The 5th International Conference – Innovative technologies for joining advanced materials
Advanced GMAW of AlMg4.5Mn alloy using different
mixture of gases
G. Buyukyildirim1, A. Sedmak2, R. Prokic-Cvetkovic2, O. Popovic2,
V. Grabulov3, R. Jovicic4, M. Burzic4
1
IWE, Istanbul, Turkey
Faculty of Mechanical Engineering, University of Belgrade, Serbia
3
Institute for Material Testing, Belgrade, Serbia
4
Innovation Center of the Faculty of Mechanical Engineering, Belgrade, Serbia
2
E-mail: [email protected]
Abstract
In this paper, the AlMg4.5Mn alloy has been welded by
GMAW process using three different mixtures (Ar+
0.0307%O2, Ar+30%He+0.0317%O2 and Ar+48%He+
0.0290%O2), together with pure Ar, in order to investigate
its influence to the quality of weldments. Testing plates,
dimension 500x250x12mm, have been welded in
horizontal position, using back-up plates, in 4 passes (1
root + 3 filler pass). Welding parameters have been chosen
so that heat input was 6-12 kJ/cm. Tensile strength,
hardness and other mechanical properties, as well as
macro- and microstructure was examined. By comparing
results of these testings for different gas mixtures the main
conlusions are that oxygen does not have important effect
on quality of metal weld, whereas increased helium
content reduces porosity in metal weld and improves the
appearance of weld metal, although its effect on
mechanical properties is not significant.
Introduction
Aluminum alloy AlMg4.5Mn is used nowadays for
constructions like storage tanks, pressure vessels and
vehicles, including yachts and small ships, due to their low
density, high strength and good weldability. Anyhow,
welding problems like pore and porosity, Al2O3 oxide layer
presence, hot and cold cracking and corrosion stability
reduction still exist and more advanced welding processes
are needed. To overcome these problems, the gas metal arc
welding (GMAW) process has been developed, offering a
wide range of shielding gasses, from the inert ones (Ar, He)
to the active one (CO2), including different mixture of
gasses. The latest possibility offers a number of advantages
compared to pure gasses, such as more efficient filler metal
transfer, better liquidity, stabilization of the electric arc, as
well as higher penetration, lower spattering and increase of
welding speed [1, 2].
In this paper three different mixtures mixture of gases
(Ar+0.0307%O2, Ar+30%He+0.0317%O2 and Ar+48%He
+0.0290%O2) have been used, together with pure Ar, to
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investigate its effects to the quality of weldments. Tensile
properties and hardness testing, together with macro- and
microstructural examinations, are presented here, whereas
other mechanical properties, like toughness and crack
resistance is reported elsewhere, [3, 4]. Also, similar study
has been presented for the same material welded by GTAW,
[5-7].
Experimental welding
The plates of the aluminium alloy AlMg4.5Mn, sized
500x250x12mm, were used (according to standard EN 2884:1992) and ``Y`` groove has been made by milling, Fig. 1.
As the filler metal, the Al alloy wire AlMg4.5MnZr was
used. The chemical composition of base and filler metal is
shown in Table 1, while the mechanical properties of base
metal is given in Table 2. As the shielding atmosphere,
different mixtures of gasses were used, with gas flow 15-16
l/min. The welding of the testing plates was performed by
GMAW procedure, using back-up ceramics plate, Fig. 2.
The plates were welded in one root pass plus three filler
passes, with large drops metal transfer in the root pass and
spray metal transfer in the filler passes. All the passes were
performed using the forward welding technique. The
welding parameters (current, voltage, welding speed and the
calculated welding heat input) are shown in Table 3. The
preheating temperature of plates was above 110°C in order
to reduce porosity, as explained in [5, 6].
Figure 1: Shape and dimensions of „Y” groove
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The 5th International Conference – Innovative technologies for joining advanced materials
The macrostructure of AlMg4,5Mn alloy used for this
experiment is shown in Figure 2. It consists of elongated
grains, typical for rolled plates, with fine system of Mg2Al3
on the grain boundaries. Also a large microcontituent is
visible, mostly Mg2Si and (Fe,Mn)Al6.
