1. Effects of Shielding Gas on
Gas Metal Arc Welding Aluminum
Contrary to the conclusion of previous investigators, argon may
be the optimum shielding gas for the gas metal arc welding of aluminum
BY W . R. REICHELT, J. W . E V A N C H O A N D M . G. H O Y
ABSTRACT. A r g o n , h e l i u m , and mix-
tures of these gases are used for shield-
ing in gas metal-arc w e l d i n g of a l u m i -
n u m . Considerable w o r k has been
d o n e previously by other investigators
to define the effects of these gases on
penetration, arc stability and porosity.
Most of this w o r k , however, was per-
f o r m e d by maintaining an " o p t i m u m "
arc gap. Consequently, for various
compositions and flow rates studies,
w e l d parameters were also varied.
To further understand the effects of
shielding gas on gas metal-arc w e l d i n g
a l u m i n u m , a study was c o n d u c t e d
w h e r e b y all w e l d settings w e r e preset
at constant values and effects of
shielding gas c o m p o s i t i o n and f l o w
rate o n arc gap, voltage, and current, in
addition to penetration, arc stability,
and porosity w e r e evaluated. Shielding
gas c o m p o s i t i o n and f l o w rate b o t h
affected d e p t h of penetration. M a x i -
m u m penetration was o b t a i n e d w i t h
pure argon at 150 c f h , whereas m i n i -
m u m depth of penetration was asso-
ciated w i t h a 25% argon/75% h e l i u m
mixture at 200 cfh.
Effects of shielding gas on d e p t h of
penetration correlated directly w i t h
effects of shielding gas o n wattage.
Gas compositions high in argon also
p r o d u c e d best arc stability, a n d the
m i n i m u m a m o u n t of micro-porosity.
Results of this w o r k suggest that, c o n -
trary to the conclusions of previous
investigators, argon my be the o p t i -
m u m shielding gas for gas metal-arc
w e l d i n g of a l u m i n u m .
Paper presented under sponsorship of the
Aluminum Alloys Committee of the Weld-
ing Research Council at the AWS 60th
Annual Meeting in Detroit, Michigan, dur-
ing April 8-12, 1979.
W. R. REICHELT, J. W. EVANCHO and M. G.
HOY are with the Joining Division of Alcoa
Laboratories, Alcoa Center, Pennsylvania.
I n t r o d u c t i o n
Shielding gas, as an i m p o r t a n t vari-
able in gas metal-arc w e l d i n g of a l u m i -
n u m , serves three primary f u n c t i o n s : It
provides a plasma for c o m m u t a t i o n of
current; it protects the w e l d p o o l f r o m
reacting w i t h the air e n v i r o n m e n t ; and
w h e n w e l d i n g using direct current re-
verse polarity (DCRP), it can provide
the cleaning action w h i c h partially
removes a l u m i n u m oxide f r o m the alu-
m i n u m plate.
The physical properties and charac-
teristics of b o t h argon and h e l i u m , the
t w o principle shielding gases used for
w e l d i n g a l u m i n u m , are c o m p a r e d in
Table 1. The ionization potential of
argon is m u c h lower than that of
h e l i u m ; ionization potential is the
voltage required to m o v e an electron
f r o m an a t o m , thereby t u r n i n g the
a t o m into an ion. Comparison of i o n i -
zation potentials gives an indication as
to the relative ease w i t h w h i c h the
shielding gas forms the plasma; the
higher the ionization p o t e n t i a l , the
more difficult it is to initiate an arc.
High ionization potentials can also
result in poor arc stability; h e l i u m ,
therefore, welds w i t h a less stable
arc.
Thermal c o n d u c t i v i t y is i m p o r t a n t ,
because a gas w i t h g o o d thermal c o n -
ductivity will help to c o n d u c t heat
into the w o r k p i e c e . Degree of thermal
conductivity has been reported to
affect the shape of the w e l d bead and
the c o n d i t i o n of the metal next to the
w e l d . Helium's high thermal c o n d u c -
tivity relative to that of argon is one
factor w h y w e l d s m a d e w i t h h e l i u m
show a broader w e l d puddle. Density
of h e l i u m is o n e - t e n t h that of argon.
