Proceedings of the ASME 2008 International Manufacturing Science and Engineering Conference
MSEC2008
October 7-10, 2008, Evanston, Illinois, USA_ICMPMSEC2008-72512
EFFECT OF ELECTRICAL PULSING ON VARIOUS HEAT TREATMENTS OF 5XXXSERIES ALUMINUM ALLOYS

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Wesley A. Salandro, Joshua J. Jones, Timothy A. McNeal, and John T. Roth1
Penn State Erie, The Behrend College
Department of Mechanical Engineering
Erie, PA, USA
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Sung–Tae Hong2 and Mark T. Smith
Pacific Northwest National Laboratory
Energy Materials and Manufacturing Group
Richland, WA, USA
2
Currently at University of Ulsan, School of Mechanical and Automotive Engineering, South Korea

KEYWORDS
Electrical Pulsing, Aluminum Sheet Metal, Tension

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ABSTRACTPrevious studies have shown that the presence of a pulsed
electrical current, applied during the deformation process of analuminum specimen, can significantly improve the formability of thealuminum without heating the metal above its maximum operating
temperature range. The research herein extends these findings by
examining the effect of electrical pulsing on 5052 and 5083 AluminumAlloys. Two different parameter sets were used while pulsing threedifferent heat treatments (As Is, 398°C, and 510°C) for each of the twoaluminum alloys. For this research, the electrical pulsing is applied
to the aluminum while the specimens are deformed, without halting
the deformation process. The analysis focuses on establishing theeffect the electrical pulsing has on the aluminum alloy’s various heat
treatments by examining the displacement of the material throughout
the testing region of dogbone shaped specimens. The results fromthis research show that pulsing significantly increases the maximum
achievable elongation of the aluminum (when compared to baseline
tests conducted without electrical pulsing). Significantly reducing
the engineering flow stress within the material is another beneficial
effect produced by electric pulsing. The electrical pulses also cause
the aluminum to deform non-uniformly, such that the material exhibits
a diffuse neck where the minimum deformation occurs near the endsof the specimen (near the clamps) and the maximum deformation
occurs near the center of the specimen (where fracture ultimately
occurs). This diffuse necking effect is similar to what can beexperienced during superplastic deformation.
However, whencomparing the presence of a diffuse neck in this research, electricalpulsing does not create as significant of a diffuse neck as superplastic
deformation. Electrical pulsing has the potential to be more efficientthan traditional methods of incremental forming since the deformation
process is never interrupted. Overall, with the greater elongation andlower stress, the aluminum can be deformed quicker, easier, and to agreater extent than is currently possible.
INTRODUCTION
When manufacturing metallic parts from sheet metal, there is alimit to which the blanks can be deformed prior to fracture. This
limit is primarily controlled by properties such as the strength, strain
hardening coefficient, and formability of the metal. For some
applications which require complex parts, such as the automotive andaircraft industries, several simpler parts must first be constructed andthen assembled using attachment methods such as rivets, screws, orwelds. Depending on the complexity of the part, this traditional wayof manufacturing can be time consuming and extremely costly to the
manufacturer. In order to address this problem, a manufacturing
process must be developed which allows complex parts to be formed
from a single sheet metal blank, rather than assembling numerous
smaller pieces.
Traditionally, a metal’s formability is increased by plastically
deforming the metallic blanks at an elevated temperature. However,there are several notable drawbacks to this, such as increased adhesion
between the specimens and dies, reduced effects of lubrication, anddecreased die strength.
Overcoming these drawbacks usuallysignificantly increases the part cost associated with equipment, energy,
and time.
Recently, a metallic deformation method, known as incremental
forming, was introduced where the blank is deformed in steps, with a1

Copyright © 2008 by ASME

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such as allowing more complex parts to be fabricated using thematerial, decreasing the weight/material usage required for the part, or
reducing the number of individual parts that must be created in orderto create complex part shapes.
Previous studies have indicated that, when continuous DC current
is applied to a part during tensile or compressive deformation, therequired flow stress is reduced [11, 12]. However, the effect of thecontinuous current on the maximum achievable elongation of the partwas significantly different for compressive and tensile loading.
When performing compression-based deformation, it was found thatthe application of a continuous current dramatically increased thematerial’s deformability. This was not true when performing tensilebased deformation, however. When continuous electricity wasapplied during tensile-based deformation it was noted that the
deformability of the material decreased.
In subsequent studies, however, it was discovered that, when apulsed current (rather than continuous) was applied during tensile
deformation, the maximum achievable elongation was increased(rather than decreased as was true for continuous). In a recent study
conducted by Roth et al., the effects of a pulsed DC current on 5754
Aluminum Alloy, a widely-used alloy for body panels in theautomotive industry, were investigated [13]. This research involved
developing an optimal pulsing parameter in order to minimize the flow
stress and maximize the material’s overall achievable elongation,
thereby placing the material into its most-workable state. The
current density at which the specimens were pulsed was held constantat 90 A/mm2, while the pulse duration and period between pulses werevaried. The electric pulsing lead to extreme increases in elongation
over non-pulsed baseline tests as shown in Figure 1, where the pulsing
period was steadily decreased. About a 400% increase in elongation
and a notable decrease in flow stress due to electrical pulsing can beseen from the figure.

