Laser Roll Welding
By Muneharu KUTSUNA
Advanced Laser Technology Research Center Co.,Ltd.
CONTENT

Chapter 1
1.1 Background and Historical aspect
1.2 Definition of process
Chapter 2: Process fundamentals, and Joint Design
2.1 Process principle
2.2 Process features
2.3 Process parameters
2.4 Process variations
2.5 Applicable materials
Chapter 3: Equipment and Supplies
3.1 Laser roll welding equipment developed
3.2 Using different laser facilities
3.3 Flux for joining
Chapter 4: Applications for dissimilar metal joints
4.1 Joining of Al alloys and Low Carbon Steels
4.2 Joining of Al alloys and zinc coated steel
4.3 Joining of Ti and Low carbon steel

1Chapter 1
1.1 Background and Historical aspect
Early 2000s, Automobile industry has been under pressure to improve the fuelefficiency of vehicle for saving fuel as well as minimizing the pollution of environment.
This requires the measures such as weight reduction of the vehicle, efficient burning of
fuel, use of hybrid systems and alternative energies like electricity, hydrogen fuel cells
or solar energy. For reduction of the weight, it is suggested that high strength steels
should be used and the amount of steel in the vehicle should be reduced by using
8replacement of steel parts is not practical owing to its strength. Therefore, use ofsteel-aluminum hybrid structures has been suggested, particularly in the structural parts.
This combination is also widely used in antifriction parts like cylinder liners and bushes.
Apart from automobile industry, the combination of dissimilar joint between steel andaluminum also finds its applications in joining of LNG storage tanks and steel
supporting structure. The LNG spherical tanks are made from 5083 aluminum alloy andits support is steel skirting. The domestic appliances like electric frying pans, water
boilers also use such joints. Therefore, it necessary to join the steel parts to aluminumalloy parts of different shapes. Various joining processes like mechanical clinching, selfpiercing riveting, adhesive bonding, diffusion bonding, explosion welding, friction
welding, resistance spot welding, forge welding and roll bonding have been used for the
purpose. So, Development of a reliable dissimilar metal joint was important. M.Kutsuna
and M.Rathod at dept. of Material Science and Processing Eng. Nagoya University has
started the study on joining of dissimilar metal joint such as Al alloys and carbon steel
since 2000 after studying the roll bonding of Aluminum and low carbon steel in 1999..
Patent application of Laser roll welding has been done in Aug.22,2003 to.Japanese
patent office. The Japanese Patent No.3535152 was issued on March 19,2004. This
process was introduced to USA by the Welding Journal Vol. 83-1(2004).p.16s-26s.
Not only Al-to steel, but also Steel to Titanium and Al to Titanium joint wasinvestigated using this process.
1.2 Definition of process
Laser Roll Welding is not fusion welding, brazing and solid state welding. It is defined
as a pressure welding with a thin melting interface for lap joint of dissimilar metal
sheets using a roller and one side laser heating . In the case of laser roll welding ofaluminum to steel, aluminum can be melt only near the interface with steel which isheated upto 1300 ℃. In the case of laser roll welding of Titanium to steel, Eutectic
phase between Titanium and TiFe intermetalic compound is formed from liquid phase2

at the interface above 1180℃. These melting interface and interlayer should becontrolled to get a ductile phase at the interlayer.
Chapter 2: Process fundamentals, and Joint Design
2.1 Process principle
Fig.1 shows the process mechanism of laser roll welding in which laser heating of
only one base metal and some pressure is applied to make contact with both metals.
This contact with both metal allows heat conduction and metal diffusion through the
Joint interface. The heating temperature , heating rate and cooling rate should becontrolled to make more ductile intermatallic compound such as FeAl or Fe3Al in thecase of AL to steel joint. The heating temperature should be higher than formation
temperature of brittle intermetallic compounds like FeAl2, Fe2Al5 and FeAl3, or theeutectic temperature of high melting point metals such as Ti to Steel joint. As a result, a
new joint interface is formed between two metals. The interface can be made by
self-melting, formation of intermatallic compound and alloying of both metals. The
thickness of the joint interface layer is about 5 μm to 10μm.

