Abstract6000 series (magnesium and silicon based) aluminum alloys are highly susceptible to hot cracking during laser beam welding. The occurrence of hot cracks depends on thermo-mechanical strain at the solidifying stage of the melt and in the micro-scale on the solidification structure. A new metallurgical approach to avoid these cracks by affecting the solidification process is using a multi-alloy aluminum with a silicon-rich layer. Within this paper infrared videos were used to investigate and compare the behavior of this new material with the 6xxx monolithic alloy at hot crack sensitive close-edge positions

Bezençon, C.

Graf, T.

Stritt, P.

Weber, R.

Weller, D.

Elsevier - Publisher Connector 

 Physics Procedia  41 ( 2013 )  164 – 168 
1875-3892 © 2013 The Authors. Published by Elsevier B.V.
Selection and/or peer-review under responsibility of the German Scientific Laser Society (WLT e.V.)
doi: 10.1016/j.phpro.2013.03.065 
Lasers in Manufacturing Conference 2013 
Remote laser welding of multi-alloy aluminum at close-edge 
position 
D. Wellera*, C. Bezençonb, P. Strittc, R. Webera, T. Grafa 
aInstitut fuer Strahlwerkzeuge (IFSW), Pfaffenwaldring 43, 70569 Stuttgart, Germany 
bNovelis Switzerland SA, Rte des Laminoirs 15, 3960 Sierre, Switzerland 
cGraduate School of Excellence advanced Manufacturing and Engineering, Nobelstr. 12, 70569 Stuttgart, Germany 
Abstract 
6000 series (magnesium and silicon based) aluminum alloys are highly susceptible to hot cracking during laser beam 
welding. The occurrence of hot cracks depends on thermo-mechanical strain at the solidifying stage of the melt and in the 
micro-scale on the solidification structure. A new metallurgical approach to avoid these cracks by affecting the 
solidification process is using a multi-alloy aluminum with a silicon-rich layer. Within this paper infrared videos were 
used to investigate and compare the behavior of this new material with the 6xxx monolithic alloy at hot crack sensitive 
close-edge positions. 
 
© 2013 The Authors. Published by Elsevier B.V.   
Selection and/or peer-review under responsibility of the German Scientific Laser Society (WLT e.V.) 
 
Keywords: Remote Laser Welding, Aluminum, AA6xxx, Multi-Alloy Aluminum, Hot Crack 
1. Motivation 
Hot cracking in AlMgSi alloys laser welding has been a subject of intensive studies over the last years. A 
hot crack appears and propagates when the residual melt is not able to fill up the volume between the 
dendrites [1]. Due to a large solidification interval aluminum alloys of the 6000 series are highly crack 
sensitive [2]. Since the hot cracking phenomenon is related to the strain on the solidifying melt and the strain 
itself depends on the weld seam position relative to the sheet edge [1], hot cracking is directly related to the 
 