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it is also time consuming and introduces possible quality issues since
the deformation process must be stopped and the part repeatedly
removed and refixtured. Therefore, if an alternative to both hot
working and incremental forming can be developed, there is thepotential to significantly improve process efficiency by decreasing
both the production time and manufacturing cost.
Beginning in the late 1960’s, researchers began investigating how
electricity affects the material properties of metals. As this research
has progressed, it has been found that a vast number of material
properties can be altered using electricity. In 1969, Troitskii
discovered that pulsed electricity lowers the flow stress within certain
metals [2]. In 1988, Xu et al. published a document demonstratingthat a continuous electric current within specific materials can increase
the material’s recrystallization rates and grain size [3]. Moreover,Chen et al. discovered a connection between electrical flow and theformation of intermetallic compounds [4, 5]. From studies conductedby Conrad, it was shown that plasticity and the phase transformationof various metals and ceramics are affected by very short duration,high current density electrical pulses [6 - 8]. Recently in 2007,
Andrawes et al. demonstrated the stress strain behavior of 6061
Aluminum Alloy can be altered using elevated amounts of DC current[9]. Also, Heigel et al. reported on the effects that DC current had
within the microstructure of 6061 Aluminum Alloy [10].
In 2007, the effect of a continuous DC current on the mechanicalproperties of numerous metals while in tension was explored by Ross
et al. [11]. Additionally, Perkins et al. investigated DC current’s
effect on metals undergoing an upsetting process [12]. These two
investigations of continuous DC current proved that the presence ofthe continuous current during plastic tensile deformation reduced theflow stress within the material. However, while the study by Ross etal. showed the formability of the metals was increased during
compressive deformation, the study by Perkins et al. found that thecontinuously applied electricity reduced the maximum achievableelongation when applied during tensile deformation (thus having anegative impact on the metals when the DC electricity wascontinuously applied during tensile deformation).

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ELECTRIC PULSING THEORY AND PREVIOUS WORKElectrical current pertains to electrons flowing through amaterial. All materials have a set resistance to electron flow due totheir bonding, atomic spacing, and atomic structure. Point defects,
dislocations, and interfacial defects (grain boundaries, cracks, voids,etc.) within a material can increase a material’s resistance to electron
flow even more. As plastic deformation takes place, the dislocations
moving through the material also experience resistance when moving
across grain boundaries, cracks, voids, impurity atoms, and otherdislocations. When a material is loaded, dislocations move throughthese obstacles by changing direction, bending, sliding, or bowing.
As the amount of cold-work is increased, the resistance to dislocation
motion also increases; thereby increasing the required flow stress.
However, if the dislocations are able to move through a material withless resistance, the material will become easier to deform. Therefore,
the principle behind electrical pulsing is to modify the material’s
properties such that the dislocations within the material are able tomove as freely as possible. By doing so, the material becomes
temporarily weaker, minimizing the force/energy that is required tofabricate the part. A second goal of the electrical pulsing is toincrease the maximum achievable elongation of the material prior to
fracture. Increasing this elongation has several potential benefits,

FIGURE 1 – 5754 ALUMINUM WITH DECREASING PULSE PERIOD
Unlike the 5754 Aluminum research, this research does not focus
on determining an optimal, or best, parameter set for the 5052 and5083 Aluminum alloys that are examined herein. Instead, thepurpose of this research is to explore the effects of a pulsed DC
current on various heat-treatments of these materials.
Morespecifically, the research discussed herein examines if theeffectiveness of the pulsed electricity is altered by the aluminum’s
heat-treatment.
To examine this possibility, it is important to use the samecombination of pulse parameters on each heat-treatment (two different
combinations will be examined as a part of this study). However, it
should be noted that, while using the same pulse parameters for eachheat-treatment improves the ability to perform a cross-comparison of
the electricity’s effectiveness, it prevents optimal parameters from2

Copyright © 2008 by ASMEFIGURE 3 – CIRCUIT SCHEMATIC
To observe possible thermal effects, a FLIR infra-red thermal
imaging camera (ThermoVision A20m) continuously monitored thetemperature profile of the specimen throughout the entire length ofeach test. High temperature black paint was applied to the back ofeach test specimen (side facing the thermal imaging camera) tostabilize the sample’s emissivity and to allow for more accurate
temperature data. Although the temperature data was not directly
used in this research, the temperature was monitored to ensure thespecimens did not exceed the aluminum’s maximum operating
temperature range.
Due to the non-uniform strain profile that is created within eachspecimen during the testing (discussed in the results section), a grid of
displacement/strain circles were acid etched on the front of thespecimens (side opposing the thermal imaging camera) prior to
testing. These grids will be used to analyze the displacement profile
along the “long-axis” of each specimen after fracture. An example ofthe displacement grid is shown below in Figure 4.