By heating and pressurizing only metal A, heat is conducted to metal B, molten
phase is formed at the faying surface and jointed
Fig.1 Joining process of Laser Roll Welding
2.2 Process features
This process has following features in the Al-Steel joint ;1) formations of ductile intermetallic compounds such as FeAl and Fe3Al or
eutectic phase after self-melting in the interface layer;2) keeping the intermetallic compound layer thickness less than 10 µm;
3) the idea of using a sharp intensified fast moving heat source to just cause
wetting and diffusion for a very short period to form a metallic bond.
4) Heating is only one metal sheet by laser
3Laser is one of such characteristic heat sources, involving a typical thermal cycle of fast
heating and cooling. This helps in quickly reaching the temperature of the interface
suitable to form ductile compounds like FeAl and Fe3Al (about 1250oC). This may
cause melting of a very thin layer of aluminium – of the order of 10 µm - at the interface.
Therefore, though the complete elimination of brittle intermetallic compounds like
FeAl3, FeAl2 and FeAl3 is not possible owing to their low free energy; their formation issuppressed to some extent. As this effect of laser heating is taking place, the heatedzone is subjected to roll pressure to improve the contact area. This also helps inincreasing the cooling rate preventing further diffusion at the interface. Such conditions
restrict the intermetallic compound layer thickness to thin levels. The existence of a thininterface layer with some ductile compounds in it is favorable for improved joint
strength. In the process suggested by Sepold et al, direct melting of aluminium with thefeeding of filler metal is involved and no pressure is applied. Whereas in Laser rollbonding process, melting of aluminium is restricted to a thin layer at the interface andpressure is applied with a roll.
2.3

Process parameters
It is observed that this joining process of the dissimilar metal combination ofaluminium and steel is quite a complex task. The process parameters discussed byvarious authors can be summarized in general as shown in Fig.2.
Condition of
faying surfaces

Base metal
Type and amount ofPresence of dirt,oil, oxide film

alloying elements in

Surfaceroughness%C and other
Alloying elements in

Type andthickness of IMC
FeAl,
Fe3Al
Fe2Al5,
FeAl3
Quality ofsteel-Al
Joint

Formation of
new surface

Solid-state
Process
Temperature,
Pressure andBreaking ofoxide film

Amount ofpressureHeating rate andPost heat
treatment

FusionProcess

cooling rate at thePeaktemperature

Geometryof joint

Process

Thermalcycle

Fig 2 Process parameter for Laser roll welding4

2.4 Process variations
Iron and aluminium are not compatible metals as far as fusion welding is concerned.
The reason for this is attributed to the great difference between their melting points(660oC for Al and 1538oC for Fe), almost zero solid-solubility in each other andformation of brittle intermetallic compounds like FeAl2, Fe2Al5 and FeAl3. Therefore,
the fusion welds of iron and aluminium are brittle. The differences in the thermal
properties - like thermal expansion coefficients, thermal conductivities and specificheats – lead to high welding stresses in fusion welding.
In laser roll welding of steel and titanium joint, steel sheet is heated upto 1200℃to
make an eutectic phase between Titanium and TiFe intermetallic conpound which
thickness is less than 20 μm in the interface layer. The heating temperature is lower
than melting points of both metals, Steel and Titanium.
2.5 Applicable materials
In the research, dissimilar metal joints such as steel to copper, steel to aluminum, steel
to titanium, stainless steel to, aluminum, galvanized steel to aluminum alloy, aluminumalloy to titanium are possible to get higher strength than that of base metals. Other
combination of dissimilar metal is possible. Binary phase diagram may give thepossibility.
Chapter 3: Equipment and Supplies
3.1 Laser roll welding equipment developed

3.3 Flux for joining]

Fig.3 Schematic drawing of Laser Roll
Bonding process

Fig.4

Setup of test specimens on X-ＹMany kinds of high power lasers can be used for laser roll welding. In the research,
2kW CO2 laser and 2kW fiber laser were used for dissimilar metal joints. The diameterof beam spot is about 3mm x 5mm on the metal sheet and 10mm far from the bottom of5

roller. Incident angles of laser beam were 45 ﾟ in CO2 laser and 30 ﾟ in fiber laser,
respectively.. Figs.3 and 4 show the facility and setup of test specimens on X-Y table.
Fig.5 shows the actual facility using 1 2kW fiber laser. Ar shielding and brazing flux are
applied to remove the oxide film during welding.