 
* Corresponding author. Tel.: +49 711 685 64146 ; fax: +49 711 685 54146. 
E-mail address: daniel.weller@ifsw.uni-stuttgart.de. 
Available online at www.sciencedirect.com
© 2013 The Authors. Published by Elsevier B.V.
Selection and/or peer-review under responsibility of the German Scientific Laser Society (WLT e.V.)
Open access under CC BY-NC-ND license.
Open access under CC BY-NC-ND license.
 D. Weller et al. /  Physics Procedia  41 ( 2013 )  164 – 168 165
welding sheet edge distance [3]. In the range of 3 to 6 mm away from the sheet edge typical centerline hot 
cracks appear [2]. These cracks typically extend over the whole length of the weld seam except of the start of 
the weld. Therefore the centerline hot cracks are macroscopic. Concerning space- and material-saving light 
weight design it is of major interest to reduce the minimum critical edge distance where hot cracks occur.
Looking at the reasons for the hot crack susceptibility one has to differ between the metallurgical properties, 
like the deformability and the thermo-mechanical load, which cause deformations [4]. A common and
successful metallurgical way to avoid hot cracks is to use silicon-rich filler material which shifts the weld
pool composition to an alloy regime that is less crack sensitive [5]. Nevertheless this technique requires a 
controlled wire feeding which has to be tracked very close to the work piece along the weld geometry. 
Hence Novelis has developed a multi-alloy aluminum, which combines the good strength and formability 
of 6000 series alloy with a specific cladding alloy to suppress crack initiation without the need of a filler wire.
In Fig. 1 a weld cross section of this multi-alloy aluminum is depicted. It consists of core material and two
outer cladding layers. The core material maintains all the advantages and required properties of a 6xxx
monolithic alloy whereas the cladding layer acts like a silicon-rich filler material [6]. Therefore this multi-
alloy aluminum is compatible with the remote laser welding technology which offers new welding geometries
and a high cycle time due to a very fast laser beam positioning.
Fig. 1. Weld cross section of a 6000 series aluminum alloy sheet [6].
Within this paper infrared videos were used to investigate and compare the behavior of this new material
with a standard 6xxx monolithic alloy at hot crack sensitive close-edge positions.
2. Experimental Setup
All experiments were done with a TruDisk 5001 laser and a fiber delivery with a 200 μm core diameter.
The laser has a maximum output power of 5000 W at a wavelength of 1030 nm. To focus the laser beam on 
the work piece a PFO 3D scanner optic with a focal length of 450 mm was used. This yields a focus diameter
of 650 μm. The welding process was monitored with an infrared camera to analyze the temperature
distribution at a framerate of 50 Hz. Furthermore a high-speed camera in the visible wavelength range was
used to investigate melt bath dynamics and analyze them with regard to the arising temperature field. The
scanner optics was mounted on an industrial robot. For the experiments no shielding gas was used. The work 
piece, i.e. the processed sheets (145 x 60 mm), was fixed as shown in Fig. 2 with a standard clamping device.
The distance from the beam position to the clamping device was kept constant at 25 mm. To vary the distance
from the weld to the free end of the work piece, mechanical stops with different lengths were used. For all
experiments overlap welds with a length of 100 mm were made. The sheets were arranged with a thickness of 
1.2 mm on the top and 1.7 mm on the bottom. Start and end of the welds were about 20 mm away from the
Core
Clad
Weld
166   D. Weller et al. /  Physics Procedia  41 ( 2013 )  164 – 168 
edge of the work piece. The clamping device itself was fixed and the laser beam was deflected with the
scanner optic.
Fig. 2. Clamping device and work piece.
3. Results and Discussion
3.1. Influence of the edge distance on the formation of the temperature field
The investigations were performed at edge distances from 0 to 10 mm. The laser beam power was set to
5 kW which was kept constant for all experiments. In order to get comparable results between the two
investigated materials the feed rate was adjusted in such a way that full penetration was guaranteed. For the
standard 6000 series aluminum this was achieved at 5.5 m/min. For the multi-alloy aluminum about 10 % less
energy input per unit length was required. The intention of these experiments was to compare the cracks
susceptibility of the two different materials. But one have to consider that beside the edge distance the hot 
crack sensitivity is dependent on parameters like laser beam power, focus diameter, speed and the structural
design of the specimen as well [3],[7].
Fig. 3. Influence of the edge distance on the temperature field for the multi-alloy 
aluminum.
Fig. 4. Position of Tmax at the edge relative to 
the keyhole regarding the edge distance.
One main reason for the thermo-mechanical load and therefore the hot cracking is the temperature field