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EXPERIMENTAL SETUP
To reduce the effect of stock variability, all of the material foreach alloy originally came from the same sheet stock. This original
stock was sectioned into the necessary sizes and then heat-treated tothe desired specification. Subsequent to performing the required
heat-treatments, dogbone test specimens were created for testing
purposes. The dogbone specimens were fabricated by initiallyshearing the sub-sheets from each heat-treatment into rectangularshapes. When performing the shearing operation, the width of therectangles was intentionally oversized. After creating the rectangularblanks, the specimens were machined on all sides in order to remove
any unintentional effects from the shearing operation.
When machining (milling) the dogbone specimens for this testing
it is important to maintain tight tolerances on all dimensions,otherwise the current density will vary slightly, introducing testing
variability. To reduce this variability, the dimensions on all of thedogbones produced for this study were held to a tolerance of less then
12.5 μm (0.0005”).
For the tensile testing described herein, a Tinius Olsen Super “L”
Universal Testing Machine was used to elongate aluminum alloy
dogbone test specimens. The electric pulses were created using a
Lincoln R35 Arc Welder with a variable voltage output and a pulse
controller. In addition, a variable, thermally cooled resistor was used
to control the magnitude of the electrical pulses. The test fixturesconsisted of hardened steel clamps, Haysite Reinforced Polyester, and
PVC tubing. The hardened steel mounts held the aluminum
dogbones in place during testing. The polyester and PVC tubing
were inserted between the steel clamps and the Tinius Olsen machine
to isolate the electricity from the testing equipment, thus sending thecurrent through the dogbone specimens only. The setup used for thisexperiment is the same setup used in the 5754 Aluminum Alloyresearch as discussed previously. This setup is shown in Figure 2.

Figure 3. Using the force vs. position data and each specimen’s
original cross-sectional area measurements, engineering stress vs.
elongation plots were generated. Elongation was used instead ofstrain due to the presence of a diffuse neck, which was the result of
non-uniform strain. Strain proves to be an incorrect parameter to use
for graphing since it does not stay constant throughout the entire test
region of the specimen [14].

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being employed to enhance the workability of each alloy/heattreatment combination.
Therefore, greater improvements areachievable for each combination of alloy and heat-treatment if aseparate optimization of the parameters is performed.

FIGURE 2 – EXPERIMENTAL SETUP

The current flowing from the welder was monitored using an
Omega HHM592D Digital Clamp-on Ammeter. PC-based Tinius
Olsen Navigator software was used to control the universal testingmachine and to continuously obtain the force vs. position data
throughout each test. The entire circuit schematic can be viewed in

FIGURE 4 – DISPLACEMENT GRID
The testing procedure consisted of elongating the aluminum
dogbone specimens at a constant platen rate of 2.54 mm/min (0.1
in/min) until fracture, while the specimens were periodically pulsedwith a specific amplitude of electrical current applied over a set
duration. It is important to note that the electrical pulses wereapplied to the specimens during the elongation process, without
interrupting the deformation. When viewing the engineering stresselongation graphs presented in the Results section, the electrical pulses
are responsible for the steep vertical drops (corresponding to a sudden
decrease in the flow stress required for the deformation). In order toexamine the effect of the heat-treatment on the effectiveness of theelectrical pulsing, two different alloys of aluminum, with threedifferent heat-treatment conditions, are examined in this research.
Table 1 lists the alloys, along with the heat-treatments examined.

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Copyright © 2008 by ASMERESULTS
In the following sub-sections, the effects of Parameter Set 1 andParameter Set 2 are cross-compared to each other and to the baselinematerial for each aluminum alloy/heat-treatment combination. In
addition, the elongation along the specimen’s axial length for eachcombination using Parameter Set 1 and 2 are cross-compared. Theseaxial elongations are also compared to the baseline’s elongation for therespective alloy/heat-treatment combination in order to determine eachparameter set’s effect on the material’s axial elongation profile.
These axial elongations are analyzed by measuring the increase inlength of each strain circle on the grid that was acid etched on one sideof the aluminum test specimens. The results are used to compare thespecimen’s “long-axis” deformation due to Parameter Set 1, ParameterSet 2, and the baseline.
From visual inspection of the tested specimens in this research, it
can be noted that the testing region of most pulsed specimens
displayed a diffuse necking effect. This diffuse neck is similar to,although less sever, the diffuse neck frequently seen with superplastic
forming [15]. The neck generated when deforming with electricalpulses, shown for one of the specimens in Figure 6 for reference,corresponds to a non-uniform displacement profile along the test
specimen. Note that, although the figure shows that the displacement
grid is applied to the entire specimen, the testing region (fillet to fillet)
is the only region of concern. Thus, the axial displacement profiles
that will be presented only focus on this region. In addition to the
local axial displacement measurements, the overall elongation(between fillets) is measured and presented for each set of conditions.

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In order to more exactly determine the effect of the electricalpulsing on each alloy/heat-treatment combination, two different sets ofpulse parameters were employed, as listed in Table 2. In theseparameter sets, the pulse duration was held constant as the current
density (magnitude) and the pulsing period were changed. Figure 5
depicts the electrical pulsing pattern used for this research. The
parameters used in this research were chosen based on preliminary
testing using a few of the material/heat-treatment combinations todetermine the overall impact that they had for all of the material
combinations. Therefore, while the parameters were consistenly
beneficial, they do not represent the optimal parameters for any
particular combination. To achieve optimal results, unique parameter
sets would need to be employed for each alloy/heat-treatment
combination. For this research, universal parameter sets were
employed in order to allow for a cross-comparison of the effectivenessof the electricity between all combinations.

representative test for each aluminum alloy/heat-treatment/parameterset combination. As was true for the stress-elongation data, once
again, sufficient repeatability was found between the various
specimens deformed under the same conditions.