Because of this difference in density,
higher f l o w rates are generally re-
quired w h e n w e l d i n g w i t h h e l i u m .
Argon possesses excellent cleaning
Table 1—Properties of Shielding Gas
Ionization potential
Arc initiation
Arc stability
Thermal conductivity
(cal/sq. cm/cm/°C/s)
Density (relative to air)
Cleaning action
Argon
15.8 eV
Good
Good
0.406 x 10
1.38
Good
Helium
24.6 eV
Poor
Poor
3.32 X 10-
0.137
Poor
Table 2—Advantages/Disadvantages of Helium and Argon
Advantages
Helium • Higher arc voltage and assumed
greater heat input (deep penetra-
tion and high welding speeds)
• Broad weld root width
Argon • Good arc initiation and stability
• More effective shielding
• Low cost
• Good cleaning
Disadvantages
• Poor cleaning
• Poor arc initiation and stability
• Cost
• Requires greater flow rates
• Narrow weld root width
W E L D I N G R E S E A R C H S U P P L E M E N T I 147-s
2. Fig. 1—Grooved 5083 plate. Groove dimensions: VA in. (6.3 mm)
deep and Yi in. (12.7 mm) wide
Fig. 2—Commercially available equipment utilized during weld evalua-
tion. Shown are the welding torch, arc viewer, track wire filler metal
feed controller
action. Helium on the other hand pro-
vides no cleaning.
Because of the differences in physi-
cal properties and characteristics of
helium and argon, each shielding gas
has its advantages and disadvan-
tages-Table 2. A higher arc voltage
associated with helium results in a
greater heat input and supposedly a
deeper penetration. This greater heat
input also permits welding at higher
speeds. The main advantage asso-
ciated with the high heat input, how-
ever, is the broad weld root width
obtained when welding with helium.
Although the greater heat input is a
major advantage for helium, this gas
also has several disadvantages. Helium
does not assist in cleaning the oxide
from aluminum plate, and its high
ionization potential results in difficult
arc initiation and poor arc stability. A
greater flow rate is also required with
helium because of its lower density.
Probably the greatest disadvantage of
this shielding gas is related to its cost.
Helium continues to be more costly
than argon.
Argon has many advantages over
helium. Because of its low ionization
potential, it demonstrates good arc
initiation characteristics and excellent
arc stability. Argon is also effective in
assisting cleaning of the oxide from
aluminum plate. Because of its higher
density, argon provides a more effec-
tive shield from the environment at
lower flow rates than are required for
helium; also, most importantly, argon
is cheaper than helium. The main dis-
advantage attributed to argon is the
narrow weld root width that results
when using this shielding gas.
Many of these statements about
argon and helium as shielding gases
have resulted from qualitative evalua-
tions over several years. However, only
limited quantitative data on the effects
of shielding gas composition or flow
rate are available in the literature. As a
result, several "rules of thumb" have
evolved as to the benefits of the vari-
ous shielding gases or the mode of
using the various shielding gases with-
out substantial theoretical verification.
In this regard, most references on arc
welding indicate that shielding gas
flow rate should be selected by reduc-
ing flow rate until an unstable arc is
observed and then increasing the flow
rate slightly for a safety margin. Anoth-
er statement is that helium provides
greater penetration.
Previous in-house process develop-
ment work has suggested that shield-
ing gas flow rates may be just as
significant as shielding gas composi-
tion in affecting weld penetration and
weld cross-section geometry. To quan-
tify the effects of shielding gas compo-
sition and flow rate, a program investi-
gating both argon and helium was
conducted.
Procedure
Effects of shielding gas composition
and flow rate on weld penetration and
weld cross-section geometry were de-
termined by automatic GMA welding
in the flat position. Shielding gas com-
positions ranging from pure argon to
pure helium, including various mix-
tures, were evaluated at flow rates
ranging from 50 cfh (23.5 liters/min) to
300 cfh (141 liters/min). The program
was conducted in two phases as
described below.
