SYNAGIC CONTROLLED LASER ROLL BONDING OF
DISSIMILAR METAL JOINTS
By Muneharu KUTSUNA, Manoj J. Rathod and Ammar Husam Azar
Department of Materials Processing Engineering, School of Engineering
Nagoya University, 1 Furo-cho, Chikusa-ku Nagoya, 464-8603, JAPANTel / Fax: +81 52 789 3365 , e-mail: kutsuna@numse.nagoya-u.ac.jp

ABSTRACT
Laser roll bonding is a new process involving simultaneous laser heating and roll bonding. In thiswork, it was used to join dissimilar metal sheets of mild steel (SPCC) and aluminum A1050 and itsalloy A5052, as this combination is used in industry to reduce weight of structural parts. The processparameters like laser power, roll pressure and travel speed were varied and synagic controlled to get
more ductile intermetallic compounds at the interface. Strength of the joints was tested by tensile shear
test and formability was tested by Erichsen cupping test. In tensile shear test, the laser bonded joint was
broken in base metal of carbon steel. The results showed that the strength of joint increases with thedecrease in the interface layer thickness, but in the absence of interface layer, no bond is formed. The shear
strength of laser roll bonded specimen ranged between 21.8 and 55.9MPa. Erichson value (cupping-depth)and shear-strength are strongly affected by laser heat-input and roll pressure. Pulsed laser power, pulsing
travel and roll pressure are effective to get better intermetallic compounds and joint strength. The basic
data for synagic control were obtained from present experimental results.
KEY WORDS：Dissimilar Metals, Laser Roll Bonding, Pulsed laser, Intermetallic Compounds,
Steel to Aluminum1. Introduction
The new automobile industry has a continuous
requirement for weight reduction to increase
efficiency and reduce air pollution. One way
suggested is the use of the combined structure
consisting of Aluminum alloy and steel sheet.
Therefore, it is necessary to join theses dissimilar
metals together for different shapes in large
continuous production suitable for the modern
automobile industry. Attempts of using resistancespot welding with inserts for this purpose havebeen already made [1]. Major problem appeared
during joining these dissimilar metals are theformation of intermetalic brittle compounds likeFeAl3 & Fe2Al5 in the interface layer. It has beenreported that if the thickness of the intermetallic
compound layer is limited below 10m, the joint
strength is improved [2] In the present work CW
and pulsed CO2 laser welding were used, CW CO2
laser were used to weld the steel sheet withaluminum A5052, and pulsed CO2 laser used toweld the pure aluminum A1050. Using of laser

beam welding of steel and aluminum were also
reported [3]. An attempt is made to identify andestimate the thickness of the intermetallic
compounds after diffusion bonding with different
conditions of pressure, travel speed, and laser
power. Due to laser heating, the material
experiences fast heating and cooling rates. It has
been found that the formation of the brittle
compounds takes place by diffusion process, which
involves slow heating and cooling rates. Therefore,a process combining laser heating and roll bondingis suggested. It is intended that the laser heating ofsteel in such a way that the interface reaches thetemperature sufficient to form the bond while it
being pressed. It was aimed to control the joining
process by varying laser power, travel speed, androll pressure so that to promote the formation ofbrittle intermetallic compounds in the interface
layer. The joint strength and formability were
determined by tensile shear test and Erichsen test
respectively.

2. Experimental Procedure
2.1 Material used
The commercial materials used in automobile
industry for car body are low carbon steel andaluminum alloys. The sheet thickness for bothtypes aluminum A5052 and A1050 is 1mm, andfor steel sheet is 0.5mm used in present work. The
chemical composition is shown in Table 1.

