welding, the plates were cleansed with acetone.
The FSW was carried out on a retrofitted vertical milling machine with a high-speed steel
(HSS) tool having a tapered cam tri-flute profile. The plates were tightly clamped in a work
fixture for easy processing or joining of the plates. The tool dimensions were kept constant
with a 26 mm shoulder diameter, 11.2 mm pin length, 10 mm pin root diameter, and 7.6 mm
pin tip diameter.
The process parameters employed to carry out the experimentation are enlisted in
Table 1. Table 2 shows the elemental makeup of the Mg base alloy.
Table 1. Process parameters utilized for FSW joints of WE43 Mg alloy.
Experiment No.
Weld Sample
Rotational Speed
(rpm)
Traverse Speed
(mm/min)
Tilt Angle
1
2
I
II
710
710
100
80
20
20
Table 2. Major Elemental composition (in %wt.) of WE43 alloy.
Elements
Mg
Y
Gd
%wt.
93
4
3
For metallographic examination, the samples of the desired shape and size were wire
drawn via a wire electric discharge machining (WEDM). After extraction, the samples
were polished with SiC abrasive papers (procured from Akshara polishing, Faridabad,
India) with grit sizes ranging from 100 to 2500, followed by polishing on a diamond
velvet cloth as per the standard metallographic practices. After polishing, the samples
were etched with 2.5 mL acetic acid, 3 gm picric acid, 50 mL ethanol, and 5 mL water
for 30 s, and then properly rinsed with demineralized water and dried (chemicals were
obtained from Insta Chemi, Noida, India). Scanning electron microscopy (SEM) using
secondary electrons (SE) with an acceleration potential of 10 kV, spot size of 50 nm, and
vacuum pressure of 1.81 × 10−5 mbar and light microscopy (LM) (provided by HD services
technology, Haryana, India) were used to scrutinize the grain morphology of the base alloy
and the welded sample. The elemental makeup of secondary phase particles (SPPs) was
examined using energy dispersive X-ray spectroscopy (EDS) (Carl Zeiss Microscopy GmbH,
Oberkochen, Germany). The line-intercept method was employed to measure the grain
size using a metallurgical image analysis software (MIAS), namely ImageJ (version-2).
Materials 2023, 16, x FOR PEER REVIEW
Materials 2023, 16, 4902
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(a)
(b)
(c)
Figure
FSWprocess
process
schematic,
(b)
tool
profile
used,
and
bottom
view
tapered
cylindrical
Figure
1. 1.(a)(a)FSW
schematic,
(b)
tool
profile
used,
and
(c)(c)
bottom
view
ofof
tapered
cylindrical
cam tri-flute tool probe.
cam tri-flute tool probe.
The processthe
parameters
employed
to carry
out the
are (BM)
enlisted
Furthermore,
polarization
tests were
performed
onexperimentation
both the base metal
andin
Table
1. Table
2 showsusing
the elemental
makeup configuration
of the Mg base(cell),
alloy.which was connected
the
welded
specimens
a three-electrode
to the Zive SP1 Potentiostat (obtained from TechScience Services, Guindy Chennai, India).
Table
1. Process
utilized
for FSW
joints of
WE43
Mg
alloy.
The
samples
wereparameters
taken as the
working
electrode
and
were
wire-drawn
from the transverse
section
in the welding direction. After
extraction,
the samples
wereSpeed
polished with abrasive
Experiment
Rotational
Speed
Traverse
Weld
Sample
Tilt Angle
papers No.
and diamond
velvet
cloth, followed
(rpm)by ultrasonic cleansing
(mm/min) with ethanol before
2
being subjected
to electrochemical
testing. In
area of 1 cm was subjected
1
I
710addition, a circular100
2⁰
to chemical
testing.
Saturated
calomel
and
platinum
electrodes
were
also
used
for
reference
2
II
710
80
2⁰
and counter electrode purposes, respectively. The corrosion rate was evaluated by an
electrochemical
techniquecomposition
called Tafel
which the polarization plot curves
Table 2. Major Elemental
(inextrapolation
%wt.) of WE43inalloy.
were obtained at a scan rate of 0.16 mV/s between potentials ranging from −400 mV
Elements
Y 3.5 %wt. brine solution
Gd as an
to +400 mV
with the incubation Mg
period of 2 h (7200 s) in
Materials 2023, 16, 4902
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electrolyte at 25 ◦ C (prepared in 300 mL of demineralized water to stabilize the initial
conditions). Using the Tafel extrapolation technique, the corrosion current density (Icorr )
and the corrosion potential (Ecorr ) were calculated. Lastly, the samples after corrosion were
analyzed using light micrographs.
3.xResults
Discussion
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This section describes the experimental results, their elucidation, as well as the experimental inferences that can be drawn.
However, in the present case, the defect is formed at the transition of the pin-affected
3.1. Grain Morphology Analysis Using Macro and Micrographs
zone (PASZ) and shoulder-affected stir zone (SASZ). These defects are sensitive to h
The FSW leads
theare
formation
distinct microstructural
zones possessing
unique
inputtoand
directly of
controlled
by the welding parameters.
In the case
of thick plat
features throughout
the
processed
region
due
to
varying
strain
rates
and
heat
input
the heat gradient is difficult to maintain across the weld depth. In the during
case of Exp. No
welding. Figurethe
2a,b
capture the
transverse
section’s
optical
corresponding
weldment
is subjected
to high
heat input
asmacrographs,
compared to Exp.
No. 1. The higher va
2/v) indicates higher
to Exp. 1 and Exp.
respectively.
The(wcharacterized
zonesheat
are well-demarcated.