Phase l-No Arc Gap Control
Initial weld parameters were deter-
mined using a shielding gas composed
of 50 cfh (23.5 liters/min) helium and
50 cfh (23.5 liters/min) argon. Wire
filler metal feed speed, current and
travel speed were adjusted to produce
a smooth welding arc and a sound
weld. The weld settings determined by
an experienced welder's observations
follow: voltage-35 V; current-404 A;
travel speed—12 ipm (5 mm/s).
These parameters resulted in an arc
length of 0.148 in. (4 mm). Subsequent
welds were made maintaining these
machine settings as shielding gas com-
position and flow rate were varied.
Initially, three welded samples were
made for each condition of shielding
gas composition and flow rate. How-
ever, uniform results permitted the
number of samples to be reduced to
one per shielding gas variable.
Phase II—Arc Gap Control
The procedure for Phase II was simi-
lar to that of Phase I. In this phase,
however, a constant arc gap of 0.150
in. (4 mm) was maintained first by
adjusting current. The procedure was
then repeated and arc gap was
adjusted by voltage (filler metal
feed).
Accurate shielding gas flow rates
were maintained through the use of
thermal mass meters. Voltage and cur-
rent were recorded using a Brush
recorder, and arc gap was observed by
means of an arc viewer mounted on
the travel carriage.
All welds were made on a grooved
5083-0 plate, 1 X 9 X 1 2 in. (25.4
x 228 X 305 mm), using 3/32 in. (2.4
mm) diameter 5183 electrode. The
groove was VA in. (6.3 mm) deep and Vi
in. (12.7 mm) wide—Fig. 1. Shielding
gas was commercial welding grade
argon and helium.
All welds were cross-sectioned at
the midpoint perpendicular to the
weld. The cross-section was polished
and etched; and weld penetration,
width at varying depths,* and crown
height were measured. In Phase II,
welders' comments concerning arc
characteristics were also docu-
mented.
*Weld width measured approximately VA in.
(6.4 mm) from bottom of weld
148-sl M A Y 1980
3. Equipment
Commercially available equipment
was utilized for this investigation—Fig.
2. This equipment included a water-
cooled welding torch with a 3
/4 in. (19
mm) gas cup, a wire filler metal feed
controller, a Gulco KAT track, and a
drooping volt-ampere characteristics
power supply.
Results
Phase I—No Arc Gap Control
When arc gap was allowed to vary,
both shielding gas composition and
flow rate significantly affected weld
penetration—Fig. 3. For pure argon,
maximum penetrations were asso-
ciated with 150 cfh (70.5 liters/min)
flow rates. Flow rates greater than or
less than 150 cfh (70.5 liters/min)
resulted in lesser penetrations. Mini-
mum penetrations were associated
with shielding gas compositions be-
tween 60 and 80% helium at approxi-
mately 150 cfh (70.5 liters/min) to 200
cfh (94 liters/min) flow rates. Increas-
ing or decreasing the flow rate or
increasing or decreasing the percent-
age of helium in the shielding gas
resulted in increased penetration. In
no case, however, was penetration as
great as the level obtained with 150 cfh
(70.5 liters/min) pure argon.
Shielding gas flow rate had little
effect on weld root width. However,
shielding gas composition significantly
affected weld root width. Root widths
less than 0.250 in. (6.3 mm) were pro-
duced with pure argon and increased
to 0.4 in. (10 mm) with compositions
NO ARC GAP CONTROL
100
ARGON - CFH
Fig. 3—Effect of shielding gas on weld penetration
containing 70% helium—Fig. 4.
Effects of shielding gas on weld
cross-sectional area were complex and
are shown in Fig. 5. For shielding gas
compositions rich in argon, flow rate
had a significant effect on cross-
sectional area. Maximum cross-sec-
tional areas of 1 square inch (645 mm2
)
was obtained at flow rates between
100 cfh (47 liters/min) and 150 cfh
(70.5 liters/min) for compositions con-
taining 50% or more argon. As the
compositions became richer in he-
lium, flow rate had less effect; howev-
er, variations in composition between
70 and 90% helium did affect cross-
sectional area.
