Document [original]

J. Laser Appl. 32, 022031 (2020); https://doi.org/10.2351/7.0000064 32, 022031

Influence of welding parameters on

electromagnetic supported degassing of die-

casted and wrought aluminum

Cite as: J. Laser Appl. 32, 022031 (2020); https://doi.org/10.2351/7.0000064

Submitted: 01 April 2020 . Accepted: 01 April 2020 . Published Online: 29 April 2020

André Fritzsche, Kai Hilgenberg , and Michael Rethmeier

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Paper published as part of the special topic on Proceedings of the International Congress of Applications of Lasers &

Electro-Optics (ICALEO<sup>®</sup> 2019)

Note: This paper is part of the Special Collection: Proceedings of the International Congress of Applications of Lasers

& Electro-Optics (ICALEO® 2019).

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Influence of welding parameters on

electromagnetic supported degassing of

die-casted and wrought aluminum

Cite as: J. Laser Appl. 32, 022031 (2020); doi: 10.2351/7.0000064

View Online Export Citation CrossMar

Submitted: 1 April 2020 · Accepted: 1 April 2020 ·

Published Online: 29 April 2020

André Fritzsche,

Kai Hilgenberg,

1,2

and Michael Rethmeier

1,2

AFFILIATIONS

BAM Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205 Berlin, Germany

Institute of Machine Tools and Factory Management, Technical University Berlin, Pascalstraße 8-9, 10587 Berlin, Germany

Note: This paper is part of the Special Collection: Proceedings of the International Congress of Applications of Lasers & Electro-

Optics (ICALEO

2019).

ABSTRACT

Laser beam welding of aluminum die casting is challenging. A large quantity of gases (in particular, hydrogen) is absorbed by aluminum

during the die-cast manufacturing process and is contained in the base material in solved or bound form. After remelting by the laser, the

gases are released and are present in the melt as pores. Many of these metallurgic pores remain in the weld seam as a result of the high solid-

ification velocities. The natural (Archimedean) buoyancy is not sufficient to remove the pores from the weld pool, leading to process instabili-

ties and poor mechanical properties of the weld. Therefore, an electromagnetic (EM) system is used to apply an additional buoyancy

component to the pores. The physical mechanism is based on the generation of Lorentz forces, whereby an electromagnetic pressure is intro-

duced into the weld pool. The EM system exploits the difference in electrical conductivity between poorly conducting pores (inclusions) and

the comparatively better conducting aluminum melt to increase the resulting buoyancy velocity of the pores. Within the present study, the

electromagnetic supported degassing is investigated in dependence on the laser beam power, welding velocity, and electromagnetic flux

density. By means of a design of experiments, a systematic variation of these parameters is carried out for partial penetration laser beam

welding of 6 mm thick sheets of wrought aluminum alloy AlMg3 and die-cast aluminum alloy AlSi12(Fe), where the wrought alloy serves as

a reference. The proportion of pores in the weld seams is determined using x-ray images, computed tomography images, and cross-sectional

images. The results prove a significant reduction of the porosity up to 70% for both materials as a function of the magnetic flux density.

Key words: laser beam welding, electromagnetic supported degassing, die-casted aluminum

Published under license by Laser Institute of America.https://doi.org/10.2351/7.0000064

I. INTRODUCTION

The concept of weight reduction is important in many indus-

tries. In particular, in the automotive industry and in the aerospace

industry, this idea is strongly associated with the use of aluminum

alloys. The die casting process offers the possibility of producing

load-adapted and complex components with good dimensional

accuracy. However, the die casting mold is quickly filled with molten

aluminum in this manufacturing process, whereby organic release

agents and other impurities are introduced into the die casting

component as a result of the occurring turbulences.

These are ini-

tially unproblematic, as they are almost completely precipitated in

the form of hydrides during casting production due to the low

cooling speeds. However, these hydrogen compounds are a great

challenge for the subsequent joint welding of die-cast aluminum

components. In the course of the welding process, the hydrides dis-

solve and release hydrogen. The hydrogen then diffuses into areas

of higher temperature

and is present in the melt in the form of

small gas bubbles. The solidification rate during welding is signifi-

cantly higher than during casting. In addition, the hydrogen solubil-

ity of aluminum decreases with declining temperature, and at the

phase transition from liquid to solid, a 20-fold increase in solubility

(for pure aluminum) occurs. As a result, the hydrogen does not

have sufficient time to transform to hydrides.