Thein mainta
of the2,pseudo
heat index
input. Due to difficulty
stir zone (SZ) ising
subjected
to severe
plastic
deformation
(SPD)
andPASZ,
is in close
proximity
flow synergy
across
the hotter
SASZ and
colder
the defect
is formed at t
to the heat source,
thereby
location
[39].resulting in dynamic recrystallization (DRX) of grains in this
region [36]. The SZ isThe
encapsulated
by a thermo-mechanically
affectedinzone
(TMAZ);
this alloy ha
light micrographs
for base alloy are captured
Figure
3. The base
coarse
grain
structure,
and the
average
sizecycles
measured
was 256
µm.
The visual
region undergoes
partial
plastic
deformation
and
lowergrain
thermal
compared
to SZ
[37].
spection elongated
of light micrographs
Exp. 1isand
Exp. 2 show
grainzone
refinement in
The grains are usually
in shape. for
TMAZ
followed
by a extensive
heat-affected
characteristic
Figure 4). The
grain
size measured
(HAZ), which isthe
characterized
byzones
coarse(refer
graintomorphology
asaverage
this zone
is subjected
to coldin SZ of E
No.
1
and
Exp.
No.
2
are
12.037
µm
and
14
µm,
respectively.
thermal cycles only [38].
Figure 2. Macrograph for Exp. 1 (a) and 2 (b) [39].
Figure 2. Macrograph for Exp. 1 (a) and 2 (b) [39].
The macrograph corresponding to Exp. No. 1 is free of any defect; however, the
macrograph of Exp. No. 2 shows a tunneling defect [39]. The existing literature suggests
that a tunneling defect is usually formed at the bottom of the weld’s advancing side (AS).
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2023,
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However, in the present case, the defect is formed at the transition of the pin-affected stir
zone (PASZ) and shoulder-affected stir zone (SASZ). These defects are sensitive to heat
input and are directly controlled by the welding parameters. In the case of thick plates,
the heat gradient is difficult to maintain across the weld depth. In the case of Exp. No. 2,
the weldment is subjected to high heat input as compared to Exp. No. 1. The higher
value of the pseudo heat index (w2 /v) indicates higher heat input. Due to difficulty in
maintaining flow synergy across the hotter SASZ and colder PASZ, the defect is formed at
this location [39].
The light micrographs for base alloy are captured in Figure 3. The base alloy has
a coarse grain structure, and the average grain size measured was 256 µm. The visual
Materials 2023, 16, x FOR PEER REVIEWinspection of light micrographs for Exp. 1 and Exp. 2 show extensive grain refinement in7 of 15
Figure
3. Light
micrographs
of (refer
base alloy
(a) Region-1,
(b) Region-2,
Region-3.in SZ of
all the
characteristic
zones
to Figure
4). The average
grainand
size(c)
measured
Exp. No. 1 and Exp. No. 2 are 12.037 µm and 14 µm, respectively.
The grain size in SZ is around 21 and 18 times lower in Exp. 1 and 2, respectively, as
compared to the as-casted base alloy. Also, the visual inspection of TMAZ and HAZ
shows a refined grain structure. The ultra-refinement in SZ is due to the SPD-assisted
DRX, while the TMAZ experienced refinement occurs due to the induced strain rates [40].
The differences in the grain size of SZ in Exp. 1 and 2 are due to the heat input, which is
attributed to the variation in traverse speed involved. The grain size has increased with a
decrease in traverse speed and is in agreement with the existing literature [41]. When the
traverse speed increases from 80 mm/min to 100 mm/min, the frictional heat reduces, consequently decreasing the average distance between the two adjacent particles [42]. At
lower traverse speed, the stirring mm/revolution increases, resulting in more heat generation,
increasing the
grain
size.
metals,(b)
the
corrosion
is directly inFigure thereby
3. Light micrographs
of base
alloy
(a) In
Region-1,
Region-2,
andresistance
(c) Region-3.
Figure 3.by
Light
basehigher
alloy (a)the
Region-1,
(b) Region-2,
and the
(c) Region-3.
fluenced
the micrographs
grain size. of
The
grain size,
the more
corrosion rate [43].
The grain size in SZ is around 21 and 18 times lower in Exp. 1 and 2, respectively, as
compared to the as-casted base alloy. Also, the visual inspection of TMAZ and HAZ
shows a refined grain structure. The ultra-refinement in SZ is due to the SPD-assisted
DRX, while the TMAZ experienced refinement occurs due to the induced strain rates [40].
The differences in the grain size of SZ in Exp. 1 and 2 are due to the heat input, which is
attributed to the variation in traverse speed involved. The grain size has increased with a
decrease in traverse speed and is in agreement with the existing literature [41]. When the
traverse speed increases from 80 mm/min to 100 mm/min, the frictional heat reduces, consequently decreasing the average distance between the two adjacent particles [42]. At
lower traverse speed, the stirring mm/revolution increases, resulting in more heat generation, thereby increasing the grain size. In metals, the corrosion resistance is directly influenced by the grain size. The higher the grain size, the more the corrosion rate [43].
Figure
4. Light micrographs of weld sample 1 (a–c) and weld sample 2 (d,e).
Figure 4. Light micrographs of weld sample 1 (a–c) and weld sample 2 (d,e).
The grain
in SZ is around
21 and 18 times
lower Using
in Exp.SEM–EDS
1 and 2, respectively,
3.2. Chemistry
andsize
Distribution
of Secondary-Phase
Particles
as compared to the as-casted base alloy. Also, the visual inspection of TMAZ and HAZ
The secondary electron (SE) micrographs of the as-cast base alloy and the stir zone of
shows a refined grain structure. The ultra-refinement in SZ is due to the SPD-assisted
specimens
corresponding to weld sample I and weld sample II are shown in Figure 5. The
DRX, while the TMAZ experienced refinement occurs due to the induced strain rates [40].
micrographs
of base
alloy
captured
byinFigure
large
grains
thewhich
presence
of
The differences
in the
grain
size of SZ
Exp. 15a,b
and reveal
2 are due
to the
heat and
input,
is
β secondary phase particles (SPPs) both within and at the grain boundaries and rectangular plate-like intermetallic compounds (IMCs). Furthermore, the Mg-containing Nd results in the precipitation of IMCs within the grains and at the grain boundaries of the αMg matrix during casting [44]. Pure REs also segregate during the solidification process.