These results are further illustrated
in Fig. 6, which shows weld cross-
section profiles as affected by shield-
ing gas composition and flow rate. Of
particular interest is the effect of flow
90% He 80% 60%
50%
20%
10%
150
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NO ARC GAP CONTROL
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ARGON - CFH
150
Fig. 4—Effect of shielding gas on weld root width
50 100
ARGON - CFH
Fig. 5—Effect of shielding gas on weld cross-sectional area
150
W E L D I N G RESEARCH SUPPLEME NT I 149-s
4. 200 NO ARC GAP CONTROL
U
uJ
I
0 0
50
100
ARGON-CFH
150 200
Fig. 6—Effect of shielding gas on weld cross-section geometry
rate on increasing the weld root width
when pure argon is used. Weld root
profile for 150 cfh (70.5 liters/min)
argon is similar to profiles using an
argon-helium gas mixture. A flow rate
of 150 cfh (70.5 liters/min) pure argon
provides adequate weld width and
deep penetration and is a significant
improvement over the narrow weld
spike typically associated with pure
argon. Wide weld widths generally
associated with pure helium or com-
positions high in helium are most evi-
dent at the top of the weld. However,
this wide weld bead provides no sig-
nificant benefit.
Phase II—Arc Gap Control
Arc Cap Controlled by Current.
When arc gap was adjusted by current
to 0.150 in. (4 mm), penetration was
primarily affected by shielding gas
flow rate; shielding gas composition
had essentially no effect—Fig. 7.
80% 60% 90% He 80%
X
O 100
50
r
.350 IN.
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.350 IN.
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/ ARC GAP - 0.150"
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20%
50 100
ARGON - CFH
50 100
ARGON - CFH
Fig. 7—Effect of shielding gas on weld penetration Fig. 8—Effect of shielding gas on weld root width
150-sl MAY 1980
5. Increasing the gas flow rate beyond
100 cfh (47 liters/min) decreased weld
penetration.
Both shielding gas flow rate and
composition affected weld root
width—Fig. 8. Mimimum weld root
widths were associated with pure
argon shielding at 50 cfh (23.5 liters/
min). Maximum weld root widths
were associated with pure helium at
flow rates exceeding 100 cfh (47 liters/
min).
Flow rate had a significant effect on
weld cross-sectional area for shielding
gas compositions rich in argon—Fig. 9.
Increasing flow rate decreased weld
cross-sectional area. On the other
hand, shielding gas compositions rich
in helium were not affected by flow
rate, although changes in helium con-
centration did affect the weld cross-
sectional area. Maximum cross-sec-
tional areas of 1 square inch (645 mm'2
)
were obtained with pure helium.
The results are further illustrated in
Fig. 10. The spike typically associated
with welds made using pure argon
shielding gas are evident in this figure.
It is also obvious that the larger cross-
sectional area associated with welds
made using pure helium shielding gas
results primarily from a broadening of
the top of the weld (weld surface
bead). Contrary to what would be
expected, the weld root width is not
significantly affected either by shield-
ing gas composition or flow rate.
Effects of shielding gas composition
I50
90% He 80% 70% 60%
E
_i
UJ
x
50%
40%
30%
20%
10%
50 100
ARGON - CFH
Fig. 9—Effect of shielding gas on weld cross-sectional area
150
and flow rate on arc characteristics are
summarized in Fig. 11. A smooth weld-
ing arc was obtained with a wide range
of shielding gas compositions at flow
rates between 100 cfh (47 liters/min)
and 125 cfh (58 liters/min). Increasing
X
I00
_j
jjj 50
0
ARC GAP =0.150 in.
ADJUSTMENT BY
CURRENT
0 50 100 150
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Fig. 10—Effect of shielding gas on weld cross-section geometry
WELDING RESEARCH SUPPLEMENT I 151-s
6. 100
50
FUZZY
ARC
~ VIOLENT /
ARC /
I
SMOOTH
ARC
V
UNDULATING
PUDDLE
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VIOLENT
ARC -
UNDULATING PUDDLE
V I
90% He 80%
Fig. 11-Effect of shielding
adjustment
100 150
ARGON -CFH
gas on arc characteristics—current
Fig. 12— Effect of shielding gas on weld penetration
SO 100
ARGON - CFH
flow rates beyond 125 cfh (58 liters/
min) resulted in a rough, undulating
arc. Violent arc characteristics were
associated when pure helium was
employed.