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Published under license by Laser Institute of America

A further aspect of partial penetration laser beam welding is

the occurrence of keyhole instabilities, which can cause the forma-

tion of process pores near the keyhole tip during the solidification

process.

Process pores and metallurgical (hydrogen-related) pores

lead to a reduction of strength of the welded joint. Therefore, pres-

sure welding processes like friction stir welding are used. However,

friction stir welding of complex aluminum die-cast components is

difficult, since the high process forces necessitate the design of

complex clamping fixtures.

For fusion welding, the porosity problem has been well solved

so far by metal inert gas welding (MIG) or tungsten inert gas welding

(TIG) welding, in which the degassing behavior has been improved

by selecting low welding velocities. Nevertheless, the associated high

energy input into the component leads to distortion and to a broad

heat affected zone. With regard to these negative properties and

under additional consideration of economic aspects (automatability,

process speed, etc.), laser beam welding offers a promising alternative

to conventional welding processes.

However, when using this

process, modifications are necessary in order to meet the challenges

of pore formation during the welding of aluminum die casting alloys.

There are two main approaches for porosity reduction. On the

one hand, the natural buoyancy caused by the difference in density

between pores and molten metal is supported by extending the exis-

tence of the molten bath over time. This has been demonstrated suc-

cessfully using a laser hybrid method

and a beam oscillation.

However, the temporal prolongation of the weld pool existence is to

a certain extent accompanied by the negative properties mentioned

above with regard to distortion and heat input. The second approach

to porosity reduction is to actively support the buoyancy behavior of

the pores. Teichmann et al.

were able to achieve this by welding

under reduced ambient pressure. Another innovative method is the

usage of an electromagnetic (EM) system to increase the resulting

buoyancy velocity of the pores.

7,8

In addition to the lower density,

the lower electrical conductivity σof the pores, compared to the

molten aluminum, is exploited. This is achieved by means of a mag-

netic field oscillating between two magnetic poles located on the left

and right above the weld pool (see Fig. 1). The alternating magnetic

flux density Bperpendicular to the welding direction is technically

implemented by the air gap between the magnetic poles. This leads

to the formation of eddy currents jparallel to the welding direction

whose direction alternates depending on B. The resulting Lorentz

force F

is always directed downward and presses the electrically

well conductive aluminum melt to the bottom of the weld pool. In

addition to the natural, density-induced buoyancy, an electromag-

netic buoyancy component is created. The buoyancy force F

com-

posed of these two parts leads to the removal of gas bubbles.

Figure 1 shows the main influencing parameters, which influence

the formation and elimination of pores. The formation of pores is

mainly determined by the base material and the laser beam welding

process. As a result of the die casting process, there are casting

defects and impurities in the material. These appear in the form of

gas bubbles, hydrides, etc. The hydrogen content can be character-

ized by the density index (among other things). The process param-

eters (welding velocity u

weld

, laser beam power P

, etc.) of the laser

beam welding in combination with the material properties (absorp-

tion coefficient, thermal conductivity, etc.) determine the weld pool

geometry as well as the point of origin of the process pores and met-

allurgical pores. In addition, the geometric boundary conditions for

porosity elimination are defined. Depending on the laser power and

the welding speed, a certain weld pool length and depth as well as

the solidification velocity of the weld pool results, which limits the

time for pore buoyancy. In contrast to this, the electromagnetic

influence of the weld pool supports the elimination of pores. In pre-

vious investigations, Fritzsche et al. found out in laser beam welding

of the aluminum die casting alloy AC-AlSi9MnMg (Silafont 36) that

a variation in the frequency of the oscillating magnetic field f,which

influences the skin depth δ, does not indicate a clear trend regarding

to porosity reduction.

The initiated electromagnetic pressure was

FIG. 1. Influencing factors and functional principle of the electromagnetic porosity reduction at partial penetration laser beam welding.

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identified as the decisive component for porosity elimination.