Materials 2023, 16, 4902
7 of 14
attributed to the variation in traverse speed involved. The grain size has increased with
a decrease in traverse speed and is in agreement with the existing literature [41]. When
the traverse speed increases from 80 mm/min to 100 mm/min, the frictional heat reduces,
consequently decreasing the average distance between the two adjacent particles [42].
At lower traverse speed, the stirring mm/revolution increases, resulting in more heat
generation, thereby increasing the grain size. In metals, the corrosion resistance is directly
influenced by the grain size. The higher the grain size, the more the corrosion rate [43].
3.2. Chemistry and Distribution of Secondary-Phase Particles Using SEM–EDS
The secondary electron (SE) micrographs of the as-cast base alloy and the stir zone of
specimens corresponding to weld sample I and weld sample II are shown in Figure 5. The
micrographs of base alloy captured by Figure 5a,b reveal large grains and the presence of β
secondary phase particles (SPPs) both within and at the grain boundaries and rectangular
plate-like intermetallic compounds (IMCs). Furthermore, the Mg-containing Nd results in
the precipitation of IMCs within the grains and at the grain boundaries of the α-Mg matrix
during casting [44]. Pure REs also segregate during the solidification process. Moreover,
the size of SPPs is large as compared to welded samples. The energy dispersive X-ray
spectroscopy (EDS) point spectrum results of these particles are shown in Table 3. The
EDS point spectrum pertaining to 1, 2, 3, 4, and 6 were directly taken on the phases found
within the matrix, thereby showing discrepancy in the chemical composition with the
rest. The EDS results confirm the elemental makeup of the SPPs. The distribution of these
particles is more pronounced on the grain boundaries. In addition, the micrographs of
SZ of Exp. 1 and 2 are represented by Figure 5c,d and Figure 5e,f, respectively. The SZ
has ultra-refined grains, and the SPPs are accumulated only at grain boundaries (refer to
Figure 5c,e). The stirring action during welding results in fragmentation and redistribution
of SPPs. These fragments’ phases are smaller in size and have a tendency to accumulate at
the grain boundaries upon plasticization [1].
Table 3. EDS point spectrum elemental makeup.
Element
(%wt.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Mg
Y
Zr
Gd
85.5
6.8
1.2
6.5
76.1
14.4
1.4
8.2
80
9.7
1.1
9.1
81.1
9.7
1.4
7.8
96.5
1.7
0.3
1.5
46.1
43.5
1.0
9.4
91.9
4.2
0.7
3.2
92.5
3.5
0.5
3.4
79.8
16.6
1.0
2.7
92.7
3.0
0.3
3.9
92.3
3.8
1.4
3.4
92.6
3.9
0.5
3.0
92.3
3.7
0.5
3.5
92.4
3.2
0.5
3.9
The presence of precipitates greatly affects the corrosion rate and is generally responsible for the development of a galvanic couple, which consequently increases the corrosion
rate [1]. The as-casted base alloy has a high density of precipitates and the distribution
is mainly non-homogenous. The welded specimens undergo high plastic deformation
coupled with high heat input, thereby resulting in the dissolution of SPPs. However,
the accumulation of precipitates is also observed at the grain boundaries. Overall, the
RE elements (Y/Gd) have a strong affinity to accumulate at the grain boundaries upon
plasticization [45].
Materials 2023, 16, 4902
the rest. The EDS results confirm the elemental makeup of the SPPs. The distribution of
these particles is more pronounced on the grain boundaries. In addition, the micrographs
of SZ of Exp. 1 and 2 are represented by Figure 5c,d and Figure 5e,f, respectively. The SZ
has ultra-refined grains, and the SPPs are accumulated only at grain boundaries (refer to
Figure 5c,e). The stirring action during welding results in fragmentation and redistribu8 of 14
tion of SPPs. These fragments’ phases are smaller in size and have a tendency to accumulate at the grain boundaries upon plasticization [1].
Figure 5. SE micrographs with EDS point spectrum marked: as-cast base alloy (a,b), Exp. No. 1 (c,d),
Figure 5. SE micrographs with EDS point spectrum marked: as-cast base alloy (a,b), Exp. No. 1 (c,d),
and Exp. No. 2 (e,f).
and Exp. No. 2 (e,f).
Table
3. EDS point spectrum
makeup.
3.3. Electrochemical
Analysiselemental
Using Potentiodynamic
Polarization Measurements
In the corrosion test, the corrosion potential (Ecorr ) and corrosion density (Icorr ) were
estimated by the potentiodynamic polarization test curves in which the cathodic and
anodic branches were obtained. The sample surfaces were exposed to a NaCl solution of
3.5 %wt. for 7200 s to obtain the open circuit potential (OCP), and the potentiodynamic
measurements were carried out as per standard practices. The Icorr and Ecorr were attained
by the intersection of the extrapolated curves of the anodic and cathodic potentiodynamic
polarization branches [46,47].
The macrographs of the transverse section of the BM and the welded samples after
corrosion are depicted in Figure 6. All the specimens have corroded; however, the base
alloy has undergone severe pitting in comparison to samples corresponding to Exp. No. 1
and 2. The micrographs of base metal and samples from Exp. No. 1 and 2 are represented
Materials 2023, 16, 4902
the intersection of the extrapolated curves of the anodic and cathodic potentiodynamic
polarization branches [46,47].