Fig. 5Laser roll welding facility using a 2kW fiber laser.

3.2 Welding condition for laser roll welding
Table 1 shows the welding condition for joining of aluminum alloy to low carbon steel
Table 1 Experimental conditions for laser roll bonding
Laser Power

１.0 kW ～ 2.0kW

Travel Speed
Beam spot dia.
Roll Pressure
Shielding Method
Insert Material used

1.0
～ 3.2 m/min
3mm ～ 5mm
100 ～ 202 MPa
Argon Gas shielding
Aluminium brazing flux,
KAlF4:K2AlF6.H2O

Welding thermal cycle at the interface is very important to minimize the thickness ofinterface layer which should be less than 10μm to get ductile intermetallic compounds.
Chapter 4: Applications for dissimilar metal joints
4.1 Joining of Aluminium and Al alloys to Low Carbon Steels
4.1.1 Introduction

6

The new automobile industry has a continuous requirement for weight reduction toincrease efficiency and reduce air pollution. One way suggested is the use of the
combined structure consisting of Aluminum alloy and steel sheet. Therefore, it isnecessary to join theses dissimilar metals together for different shapes in large
continuous production suitable for the modern automobile industry. Attempts of using
resistance spot welding with inserts for this purpose have been already made [1]. Major
problem appeared during joining these dissimilar metals are the formation ofintermetalic brittle compounds like FeAl3 & 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 with aluminum A5052, and pulsed CO2 laser used to
weld the pure aluminum A1050. Using of laser beam welding of steel and aluminum
were also reported [3].
An attempt is made to identify and estimate 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 coolingrates. It has been found that the formation of the brittle compounds takes place bydiffusion process, which involves slow heating and cooling rates. Therefore, a process
combining laser heating and roll bonding is suggested. It is intended that the laser
heating of steel in such a way that the interface reaches the temperature sufficient toform the bond while it being pressed. It was aimed to control the joining process byvarying laser power, travel speed, and roll 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.
4.1.2 Experimental Procedure(1) Materials used
The common materials used in automobile industry for structural components are
low carbon steel and aluminum alloys. The sheet thickness for both types aluminum
A5052 and A1050 is 1mm, and for steel sheet is 0.5mm used in this study. The
chemical composition is shown in Table 2.
Table 2 Chemical Composition of Materials used(in mass %)
Alloy

Mg

Cr

Si

Fe

Cu

Mn

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

7

SPCC
steel

C

Mn

P

S

0.12 max

0.5 max

0.04 max

0.045 max

(2) Laser Roll welding
A lap joint was used to combine the steel sheet with the aluminum alloys as shownin Fig. 6-(a), the steel was placed on the top of the aluminum in order to absorb the heatfrom the incident laser beam without melting and conduct the heat to the interface. The
over lap was 9mm, and the Gaussien beam was defocused to give elliptical spot of
2.5mm minor and 3.5mm major diameter on the steel surface.

(a) Clamping setup
Fig.6(b) Laser Roll Bonding
Schematic drawing

In order to heat the interface between the steel and aluminum to a suitabletemperature by laser beam and apply pressure to this interface at the right time, the laserroll-welding fixture used in this study is made as shown in Fig.6-(b).
A spring is used to press the joint against the table through the roll; this pressure canbe determined by the spring deflection. Prior to joining, the faying surfaces of both
sheets were cleaned by using the suitable way, for Aluminum sheets, ultrasonic cleaning
was applied to remove the hard aluminum oxide film, then it was merged with brazing
flux (KalF4:K2AlF5.H2O) to prevent further oxidation and remove any if exist.
Laser Roll welding with varying travel speed, laser power, and roll pressure werecarried out. The joints were cut transversely to observe the macrostructure andmicrostructure. 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 the8strength and formability of the joints, three samples were prepared for tensile shear test
and one specimen for Erichsen test.
4.1.3 Experimental results
The main purpose of using CO2 Laser Roll welding is to achieve fast heating andfast cooling, which may suppress the formation of the brittle intermetallic compounds.
To increase the possibility of formation of the ductile intermetallic compounds(FeAl+Fe3Al), the interface temperature should be in the range 1100-1300C as shownin Fig.7[4] for Iron-Aluminum phase
diagram. Temperature is the mostinfluential variable since it, together
with pressure, determine the extent ofcontact area during diffusion bonding
and it alone determine the rate ofdiffusion that governs void elimination.
Changing pressure values withinterface temperature (by varying thelaser power or travel speed), we cancontrol the interface layer thickness
Fig.7 Iron-Aluminum Phase
until the optimum is reached, in which
diagramthe brittle compounds layer thickness
will be the minimum and the ductile one will be the maximum. In addition to theseparameters, a pulsed laser welding is used in welding the pure Aluminum A1050, whichenable us for more control of the heating and cooling rates by changing the pulse.
As the interface layer temperature reaches the required range, a thin surface
region of aluminum undergoes melting. Bonding was achieved as shown in themacrostructure samples in Fig.8. A typical microstructure of laser roll bonding joints isshown in Fig.9.