The

magnetic pressure p

can be calculated according to

pm¼B2

(2 μ0), (1)

where in the welding process, it is controlled via B, the magnetic

flux density. μ

(=4π×10

−7

−2

) is the magnetic field constant.

This pressure also propagates at weld pool depths that exceed the

frequency-dependent skin depth. It is, therefore, assumed that the

initiated pressure is also the main influencing factor for porosity

reduction at higher laser intensities and deeper weld pools.

In the

present study, this aspect is specifically investigated in partial pene-

tration laser beam welding of the aluminum die casting alloy AlSi12

(Fe). The background of this systematic investigation is that an adap-

tation of the process parameters is necessary for practical, real appli-

cations, e.g., by changing component geometries. The robustness of

the EM influence shall be investigated at different welding parame-

ters. Using a design of experiments, the laser beam power, welding

velocity, and magnetic flux density are varied. Based on the findings

from previous investigations,

7,8

the frequency is not considered as an

influencing variable. The same design of experiments is applied to

AlMg3. This wrought aluminum alloy serves as a reference material

to compare and interpret the results of this investigation. The criteria

and values for the classification of welds with regard to permitted

porosity ratios and pore sizes are regulated for aluminum materials

in DIN EN ISO 13919-2:2001-12.

II. EXPERIMENTAL SETUP

The laser beam welding experiments were carried out on 6 mm

thick sheets of die-cast aluminum alloy AlSi12(Fe) (EN AC-44300)

and of wrought aluminum alloy AlMg3 (EN AW-5754). The param-

eters used for the die casting manufacturing process can be found in

Table I. The chemical compositions according to the standard and

the values measured by spark emission spectrometry for both materi-

als are listed in Tables II and III Both aluminum alloys are nonhar-

denable alloys, although they differ greatly in their silicon and

magnesium content. AlMg3 is used as a reference material, as good

results with respect to electromagnetic porosity reduction have

already been demonstrated (see Ref. 11). A pretreatment by pickling

or grinding of the aluminum materials was not carried out. Right

before the welding process, the sample surface was degreased with

ethanol. A schematic illustration of the setup is shown in Fig. 2.The

laser beam hits the material surface at an angle of entry of 10° and is

backhand orientated. A ceramic shielding gas nozzle is placed with

opposite orientation at an angle of 20°. Argon with a volume rate of

35 l min

−1

is used to protect the weld pool against the atmosphere.

The welds are performed in flat position in a bead-on-plate

configuration by using a fiber laser with a wave length of 1070 nm.

The laser optics is a BIMO HP with a focal length of 350 mm and

a laser spot diameter of 0.56 mm. The beam parameter product is

11.5 mm × mrad. Laser and magnet are located above the work-

piece, and their position to each other is fixed. The laser beam hits

the workpiece surface exactly in the center of the 18 mm wide air

gap between the magnetic poles as well as in the middle of the

16 mm wide magnetic pole (in the x-direction) (see Fig. 2). The

focus position is kept constant at a level of −6 mm. Furthermore,

the workpiece is attached to an x–y positioning stage. By its move-

ment relative to the fixed laser-magnet configuration, the welding

velocity is achieved. The vertical clear distance between magnet and

workpiece is 2 mm. The generated weld seams have a minimum

length of 170 mm. The magnetic field oscillates between the two

magnetic poles, which are exactly perpendicular to the welding

direction, with a frequency fof 3250 Hz for the entire measuring

series with electromagnetic weld pool influence.

To investigate the effect on porosity, three influencing factors

B,P

, and u

weld

are varied within the design of experiments. A

central composite design (CCD) is used to derive a quantitative

model for predicting the porosity fraction in the weld seam based

on a function of the three influencing parameters. 0 represents the

central point for each influencing factor and is repeated a total of

six times. Around this central point, a full-factorial (2

) experimen-

tal design is realized, which consists of eight experiments. This is

done symmetrically at the eight corners around the central point.

The CCD plan is extended by means of a star design (face centered,

α= ±1) in order to be able to estimate additional quadratic terms.