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TABLE 1 - ALLOYS AND HEAT TREATMENT CONDITIONS
AlloysHeat-Treatment Conditions
As-Is
5052-H32
398°C for 10 minutes
510°C for 6 hours
As-Is
5083-H32
398°C for 10 minutes
510°C for 6 hours

TABLE 2 - ELECTRICAL PULSING PARAMETERS
Current Density
Duration
PeriodParameter Set(A/mm2)(Seconds)(Seconds)
1
90
1
60
2
60
1
30

FIGURE 6 – PULSED SPECIMEN WITH DIFFUSED NECKSA

FIGURE 5 – ELECTRICAL PULSING PATTERN

To verify the repeatability of the results, five specimens were
tested for each aluminum alloy/heat-treatment/parameter-set
combination.
Also, to provide a means of establishing theelectricity’s effect, multiple baseline tests (where electricity was notapplied) were conducted for each heat-treatment of the two aluminumalloys examined. While multiple tests were run for each set of
conditions, to ease the ability to visualize the effect of the pulsed
electricity for each engineering stress-elongation diagram within the
Results section, only a single representative curve is plotted for eachcondition. Thus, each plot only contains one pulsed test and its
respective baseline test for each specific aluminum alloy/heattreatment/parameter-set combination. However, while not shown, allfive tests were examined for each combination to verify satisfactory
repeatability between the tests. As with the engineering stress vs.
elongation plots, the displacement analysis plots also only depict one

As previously mentioned, for both alloys, the pulsed electricity’seffect on three different heat-treatments is examined using two
different parameter sets. For each alloy, the first set that is presented
corresponds to the “As Is” stock state (i.e., the state of the stock
material without secondary heat-treatments). The second heattreatment presented for each alloy corresponds to the secondary
treatment of the “As Is” material at 398°C for 10 minutes. The finalheat-treatment presented for each alloy involves the secondary
treatment of the “As Is” material at 510°C for 6 hours.

Effect on 5052-H32 Aluminum Alloy
For the 5052 Aluminum alloy examined as a part of this research,the “As Is” state corresponds to 5052-H32.
5052-“As Is”: As previously mentioned, in order to establish
the effect of the pulsed electricity on the mechanical properties of the5052-“As Is”, five repetitions of each test condition were conducted.

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FIGURE 7 - 5052 - AS IS - PARAMETER SET 1

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While slight variability was found to exist between the repetitions, thisvariability was deemed negligible for the purposes of this analysis.
The representative curves of the engineering stress versus
elongation behavior of the 5052-“As Is” material, when deformed
while applying the pulsed current conditions associated withParameter Set 1 and Parameter Set 2, are shown in Figures 7 and 8
respectively. To improve the ability to visualize the effect of thepulsed current on the material’s behavior, the baseline stresselongation behavior of the material is also plotted in the figures.
When interpreting these images, the sharp drop in the material’s flow
stress (the stress to continue deformation at any given elongation)corresponds to the application of each individual pulse of electricity.
When comparing the average elongation of the 5052-“As Is”
material from deforming while applying the conditions associated withParameter Set 1 (7.1 mm) to the average baseline deformation (4.6mm), an increase of 54.3% is observed (Figure 7). Note that, when
computing this percent increase (and for all subsequent calculations),
the average elongation for each condition are used (i.e., the average
elongation from all of the baseline tests is compared to the average
elongation from all of the 5052 As-Is specimens deformed using
Parameter Set 1). In addition, the flow stress also decreased due tothe application of the pulsed electricity. To this end, each pulse ofelectricity results in a material response that is similar to an
instantaneous anneal of the material.
Likewise, when applying the conditions associated withParameter Set 2 (Figure 8), an increase in the overall elongation of thematerial is also observed in comparison to the baseline behavior.
Unfortunately, the improvement in the material’s overall elongation
while pulsed under Parameter Set 2 is significantly reduced incomparison to Parameter Set 1; yielding an average elongation fromusing Parameter Set 2 of only 4.7 mm, a 2.2% elongation increase
from baseline. Not surprisingly, when applying the conditions of
Parameter Set 2, the flow stress is not lowered to the same extent as
occurred when pulsing under the conditions of Parameter Set 1.
To provide a more detailed analysis of the electricity’s effect on
the material’s axial elongation, the displacement grid profiles of thespecimens are also examined. The 5052-“As Is” displacement
profile for Parameter Set 1, Parameter Set 2, and its respective
baseline are all depicted in Figure 9. As can be seen, the baseline
plot shows a minimal necking region (corresponding to the peaks leftof center). However, it also reveals an inconsistent displacement
profile (note the significant variations in strain levels throughout thetesting region in the figure) compared to the other, more consistent,
5052 Aluminum Alloy baseline displacement profiles (to be presented
in the following sub-sections).
When deforming the specimens with the pulsed Parameter Set 1,
however, a significant diffuse neck region is found to exist (i.e., thedegree of elongation is not constant along the profile but instead
consistently increases as the neck is approached). An additional
observation regarding the necking event is that, while the point
necking was located for the baseline specimens at approximately onethird of the testing length, when pulse Parameter Set 1 is applied, theneck consistently occurred at the specimen’s midpoint. This occurs
due to the conductive influence of the fixtures causing the center ofthe specimen to increase in temperature the most due to Joule heating.
For Parameter Set 2, however, only a minimal diffuse neck is observed
and the fracture event once again occurred at approximately one-third
along the testing region length. This similarity between the baseline
behavior and that for Parameter Set 2 is not unexpected given theminimal effect on the material’s behavior due to the pulsing under theconditions of Parameter Set 2.