Table 1 Chemical composition of materials used (in mass %)Alloy

MgCrSiFeCuMn

Zn

OthersA1050

0.05max-----

0.25max

0.4max0.05max

0.05max

0.05max

0.03

A5052

2.5

0.23

0.25max

0.4max0.1max0.1max0.1max

0.05

SPCC
steelC

Mn

PS

0.12max

0.5 max

0.04max

0.045max

2.2 Laser Roll Bonding
A lap joint was used to combine the steel sheetwith the aluminum alloys as shown in Figure (1)-a,the steel was placed on the top of the aluminum inorder to absorb the heat from the incident laser
beam without melting and conduct the heat to theinterface. The over lap was 9mm, and the Gaussian
beam was defocused to give elliptical spot of 2.5mm minor and 3.5mm major diameter on the steel
surface.
In order to heat the interface between the steel
and aluminum to a suitable temperature by laser
beam, and apply pressure to this interface at theright time, the laser roll-bonding fixture used in thepresent work is made as shown in Figure (1)-b.
A spring is used to press the joint against thetable through the roll; this pressure can bedetermined by the spring deflection. Prior tojoining, the faying surfaces of both sheets werecleaned by using the suitable way, for Aluminum
sheets, ultrasonic cleaning was applied to remove
the hard aluminum oxide film, then it was mergedwith brazing flux (KalF4:K2AlF5.H2O) to prevent
further oxidation and remove any if exist.
Laser Roll Bonding with varying travel speed,
laser power, and roll pressure were carried out.
The Joints were cut transversely to observe themacro-structure and microstructure. The same
were used to identify and estimate the intermetallic
compounds through the interface layer by EPMA
with WDX method. Based on the EPMA results
the thickness of the interface layer was divided
into ductile compounds (FeAl+Fe3Al) and brittle
compounds thickness (FeAl3+Fe2Al5). For
estimating the strength and formability of the joints,
three samples were prepared for tensile shear test
and one specimen for Erichsen test.

(a) Clamping setup(b) Laser Roll Bonding processFigure( 1) Schematic drawing of Laser Roll Bonding

3. Experimental results and discussions
The main purpose of using CO2 Laser Rollwelding is to achieve fast heating and fast cooling,which may suppress the formation of the brittle
intermetallic compounds. To increase thepossibility of formation of the ductile intermetallic
compounds (FeAl+Fe3Al), the interface
temperature should be in the range 1200-1300C
as shown in Figure (2) for Iron-Aluminum phase
diagram. Temperature is the most essential

variable since it, together with pressure, determine
the extent of contact area during diffusion bonding
and it alone determine the rate of diffusion thatgoverns void elimination.
Changing pressure values with interface temperature(by varying the laser power or travel speed), we cancontrol the interface layer thickness until theoptimum is reached, in which the brittle compounds
layer thickness will be minimum and the ductile one
will be maximum. In addition to these parameters, apulsed laser welding is used in welding the purealuminum A1050, which enable us for more controlof the heating and cooling rates by changing thepulse.
As the interface layer temperature reaches therequired range, a thin surface region of aluminumin the macrostructure in figure (3). And typicalmicrostructures of laser roll bonding joints are shownin Figure (4).

Figure (2) Fe-Al Phase Diagram

1.5kW-1.5m/min-150MPa
1.5kW-2.2m/min-202MPa(a) SPCC-A1050(b) SPCC- A5052
Figure (3) Macrostructure Samples

1.5kW-150MPa-4.0m/min
1.5kW-150MPa-2.0m/min(a) SPCC- A1050(b) SPCC- A5052
Figure (4) Macrostructure Specimens
The width of intermetallic compound layer shown
were less than 10 μｍ and homogeneous.
The interface layer was analyzed by using EPMA
method; the EPMA results in Figure (5) for A5052
show the existence of the ductile compound on thesteel side and brittle compound on the aluminumside for a constant pressure, and laser power for
two travel speeds. Figure (6) show the fraction
thickness for both ductile and brittle compounds
through the interface layer is changing with travel

speed. In general, for a constant laser power andpressure, starting with a low speed, will offer alonger time for the diffusion process to take placein which in turn produces a thicker layer withhigher percentage of the brittle compounds.
With increasing the travel speed the percentage
thickness of the ductile compounds increases from23% to 51% for A5052 alloy and from 7.6% to40.6% for A1050. The reason is related tocontrolling the diffusion rate by changing heatingand cooling rate s with travel speed.