1.5kW-1.5m/min-150MPa
1.5kW-2.2m/min-202MPa(a) SPCC-A1050(b) SPCC- A5052
Fig. 8 Macrostructure Samples

91.5kW-150MPa-4.0m/min
1.5kW-150MPa-2.0m/min(a) SPCC- A1050(b ) SPCC- A5052
Fig. 9 Macrostructure Specimens(a) 1.5kW-150MPa-2.25m\min(b) 1.5kW-150MPa-6.0m/min
Fig.10 EPMA analysis for SPCC-A1050
The interface layer was analyzed by using EPMA method; the EPMA traces in
Fig.10 for A1050 and Fig.11 for A5052 show the existence of the ductile compound on
the steel side and brittle compound on the aluminum side for a constant pressure, andlaser power for two travel speeds. These figures also show the fraction thickness forboth ductile and brittle compounds through the interface layer is changing with travel
speed. In general, for a constant laser power and pressure, starting with a low speed,
will offer a longer time for the diffusion process to take place in which in turn producesa thicker layer with higher percentage of the brittle compounds as shown in Fig.12.

10(a) 1.5kW-150MPa-1.2m/min(b) 1.5kW-150MPa-2.0m/min
Fig.11 EPMA analysis for SPCC-A5052
The higher the interface thickness, the higher percentage of brittle compounds
exist. With increasing the travel speed the percentage thickness of the ductile
compounds increases from 23% to 51% for A5052 and from 7.6% to 40.6% for A1050.
The reason is related to “as discussed earlier “ controlling the diffusion rate by changing
heating and cooling rates with the travel speed.
In this experiment, different laser’s powers and pressures were used to study their(a) SPCC- A1050 (1.5kW-150MPa)(b) SPCC- A5052 (1.5kW-150MPa)
Fig. 12 Composition of IMC in the interface layer
effect on the interface compounds. Increasing the power has the same effect of
decreasing the speed, but if power reaches to high values, it will cause melting of the
11steel sheet, and if it reaches to low values, the heat input may not be sufficient toproduce bond. As for the pressure, it is necessary for increasing the contact area directly
after heating for a short time to allow diffusion process to take place, and help inincreasing the cooling rate of the joint by heat conduction.
Fig.13 shows the relation between tensile shear strength and interface layer

30.00
10.0
20.00
5.0

10.00
0.00
2.0

4.0

6.0

12.0

40.0

8.0

20.0

4.0
0.0
1.0

8.0

Travel speed, m/min

16.0

60.0

0.0

0.0
0.0

Average shear strength, MPa
Average interface thickness, µm

A v erag e in terface th ickn es s , µm

15.0

80.0

Sh ear s tren g th , M Pa

Interface Thickness, µm

40.00
Shear Sttength, MPa

20.0

Average shear strength, MPa

Average interface layer thickness, µm

50.00

1.5

2.0
Travel speed, m/min

2.5

3.0

(a) SPCC- A1050(b) SPCC-A5052
Fig.13 Effect of travel speed on shear strength
thickness with travel speed.
By increasing the travel speed, the 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, theshear strength drops down for fast travel speed, owing to insufficient temperature due tothe 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 out and evaluated withdifferent speeds as shown in Fig.14. The cupping height increases with speed until itreaches a maximum value then starts to decrease almost in the same manner with shear
strength analysis. The maximum cupping value is related to the existence of the
optimum thickness of the interface layer, which is responsible of relatively highpercentage of ductile compounds with a sufficient heat for satisfactory strong bonding.