The macrographs of the transverse section of the BM and the welded samples afte
corrosion are depicted in Figure 6. All the specimens have corroded; however, the base
9 of 14
alloy has undergone severe pitting in comparison to samples corresponding to Exp. No. 1
and 2. The micrographs of base metal and samples from Exp. No. 1 and 2 are represented
by Figure 7 and Figure 8, respectively. From the visual inspection of these samples, it is
by Figures 7 and 8, respectively. From the visual inspection of these samples, it is evident
evident that the corrosion in the base alloy is more prominent. Moreover, there is less
that the corrosion in the base alloy is more prominent. Moreover, there is less observable
observable
corrosion
in the sampletocorresponding
to Exp.
No.
1 compared
to the sample
corrosion
in the
sample corresponding
Exp. No. 1 compared
to the
sample
corresponding
corresponding
to
Exp.
No.
2.
to Exp. No. 2.
Figure6.6.The
Themacrographs
macrographs
(a) base
(b) No.
Exp.1 No.
1 sample
(weld sample
I),Exp.
and No.
(c) 10
Exp.
Materials 2023, 16, x FOR PEER REVIEW
of No.
15 2 (weld
Figure
for for
(a) base
alloy,alloy,
(b) Exp.
(weld
I), and (c)
2 (weld
sampleII).
II).
sample
Figure 7. Optical micrographs of base alloy after corrosion (a) base alloy, (b) Exp. No. 1 (weld samFigure 7. Optical micrographs of base alloy after corrosion (a) base alloy, (b) Exp. No. 1 (weld
ple I), and (c) Exp. No. 2 (weld sample II)
sample I), and (c) Exp. No. 2 (weld sample II).
The open circuit potential (OCP) curves for base alloy and welded samples are shown
in Figure 9. For the base alloy, the OCP dropped in the first 1000 s, which indicates an
increase in the anodic reaction and, therefore, suggesting more dissolution of the base
alloy. After 1000 s, the anodic and cathodic reaction rates became almost equal (reached
equilibrium) and may have formed a passivation layer afterwards. In the case of weld
sample I, for the first 1000 s, a decrease in the anodic reaction and an increase in the cathodic
reaction was observed, indicating the formation of passivation layer and the evolution of
sufficient oxygen. The weld sample II behaved ideally. For the initial seconds of the test, no
shift in potential was observed, meaning that the anodic and cathodic reactions have the
same rate.
Figure 8. Microstructure of weld sample 1 (a–c) and weld sample 2 (d,e) after corrosion.
Materials 2023, 16, 4902
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Figure 7. Optical micrographs of base alloy after corrosion (a) base alloy, (b) Exp. No. 1 (weld sample I), and (c) Exp. No. 2 (weld sample II)
Materials 2023, 16, x FOR PEER REVIEW
11 of 15
The corrosion rate of the metal Is controlled by the redox reaction, with a higher anodic reaction rate representing faster oxidation of Mg alloy by promoting the yield of Mg2+
ions, thereby causing the dissolution of the alloy at a higher rate, consequently depicting
the lower corrosion resistance and vice versa. On the other hand, the cathodic reaction
controls the yield of oxide/hydroxide ions. The higher the reaction rate, the more likely
the formation of oxide/hydroxide ions takes place. Thus, Mg2+ ions react with oxide/hydroxide ions and form a passive protective layer of MgO/Mg(OH)₂, which prevents further corrosion. The redox reactions are given as follows:
Anodic reaction: 𝑀𝑔 → 𝑀𝑔
Cathodic reaction: 2𝐻 𝑂 + 2𝑒
+ 2𝑒
→ 2𝑂𝐻 + 𝐻
Overall reaction: 𝑀𝑔 + 2𝐻 𝑂 → 𝑀𝑔(𝑂𝐻) + 𝐻
here, the anodic and cathodic reaction rates are determined by the slopes of the anodic
and cathodic curves in the Tafel plots (refer to Figure 10): the higher the slope of the corFigure
8. Microstructure
weld sample
1 (a–c)rate
and weldvice
sample
2 (d,e) after corrosion.
responding
curve, the of
higher
the reaction
versa.
Figure
8. Microstructure
of
weld sample
1 (a–c) and and
weld sample
2 (d,e) after corrosion.
The open circuit potential (OCP) curves for base alloy and welded samples are shown
in Figure 9. For the base alloy, the OCP dropped in the first 1000 s, which indicates an
increase in the anodic reaction and, therefore, suggesting more dissolution of the base
alloy. After 1000 s, the anodic and cathodic reaction rates became almost equal (reached
equilibrium) and may have formed a passivation layer afterwards. In the case of weld
sample I, for the first 1000 s, a decrease in the anodic reaction and an increase in the cathodic reaction was observed, indicating the formation of passivation layer and the evolution of sufficient oxygen. The weld sample II behaved ideally. For the initial seconds of
the test, no shift in potential was observed, meaning that the anodic and cathodic reactions
have the same rate.
Figure 10 illustrates the potentiodynamic curves obtained for the base metal and
welded samples from Exp. No. 1 and 2 (samples I and II, respectively). The Icorr, Ecorr, and
corrosion rate (in mils penetration per year) of the BM and welded samples (I and II) are
given in Table 4. According to the existing corrosion thermodynamics research, the corrosion potential expresses the degree of difficulty of corrosion. It implies that with a higher
positive (or less negative) corrosion potential, the material is more resistant to corrosion
and, according to corrosion kinetics, the higher the corrosion density, the lower the exhibited corrosion resistance [48]. The welded samples (I and II) showed lower corrosion current density and higher corrosion potential compared to the base metal (refer to Table 4).
The corrosion rate obtained for the base metal is 95.604 mpy, while for the welded samples
I and II, it is 4.315 mpy and 13.69 mpy, respectively. Hence, the potentiodynamic results
show that the welded samples are more resistant to corrosion.
Figure 9.