This results in 20 tests each for both aluminum alloys (see

Table IV). The coefficients of the variables were determined by

multiple linear regression, according to Eq. (2),

y¼b1x1þb2x2þb3x3þb12x1x2þb13x1x3þb23x2x3

þb11x2

1þb22x2

2þb33x2

3þk:(2)

TABLE I. Selected parameters of the manufacturing process of aluminum die

casting AlSi12(Fe).

Material/brand name AlS12(Fe)/230 D

Release agent Safety-Lube 7477

Mixing ratio 1:100

Piston lubrication Power-Lube 824

Density index 4.2%

Mold temperature 250 °C

Piston temperature 20 °C

Oven temperature 740 °C

Vacuum Without vacuum

TABLE II. Chemical composition of AlSi12(Fe) (EN AC-44300) according to DIN EN 1706 (Ref. 12) and measured by optical emission spectrometer (OES), data in wt. %.

Si Fe Cu Mn Mg Cr Zn Ti Al

DIN EN 1706 10.5–13.5 0.45–0.9 0.1 0.55 0 0 0.15 0.15 Bal.

OES 13.21 0.53 0.31 0.34 0.006 0.002 0.022 0.068 Bal.

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Published under license by Laser Institute of America

The coefficient of determination R

reflects the quality between

the model and the experimental values by determining their devia-

tion from each other [see Eq. (3)]. The closer the value is to 1.0, the

better the agreement,

R2¼1PI

i¼1(y ^

y)2

i¼1(y ^

y)2:(3)

After conducting the design of experiments, the quantity of

porosity was determined by x-ray images in top view and evaluated

by using the software IMAGEJ via a threshold method. First, the mean

gray value and its standard deviation of the entire sheet were deter-

mined. The contour of the weld seam to be evaluated was then

traced, and the weld seam was cut using the “Crop”-function. To

reduce the image noise, the “Smooth”-function was used to replace

each pixel with the average gray value of the surrounding 3 × 3 pixel

square. A pixel is recognized as a pore when the mean gray value of

the sheet minus the standard deviation is exceeded. The minimum

pore size is 4 square pixels, which corresponds to a pore area of

0.01 mm

. A value of 0.3 is defined as the minimum roundness

(0 ≙infinitely elongated polygon and 1 ≙perfect circle). In addition,

the functions “Exclude edges”(dark edge areas caused by the

smoothing process are not counted as pore) and “Include holes”

(material within a pore is evaluated as belonging to the pore) are

used. The x-ray images are evaluated over the whole weld seam

length. Subsequently, a 70 mm long area from the center of the

respective weld seam was evaluated by computed tomography (CT)

(100 kV microfocus x-ray source). The used detector is a Dexela

1512NDT CMOS detector with cesium iodide scintillator crystals and

a GigE-Interface. Representative parameter combinations of the CCD

plan were selected. The pore analysis was carried out using the VG

STUDIO software. In order to be able to determine the proportion of

pores related to the weld seam volume, cross-sectional images were

taken at the two end faces of the separated area of the respective weld

seam. The weld pool limitation is not recognizable from the mere CT

image, so this step is necessary. In VG STUDIO, a so-called region of

interest (ROI) can be defined on the basis of the contour of the cross-

sectional image and the weld seam length. By superimposing the

ROI’s, which are based on two cross-sectional images for the respec-

tive weld seam, it is possible to determine a meaningful proportion of

pores in the weld. The porosity was determined using the VGDefX

algorithm. The edge length of a voxel (cube-shaped) is 0.0374 mm,

whereby the minimum size of a pore is 8 voxels. This results in a

smallest detectable pore diameter of approximately 0.1 mm. In

summary, it can be said that the evaluation of the x-ray images deter-

mined the pore content related to the weld seam area (weld seam

contour in top view) and the CT evaluation measured the pore

content related to the weld seam volume.

III. RESULTS AND DISCUSSION

The quantitative development of the influencing variables

with indication of the standard deviation on the porosity measured

by x-ray image evaluation is shown in Figures 3 and 5.

TABLE III. Chemical composition of AlMg3 (EN AW-5754) according to DIN EN 573-3 (Ref. 13) and measured by OES, data in wt. %.

Si Fe Cu Mn Mg Cr Zn Ti Al

DIN EN 573-3 0.4 0.4 0.1 0.5 2.6–3.6 0.3 0.2 0.15 Bal.