12

10

Cupping Hight, mm

8.00

8

6.00

6
4.00

4
2.00

2

1 5kW 150MPa

0.00
0.0

2.0

4.0

6.0

Travel speed, m/min

0

2

4

6

8

Travel Speed, m/min

10122.0kW-175MPa-2.0m/min

1.5kW-150MPa-1.5m/min(b) SPCC-A5052(a) SPCC-A1050
Fig.14220kW
0kW175MPa
175MPa0
8.0

Results of Erichsen Test performed on laser roll bonded joints

4.1.4 Conclusions
1. It is possible to joint the aluminum alloys to steel by using laser roll welding.
Moreover, by controlling the parameters such as laser power, travel speed, rollpressure and pulse; we can get 55.9MPa shear strength for A5052 and about
30MPa for A1050.
2. With good contact of the faying surfaces by roll pressure, heat conduction can beaccomplished from steel to the aluminum. Laser heating provides high energy
density in the beam spot and rapid heating and cooling cycle. Therefore,
diffusion bonding takes a place for a short period because of the short thermal
cycle.
3.
For both joints made from A1050 and A5052 aluminum alloys with SPCC
steel after laser roll bonding, the EPMA analysis shows that interface layer
consist of brittle intermetallic compounds – FeAl3 and Fe2Al5 – on aluminumside and ductile one – FeAl and Fe3Al - on the steel side. As the travel speed
increased, the total thickness of the interface layer decreased with increasing of
the thickness of ductile compounds.
134.2 Joining of Al Alloys and Zinc coated steel
There is an issue to reduce the weight of car body by aluminum alloys replace steel assome structural body parts for improving fuel consumption and CO2 generation. As oneof the solutions, the multi material car body concept using aluminum alloys and highstrength steels is discussed recently. Therefore, new welding processes by which these
dissimilar materials can be joined in high reliability and productivity are demanded.
Laser Roll Welding was developed for joining of dissimilar metals by M.Kutsuna and
M.Rathod in 2002. In this section, Laser Roll Welding of zinc coated steel andaluminum alloy was investigated, and the process parameters were studied. Otherwise,
the influences of process parameters on the weldability, the formation of intermetallic
compound layer and the mechanical properties have been investigated. Whenintermetallic compound layer thickness was less than 10 μm, failure of tensile-shear test
specimen occured in the base metal of the zinc coated steel.
The car industry has subjects to improve fuel efficiency. One of the solutions is to
reduce the weight of car body such as car panels shown in Fig.23. To be replaced steel
parts by aluminum alloys is very effective to achieve large weight reduction.

Fig.15 Example of laser roll welding application : Car panel
The technology for joining of steel to aluminum with high reliability and productivity isnecessary to realize this "hybrid body structure". However, it is difficult to join steel toaluminum by fusion welding. The reason is attributed to the formation of intermetallic
compounds such as FeAl3 and Fe2Al5. Shown in Fig.7 [4].
The intermetallic compounds presented on it are grouped as Fe-rich compounds (FeAland Fe3Al) and Al-rich compounds (FeAl2, Fe2Al5 and FeAl3). Mechanical properties ofcast intermetallic compounds by compressive test are shown in Fig.16 [1]. While
Al-rich intermetallic compounds are brittle, iron-rich intermetallic compounds show
slight ductility and high strength. Then, it is desirable that the brittle intermetallic
compound could be controlled by application of Laser Roll Welding.
14