TABLE 4: ALUMINUM ALLOY ALMG4,5MN MECHANICAL
PROPERTIES
Specimen
No
Figure 2: Back-up ceramics plate
Rm (Mpa)
TABLE 1: CHEMICAL COMPOSITION OF BASE METAL
ALMG4,5MN AND FILLER MATERIAL, WT-%
El
Si
Fe
Cu
Mn
Mg
Zn
Cr
Ti
base
metal
0.13
0.21
0.04
0.66
3.95
0.03
0.06
0.025
filler
metal
0.07
0.21
0.01
0.71
4.6
0.02
Tensile
Strength,
0.07
Elongation
A (%)
Roll
direction
1
293.6
135
26.3
2
293.0
131
23.7
Cross
direction
1
304.4
145
25.7
2
304.8
142
28.3
Zr
0.09
Yield
Strength,
R0.2(Mpa)
0.11
TABLE 2: MECHANICAL PROPERTIES OF ALMG4,5MN ALLOY
Tensile
strength,
Rm
(MPa)
Yield
strength,
R0.2
Elongation
Toughness,
A (%)
J
(MPa)
Longitudinal
direction
293-294
131-135
23-26
41
Transversal
direction
304-305
142-145
25-28
32
Figure 3: Aluminum alloy AlMg4,5Mn microstructure
TABLE 3: WELDING PARAMETERS
Shiel-
Pass
Current,
ding
No
A
Voltage,
V
gas
Welding
speed,
cm/min
Heat
input,
kJ/cm
Interpass
temp. C
1
160
19.2
29.1
6.3
75
Ar
2-4
167-171
22.9-23.5
26.5-33.7
7.0-8.9
73-80
Ar+
1
155
19.3
20.4
8.8
75
0,0307%
O2
2-4
171-174
23-23.4
24-32.7
7.3-10.2
70-75
Ar+30%
He+
1
145
19.2
23.5
7.1
75
2-4
159-201
22.9-24.9
21-43.5
6.1-10.4
65
1
148
19.7
23.3
7.5
75
2-4
186-206
25-25.9
24.2-54.5
5.9-11.6
70
0,0317%
O2
Ar+48%
He+
0,0290%
O2
To identify mechanical properties of base metal, the
specimens with circular cross section (Ø6 mm) have been
tested and results shown in Table 4.
2
Results and discussion
Macrostructure of weld metal is shown in Fig. 3, and
microstrucures of weld metal and HAZ are shown in Fig. 4
and 5, respectively. In Fig. 3 one can notice the effect of He
on weld metal shape, being wider and having better shape in
general. The best appearance of the weld metal is with 30%
He. Figure 4 indicates that the weld metal microstructure of
all welded plates is practically the same, consisting of
directed dendrites and homogeneously distributed intermetallic particles. This was to be expected, since the welding
conditions were approximately the same, the only difference
being the shielding atmosphere. The basic difference in the
microstructure is their porosity, being pronounced for pure
Ar, including presence of gas pores. Porosity is still present,
but to much lesser content for Ar+0.0307%O2 and
practically absent when He is added. The presence of other
types of defects that could affect the quality of welded joints
was not observed. Figure 5 indicates that the base metal
elongated grains are transformed in HAZ into coarsened
equiaxial grains which gradually change their shape into fine
grain directed dendrites.
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The 5th International Conference – Innovative technologies for joining advanced materials
140
ploca 10
Nivo 2
120
Tvrdoca, HV5
100
80
60
OM
20
ZUT
ZUT
40
MŠ
OM
0
a)
0
2
4
6
8
10
12
14
16
18
20
Merno mesto
140
Ploca 11
Nivo 2
120
Tvrdoca, HV5
100
Figure 4: Macrographs of the weld joints
80
60
OM
20
ZUT
ZUT
40
MŠ
OM
0
0
2
4
6
b)
8
10
12
14
16
18
2
Merno mesto
140
Ploca 12
Nivo 2
120
Tvrdoca, HV5
100
80
60
Figure 5: Microstructure of the weld metal
ZUT
OM
20
ZUT
40
MŠ
OM
0
0
c)
2
4
6
8
10
12
14
16
18
2
Merno mesto
140
Ploca 13
Nivo 2
120
Tvrdoca, HV5
100
80
60
ZUT
OM
20
d)
ZUT
40
MŠ
OM
0
0
2
4
6
8
10
12
14
16
18
2
Merno mesto
Figure 6: Microstructure of the HAZ
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Figure 7: Hardness distribution a) Ar; b); Ar+
0,0307%O2 c) Ar+30%He+0,0317%O2 ; d) Ar+48%He+
0,0290%O2; (OM=BM, MS=WM, ZUT=HAZ,
tvrdoca=hardness)
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The 5th International Conference – Innovative technologies for joining advanced materials
Hardness distribution is shown in Fig. 7 indicating values
72-84 HV5 in HAZ and 68-87 HV5 in the weld metal, being
cca 10% more than for the base metal. The highest values of
hardness are obtained with shielding gas mixture
Ar+0.0307%O2, the lowest with pure Ar, but the overall
effect of shielding gas on hardness is not significant.