FIGURE 8 - 5052 - AS IS - PARAMETER SET 2

FIGURE 9 - 5052 - AS IS - DISPLACEMENT ANALYSIS

5052-After 398°C for 10 minutes: The next series of tests
were run after heat-treating the aluminum at 398°C for 10 minutes.
The effect of the pulsing under Parameter Set 1 and Parameter Set 2
are shown in Figures 10 and 11 respectively. Once again, thebaseline data is plotted on both graphs along with a representative
pulsed test to ease comparison. In examining the two graphs, it isapparent that the pulsed electricity had a more consistent effect (lessvariability between repetitions) on the 5052 398°C material, both forthe first and second set of pulse parameters. As will be shown later,
this was also true for the heat-treatment at 510°C for 6 hours.
For the 398°C series of tests (Figures 10 and 11), the overall
baseline elongation was 18.4 mm. As was done previously for the“As Is” stock tests, this baseline will be used to determine the amountby which the pulsed electricity altered the elongation of the material.
For the samples tested using Parameter Set 1 (Figure 10), the overall
elongation (28.8 mm) corresponds to a 56.5% increase in comparison

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FIGURE 11 - 5052 - 398°C - PARAMETER SET 2

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to the baseline’s elongation and also decreases the engineering flow
stress. For the tests pulsed under Parameter Set 2 (Figure 11), theoverall elongation (27.8 mm), resulted in an increase of 51.1%
compared to the same respective baseline test. As was the case withParameter Set 1, this parameter also decreased the engineering flow
stress a notable amount.
When considering both achievable elongation increases, alongwith decreases in flow stress, it is apparent that both pulse conditions
had beneficial effects on the 5052 398°C material. Both parametersets achieved roughly the same amount of elongation, with ParameterSet 1 proving to be slightly better. Furthermore, although bothparameter sets decreased the flow stress, Parameter Set 1, again,
evidencing a greater decrease in flow stress than Parameter Set 2
indicating that the magnitude of the current played a greater role thanthe pulsing frequency in determining the peak flow stress reached
between pulses for these two particular sets of conditions. In
addition, each pulse caused a greater decrease in the stress (note theextent of the “drop-off” on the graphs each time the current wasapplied) for Parameter Set 1. This is expected considering thegreater magnitude of the current used for Parameter Set 1.
When viewing the displacement profile in Figure 12, it becomesapparent that the electric pulsing with both parameters causes a diffuse
neck within the specimen.
The baseline profile displaced
consistently with minimal necking near the point of fracture. The
baseline displacement profile for this heat-treatment proved to be
more consistent than the “As Is” profile (notice less variability instrain over the testing region).
The specimens pulsed under conditions of Parameter Sets 1 and
2, however, both elongated non-uniformly over the entire testingregion (fillet to fillet). The specimens pulsed under Parameter Set 2’s
conditions displayed a slightly longer diffused neck up to fracture than
the specimens pulsed under Parameter Set 1’s conditions. One
possible reason for this is that, since the material’s width wasconsiderably decreased by this point in the test, the lower magnitude
pulses of Parameter Set 2 may have been more beneficial than thehigher magnitude pulses of Parameter Set 1. More specifically, thegreater magnitudes of Parameter Set 1 may have caused premature
failure of the specimen due to highly localized heating within thisnarrowed region. Also of note, both pulsed tests fractured at
approximately the center of the testing region, while the un-pulsed
baseline test fractured asymmetrically (slightly left of center).
Therefore, while pulsing the specimens, the high temperatures reachedin this central area lead to consistent fracture at this location for all
tests conducted at this material/heat-treatment combination.

FIGURE 12 – 5052 - 398°C – DISPLACEMENT ANALYSIS

5052-After 510°C for 6 hours: The final series of 5052 tests
were run after heat-treating the original aluminum “As-Is” sheet stockat 510°C for 6 hours. Once again, the overall elongation of thebaseline specimens and the pulsed tests are used for comparison
purposes. From this, when Parameter Set 1 was used (Figure 13), theoverall elongation of 27.8 mm represents an increase in this aluminumalloy’s elongation by about 47.1% with respect to the baseline
elongation (18.9 mm). Furthermore, with the use of Parameter Set 2
conditions (Figure 14), a 57.1% increase from beyond the baseline
elongation was calculated (the overall elongation associated with thetests conducted under the conditions of Parameter Set 2 was 29.7 mm).
Overall, both Parameter Set 1 and Parameter Set 2 had a greater
effect on the 5052 Aluminum’s elongation when applied to the heattreatment at 510°C for 6 hours than was the case for either of the two
previous heat-treatments. Moreover, for this heat treatment, theconditions of Parameter Set 2 resulted in a greater improvement in theelongation than was found with the conditions of Parameter Set 1.
However, once again, Parameter Set 1 resulted in a greater decrease in
the material’s peak flow stress between pulses than Parameter Set 2
and also resulted in greater “drop-offs”.
From Figure 15, the same diffuse necking effect as experienced
in the 5052 398°C specimens was also present in the specimens heattreated at 510°C for 6 hours. Once again, the baseline profile
displayed relatively uniform displacement throughout most of thetested region. Both pulsed specimens proved to have similar
displacement profiles over most of the testing region. In this case,Parameter Set 2 depicted an even greater diffuse necking effectcompared to Parameter Set 1 than was the case for the 398°C heattreated alloy.