9. OCP curves for
for base
base alloy,
alloy,weld
weldsample
sampleIIand
andII.
II.
Figure
Figure 10 illustrates the potentiodynamic curves obtained for the base metal and
welded samples from Exp. No. 1 and 2 (samples I and II, respectively). The Icorr , Ecorr ,
and corrosion rate (in mils penetration per year) of the BM and welded samples (I and
II) are given in Table 4. According to the existing corrosion thermodynamics research,
the corrosion potential expresses the degree of difficulty of corrosion. It implies that with
a higher positive (or less negative) corrosion potential, the material is more resistant to
corrosion and, according to corrosion kinetics, the higher the corrosion density, the lower the
exhibited corrosion resistance [48]. The welded samples (I and II) showed lower corrosion
current density and higher corrosion potential compared to the base metal (refer to Table 4).
The corrosion rate obtained for the base metal is 95.604 mpy, while for the welded samples
Materials 2023, 16, 4902
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Materials 2023, 16, x FOR PEER REVIEW
12 of 15
I and II, it is 4.315 mpy and 13.69 mpy, respectively. Hence, the potentiodynamic results
show that the welded samples are more resistant to corrosion.
Figure 10. Potentiodynamic polarization curve for (a) base alloy and (b) weld samples I and II exFigure 10. Potentiodynamic polarization curve for (a) base alloy and (b) weld samples I and II
posed to 3.5 %wt. electrolyte.
exposed to 3.5 %wt. electrolyte.
Table 4. Electrochemical parameters of the tested samples exposed to 3.5% wt electrolyte.
Table 4. Electrochemical parameters of the tested samples exposed to 3.5% wt electrolyte.
Icorr (µA/cm2)
CR (mpy)
CR (mmpy)
Specimen
Ecorr (V)
Specimen
Ecorr
(V)
CR (mpy)
CR (mmpy)
Icorr (µA/cm
Base alloy
−1.629
1032 )
95.604
2.428
Weld
I
0.109
Base
alloy
−−1.472
1.629
103 4.12
95.6044.314
2.428
Weld
0.034
Weld II
I
−−1.570
1.472
4.12 13.1
4.314 13.68
0.109
Weld II
−1.570
13.1
13.68
0.034
There are two possible reasons for this type of corrosion behavior; first, the grain size
and, The
second,
the distribution/dissolution
of secondary-phase
particles
(SPPs)
the
corrosion
rate of the metal Is controlled
by the redox
reaction,
withwithin
a higher
substrate.
The
base
metal
has
large
grains,
and
there
is
a
larger
presence
of
solute
precipanodic reaction rate representing faster oxidation of Mg alloy by promoting the yield
2+ ions, thereby
itates
to welded
samples.
This large of
grain
does
allow
the consequently
development
of
Mgcompared
causing
the dissolution
the size
alloy
at anot
higher
rate,
of
a
protective
layer
over
the
surface
[6].
However,
a
reduction
in
grain
size
results
in more
depicting the lower corrosion resistance and vice versa. On the other hand, the cathodic
grain
boundaries,
which
inhibits
the
formation
of
a
galvanic
couple
[31,43].
Moreover,
the
reaction controls the yield of oxide/hydroxide ions. The higher the reaction rate, the
2+
presence
of
SPPs
accelerates
the
corrosion
rate
by
forming
the
galvanic
couple
with
the
more likely the formation of oxide/hydroxide ions takes place. Thus, Mg ions react
Mg matrix,
possessingions
higher
potential
than the
matrix,
which leads 2to
more
with
oxide/hydroxide
andcorrosion
form a passive
protective
layer
of MgO/Mg(OH)
, which
localizedfurther
corrosion
in the form
pitting
corrosion,
as observed
in the base alloy [1]. After
prevents
corrosion.
Theof
redox
reactions
are given
as follows:
FSW, SPPs are redistributed and fragmented; hence, the corrosion rate decreases or the
Anodic reaction
: Mgcorrosion
→ Mg2+decrease
+ 2e− [49]. The localized sites
preferred sites of grain boundaries
for pitting
of corrosion, which are at the grain boundaries decreased and, thereby, their detrimental
effect has been significantly reduced. The intensity of the formation of the galvanic couple
−
−
reactionrate
: 2Hin2 O
+ 2esample
→ 2OH
+ H2
has diminished. TheCathodic
higher corrosion
weld
II as compared
to weld sample
I is preferably due to the difference in grain size and due to the presence of the defect.
Overall reaction : Mg + 2H2 O → Mg(OH)2 + H2
4. Conclusions
here, the anodic and cathodic reaction rates are determined by the slopes of the anodic
This experimental work evaluates the electrochemical/corrosion behavior of friction
and cathodic curves in the Tafel plots (refer to Figure 10): the higher the slope of the
stir welded WE43 Mg plates using potentiodynamic tests and simultaneously evaluates
corresponding curve, the higher the reaction rate and vice versa.
the impact of welding speed on the corrosion rate. The microstructural properties were
There are two possible reasons for this type of corrosion behavior; first, the grain size
scrutinized using light microscopy and scanning electron microscopy and were co-related
and, second, the distribution/dissolution of secondary-phase particles (SPPs) within the
with the corrosion
the grains,
specimens.
drawnprecipibased
substrate.
The base behavior
metal hasoflarge
and The
therefollowing
is a largeroutcomes
presence are
of solute
on
the
results
obtained:
tates compared to welded samples. This large grain size does not allow the development of
A defect-free
weldment
was[6].
obtained
at aa reduction
traverse and
rotational
speedinofmore
100
a1.protective
layer over
the surface
However,
in grain
size results
and which
710 rpm,
respectively.
With aof
decrease
in the
traverse
speed,
a tunneling
grainmm/min
boundaries,
inhibits
the formation
a galvanic
couple
[31,43].