OES 0.28 0.33 0.042 0.23 3.14 0.042 0.044 0.022 Bal.

FIG. 2. Schematic illustration of the experimental setup with the most important geometrical parameters.

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Published under license by Laser Institute of America

Figure 3 demonstrates for the experiments with AlSi12(Fe) that

an increase of the magnetic flux density Bleads to a reduction of the

porosity from 12.4% at 0 mTorr (welds without EM influence) to

3.9% at 350 mTorr. This corresponds to an improvement of 69%. In

contrast, an increase of the laser power P

from 3 to 5 kW is associ-

ated with an increase of the porosity by 61%, from 4.7% to 7.9%.

Considering the correlation of all influencing variables, a linear rela-

tionship is recognizable across the individual factor levels. The

welding velocity u

weld

has no significant influence and leads to a

slight decrease in porosity. This is also expressed in the calculation

of porosity according to the multiple linear regression equation,

y¼6:5505 þ1:6006 PL0:4957 uweld 3:8816 B:

The coefficient of determination R

, which represents the

quality of the regression model and test results, is 0.927 and thus

very good. The value of the standard deviation of the model, root

mean square (RMS) value, is 0.9419. The probability of error for

the hypothesis that there is a so-called “Lack of Fit”is 0.656. This

means that the size of the model error can be neglected.

To illustrate the effect of the two essential parameters for

AlSi12(Fe), a contour line chart is used (see Fig. 4). It can be

clearly seen that the pore content falls linearly with decreasing

laser power and increasing flux density. The pore content can be

reduced to such an extent by the magnetic flux density alone, i.e.,

independent of the laser power and the welding speed, that the

weld seams can be classified in valuation group C of the DIN EN

ISO 13913-2 standard.

In order to be able to classify and evaluate the results at the

die-cast aluminum alloy, the same experiments were performed on

wrought alloy AlMg3, which thus serves as a reference material.

Comparing the progressions of laser power and welding velocity

with regard to pore content, it can be seen that this is qualitatively

and quantitatively similar to the die casting alloy (see Fig. 5).

With rising laser power, the measured porosity doubles,

starting with 4.2% at 3 kW. The influence of the welding velocity

is negligible, just like within the tests of the die casting. In con-

trast to P

and u

weld

,Bis not linear and shows quadratic relation.

Quantitatively, the porosity level is significantly lower than with

die casting.

It drops from 7.1% for welds without EM influence (at

0 mTorr) to approximately 2% at 350 mTorr, which corresponds to

a reduction of approximately 72%. The equation of the regression

model for the material AlMg3 is as follows:

y¼6:3011 þ2:0843 PLþ0:4676 uweld 2:5728 B

1:1665 PLB1:7461 B2

TABLE IV. Coded factors and the composition of the CCD plan for determining the

response (porosity ratio).

Parameters

Coded levels

−10 1

(kW) 3 4 5

weld

(m min

−1

)2 3 4

B(mT) 0 175 350

Experiment

Coded CCD

1111

211−1

31−11

41−1−1

5−11 1

6−11−1

7−1−11

8−1−1−1

900−1

10 0 0 1

11 0 1 0

12 0 −10

13 1 0 0

14 −10 0

15 0 0 0

16 0 0 0

17 0 0 0

18 0 0 0

19 0 0 0

20 0 0 0

FIG. 3. Graphical representation of the relationship of the respective influencing

factor on the porosity at AlSi12(Fe).

FIG. 4. Representation of the effect on porosity as a function of the relationship

between magnetic flux density and laser power in the tests with AlSi12(Fe), cal-

culated based on the statistical correlations.

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Published under license by Laser Institute of America

It can be seen that, in addition to the linear influences of the

three influencing factors, the interaction between laser power and

magnetic flux density as well as the quadratic term of the magnetic

flux density is also important. In this case, R

has a value of 0.932.