FIGURE 10 - 5052 - 398°C - PARAMETER SET 1

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FIGURE 13 - 5052 - 510°C - PARAMETER SET 1

frequent as that of Parameter Set 1, resulting in a greater percentage ofthe testing time over which the electricity was actually applied to thespecimen. Finally, as expected, the higher magnitude of the current
applied by the conditions of Parameter Set 1 resulted in a greater“drop-off” in the stress when the pulse was applied than was occurred
due to Parameter Set 2’s conditions.
Comparing all three heat-treatments of the 5052 Aluminum Alloy,
the overall effect of Parameter Sets 1 and 2 created a diffuse neckwithin the tested region of the specimens. Parameter Set 2 caused agreater diffuse neck for heat-treatments of 398°C and 510°C, leading
to belief that pulsing frequency determined the extent of the diffuse
neck. This was not the case for the “As Is” material, where
Parameter Set 1 created a significantly larger diffuse neck. In mostcases, excluding the 5052-“As Is” Parameter Set 2 pulsed specimens,
the electrical pulsing caused the ultimate fracture to occur at the
middle of the testing region, while the baseline fractures occurredasymmetrical. Once again, this may have been due to the absence ofthermal sinks near the middle of each specimen’s testing region.

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Effect on 5083-H32 Aluminum Alloy
As was true for the 5052 Alloy, the first 5083 Aluminum Alloyheat-treatment that will be examined corresponds to the “As Is” stock
state of the material (i.e., the state of the stock material without
secondary heat-treatments), followed by the 398°C for 10 minutes
series and, finally, the 510°C for 6 hours series of tests. The 5083“As Is” state corresponds to 5083-H32.

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FIGURE 14 - 5052 - 510°C - PARAMETER SET 2

FIGURE 15 – 5052 - 510°C – DISPLACEMENT ANALYSIS

5052-Summary: As shown, with respect to the material’s
maximum achievable elongation, Parameter Set 1 proved to be themost successful when applied to the 5052-“As Is” stock specimens
and the 5052-398°C for 10 min. specimens while Parameter Set 2yielded the best results when applied to the 5052-510°C for 6 hours
specimens. Furthermore, for the 5052 Alloy, the pulsed electricity’seffect increased as the heat-treatment temperature and time increased.
With respect to the required engineering flow stress, however, a moreconsistent effect was evidenced in so far as, for all of the tests
conducted on the three heat-treatments of the 5052 Aluminum Alloy,
the peak engineering flow stress was reduced to a greater extent when
the conditions associated with Parameter Set 1 were used(demonstrating that the pulse magnitude had a greater effect than thepulse frequency for these two sets of conditions). This result issomewhat unexpected since Parameter Set 2 called for pulses twice as5083-“As Is”:
As was done previously for the 5052
Aluminum Alloy tests, the plots will consist of a baseline test alongwith a pulsed test representative of the five tests conducted for eachcombination, as seen in Figures 16 and 17. The average baseline
elongation was determined to be 9.6 mm for the “As Is” material.
The results of applying the conditions of Parameter Set 1 are shown in
Figure 16. As can be seen, the application of the pulsed electricity
significantly increased the elongation of the specimens with an overall
elongation of 17.3 mm. This overall elongation corresponds to anincrease of 80.2% over the respective baseline elongation.
Moreover, the effects associated with applying Parameter Set 2(Figure 17) to this material were even more promising with an overall
elongation of 18.3 mm. This elongation corresponds to a percent
increase of 90.6%.
Therefore, while the pulsed Parameter Set 2 conditions did not
significantly improve the 5052-“As Is” specimens, it had a significant
effect on this alloy. In addition, while both parameter sets once again
were found to reduce the peak flow stress between pulses, for thisalloy/heat-treatment combination, Parameter Set 2 proved to reduce
the engineering stress more rapidly and effectively than Parameter Set
1 (a different result than that found with the 5052 Alloy). This leads
to the conclusion that the pulse frequency played a greater role in
reducing the flow stress rather than the pulse magnitude (themagnitude was the greater factor with the 5052 Aluminum Alloy).
One similarity between the effects of the parameters on the two alloys,
however, is that, Parameter Set 1 provided a greater “drop-off”, as
expected due to the larger current density per pulse.
The displacement analysis for this alloy is also conducted in thesame manner as the 5052 Aluminum Alloy. Each profile plot in thedisplacement analysis figure is representative of the five specimens
tested for each material/heat-treatment/parameter-set combination.
The 5083-“As Is” displacement profiles in Figure 18 show auniformly-displaced baseline test, along with diffused necks resulting
from both pulsed parameter set tests. Unlike the 5052-“As Is”