(a) 1.5kW-150MPa-1.2m/min(b) 1.5kW-150MPa-2.0m/min
Figure (5) EPMA analysis for SPCC-A5052
In this experiment, different laser powers androll pressures were used to study their effect on theinterface compounds. Increasing the power has thesame effect of decreasing the speed, but if laser
power reaches to high values, it will cause meltingof the steel sheet, and if it reaches to low values,
the heat input may not be sufficient to producebond. As for the pressure, it is necessary forincreasing the contact area directly after heating
for a short time to allow diffusion process to takeplace, and help in increasing the cooling rate of thejoint by heat conduction.
Figure (7) shows the relation between tensile
shear strength and interface layer thickness withtravel speed. By increasing the travel speed, the(a) SPCC- A1050 (1.5kW-150MPa)

interface layer thickness decreases, at the sametime shear strength increases up to 33.1MPa for
A1050 and to 55.9MPa for A5052. Although in
higher speeds, the percentage of ductile
compounds is relatively high, the shear strength
drops down for fast travel speed, owing to
insufficient temperature due to the lack of heat
energy at the interface layer.
To detect the formability of these joints, which it
is a major characteristic of the sheets used in
automobile industry, Erichsen test was carried outand evaluated with different speeds as shown infigure (8). The cupping height increases with speed
until it reaches a maximum value then starts todecrease(b) SPCC- A5052 (1.5kW-150MPa)

Figure (6) Composition of IMC in the interface layer

Shear Sttength, MPa

40.00

15.0

30.00
10.0
20.00
5.0

10.00
0.00

80.0

Shear strength, MPa

Interface Thickness, ｵm

2.0

4.0

6.0

12.0

40.0

8.0

20.0

4.0
0.0

1.0

8.0

16.0

60.0

0.0

0.0
0.0

Average shear strength, MPa
Average interface thickness, ｵmAverage interface thickness, ｵm

20.0Average shear strength, MPa

Average interface layer thickness, ｵm

50.00

1.5

Travel speed, m/min

2.02.5
Travel speed, m/min

3.0(a) SPCC- A1050(b) SPCC-A5052
Figure (7) Effect of travel speed on shear strength

10Cupping Hight, mm

8.00

86.00

64.00

42.00

21.5kW-150MPa

2.0kW-175MPa

0.00

00.0

2.0

4.0

6.0

8.0

Travel speed, m/min

1.5kW-150MPa-1.5m/min

02468

Travel Speed, m/min

10122.0kW-175MPa-2.0m/min

Figure (8) Results of Erichsen Test performed on laser roll bonded joints
almost in the same manner with shear strength
analysis. The maximum cupping value is related tothe existence of the optimum thickness of theinterface layer, which is responsible of relatively
high percentage of ductile compounds with asufficient heat for satisfactory strong bonding.

4.Conclusions
1. It is possible to joint the aluminum alloys
to steel by using laser roll bonding.
Moreover, by controlling the parameterssuch as laser power, travel speed, rollpressure and pulse; we can get 55.9MPa
shear strength for A5052 and about30MPa for A1050.

bonding takes a place for a short period
because of the short thermal cycle.
3. For both joints made from A1050 andA5052 aluminum alloys with SPCC steel
after laser roll bonding, the EPMA
analysis shows that interface layer consistof brittle intermetallic compounds – FeAl3
and Fe2Al5 – on aluminum side andductile one – FeAl and Fe3Al - on the steel
side. As the travel speed increased, thetotal thickness of the interface layer
decreased with increasing of the thicknessof ductile compounds.

2. With good contact of the faying surfacesby roll pressure, heat conduction can beaccomplished from steel to the aluminum.
Laser heating provides high energy
density in the beam spot and rapid heatingand cooling cycle. Therefore, diffusion

5. Acknowledgement
Authors are thankful to Applied Laser Engineering Center (ALEC), Nagaoka,Japan for the help in thisresearch.

6. Rerences[1] M. Yasuyama, K. Ogawa and T. Taka, 1996.
Spot welding of aluminum and steel sheet withinsert of aluminum clad steel sheet – Part 1.
Journal of Japan Welding Society, 14(2): 314320[2] C E Albright, 1981. The Fracture toughness ofsteel-aluminum deformation welds, WeldingJournal, 60(11): 207s-214s[3] G. Seplod, E. Schubert and I. Zerner, 1999.
Laser beam joining of dissimilar materials,IIW. IV (734): 1-10.