Research Paper

1. E
A
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in
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a
K
1
M
T
a
p
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a
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d
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th
m
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Experim
Abstract: Tung
using Argon g
nvestigated. Th
zone is coarser
fracture occurs
and cerium are
Keywords: Mg-
1. Introduction
Magnesium all
These alloys ar
alloys with a d
potentially broa
have done a lot
applications. B
expansion coef
deformation du
et al [11] foun
welding becaus
hermal expans
materials cause
welding using
discussed. The
ithium alloy.
2. Experiment
The alloy used
atmosphere. Th
composition of
ested by Archi
MPa and the e
shown in Fig.1
Before welding
acetone, washin
ental inv
for a
P. V
1
Resear
2 ,3, 4
Depa
*Corre
gsten inert gas
gas as a prote
he results indic
r than the pare
in a mixed typ
enriched at gra
-Li alloy; TIG
n
loys have low
re also recyclab
density smalle
ad applications
t of work on th
Because Mg all
fficient, they a
uring welding p
nd that many d
se magnesium
sion coefficien
es great concer
a homogeneou
results provid
tal
d in this exper
he ingot was
f the magnesium
imedes’ metho
elongation was
on the plates.
g, the surfaces
ng with water,
Copyrights ©
IOSRD
Vo
vestigatio
a single p
Vijayasarath
rch scholar, De
artment of Mec
esponding auth
weld was carr
cting atmosph
cate that the m
ent metal. The
pe of toughnes
ain Boundaries
welding; micro
w density, high
ble, making th
er than normal
s in aerospace
he welding of m
loys have a lo
are chemically
process, the so
difficulties, suc
m alloys have a
t. Mg-Li alloy
rns. In this wo
us wire. The m
de an effective
riment was me
then extruded
m-lithium allo
od and found to
s 34.7%. The t
Table 1. Chem
of the specime
, washing with
© www.iosrd.or
Availabl
D Internati
olume 1, Issu
Journal home
ons of mic
pass TIG
hi1*
, V. Caleb
epartment of M
chanical Engin
hor, E-mail ad
ried out on sup
here. The micr
microstructure in
tensile streng
s and brittlene
s in the fusion
ostructure; me
h-specific stren
hem a kind of g
l magnesium a
, transportation
magnesium all
ow melting poi
y active and re
lidification cra
ch as coarse gr
a low melting
ys have similar
ork, a superligh
microstructure
theoretical an
elted in a vacu
d with an extr
oy plates used i
o be 1.45 g/cm
thickness of th
mical composit
Li Al
10.36 2.69
en’s and wires
h alkali, washin
rg | All Rights
e online at ww
tional Journ
ue 1, Novemb
e page: http://io
crostruct
G welding
bEugene2,
S.
Mechanical Eng
neering, Jeppia
ddress: vijayasa
per-light magne
rostructure and
n the fusion zo
th of the weld
ss in the heat-a
zone.
echanical prope
ngth, excellent
green metallic
alloys have at
n, electronic an
loy [4−6], as jo
int, high therm
eadily oxidized
acks of TIG we
rains, oxidatio
point and larg
r problems, and
ht magnesium-
is analyzed an
d experimenta
uum intermedi
rusion ratio o
in this experim
m3. The tensile
he base metal
tion of Mg-Li a
Zn Ce
0.91 0.81
were cleaned.
ng with water,
Reserved
ww.orsrd.org
nal of Engi
er 2014, Page
osrd.org/journa
ture and
g with Mg
Prabhu3
and
gineering, Anna
aar Institute of
arathiprabakar
esium-lithium
d mechanical
one is fine, and
ded joint is abo
affected zone. D
erties; segrega
t dimensional
structural mat
ttracted much
nd military ind
oints are impor
mal conductivit
d [7−8]. ASAH
elded magnesiu
on, volatilizatio
ge thermal con
d as their appl
-lithium alloy
nd the mechan
al basis for exp
ate induction
f 16 at 653 K
ments shown in
e strength of th
was 2 mm be
alloy (mass fra
Mg
85.23
The specific p
, washing with
ineering
es 21-25
als
mechan
g-Li alloy
d V. Anish4
a university Ind
f Technology, In
ran@gmail.com
alloy plates w
properties of
d the microstruc
out 84% that o
During the we
ation
stability and g
terial for the21
attention amo
dustries [3]. C
rtant for advan
ty, electrical c
HING [6] poin
um alloy were
on and therma
nductivity, ele
lications increa
is welded by t
nical properties
panding the app
furnace under
Kand rolled a
n Table 1. The
he base metal b
fore welding b
action, %)
process involve
h acid, washing
21 | Pa
ical prop
y
dia
ndia
m
with a thickness
the welded jo
cture in the hea
of the parent m
lding process,
good energy a
1st century [1−
ong researchers
onsequently, r
nced materials
conductivity an
nted out that d
restrained [9−
l cracking, occ
ectrical conduc
ase, the weldin
tungsten inert
s of the welded
plication of m
the protection
at 473 K. The
density of the
before welding
bevels was pro
ed sanding, wa
g with water a
age
perties
s of 2 mm,
oints were
at-affected
metal. The
aluminum
absorption.
−2]. Mg-Li
s for their
researchers
with wide
nd thermal
due to the
−10]. CAO
cur during
ctivity and
ng of these
gas (TIG)
d joint are
magnesium-
n of argon
e chemical
e alloy was
g was160.8
ocessed as
shing with
and drying,