Results for tensile properties are given in Table 5, indicating
weak effect of shielding gas on Tensile strength, and
somewhat more pronounced effect on Elongation.
Comparing with the base metal, Elongation is significantly
reduced, especially with pure Ar, whereas Tensile Strength
is practically the same. The complete stress-strain curve for
standard welded joint specimen is shown in Fig. 8,
indicating similar behaviour as the base metal.
TABELA 5: RESULTS FOR TENSILE PROPERTIES OF WELDED
JOINTS
Shielding gas Specime Specimen
n
thickness,
No
Ar
Ar+0.0307%O2
d (mm)
Tensile Elongati
Strength,
on
Rm (MPa)
Fracture
Location
A (%)
1
12
287
14
HAZ
2
12.1
272.1
12.5
HAZ
1
12
300
20.5
HAZ
2
12
300
19
HAZ-WM
Ar+30%He+
0.0317%O2
1
12
274
14
HAZ-WM
2
12
293.2
20
HAZ-WM
Ar+48%He+0.0
290%O2
1
12
294.8
20
HAZ
2
12
289.5
17
HAZ -WM
Conclusion
Based on the results and discussion presented in this paper,
one can make following conclusions:
•
•
•
Adding Helium to Argon and Oxygen mixture
decreases the porosity level in weld metal, producing
high quality welded joints, including better shape od
weld metal, with both 30% and 50% of He.
The tensile strength and hardness have not been
significantly affected by the shielding gasses, whereas
the elongation has been significantly reduced,
compared to the base metal, and also affected more
pronounced by the shielding gas composition.
Increasing the amount of helium in the shielding
atmosphere has weak effect on mechanical properties,
whereas it has significant effect on porosity reduction.
Having in mind the cost of He compared to Ar and
Oxygen, and the fact that 30% He also produces the
smallest overlay and the best appearance of weld metal,
one can conclude that more than 30% of He is probably
not a reasonable choice.
Acknowledgements
This article is part of the research in project “Application of
modern aluminium alloys for welded structures”, financed
by Ministry of Science of the Republic of Serbia. The
project is referenced under record number TR-14025.
References
Figure 8: Typical stress-strain diagram for welded joint
Other mechanical properties, like Charpy toughness and
crack resistance (both static, the fracture toughness, and
dynamic – Paris law) is reported elsewhere [3-5].
4
[1]. Welding handbook, 9th Edition, Vol. 3, AWS, 2010
[2]. Sven-Frithjof Goecke: Effect of adding active gases in the
vpm range to argon on pulsed MIG welding of aluminium, PhD
Thesis, Berlin, 2004.
[3]. G. Buyukyildrim, A. Sedmak, Z. Burzic, R. ProkićCvetković, M. Burzic, R. Jovicic, Crack Resistance of Al-Mg4.5Mn weld metal made by GMAW, Structural Integrity and Life,
Vol. 11, No.2, 2011, pp. 61-66
[4]. G. Buyukyildrim, A. Sedmak, R. Prokić-Cvetković, O.
Popovic, R. Jovicic, The effect of shielding gas on the toughness of
AlMg4,5Mn weld metals made by GMAW, accepted for print,
FME Transaction, No3/2011
[5]. S. Kastelec-Macura Ph.D. (in serbian), Faculty of Mechanical
Engineering, University of Belgrade, 2011
[6]. S. Kastelec-Macura, R. Prokić-Cvetković, O. Popović, R.
Jovičić, M. Burzić, Porosity of welded joints of AlMg4.5Mn alloy,
Structural integrity and life, Vol.8, No.2, 2008, pp. 114-120
[7]. R. Prokić-Cvetković, S. Kastelec-Macura, A. Milosavljević,
O. Popović, M. Burzić, The effect of shielding gas composition on
the toughness and crack growth parameters of AlMg4,5Mn weld
metals, J. Min. Metall. Sect. B-Metall. 46 (2) B (2010) 193 - 202
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