The RMS value here is 0.849. The size of the model error can be

neglected here too, since the probability of error for the hypothesis

that there is a lack of fit is 0.378. Thus, the porosity value is again

significantly influenced here by P

and B. Therefore, a contour line

plot is created based on the statistical correlations, which illustrates

the pore content depending on these two variables (see Fig. 6). For

experiments up to a Bfield of 175 mTorr, the laser power is the

dominant factor by which the porosity is determined. From a value

of B= 175 mTorr, the quadratic influence of the magnetic flux

density becomes noticeable and the porosity drops to a level below

3%, independent of P

. These welding results can be classified in

evaluation group B of DIN EN ISO 13919-2. Due to the differences

between the materials with regard to the qualitative course of the

magnetic flux density, it is assumed that this influences the weld

pool geometry, respectively, weld pool flow. The die casting alloy

clearly shows a linear decrease of the pore content, a quadratic

decrease in the wrought alloy, which is only noticeable from a value

greater than 175 mTorr. This aspect must be investigated in the fol-

lowing by means of simulations. An increase of the laser power leads

mainly to an increase of the welding depth. Therefore, a higher mag-

netic flux density seems to be necessary in order to be able to

remove pores from deeper regions of the weld pool by increasing the

initiated electromagnetic pressure.

The increase of Balone leads to a porosity decrease of approxi-

mately 70%, independent of the material. The findings show for

subsequent welding tests on overlapping joints that the lowest possi-

ble laser power and a high magnetic flux density should be selected.

The evaluations carried out by means of x-ray images are

further analyzed in detail with randomly selected CT images. The CT

FIG. 5. Graphical representation of the relationship of the respective influencing

factor on the porosity at AlMg3. FIG. 6. Representation of the effect on porosity as a function of the relationship

between magnetic flux density and laser power in the experiments with AlMg3,

calculated based on the statistical correlations.

FIG. 7. Comparison of selected CT images at constant laser power (5 kW) and welding velocity (2 m min

−1

) of AlSi12(Fe) (above) and AlMg3 (below) with reference to

the porosity measured at the weld seam volume.

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images qualitatively confirm the trend in terms of the findings previ-

ously obtained from x-ray images. The following CT images show the

defect volumes for both materials with the same laser power

= 5 kW) and the same welding velocity (u

weld

=2mmin

−1

) (see

Fig. 7). In die casting, a defect volume of 9.12% can be seen without

EM influence, which is successively reduced to a value of 0.98% as

the Bfield increases [Fig. 7 (above)]. This corresponds to an

improvement of approximately 90%. A total of 29 large pores in

the range from 1 to 8.7 mm

could be detected at B= 0 mTorr.

These defect volumes can no longer be proven at B=350mTorr.

Here, the largest single pore has a defect volume of approximately

0.5 mm

. For AlMg3, the CT images for identical parameters are

visualized in Fig. 7 (below). Here, the degree of reduction (−83%)

is at a similar level, from initially 2.2% to 0.37% at B= 350 mTorr.

Four pores larger than 1 mm

are contained in the CT image with

B= 0 mTorr. At B= 350 mTorr, the largest single pore is 0.84 mm

and the next smaller one is 0.24 mm

. The CT images were ana-

lyzed in more detail with regard to the defect volumes (see Figs. 8

and 9). Three volume groups were formed, and the number of

pores for each group was counted. Figure 8 shows the number of

pores corresponding to the defect volume classes for the die

casting alloy. First, for welding without EM influence, a large

number of pores is counted for each volume class, especially pores

with a volume of more than 0.4 mm

(46 counts). With a magnetic

flux density of 350 mTorr, the number of pores can be significantly

minimized, in this case to less than ten pores in the class up to

0.25 mm

and to two remaining pores for the other two classes.

Even with pore volumes in the range from 0.01 to <0.1 mm

,the

number of pores could be reduced from 836 (at B= 0 mTorr) to

289 (at B= 350 mTorr). The same trend can also be observed at

the wrought alloy in Fig. 9 with a reduction from 103 counts to 42

at B= 350 mTorr.

For the listed groups, the pores were eliminated, starting from

more than ten pores without EM influence on less than three pores

at B= 350 mTorr.

Thus, a significant reduction of the pores can be determined

for the parameter sets analyzed by means of CT images, both

regarding their number and regarding the defect volume during

laser beam welding. It is especially the case with wrought alloy, but

this was expected due to the higher hydrogen content in AlSi12

(Fe). Nevertheless, impressive results on a very good level are

achieved by the EM support also in die casting.