Fig16 Stress-Strain Curve in compressive test of Fe-Al intermetallic compounds [1]In the present work, Laser Roll Welding of the zinc coated steel and the aluminum alloy
was investigated, and the process parameters were studied. Otherwise, the influences ofthe process parameters on the weldability, the formation of intermetallic compound
layer and the mechanical properties of joints.
4.2.2 Experimental Procedure(1) Matreials used
Zinc coated steel sheet (GI) and aluminum alloy 6000 sheet (Al-0.5Mg-1.0Si) wereused for joining. The dimension of the steel sheet was 180 x 125 x 0.55 mm and that of
the 6000 series aluminum alloy was 180 x 125 x 1 mm.
(2)Laser Roll Welding Facility
A schematic diagram of Laser Roll Welding process is shown in Fig.3. A pressureroller was mounted on a 2.4 kW pulse CO2 laser facility. It is desirable that thermal
cycle for joining can be shortened by heating of the laser. Therefore, the formation of
the brittle intermetallic compound can be easily controlled. Furthermore, good contactof steel sheet and aluminum sheet and rapid heat transfer from a steel sheet to analuminum alloy sheet are conducted by a pressure roller.
(3) Process Parameters of Laser Roll Welding
Process parameters are shown in Table 3. Travel speed was varied from 0.2 to 0.7
m/min. The steel surface exposed to the laser beam was coated with graphite to increase
the absorption of laser beam. The faying surface was coated aluminum brazing flux.
Argon gas with 25 l/min flow rate was used for shielding of joint.
4.2.3 Experimental results and discussions(1) Bead Appearance and Cross-Section of Laser Roll Welded Joints
Bead appearance of Laser Roll Welded specimen with travel speed of 0.5 m/min isshown in Fig.17. Top bead is shown in Fig.17 (a). Cockles are observed on the zinc
15

Table 3 Process parameters for Laser Roll Welding for Zinc coated steel to Al alloy

coated steel near the weld bead. Bottom bead is shown in Fig.17 (b), and cross-sectionof the weld bead is shown in Fig.18. These figures show partial melting and spreadingof molten metal on steel sheet occurs in aluminum sheet.

Fig. 17 Bead appearance of laser roll welded joint of GI steel to A6000 alloy

Fig. 18 Macro-section of laser roll welded joint of GI steel to A6000 alloy(2)Effect of travel speed on intermetallic compound layer thickness at the interface

Interface microstructures of Laser Roll Welded joint with travel speed of 0.5 m/min
is shown in Fig.19.

Fig. 19 Microstructure of laser roll welded joint of GI steel to A6000 alloy
16

Existence of intermetallic compound layer was confirmed at the weld interface between
GI and A6000. Effect of travel speed on intermetallic compound layer thickness isshown in Fig.20. Intermetallic compound layer thickness decreases significantly from22 to 5 μm as the travel speed is increased from 0.3 to 0.6 m/min.

Fig.20 Effect of travel speed on intermetallic compound layer thickness(3) Electron-probe microanalysis (EPMA)
As the optical microstructure does not reveal the details of the interface layer, EPMAof iron, aluminum and zinc across it were made to identify intermetallic compounds andexistence of zinc. Three such traces for specimens welded with travel speed of 0.5
m/min are shown in Fig.21.

Fig. 21 EPMA result of interface layer of laser roll welded joint
Variation in composition of the intermetallic compound layer is observed as steppedlines. Intermetallic compound layers are indicated by yellow color zone.
17

From the position of stepped lines, it is suggested that most intermetallic compound
layer is formed mainly by brittle FeAl3. When the travel speed is faster than 0.6 m/min,zinc is confirmed in aluminum alloy.
(4) Tensile shear test
Tensile shear test was done to investigate the influence of the travel speed on theweldability. Effect of travel speed on tensile load and intermetallic compound layer
thickness is shown in Fig.22. Failure in base metal of zinc coated steel is shown as theblue circle in the figure, and failure in interface is shown as a solid blue mark. Whenintermetallic compound layer thickness was less than 10 μm, failure of specimen
occured in base metal of zinc coated steel. When intermetallic compound layer was lessthan 10 μm, failure of specimen occured in the base metal of the zinc coated steel.
Therefore, it is thought that the intermetallic compound layer thickness should be lessthan 10 μm to get a good Laser Roll Welded joint.