Moreover,
the
defect
was
obtained
at
the
transition
of
the
pin-affected
and
shoulder-affected
stir
presence of SPPs accelerates the corrosion rate by forming the galvanic couple with the
zone.
2. Ultra-refined grains were observed in both weldments. The average grain size decreased from 256 µm (base metal) to 12.037 µm and 14 µm in weld I and weld II,
Materials 2023, 16, 4902
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Mg matrix, possessing higher corrosion potential than the matrix, which leads to more
localized corrosion in the form of pitting corrosion, as observed in the base alloy [1]. After
FSW, SPPs are redistributed and fragmented; hence, the corrosion rate decreases or the
preferred sites of grain boundaries for pitting corrosion decrease [49]. The localized sites
of corrosion, which are at the grain boundaries decreased and, thereby, their detrimental
effect has been significantly reduced. The intensity of the formation of the galvanic couple
has diminished. The higher corrosion rate in weld sample II as compared to weld sample I
is preferably due to the difference in grain size and due to the presence of the defect.
4. Conclusions
This experimental work evaluates the electrochemical/corrosion behavior of friction
stir welded WE43 Mg plates using potentiodynamic tests and simultaneously evaluates
the impact of welding speed on the corrosion rate. The microstructural properties were
scrutinized using light microscopy and scanning electron microscopy and were co-related
with the corrosion behavior of the specimens. The following outcomes are drawn based on
the results obtained:
1.
2.
3.
4.
5.
6.
A defect-free weldment was obtained at a traverse and rotational speed of 100 mm/min
and 710 rpm, respectively. With a decrease in the traverse speed, a tunneling defect
was obtained at the transition of the pin-affected and shoulder-affected stir zone.
Ultra-refined grains were observed in both weldments. The average grain size decreased from 256 µm (base metal) to 12.037 µm and 14 µm in weld I and weld II,
respectively. As traverse speed decreased, the grain size of the welded samples
increased. The grains were more refined and equiaxed at a higher traverse speed
compared to a lower traverse speed.
The base alloy had a significant presence of secondary-phase particles. These precipitates were redistributed within the Mg substrate after performing the FSW.
A substantial enhancement in corrosion resistance was obtained in both weldments in
comparison to the base alloy. The corrosion rate for the defect-free welded sample
was 22 times lower as compared to the base alloy.
The primary reasons for the enhancement in corrosion resistance are the decrease in
grain size and the dissolution of solute particles within the substrate. A larger grain
size is more prone to corrosion. Furthermore, the presence of precipitates/solute
particles intensifies the formation of the galvanic couple, thereby increasing the
corrosion potential.
Corrosion resistance decreases with an increase in grain size in the case of the welded
specimens.
Author Contributions: Conceptualization, Y.S.K., M.H.A., W.M. and N.F.L.; methodology, Y.S.K.,
M.H.A., N.F.L. and M.K.M.; formal analysis, W.M. and M.K.A.; investigation, Y.S.K., W.M. and N.F.L.;
resources, M.H.A. and N.F.L.; data curation, Y.S.K., M.K.A. and M.K.M.; writing—original draft
preparation, Y.S.K., M.H.A., N.F.L. and M.K.M.; writing—review and editing, M.H.A., N.F.L. and
M.K.A.; funding acquisition, M.H.A. All authors have read and agreed to the published version of
the manuscript.
Funding: The authors extend their appreciation to the Deputyship for Research & Innovation,
Ministry of Education in Saudi Arabia, for funding this research (IFKSURC-1-0903).
Institutional Review Board Statement: Not applicable.
Data Availability Statement: All the relevant data are available in the manuscript.
Acknowledgments: The authors extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia, for funding this research (IFKSURC-1-0903).
Conflicts of Interest: The authors declare no conflict of interest.
Materials 2023, 16, 4902
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References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
Maqbool, A.; Lone, N.F.; Ahmad, T.; Khan, N.Z.; Siddiquee, A.N. Effect of hybrid reinforcement and number of passes on
microstructure, mechanical and corrosion behavior of we43 mg alloy based metal matrix composite. J. Manuf. Process. 2023, 89,
170–181. [CrossRef]
Calado, L.M.; Carmezim, M.J.; Montemor, M.F. Rare earth based magnesium alloys—A review on we series. Front. Mater. 2022, 8,
804906. [CrossRef]
Jayasathyakawin, S.; Ravichandran, M.; Baskar, N.; Anand Chairman, C.; Balasundaram, R. Mechanical properties and applications of magnesium alloy—Review. Mater. Today Proc. 2020, 27, 909–913. [CrossRef]
Woodall, B. Gm Tests Magnesium Sheet Metal to Make Cars Lighter. Available online: https://www.reuters.com/article/us-gmmagnesium-idUSBRE89M0UP20121023 (accessed on 1 June 2023).
Song, K.; Pan, F.S.; Chen, X.H.; Zhang, Z.H.; Tang, A.T.; She, J.; Yu, Z.W.; Pan, H.C.; Xu, X.Y. Effect of texture on the electromagnetic
shielding property of magnesium alloy. Mater. Lett. 2015, 157, 73–76. [CrossRef]
Ghorbanpour, S.; McWilliams, B.A.; Knezevic, M. Effect of hot working and aging heat treatments on monotonic, cyclic, and
fatigue behavior of we43 magnesium alloy. Mater. Sci. Eng. A 2019, 747, 27–41. [CrossRef]
Esmaily, M.; Svensson, J.E.; Fajardo, S.; Birbilis, N.; Frankel, G.S.; Virtanen, S.; Arrabal, R.; Thomas, S.; Johansson, L.G.