Arc Cap Adjusted by Wire Feed.
Contrary to the results obtained when
arc gap was adjusted by current, when
arc gap was adjusted by wire feed,
shielding gas flow rate did not affect
weld penetration significantly. Pene-
tration, however, was significantly
affected by shielding gas composition
— Fig. 12. Maximum penetrations were
obtained for pure argon and decreased
as percentage of helium was in-
creased.
Weld root width was affected pri-
marily by shielding gas composition.
However, shielding gas flow rate
slightly affected root width, especially
at flow rates exceeding 150 cfh (70.5
liters/min). Minimum weld root
widths were associated with pure
argon, and maximum weld root widths
were associated with pure helium, as
shown in Fig. 13.
Both shielding gas flow rate and
composition affected weld cross-sec-
tional area slightly. Maximum cross-
sectional areas are associated with
pure argon at flow rates less than 100
cfh (47 liters/min)—Fig. 14. These
results are dramatically illustrated in
Fig. 15. The tremendous benefit of
pure argon on weld penetration is
obvious from Fig. 15. Of particular
interest is the tendency towards a
wider weld root width for pure argon
at 100 cfh (47 liters/min) than is
normally associated with pure argon
shielding. Weld root width increased
considerably when pure helium was
employed; however, penetration de-
creased significantly. Benefits of ad-
150
100
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450 IN
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Y400 IN.
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.500 IN.
4
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ARC GAP - 0.150"
ADJUSTMENT BY /
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50%
30%
50 100
ARGON - CFH
Fig. 13-Effect of shielding gas on weld root width
50 100
ARGON - CFH
150
Fig. 14—Effect of shielding gas on weld cross-sectional area
152-sl M A Y 1980
8. 1 1 1
ARC GAP = 0.150*
0 CURRENT ADJUSTMENT
O W I R e F E E D
ADJUSTMENT
"
•
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ft
°o%§*
%
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JOULES x 103
.600
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ARC GAP - 0.150"
m CURRENT ADJUSTMENT
O WIRE FEED ADJUSTMENT
•
•
I I
40 50 80 90
Fig. 18—Effect of heat input and method of arc adjustment on
weld cross-sectional area
60 70
JOULES X 103
Fig. 19—Effect of heat input and method of arc adjustment on penetra-
tion
.6
J5
A
3
2
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ARC GAP = 0.150"
CURRENT ADJUSTMENT
WIRE FEED ADJUSTMENT
• •
I I
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-
-
-
-
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cA*
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-
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75%
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60 70
JOULES x 103
Fig. 20—Effect of heat input and method of arc adjustment on weld
root width
WIDTH (IN)
Fig. 21—Effect of shielding gas composition on weld penetration/
weld root width ratio
however, are not consistent with those
previously reported in the literature.
Depending on how arc gap was
adjusted, much deeper penetration
could be obtained when pure argon
was employed. More important, how-
ever, is the effect of flow rate. Flow
rate not only affects weld penetration
but weld root width and, by employ-
ing proper controls, a desirable weld
cross-section geometry can be ob-
tained when using pure argon.
Reasons for the effects of shielding
gas composition and flow rate on weld
cross-section geometry are not ob-
vious. Contrary to what had been
reported previously, greater penetra-
tion did not result from a higher arc
voltage associated with pure helium
shielding. Penetration, however, was
affected by the welding parameters,
particularly current (Fig. 17), regardless
of voltage (wire feed speed) em-
ployed. The differences in weld cross-
section geometry then are attributed
to the effects of changing shielding gas
composition and flow rate on welding
current. This is further illustrated in
Figs. 18,19 and 20.
The effect of heat input on weld
cross-sectional area is indicated in Fig.