.
Fig. 22 Results of tensile shear test of laser roll welded joint of
GI steel to A6000 alloy
4.2.4 Conclusions
In this section, joining of a dissimilar metal joint of zinc coated steel and 6000
series aluminum alloy by laser roll welding is discussed The following conclusions
can be drawn.
1) Increase in travel speed of the table led to decrease the thickness of the intermetallic
compound layer at the interface.
2) Increase in travel speed led to lowering of the peak temperature and shortening of theholding time more than 500 oC at the interface.
3) It is suggested that intermetallic compound layer that is formed mainly is brittle
FeAl3. As the travel speed is faster than 0.6 m/min, zinc is confirmed in aluminumalloy.
184) When intermetallic compound layer was less than 10 μm, failure of specimen
occured at the base metal of zinc coated steel in tensile shear test.
4.3 Joining of Ti and Low carbon steel
4.3.1 Introduction
Titanium is one of structural materials. It has several advantages such as highcorrosion resistance and high strength-to-weight ratio. The demand of titanium
structural panel and the dissimilar joint has been increased in industry. It is well known
that joining of steel and titanium is difficult because of generating the brittle
intermetallic compound. In this section, the laser roll welding of dissimilar metals,
titanium to low carbon steel is discussed. Using a 2.4kW CO2 laser and a 2kW fiber
laser, the effects of process parameters on the formation of intermetallic compound at
the interlayer and on the mechanical properties were investigated to get a sounddissimilar metal joint.
In this section, the laser roll welding of dissimilar metals, titanium to low carbon steel
been investigated using a 2.4kW CO2 laser and a 2kW fiber laser. It is easy to control
intermetallic compound by this welding process. When welding speed, laser power androll pressure were controlled, interlayer thickness and intermetallic compound(IMC)
was minimized. In order to estimate joint performance, tensile-shear test and EPMA
analysis were done.

Fig.23 Application of Ti-Fe dissimilar metal panel for the leg of bridge
4.3.2

Experimental Procedure(1) Materials.
19Pure titanium sheet (JIS H4600-TP340C) and low carbon steel (JIS SPCC) sheet wereused for joining. The dimension of the titanium sheet and the steel sheet were 40 x 200 x
0.5 mm. The equilibrium diagram of Ti-Fe binary alloys is shown in Fig. 24. The
eutectic point is 1085℃. So, laser heating temperature at the interface should be higher
than 1085℃.

Fig. 24 The equilibrium diagram of Ti-Fe binary alloys(2) Laser Roll Welding Process.
A schematic diagram of Laser Roll Welding process is shown in Fig.3. A pressureroller, bonding mirror, and a 2.4kW pulse CO2 laser facility were used for the joining.
It is desirable that thermal during the joining should be shortened by rapid heating of laser.
Therefore, the formation of the brittle intermetallic compound can be easily controlled.
Furthermore, good contacts of steel sheet to titanium sheet and rapid heat transfer from asteel sheet to a titanium sheet are conducted by a pressure roller.
Table 4 Process parameters for laser roll welding

Fig.25 The microstructures of Welded joint(2) Process Parameters of Laser Roll Welding.
Process parameters are shown in Table 4. Travel speed was varied from 1.2 to 1.7 m/min.
The steel surface exposed to the laser beam was coated with graphite to increase the20absorption of laser beam. The faying surface was polished and degreased. Argon gas at
the flow rate of 25 L/min was used for shielding of joints.
4.3.3 Experimental Results
4.3.3-1 Laser Roll Welding Using a CO2 Laser(1) Microstructures of Joint interface.
The microstructures of Welded joint with laser average power of 2.0 kW and travel
speed of 1.4 m/min is shown in Fig.25. The interlayer thickness at the center of laser
beam spot is the thickest and at the edge of steel to titanium.is the thinnest.

Fig.26

Result of EPMA Analysis of welded joint interface(2) EPMA Analysis.
As the optical microstructure does not reveal the details of the interface layer, EPMA ofiron and titanium across it were made to identify phases of interlayer. Two such traces for
specimens are shown in Fig.26. The interlayer thickness was 17 μm with laser power of
1.8 kW and travel speed of 1.5 m/min, 33 μm with laser average power of 2.0 kW andtravel speed of 1.7 m/min. From the EPMA results, it is suggested that the mixed layer of
β-Ti and TiFe intermetallic compound is formed at the interface.
(3)Tensile Shear Test.
Tensile shear test was done to investigate the joint performance of welded joint. Tensile
shear specimens after testing of Laser Roll Welded joints are shown in Fig.27. Some
specimens were broken in the interface (a), others were broken in the base metal of steel
sheet (b). When interlayer thickness was less than 25 μm, failure of specimen occurred in
the base metal of steel sheet