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Copyright © 2008 by ASMEM
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FIGURE 16 - 5083 - AS IS - PARAMETER SET 1

less after the heat-treatment. This decrease in effectiveness after
treatment is the opposite of that exhibited by the 5052 Alloy.
As was the case with the 5083-“As Is” stock material, bothparameter sets once again reduced the peak flow stress between
pulses, for this alloy/heat-treatment combination.
Moreover,Parameter Set 2 once again proved to reduce the engineering stressmore rapidly and effectively than Parameter Set 1 for this alloy. This
result seems to indicate that the pulsing frequency played a greaterrole than the magnitude of the current in determining the peakengineering flow stress reached between pulses for these twoparticular sets of conditions. Parameter Set 1, however, once again
provided the greatest “drop-off” in stress while the electricity wasflowing through the material during deformation. Moreover, at thehigher elongations, this “drop-off” nearly reached zero stress as seenin Figure 19, a remarkable stress-state considering the continuous ongoing deformation of the specimen while the pulse was applied.
The displacement profiles of the 5083 398°C Aluminum Alloyare similar to the displacement profiles of the same “As Is” AluminumAlloy. In Figure 21, the baseline profile is somewhat uniform
compared to the displacement profiles of the two pulsed parameters.
From the figure, it is apparent that the electrical pulsing used in bothparameter sets resulted in the specimen having a diffuse neck. As
was the case with the “As Is” material, the electrical pulsing of
Parameter Set 2 caused a greater diffuse neck compared to ParameterSet 1. Both parameter sets ensured the fracture occurred in the
middle of the test region.

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Aluminum’s baseline profile, this baseline displacement profile wasmore consistent throughout the testing region. Parameter Set 2
caused a greater diffused neck and both parameter sets caused ultimate
fracture in the center of the test region.

FIGURE 17 – 5083 – AS IS – PARAMETER SET 2SAFIGURE 19 - 5083 - 398°C - PARAMETER SET 1

FIGURE 18 – 5083 – AS IS – DISPLACEMENT ANALYSIS

5083-After 398°C for 10 minutes: Figures 19 and 20
clearly show that both parameters extended the elongation of the5083-398°C for 10 min. specimens past the comparable baseline
elongation of 18.3 mm. More specifically, the overall elongation for
Parameter Set 1 (Figure 19) was 22.1 mm, a 20.8% increase inelongation from the respective baseline. The conditions associatedwith Parameter Set 2 (Figure 20) were more successful with a 41.5%
increase in elongation (overall elongation was 25.9 mm). It is of note
that, while the total elongation of the specimens for both parameter
sets is greater than the “As Is” elongations, the percent improvement is

FIGURE 20 – 5083 - 398°C – PARAMETER SET 2

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Copyright © 2008 by ASMEFIGURE 22 – 5083 – 510°C – PARAMETER SET 1

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5083-After 510°C for 6 hours: The results of applying theconditions associated with pulse Parameter Set 1 and 2 to the 5083H321 Aluminum heat-treated at 510°C for 6 hours are shown in
Figures 22 and 23, respectively. As was done with the other series,
the baselines and the pulsed tests are compared. Once again, the5083-510°C for 6 hours Aluminum’s elongation was increased due tothe conditions applied by both parameter sets. For this alloy/heattreatment combination, the overall baseline elongation is 18.5 mm.
By comparing Figures 22 and 23, it can be seen that, for thisalloy/heat-treatment, Parameter Set 1 was once again less effective atincreasing the material’s maximum achievable elongation (as was thecase with all of the other heat-treatments for this alloy). Morespecifically, for Parameter Set 1, the pulsed electricity resulted in an
overall elongation of 24.3 mm, an increase by 31.4% over the baseline
distance. Similarly, for Parameter Set 2, the application of the pulsed
electricity during deformation resulted in an overall elongation of 27.6mm, a 49.2% increase over the comparable baseline.
When examining the effect of the pulsed conditions on thespecimen’s peak engineering flow stress, however, a slightly different
result is found for this heat-treatment. In this case, the conditions of
Parameter Set 1 initially decrease this stress to a greater extent.
However, as the elongation is increased, the conditions of ParameterSet 2 begin to have a greater effect on the stress, ultimately resulting
in Parameter Set 2 finishing with the lower peak stress of the two.
Also of note, once again the Parameter Set 1 causes a greater “dropoff” in stress while the electricity is applied. Furthermore, as wastrue with the 5083 398°C Aluminum specimens, at higher elongations
this “drop-off” nearly reaches a state of zero stress (refer to Figure22), irrespective of the on-going deformation of the specimen during
the pulsing.
The displacement analysis for the 5083 510°C Aluminum Alloycan be found in Figure 24.
Just like the other heattreatment/parameter-set combinations for this alloy, a diffuse neck ispresent in both electrically-pulsed tests, while the baseline displayedno sign of a diffuse neck. Moreover, Parameter Set 2 registered agreater necking effect, leading to the conclusion that the frequency ofthe pulses had a greater effect on the diffuse neck than the magnitudeof the current.