Fundamentals and advances in magnesium alloy corrosion. Prog. Mater. Sci. 2017, 89, 92–193. [CrossRef]
Pereira, G.S.; Koga, G.Y.; Avila, J.A.; Bittencourt, I.M.; Fernandez, F.; Miyazaki, M.H.; Botta, W.J.; Bose Filho, W.W. Corrosion
resistance of we43 mg alloy in sodium chloride solution. Mater. Chem. Phys. 2021, 272, 124930. [CrossRef]
Singh, I.B.; Singh, M.; Das, S. A comparative corrosion behavior of mg, az31 and az91 alloys in 3.5% nacl solution. J. Magnes.
Alloy. 2015, 3, 142–148. [CrossRef]
Jiang, Y.F.; Zhai, C.Q.; Liu, L.F.; Zhu, Y.P.; Ding, W.J. Zn–ni alloy coatings pulse-plated on magnesium alloy. Surf. Coat. Technol.
2005, 191, 393–399. [CrossRef]
Kubásek, J.; Dvorský, D.; Čavojský, M.; Roudnická, M.; Vojtěch, D. We43 magnesium alloy-material for challenging applications.
Kov. Mater. (Mettalic Mater.) 2019, 57, 159–165. [CrossRef]
Jiang, H.S.; Zheng, M.Y.; Qiao, X.G.; Wu, K.; Peng, Q.Y.; Yang, S.H.; Yuan, Y.H.; Luo, J.H. Microstructure and mechanical properties
of WE43 magnesium alloy fabricated by direct-chill casting. Mater. Sci. Eng. A 2017, 684, 158–164. [CrossRef]
Loukil, N. Alloying elements of magnesium alloys: A literature review. In Magnesium Alloys Structure and Properties; Intech Open:
London, UK, 2021; pp. 58–78.
Makar, G.L.; Kruger, J. Corrosion of magnesium. Int. Mater. Rev. 1993, 38, 138–153. [CrossRef]
Hu, H.; Nie, X.; Ma, Y. Corrosion and surface treatment of magnesium alloys. In Magnesium Alloys-Properties in Solid and Liquid
States; Czerwinski, F., Ed.; IntechOpen: London, UK, 2014; pp. 23–29.
Afrin, N.; Chen, D.L.; Cao, X.; Jahazi, M. Microstructure and tensile properties of friction stir welded az31b magnesium alloy.
Mater. Sci. Eng. A 2008, 472, 179–186. [CrossRef]
Singh, K.; Singh, G.; Singh, H. Review on friction stir welding of magnesium alloys. J. Magnes. Alloys 2018, 6, 399–416. [CrossRef]
Jacob, A.; Maheshwari, S.; Siddiquee, A.N.; Al-Ahmari, A.; Abidi, M.H.; Konovalov, S.; Chen, X. The effects of in-process cooling
during friction stir welding of 7475 aluminium alloy. Sains Malays. 2021, 50, 2743–2754. [CrossRef]
Lone, N.F.; Bajaj, D.; Gangil, N.; Khan, T.; Abidi, M.H.; Al-Ahmari, A.; Siddiquee, A.N. Multi principal element alloy particle
reinforced metal matrix composites: Synthesis, microstructure, and mechanical aspects. Manuf. Lett. 2023, 36, 46–51. [CrossRef]
Beygi, R.; Galvão, I.; Akhavan-Safar, A.; Pouraliakbar, H.; Fallah, V.; da Silva, L.F. Effect of Alloying Elements on Intermetallic
Formation during Friction Stir Welding of Dissimilar Metals: A Critical Review on Aluminum/Steel. Metals 2023, 13, 768.
[CrossRef]
Weng, F.; Liu, Y.; Chew, Y.; Lee, B.Y.; Ng, F.L.; Bi, G. Double-side friction stir welding of thick magnesium alloy: Microstructure
and mechanical properties. Sci. Technol. Weld. Join. 2020, 25, 359–368. [CrossRef]
Kasai, H.; Morisada, Y.; Fujii, H. Dissimilar FSW of immiscible materials: Steel/magnesium. Mater. Sci. Eng. A 2015, 624, 250–255.
[CrossRef]
Carlone, P.; Astarita, A.; Palazzo, G.S.; Paradiso, V.; Squillace, A. Microstructural aspects in Al–Cu dissimilar joining by FSW. Int.
J. Adv. Manuf. Technol. 2015, 79, 1109–1116. [CrossRef]
Gangil, N.; Maheshwari, S.; Siddiquee, A.N.; Abidi, M.H.; El-Meligy, M.A.; Mohammed, J.A. Investigation on friction stir welding
of hybrid composites fabricated on al–zn–mg–cu alloy through friction stir processing. J. Mater. Res. Technol. 2019, 8, 3733–3740.
[CrossRef]
Singh, G.; Singh, H.; Singh, K. Friction stir welding of magnesium alloys: A review. Asian Reviwes Mech. Eng. 2016, 5, 5–8.
[CrossRef]
Palanivel, S.; Mishra, R.S.; Davis, B.; DeLorme, R.; Doherty, K.J.; Cho, K.C. Effect of initial microstructure on the microstructural
evolution and joint efficiency of a we43 alloy during friction stir welding. In Friction Stir Welding and Processing VII; Mishra, R.,
Mahoney, M.W., Sato, Y., Hovanski, Y., Verma, R., Eds.; Springer International Publishing: Cham, Switzerland, 2016; pp. 253–261.