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Fig.27 Tensile shear specimens after testing of Laser Roll Welded jointsof Titanium to low carbon steel
4.3.3-2 Laser Roll Welding Using a Fiber Laser(1) Process parameters
2KW fiber laser has more higher power density of beam. It is used for laser rollwelding in this section. The process parameters are shown in Table 5. The steel surface
heated by laser beam was coated with graphite to increase the absorption of laser beam.
The faying surface was polished and degreased. Argon gas was used for shielding of
joints at a flow rate of 15 L/min.
Table 5 Process parameters for laser roll welding(2) Microstructures of Welded Joint.
Macro-section of Laser Roll Welded joints are shown in Fig.28. A thin intermetallic
compound layer is observed as shown in Fig.28(a), However, However, too muchheating makes very thick interface layer which thickness is 200~300 μm as shown in
Fig.28(b). Fig.29 shows the Microstructures of Laser Roll Welded joints. In the interface
layer, titanium layer (β-Ti) , eutectic phase between β-Ti and TiFe and TiFe
intermetallic compound can be observed.
22.

Fig. 28 macro-sections of laser roll welded joint.

Fig.29 Microstructures of Laser Roll Welded joints

Fig. 30

Result f EPMA analysis of interface layer(3) EPMA line analysis. EPMA line analysis of iron and titanium across the interface
were made to identify interlayer. Composition penetration plots of chemical species for
specimen that the interlayer thickness was 30 μm with laser average power of 2.0 kW
and travel speed of 2.1 m/min is shown in Fig.30. From the EPMA results, it issuggested that the mixed layer of β-Ti and TiFe is formed at 21
23

the interface. This layer is eutectic structure composed of β-Ti and TiFe. When there arevery thick 200~300 μm intermetallic compound layers, a number of intermetallics
TiFe,TiFe2 and β-Ti have been identified.
(3) Tensile Shear Test.
Some specimens were broken in joint interface, others were broken in the base metalof steel sheet in tensile shear test as shown in Fig.27. Even when interlayer thickness
was measure up to 200 μm, some specimens were broken in the base metal of steel
sheet.
4.3.3 Conclusion
The effect of laser power and travel speed on the formation and composition ofinterlayer have been investigated in laser roll welding of titanium to low carbon steel
using a pulsed CO2 laser or cw fiber laser. As a result, laser roll welded joint showedenough tensile strength each type of laser. The composition of thin intermetallic
compound layer was eutectic structure composed of β-Ti and TiFe. However, thicker
intermetallic compound layer is composed of β-Ti, eutectic structure of β-Ti and TiFe,
TiFe or TiFe2 IMC. Most of welded joints were broken at the base metal in the tensile
shear test.
Acknowledgement:
Author are thankful to METI of Japan for the financial help in this research, Laser X
co. , Chuoseiki Co. Horie Metal Co and my students, M.J.Rathod, A. Ammar,
N.Yamagami, H.Ozaki, R.Ichioka et al at dept. of Material Processing Eng, Nagoya
University for their works to develop Laser roll welding process.
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sheet with insert of aluminum clad steel sheet – Part 1. Journal of Japan Welding
Society, 14(2): 314-320[2] C E Albright, 1981. The Fracture toughness of steel-aluminum deformation welds,
Welding Journal, 60(11): 207s-214s[3] G. Seplod, E. Schubert and I. Zerner, 1999. Laser beam joining of dissimilarmaterials, IIW. IV (734): 1-10.
[4] T.B.Massalski, et al. (1986) Binary Alloy Phase Diagrams Volume 1, American
Society for Metals, 148.
[5] J.Rathod, et al. (2004) Joining of Aluminum Alloy 5052 and Low-Carbon Steel by24

Laser Roll Welding, Welding Journal 83-1, 16s-26s[6] Rathod Manoj and Muneharu Kutsuna: Laser Roll Bonding of A5052 AluminumAlloy and SPCC Steel, Quar. J. JWS, 21-2 (2003), 282-294. (in Japanese)[7] M. J. Rathod，M. Kutsuna: Joining of Aluminum Alloy 5052 and Low-Carbon Steelby Laser Roll Welding, Welding Journal, 83-1 (2004), 16s-26s.

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