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consequently. In order to prevent dislocations during the welding process, the two pieces were fixed. There were indentations
in the back of the sizing block, which were used to control the penetration and shape. The parameters of the welding
procedure are shown in Table 2. In order to reduce overheating and prevent burn-through, a high welding speed was used in
the process.
Table 2. Parameters of welding procedure
Welding
current/A
Welding speed/
(cm·min−1)
Gas flow/
(L·min−1)
Welding arc
voltage/V
80 30 13 18
After welding, the sample was cut perpendicularly to the welding seam. These specimens were then prepared using standard
metallographic procedures. The specimens were etched by a 2% nital for 10−30 s until the microstructure was revealed. The
microstructure was subjected to optical and scanning electron microcopy and the distribution of the alloying elements was
measured using energy dispersive X-ray spectroscopy. After removing the residual part of the coronal zone, the plates were
machined into tensile specimens according to the ASTM E8M-04 standard procedure. The schematic diagram of tensile
specimens is shown in Fig.1, and the tensile test was brought out at a speed of 5mm/min on five specimens. Bending
properties were also tested.
Fig.1. Dimensions of tensile specimen (All dimension are in mm)
3. Results and discussion
3.1. Macro-morphology of welding seam
The macro-morphology of the welding seam is shown in Fig.2. There are no macroscopic irregularities, such as weld
beadings or crater cracks.
Fig.2. Macro-morphology of welded seam: (a) Front face; (b) Back face
3.2. Microstructure of welded joint
The TIG-welded joint included a fusion zone, a heat-affected zone (HAZ) and a base metal zone. The microstructure of the
welded joint is shown in Fig.4. The base metal is composed of single phase (β phase) with equiaxed grains which are not
uniform. The microstructure in heat-affected zone is coarser than that in the parent metal. In Fig.3(c), the microstructure of
the fusion zone exhibits refined grains. As shown in Fig.4 (d), the base metal and welding seam are fused well and the
structure is tight. The microstructures in different areas are not uniform, which are mainly related to the TIG welding thermal
cycle process and the physical properties of magnesium alloys. During the welding process, the metal in the fusion zone

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absorbs a large amount of heat and melts, and then quickly solidifies because the thermal conductivity coefficient of
magnesium alloy is high (154W/ (m·K)) [12−13]. On the other hand, the pulses in the welding process contribute to the rapid
solidification of the metal. Therefore, the microstructure of the fusion zone is refined. During the welding process, because
the melting point of magnesium alloys is low (usually500−600 °C) [14−15], the heat-affected zone is wide and easily
overheated, so the absorbed heat promotes grain growth, resulting in coarser grains in the heat-affected zone. After rolling
deformation, the stored energy is relatively high and the grains are extremely unstable. Therefore, the grains grow rapidly
when they are heated.
Fig.3. Microstructures of welded joint: (a) Base metal; (b) HAZ; (c) Fusion zone;
(d) Junction of base metal and heat-affected zone
3.3. Mechanical properties of TIG welded plate
The mechanical properties of the TIG welded specimens and the base metal are given in Table 3. The tensile strength of the
TIG welded plate is 84% that of the parent metal.
Table 3. Tensile properties of Mg-Li alloys
Sample Tensile strength/MPa Fault location
Base metal 170.75 Middle of sample
Welded plate 143.76 Welding zone
According to Fig.4, the grains in the heat-affected zone are clearly coarser than those in the fusion zone and the base metal.
These coarse grains result in a decrease of mechanical properties. As proved by the tensile test, fractures occurred in the