Abidi, M.H.; Moiduddin, K.; Siddiquee, A.N.; Mian, S.H.; Mohammed, M.K. Development of aluminium metal foams via friction
stir processing by utilizing mgco3 precursor. Coatings 2023, 13, 162. [CrossRef]
Materials 2023, 16, 4902
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
14 of 14
Pouraliakbar, H.; Beygi, R.; Fallah, V.; Monazzah, A.H.; Jandaghi, M.R.; Khalaj, G.; da Silva, L.F.; Pavese, M. Processing of
Al-Cu-Mg alloy by FSSP: Parametric analysis and the effect of cooling environment on microstructure evolution. Mater. Lett. 2022,
308, 131157. [CrossRef]
Mehdi, H.; Mishra, R.S. Influence of friction stir processing on weld temperature distribution and mechanical properties of
TIG-welded joint of AA6061 and AA7075. Trans. Indian Inst. Met. 2020, 73, 1773–1788. [CrossRef]
Charandabi, F.K.; Jafarian, H.R.; Mahdavi, S.; Javaheri, V.; Heidarzadeh, A. Modification of microstructure, hardness, and
wear characteristics of an automotive-grade Al-Si alloy after friction stir processing. J. Adhes. Sci. Technol. 2021, 35, 2696–2709.
[CrossRef]
Argade, G.R.; Panigrahi, S.K.; Mishra, R.S. Effects of grain size on the corrosion resistance of wrought magnesium alloys
containing neodymium. Corros. Sci. 2012, 58, 145–151. [CrossRef]
Chu, P.-W.; Marquis, E.A. Linking the microstructure of a heat-treated we43 mg alloy with its corrosion behavior. Corros. Sci.
2015, 101, 94–104. [CrossRef]
Yang, C.; Gupta, N.; Ding, H.; Xiang, C. Effect of microstructure on corrosion behavior of we43 magnesium alloy in as cast and
heat-treated conditions. Metals 2020, 10, 1552. [CrossRef]
Sharma, C.; Dwivedi, D.K.; Kumar, P. Heterogeneity of microstructure and mechanical properties of friction stir welded joints of
Al-Zn-Mg alloy AA7039. Procedia Eng. 2013, 64, 1384–1394. [CrossRef]
Ubaid, M.; Bajaj, D.; Mukhopadhyay, A.K.; Siddiquee, A.N. Friction stir welding of thick AA2519 alloy: Defect elimination,
mechanical and micro-structural characterization. Met. Mater. Int. 2020, 26, 1841–1860. [CrossRef]
Khan, N.Z.; Siddiquee, A.N.; Khan, Z.A. Friction Stir Welding: Dissimilar Aluminium Alloys; Routledge: Hoboken, NJ, USA,
2017; p. 180.
Zolghadr, P.; Akbari, M.; Asadi, P. Formation of thermo-mechanically affected zone in friction stir welding. Mater. Res. Express
2019, 6, 086558. [CrossRef]
Hashmi, F.A.; Mohamed Ali, H.B.; Lone, N.F.; Azma, R.; Siddiquee, A.N.; Ashraf Mir, M.; Ahmad, T.; Mir, F.A. Friction stir welds
of aluminium alloy pipes: An investigation of defects and mechanical properties. Adv. Mater. Process. Technol. 2023, 9, 169–185.
[CrossRef]
Moiduddin, K.; Siddiquee, A.N.; Abidi, M.H.; Mian, S.H.; Mohammed, M.K. Friction stir welding of thick plates of 4y3gd mg
alloy: An investigation of microstructure and mechanical properties. Materials 2021, 14, 6924. [CrossRef]
Ali, N.; Lone, N.F.; Khan, T.; Qazi, A.M.; Mukhopadhyay, A.K.; Siddiqueee, A.N. A Comparative Study of Effect of Tool-Offset
Position on Defect Dynamics and Formation of Intermetallic Compounds in Friction Stir Welding of Al-Ti Dissimilar Joints. J.
Mater. Eng Perform 2023. [CrossRef]
Singh, B.; Singhal, P.; Saxena, K.K. Effect of transverse speed on mechanical and microstructural properties of friction stir welded
aluminium aa2024-t351. Adv. Mater. Process. Technol. 2020, 6, 519–529. [CrossRef]
Thangarasu, A.; Murugan, N.; Dinaharan, I.; Vijay, S.J. Influence of traverse speed on microstructure and mechanical properties of
aa6082-tic surface composite fabricated by friction stir processing. Procedia Mater. Sci. 2014, 5, 2115–2121. [CrossRef]
Zheng, T.; Hu, Y.; Yang, S. Effect of grain size on the electrochemical behavior of pure magnesium anode. J. Magnes. Alloys 2017, 5,
404–411. [CrossRef]
Jarosz, R.; Kiełbus, A.; Stopyra, M. Influence of sand-casting parameters on microstructure and properties of magnesium alloys.
Arch. Metall. Mater. 2013, 58, 635–640.
Asqardoust, S.; Zarei Hanzaki, A.; Abedi, H.R.; Krajnak, T.; Minárik, P. Enhancing the strength and ductility in accumulative back
extruded we43 magnesium alloy through achieving bimodal grain size distribution and texture weakening. Mater. Sci. Eng. A
2017, 698, 218–229. [CrossRef]
Loto, R.T. Potentiodynamic polarization studies of the pitting corrosion resistance and passivation behavior of p4 low carbon
mold steel in chloride and acid chloride solution. Mater. Res. Express 2018, 5, 116509. [CrossRef]
Shi, Z.; Liu, M.; Atrens, A. Measurement of the corrosion rate of magnesium alloys using tafel extrapolation. Corros. Sci. 2010, 52,
579–588. [CrossRef]
Zhang, L.; Duan, Y.; Gao, Z.; Ma, J.; Liu, R.; Liu, S.; Tu, Z.; Liu, Y.; Bai, C.; Cui, L.; et al. Graphene enhanced anti-corrosion and
biocompatibility of niti alloy. NanoImpact 2017, 7, 7–14. [CrossRef]
Eivani, A.R.; Mehdizade, M.; Chabok, S.; Zhou, J. Applying multi-pass friction stir processing to refine the microstructure and
enhance the strength, ductility and corrosion resistance of we43 magnesium alloy. J. Mater. Res. Technol. 2021, 12, 1946–1957.
[CrossRef]
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