article

1. International Journal of Advanced Engineering Technology E-ISSN 0976-3945
IJAET/Vol.II/ Issue III/July-September,2011/10-13
Research Article
FRICTION STIR WELDED JOINTS OF CAST SCANDIUM
ADDED ALUMINUM-MAGNESIUM ALLOY
K.Subbaiah1
, Geetha Manivasagam2
, Govindarajan3
, S.R.K.Rao4
Address for Correspondence
1
Sri Sivasubramaniya Nadar College of Engineering, Chennai, Tamil Nadu, India.
2
SMBS, VIT University, Vellore, Tamil Nadu, India.
3
Center for Non-Ferrous Technology Development Center, Hyderabad.
4
Tagore Engineering College, Chennai, Tamilnadu , India
E Mail subbaiahk@ssn.edu.in
ABSTRACT:
Cast scandium added aluminum-magnesium alloy was friction stir welded, and the tensile properties of the global joint
and its component parts were examined and analyzed. The weld composed of weld nugget and thermo-mechanically
affected zone exhibited better mechanical properties than the base metal. The global joint fractured in the base material,
and thus possessed slightly greater tensile strength than the base metal. These results clearly show that friction stir
welding is an optimum welding process for cast Al-Mg-Sc alloys.
KEYWORDS: Friction stir welding, cast Al-Mg-Sc alloy, mechanical properties.
INTRODUCTION:
Cast aluminum alloys are widely used in the
transportation industries and can be arc welded
(either Metal Inert Gas or Tungsten Inert Gas
welding) in a protective atmosphere or joined by
brazing.[1] Unfortunately, the welding production
cost is relatively high and some welding defects
such as porosity and slag inclusion are easily
formed in the weld. Friction Stir welding (FSW) is
a promising process that can produce high quality,
low cost joints [2]. This welding process is being
extensively and intensively studied in order to weld
various types of wrought aluminum alloys,
especially Non-heat-treatable aluminum alloys [3-
9]. It is also being developed to weld other
materials such as magnesium, inconel, titanium,
invar, brass, steel, and aluminum matrix
composites [10-18]. Scandium is classified among
3d transition metals and, hence, its reaction with
aluminum has salient features inherent in reaction
of other 3d transition metals with aluminum.
Scandium is one of the most effective modifiers of
a cast grain structure in aluminum alloys.
Continuously cast commercial scandium-bearing
aluminum alloy ingots have, as a rule, a
nondendritic structure which has no internal
structure (its grains are not divided into small
constituents) and shows geometrical equality of
grains and the dendritic parameters. The ability of
scandium to refine grains is used in the case of
fusion welding of aluminum alloys;
susceptibility of the alloys to crack formation
reduces sharply, while mechanical properties of
weld joints increase noticeably [19]. Scandium
tends to formation of anomalous supersaturated
solid solutions at rather low cooling rates
feasible in casting of rather large ingots. In
heating, scandium solid solution in aluminum
decomposes to form Al3Sc dispersed particles,
which makes a great contribution to
strengthening of the alloy [20]. In this study, a
Cast Scandium added Aluminum- Magnesium
alloy was selected as the experimental material
to demonstrate the feasibility of FSW. Emphasis
is placed on the mechanical properties such as
yield stress, ultimate tensile strength and
percentage elongation of the joint.
EXPERIMENTALmPROCEDURE:
The starting materials used in the preparation of
the experimental cast Al-Mg-Sc alloy were AA
5083 alloy and Al-2% master alloy. Appropriate
amounts of the starting materials were melted in
a vacuum induction melted furnace to produce an
Al-Mg-Sc alloy with a nominal composition
similar to AA 5083 with 0.29 wt % Sc addition.
The chemical composition of the alloy was
analyzed by inductively coupled plasma atomic
emission spectroscopy. The aluminum alloy
studied in the present experiment is having
chemical composition of (in wt %) Mg-4.214,