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heat-affected zone, which indicates that coarse grains are the main reason for the decrease in the mechanical properties of the
weld plate. Table 4 shows the results of the bend test. The angle of the normal bend test and the root bend test approach show
similar ductility in the front and back. Therefore, it is confirmed that there is no front/back difference in properties in this
welding procedure.
Table 4. Result of bend test
Bending mode Angle/(°)
Front bend 30.3
Back bend 30.1
Fig.4. (a) Fractographs of base metal and (b) TIG welded sample
3.4. Fracture analysis
According to the macro-fracture morphology, the base metal fractures in the middle of the specimen, the angle between the
fracture plant and the tensile direction is 45°. The fracture of the TIG welded sample occurs in the heat-affected zone, and the
facture face is rough and dark. There is no obvious necking before failure. Figure 4 shows the fractographs of the base metal
and the TIG welded specimen. The fracture microstructure of the base metal consists of dimples, which is a typical micro-
void coalescence fracture. The fracture microstructure of TIG welded sample is composed of dimples and cleavage planes,
which is characteristic of a mixed-type fracture. This is caused by the change of the microstructure.
3.5. Composition analysis
The microstructure of the compounds is shown in Fig.5. The compositions in the fusion zone were analyzed by EDS, and the
results are shown in Table 5.The compound mainly consists of magnesium, aluminum and cerium, and the content of zinc is
zero. The solid solubility of cerium in magnesium is 0.5%. During solidification, most of the cerium reacts with other
elements to form compounds [16]. The electronegative difference between the magnesium and cerium is 0.1, while that
between aluminum and cerium, zinc and cerium is about 0.4. Cerium should first react with Aluminum. The solid solubility
of zinc in magnesium is large. The content of zinc in this work is lower than 1%, and it can be assumed that all the zinc is
soluted in magnesium. Considering that magnesium is the matrix, the molar ratio of aluminum to cerium is about 2:1, so it
can be predicted that the compound is Al2Ce.During the welding process, the alloy in the welding zone undergoes re-
solidification. Therefore, segregation may occur. As shown in Table 5, the contents of magnesium and zinc at the
intracrystalline phases (Point A) are higher than those at grain boundaries (Point B), and the contents of aluminum and
cerium at the intracrystalline phase are lower than those at grain boundaries. This illustrates that during re-solidification,
aluminum and cerium enrich at the front of the solid-liquid interface after reacting, so that the contents of aluminum and
cerium in the matrix decrease, leading to under cooling and refinement of grains in the weld zone.

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Fig.5. SEM images of compound in fusion zone (a) and grain boundary and infra crystalline phase (b)
Table 5. Microanalysis of positions in Fig.5 (molar fraction, %)
Element Point A Point B Point C
Mg 46.11 88.76 83.40
Al 34.97 0.21 1.65
Zn 0 0.79 0.41
Ce 18.62 0.20 2.40
4. Conclusions
Using the same material as wire, a TIG weld was implemented on the Mg-10.36Li-2.7Al-0.91Zn-0.81Cealloy. There are no
obvious weld defects. The microstructure in the fusion zone is fine, while that in the heat-affected zone is coarse. The heat-
affected zone is the weaker part of the weld plate. The tensile strength of the TIG welded plate is143.73 MPa, which is 84%
that of the parent metal. Fractures occurred in the heat-affected zone, which exhibits a mixed-mode fracture of ductile-brittle.
The segregation and enrichment of Al and Ce are found at the grain boundaries.
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