which is developing during welding [3]. In order to get comparable strain situations this was analyzed for both 
investigated materials. In Fig. 3 the influence of the edge distance on the temperature field for the multi-alloy 
 D. Weller et al. /  Physics Procedia  41 ( 2013 )  164 – 168 167
aluminum is depicted. To reduce the dependence on the local emissivity, the aluminum sheets were coated 
with a black graphite layer. However Fig. 3 shows a qualitative temperature distribution. Due to the destroyed
graphite layer in the weld seam, the emissivity is changed there and therefore the temperature appears lower 
in that region, even though this is actually not the case. As it can be seen in Fig. 3, welding at an edge distance
below 10 mm leads to a heat accumulation due to a reflected heat flow at the edges. This results in a non-
symmetric temperature field which implies a changed thermo-mechanical load. To quantify the influence of 
the edge distance on the field distribution the position of the highest temperature Tmax on the edge relative to
the capillary was measured. By decreasing the edge distance, the position of Tmax comes closer to the
capillary. Within this process the range of the heat accumulated zone is elongated too, which leads at a
distance of 2 mm to a sudden melting of the edge. Comparing the position of Tmax for the two materials shows 
no different behavior, as depicted in Fig. 4. Thus being an indicator for a similar strain situation.
3.2. Hot crack susceptibility at close-edge position
Looking at the resulting hot cracking susceptibility out of the trials for the multi-alloy aluminum, hot 
cracks were observed between 2.5 and 5 mm from the edge. No typical centerline hot cracks can be observed 
for smaller distances starting at 0 up to 2 mm and for larger edge distances exceeding 5 mm as summarized in 
Fig. 5.
Fig. 5.Cross-sections of the multi-alloy aluminum at varying edge 
distances.
Fig. 6. Dye penetration inspection at an edge distance of 5 
mm for multi-alloy aluminum and standard 6000 series
aluminum.
For the standard 6000 series aluminum still a center-line crack occurs at an edge distance of 5 mm, as 
depicted in Fig. 6. Its expansion is in the scale of the weld length and separates the two arising sides of the
weld. Nevertheless the appearance of such a weld seam does not differ from a crack-free one. It is still very 
uniform and the observed high-speed videos confirmed a steady state weld process as well.
4. Conclusion
Using a multi-alloy aluminum with a silicon-rich cladding layer offers the possibility for remote welding.
Furthermore the investigation in this paper showed that with this material about 10 % less energy input per 
unit length was required to achieve a full penetration weld compared to a standard 6000 series aluminum. By 
measuring the developing temperature field during welding a clear influence of the edge could be seen.
Regarding the two investigated materials, both showed a similar temperature distribution which is an indicator 
168   D. Weller et al. /  Physics Procedia  41 ( 2013 )  164 – 168 
for a comparable strain situation. The resulting welds showed that for a multi-alloy aluminum the hot crack 
susceptibility at close-edge position is reduced compared to a standard 6000 series aluminum. With a multi-
alloy aluminum crack-free welds are possible for edge distances larger than 5 mm. 
Acknowledgements 
The authors would like to thank the Novelis Switzerland SA and the Institut fuer Strahlwerkzeuge (IFSW) 
for fruitful collaboration. 
References 
[1] Ploshikin, V. et al.: Zum Mechanismus der Heißrissbildung beim Schweißen von Al-Legierungen, 2003. 
[2] Stritt, P.; Weber, R.; Graf, T.; Mueller, S., Weberpals, J.-P.:. New hot cracking criterion for laser welding in close-edge 
position. In Proceedings of ICALEO, 2012. 
[3] Hilbinger, R.M.: Heissrissbildung beim Schweißen von Aluminium in Blechrandlage, Dissertation Bayreuth, Herbert Utz 
Verlag, 2000. 
[4] Göbel, G.: Erweiterung der Prozessgrenzen beim Laserstrahlschweißen heißrissgefährderter Werkstoffe. Dissertation 
Technische Universität Dresden, 2007. 
[5] Coniglio, N.; Cross, C. E.; Michael, T.; Lammers, M.: Defining a Critical Weld Dilution to Avoid Solidification Cracking in 
Aluminum. In Welding Journal Vol. 87, September 2008. 
[6] Bezençon, C.; André, P.-D.; Bassi, C.: Remote Laser Welding of AA6xxx Multi-Layer FusionTM Material. In Proceedings of 
LATEST2 Joining Conference, 2011. 
[7] Gruss, H.; Pshennikov, A.; Herold, H.: The integral approach  a tailored method to optimize structural behaviour and 
weldabilty. In Hot Cracking Phenomena in Welds II, Springer Verlag, 2008. 


Remote Laser Welding of Multi-Alloy Aluminum at Close-Edge Position 

D. Weller

C. Bezençon

P. Stritt

R. Weber

T. Graf

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Physics Procedia

Remote Laser Welding of Multi-Alloy Aluminum at Close-Edge Position

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Remote Laser Welding of Multi-Alloy Aluminum at Close-Edge Position

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