2. International Journal of Advanced Engineering Technology E-ISSN 0976-3945
IJAET/Vol.II/ Issue III/July-September,2011/10-13
Mn-0.787, Fe- 0.407, Si-0.165, Zn-0.12, Cu- 0.025,
Cr- 0.01, Ti- 0.01, Sc-0.29 and the rest aluminum.
Bead-on-plate Friction Stir Welding was applied to
the 5 mm thick cast Al-Mg-Sc material. Rotation
speed of the welding tool was 650 rpm, and the
traverse speed was 158 mm/min. A vertical plunge
force of 17 KN was applied over the tool. Features
for the welding tool included a shoulder diameter
of 15 mm, a pin diameter of 5 mm on the top and 4
mm on the bottom and a pin length of 4.7 mm
(Fig.1.). The utilized tool was made in M2 steel
having chemical composition of (in wt %) C-0.85,
Cr-4.0, W-6.0, Mo-5.0, V-2.0, and rest iron. The
high speed tool was quenched at 10200
C,
characterized by a 50 ~55 HRc hardness. An
indigenously designed and developed machine (30
KN; 3000 RPM; 15 HP) has been used to fabricate
the joints. After welding, the joints were cross-
sectioned perpendicular to the welding direction
for metallographic analyses. Specimens for tensile
tests were cut using an EDM machine. The tensile
properties of the joint and its component parts were
measured by conducting tensile tests on universal
testing machine. The configuration and size of the
transverse tensile specimens were prepared
according to Fig.2, in which different size
specimens were used to determine the mechanical
properties of the joint and its component parts.
Fig.1. photograph of friction stir welding tool.
Fig. 2 a) Global joint (ASTM-E8 standard
specimen)
Fig. 2 b) component joint part (Small)
Fig. 2 c) component joint part (Very small)
RESULTS AND DISCUSSIONS:
Tensilekproperties:
The average values of the tensile properties of
cast Al-Mg-Sc alloy plate, i.e., yield stress;
ultimate tensile stress and percentage
elongation are 203 MPa, 214MPa and 7%
respectively. With regard to the global joint,
the yield stress, the ultimate tensile strength,
and percentage elongation are 207 MPa, 232
MPa, and 6.8 % respectively. The joint is
fractured in base metal far distant from the
weld. The weld properties are better than the
base metal properties. This correlates well
with the earlier results corresponding to cast
aluminum alloys [21& 22].
In order to further evaluate the tensile
properties of the weld nugget, the gauge length
of the tensile specimens was reduced to 15 mm
(Fig.2). The yield stress, the ultimate tensile
strength, and percentage elongation of the
weld nugget were measured to be 212 MPa,
242 MPa, and 5.6 % respectively. This
indicates that the tensile properties of the weld
nugget are much higher than those of the base
metal. This result also denotes that the weld
nugget is also shown to have higher tensile

3. International Journal of Advanced Engineering Technology E-ISSN 0976-3945
IJAET/Vol.II/ Issue III/July-September,2011/10-13
properties than the thermo-mechanically affected
zone of the joint.
In order to further evaluate the tensile properties
of the weld, the gauge length of the tensile
specimens was reduced to 4 mm [Fig .2]. The
yield stress, the ultimate tensile strength, and the
percentage of elongation of the weld were
measured to be 232 MPa, 259 MPa, and 11%
respectively. This indicates that the tensile
properties of the weld are much higher than
those of the base metal. The best values for the
FSW welded cast aluminum-magnesium-
scandium alloy were found as 253 MPa, 287
MPa, and 11 % for the yield stress, ultimate
tensile strength, and the percentage of elongation
respectively. When we compare this value with
the highest values obtained for the base metal
values of cast Al-Mg-Sc alloy, the FSW weld
has produced better tensile properties because of
grain refinement in the microstructure and
elimination of casting voids from the welded
portion.
TENSILE PROPERTIES
203 214207
230
212
242232
259
0
50
100
150
200
250
300
YIELD UTS
STRESS,MPa
Base
Global
Small
V.Small
Fig.3.Tensile properties
DUCTILITY PROPERTIES
7 6.8
5.6
11
0
2
4
6
8
10
12
% EL
%,ELONGATION
Base
Global
Small
V.Small
Fig.4. Ductility properties
CONCLUSIONS
1. The tensile properties of the component
parts are better than the tensile properties
of the global joints.
2. The tensile failure occurred in the global
joint at the base metal, whereas, the
failures occurred in the weld nugget in the
case of component joints.
3. The best values of yield stress, ultimate
tensile strength, and percentage elongation
for the Friction Stir Welded cast Al-Mg-
Sc aluminum alloy plates are 253 MPa,
287 MPa, and 11 % respectively.
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