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FIGURE 21 - 5083 - 398°C - DISPLACEMENT ANALYSISFIGURE 23 – 5083 - 510°C – PARAMETER SET 2

FIGURE 24 - 5083 - 510°C - DISPLACEMENT ANALYSIS

5083-Summary: As was true with the 5052 Aluminum Alloy,
for all of the 5083 heat-treatments, both parameter-sets resulted in an
increase in the maximum achievable elongation of the alloy.
However, unlike with the 5052 Alloy tests, for this alloy, ParameterSet 2 consistently reached greater elongations than Parameter Set 1.
This indicates this alloy is more sensitive to frequency thanmagnitude. Also, Parameter Set 2 decreased the peak engineering
flow stress between pulses to a greater extent than Parameter Set 1 (aresult also opposite than found for the 5052 Alloy). Both alloys,
however, exhibited a greater “drop-off” in the stress due to the pulses
associated with Parameter Set 1. Moreover, in some cases, this“drop-off” nearly reached a stress-state of zero, even though thespecimens were still undergoing deformation during the pulse.
All of the pulsed specimens for each heat-treatment/parameter-set
combination for the 5083 Aluminum Alloy display a diffuse neck intheir respective test region. Baseline specimens show minimal or no9

Copyright © 2008 by ASME

diffuse necking in their test regions. The conditions of Parameter Set
2 consistently produced a greater diffuse necking effect on thespecimens than the conditions of Parameter Set 1. This concludes
that the more frequent, slightly less magnitude pulses of Parameter Set
2 are more effective in producing a diffuse neck than the shorter,
greater magnitude pulses of Parameter Set 1.

[2] Troitskii, O.A., (1969). “Electromechanical Effect in Metals.”
Pis’ma Zhurn. Experim. Teoret. Fiz., No. 10, pp. 18.

CONCLUSION
As was shown, the effectiveness of the pulsed electricity isdependent on both the alloy and its heat-treatment. The material thatobtained the most increase in formability due to the electric pulses was
the 5083 Aluminum Alloy. For this material, not only was theelongation increased by the greatest percentage, the engineering stress
was reduced by the greatest amount. Parameter Set 2, with more
pulses of slightly smaller magnitude, worked the best in conjunction
with this material, for all of the heat-treatments.
The 5052 Aluminum Alloy, although not as successful as the5083 material, did illustrate signs of formability improvement fromthe electric pulsing. For this alloy, Parameter Set 1 was more
successful with the “As Is” and 398°C heat-treatments, but ParameterSet 2 proved more successful with the 510°C heat-treatment.
However, on average, Parameter Set 1 lowered the engineering stressto a greater extent than Parameter Set 2. The engineering stress of
the 5052-“As Is” material was the only case whose stress was not
significantly affected by either parameter.
The size of the diffuse neck resulting from electrical pulsing was
found to be irrespective of the material pulsed, but dependent on theparameter set used for pulsing. Considering both aluminum alloys,
every heat-treatment/parameter-set combination (excluding the 5052“As Is” specimen) displayed a diffuse neck in their respective
displacement profile. Parameter Set 2 consistently produced agreater diffuse neck throughout all combinations. This leads to theconclusion that with any aluminum alloy/heat-treatment combination,
the greater pulsing frequency of Parameter Set 2 developed a larger
diffuse neck compared to the greater magnitude of pulses in ParameterSet 1. As stated previously, the diffuse necks produced by electricalpulsing are minute compared to diffuse necks due to superplastic
deformation [15, 16]. Another notable difference experienced with theelectrically pulsed tests was where fracture occurred. On a majorityof the non-pulsed baseline tests, ultimate fracture occurred at roughly
one-third or two-thirds of the test region. The electrically pulsed
tests consistently fractured near, or at, the center of the testing region.

[4] Chen, S.W., C.M. Chen, and W.C. Liu (1998). “Electric Current
Effects Upon the Sn/Cu and Sn/Ni Interfacial Reactions.” J. of
Electronic Mat., 27, pp. 1193.

[3] Xu, Z.S., Z.H. Lai, and Y.X. Chen (1988). “Effect of Electric
Current on the Recrystallization Behavior of Cold Worked Alpha-Ti.”
Scripta Metallurgica, 22, pp. 187-190.

[5] Chen, S.W., and C.M. Chen (1999). “Electric Current Effects on
Sn/Ag Interfacial Reactions.” J. of Electronic Mat., 28, pp. 902.

E[6] Conrad, H., (2000a). “Effects of Electric Current on Solid State
Phase Transformations in Metals.” Mat Sci & Engr, A287, pp.227-237.
[7] Conrad, H., (2000b). “Electroplasticity in Metals and Ceramics.”
Mat. Sci. & Engr., pp. 276-287.

MPL[8] Conrad, H., (2002). “Thermally activated Plastic Flow of Metals
and Ceramics with an Electric Field or Current”, Mat. Sci. & Engr.,
A322, pp. 100-107.

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FUTURE WORK
For this research, each of the materials was investigated using thesame pulsed parameter sets.
While this allows for a crosscomparison of the effectiveness of the globalized parameter set,increased performance would be expected for each material if
individual optimized conditions were determined for each material.
Before using this technique on any one of these materials, it is highly
recommended that this optimization be performed.

ACKNOWLEDGEMENT
This work was supported by the Department of Energy, Vehicle
Technologies Office, Dr. Joseph Carpenter Technology ThrustManager.
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