18. Regardless of shielding gas compo-
sition and method of arc gap adjust-
ment, weld cross-sectional area in-
creased as expected with increasing
heat input. The method of arc gap
adjustment did, however, affect the
weld cross-section geometry. As indi-
cated in Fig. 19, increasing heat input
increased weld penetration when ad-
justment in arc gap was made by wire
feed adjustments. Current adjust-
ments, however, resulted in a constant
weld penetration even though total
heat input was affected substantially.
The opposite effect is noted for weld
root width—Fig. 20. Increasing heat
input by wire filler metal feed adjust-
ment decreased weld root width as
heat input increased. Conversely, in-
creasing heat input increased weld
root width when arc gap was main-
tained by current adjustment.
True improvements in weld bead
geometry are associated with increas-
ing weld root width while maintaining
a constant penetration or increasing
penetration. Such improvement has
normally been attributed to the use of
helium mixtures in shielding gas. Fig-
ure 21 shows the ratio of weld penetra-
tion to weld root width as a function
of shielding gas composition. Greater
weld root widths for a given penetra-
tion were obtained when pure helium
was employed; however, greater
depths of penetration were obtainable
with pure argon. Most interesting,
however, is that additions of helium to
shielding gas up to a level of 75%
helium did not significantly affect ratio
of weld penetration to weld root
154-sl M A Y 1980
9. width.
Conclusion
Results of this work indicate that
selection of shielding gas in gas metal-
arc welding is an important criteria
which affects not only the arc charac-
teristics but the weld geometry.
Although much concern has previous-
ly been expressed regarding the nar-
row weld root widths resulting from
argon shielding, proper selection of
shielding gas flow rate and method of
arc adjustment can optimize weld root
width when pure argon shielding is
employed and produce satisfactory
weld geometries. Consequently, the
following conclusions are warranted:
1. Shielding gas composition and
flow rate can affect weld penetration
and cross-sectional area.
2. The manner by which shielding
gas composition and flow rate affected
weld penetration and cross-sectional
area is dependent on method of arc
gap adjustment.
3. Maximum penetrations are pro-
duced with pure argon or argon-rich
shielding gas.
4. Desirable weld cross-sectional
geometry can be obtained with pure
argon shielding provided flow rate is
optimized.
0-
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WRC Bulletin 256
January 1980
Review of Data Relevant to the Design of Tubular
Joints for Use in Fixed Offshore Platforms
by E. C. Rodabaugh
The program leading to this report was funded by 13 organizations over a two-year period. The objective was
to establish and/or validate design methods for tubular joints used in fixed offshore platforms. The report is
divided into four self contained chapters (1) Static Strength (2) Stresses (3) Fatigue (4) Displacements,
wherein detailed cross comparisons of various types of test data and design theories are reviewed.
Publication of this report was sponsored by the Subcommittee on Welded Tubular Structures of the
Structural Steel Committee of the Welding Research Council.
The price of WRC Bulletin 256 is $13.00 per copy, plus $3.00 for postage and handling. Orders should be
sent with payment to the Welding Research Council, 345 East 47th St., Room 801, New York, NY 10017.
WRC Bulletin 257
February 1980
Analysis of the Ultrasonic Examinations of PVRC Weld
Specimens 155, 202 and 203 by Standard and Two-Point
Coincidence Methods
by R. A. Buchanan, prepared for publication by 0. F. Hedden
This report describes two methods of analysis of ultrasonic examination data obtained in a 13-team
round-robin examination of three intentionally flawed weldments. The objective of the examinations is to
determine the accuracy of independently detecting, locating and sizing the weld flaws, using a fixed
procedure.
Computer programs to facility comparison of flaw locations with the ultrasonic data, for each of the
specimens and both of the methods, are appended to the report.
Publication of this report was sponsored by the Subcommittee on Nondestructive Examination of Materials
for Pressure Components of Pressure Vessel Research Committee of the Welding Research Council.
The price of WRC Bulletin 257 is $11.00 per copy, plus $3.00 for postage and handling. Orders should be
sent with payment to the Welding Research Council, 345 East 47th St., Room 801, New York, NY 10017.
W E L D I N G RESEARCH SUPPLEMENT I 155-s