IV. SUMMARY

This paper describes a systematic investigation of the EM influ-

enced laser beam welding of the aluminum die casting alloy AlSi12

(Fe) in comparison to a reference material, a wrought aluminum

alloy AlMg3. By using of a face centered CCD test plan, the influenc-

ing variables laser power, welding velocity, and magnetic flux density

are varied with regard to their influence on the remaining porosity.

The global pore fraction of the weld seams was analyzed by x-ray

images with IMAGEJ. This enabled a qualitatively very good regression

model to be derived for the respective material, which identifies the

dominant influencing variables. The results proved, statistically veri-

fied, for the investigated parameter range, that

•the magnetic flux density is the main cause for the porosity

reduction,

•the porosity rises with increasing laser power, and the porosity in

the weld seams rises,

•the influence of the welding velocity is negligible, and

FIG. 8. Bar chart regarding the number of pores as a function of the defect

volume for AlSi12(Fe), based on the CT images in Fig. 7 (above).

FIG. 9. Bar chart regarding the number of pores as a function of the defect

volume for AlMg3, based on the CT images in Fig. 7 (below).

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J. Laser Appl. 32, 022031 (2020); doi: 10.2351/7.0000064 32, 022031-7

Published under license by Laser Institute of America

•the porosity decreases due to the EM influence by approximately

70% compared to the unaffected welds. This effect is emphasized

by the contour line charts, which illustrate the relationship

between laser power and magnetic flux density.

With the exception of the quadratic influence of Bat the wrought

alloy, the statistical correlation shows a linear development of the

respective influence variables for both aluminum alloys. In order to

investigate these deviations, further simulations with a focus on

weld pool geometry and weld pool flow are to be performed. In

addition, the welding results can be classified in accordance with

DIN EN ISO 13919-2 in the highest evaluation group B for AlMg3

and in evaluation group C for AlSi12(Fe) by applying a magnetic

flux density of 350 mTorr. The analysis of the CT images at cons-

tant laser power and welding velocity allows a direct comparison

both between the two alloys and also as a function of the magnetic

flux density with regard to the number and size of pores. An

increase in the magnetic flux density leads to a significant decrease

in the number and volume of pores, which can be seen more

clearly in wrought alloy than in die casting. Very acceptable results

can be achieved for both materials and different welding parame-

ters. This successfully demonstrates the desired process robustness

and functionality of the EM system for practical applications. For

subsequent investigations of overlap joints, the lowest possible laser

power and a high magnetic flux density are recommended.

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Meet the Authors

André Fritzsche, born in 1987, received his M.Sc. in the field

of mechanical engineering at the Technical University Berlin

Institute. Since 2011, he has been a member of the department

“Welding Technology”at BAM Federal Institute for Materials

Research and Testing. Since 2015, he has been working as a

research assistant at the same department. Currently, he is working

in the field of electromagnetic influenced laser beam welding

processes.

Professor Dr.-Ing. Kai Hilgenberg conducted his Ph.D. studies

at the Chair of Metal Forming Technology at the University of

Kassel until 2014. Afterward, he began working as team leader at

BAM Federal Institute for Materials Research and Testing in the

area of laser material processing. Since 2015, he has been holding a

position as Junior Professor at the Institute of Machine Tools and

Factory Management, Technical University Berlin.

Professor Dr.-Ing. Michael Rethmeier is with the BAM

Federal Institute for Materials Research and Testing. He is the head

of the division “Welding Technology.”He is also heading the

“Chair of Joining Technology”at the Institute of Machine Tools

and Factory Management, Technical University Berlin and is divi-

sion director of “Joining and Coating Technology”at the

Fraunhofer Institute for Production Systems and Design

Technology. His present research topics include, among others,

innovative arc welding processes, high power laser beam welding,

and numerical simulations in various welding processes.

Journal of

Laser Applications ARTICLE scitation.org/journal/jla

J. Laser Appl. 32, 022031 (2020); doi: 10.2351/7.0000064 32, 022031-8

Published under license by Laser Institute of America