Copyright # 2011 ASM InternationalW
All rights reserved
www.asminternational.org

ASM Handbook, Volume 6A, Welding Fundamentals and Processes
T. Lienert, T. Siewert, S. Babu, and V. Acoff, editors

Roll Welding and Laser Roll Welding*
Muneharu Kutsuna, Advanced Laser Technology Research Center Co., Ltd.

DISSIMILAR METALS in sheet or strip are
joined for a variety of product applications.
Domestic appliances such as electric frying
pans and water boilers, for example, use combinations of dissimilar metals. Steel-aluminum
sheet has structural application in automobiles
and in antifriction parts such as cylinder
liners and bushes. Dissimilar joining between
steel and aluminum sheet also finds applications
in liquefied natural gas storage tanks and steel
supporting structure. Besides joining steel toaluminum to obtain higher strength than thatof the base metals, other combinations of interest include:






Steel to copper
Steel to titanium
Stainless steel to aluminum
Galvanized steel to aluminum alloy
Titanium to aluminum alloy

Joining for this purpose can be done in various
ways, such as mechanical clinching, self-piercing riveting, adhesive bonding, diffusion bonding, explosion welding, friction welding,resistance spot welding, forge welding, and rollbonding.
This article describes two methods based on
rolling of sheet. The first is roll welding, where
two or more sheets or plates are stacked together
and then passed through rolls until sufficient
deformation has occurred to produce solid-state
welds. The other process is laser roll welding,which is a hybrid process based on a thin-melting
interface for a lap joint of dissimilar-metal sheets
using a roller and one-sided laser heating.

Roll Welding
Two types of roll welding are common. In
the first, the parts to be welded are merely
stacked and passed through the rolls. The second method, usually termed pack rolling,
involves sealing the parts to be rolled in a packor sheath and then roll welding the packassembly.
The first method is more generally employedin the cold welding of ductile metals and alloys.

Sometimes the stack to be welded is first tackwelded at several locations to ensure alignment
during rolling. Also, when using this method,
the deformation during the first rolling passmust exceed the threshold for welding (typically greater than 60% for cold rolling) to keep
the parts together. The required first pass reduction can be reduced by hot rolling, if the metals
to be rolled can tolerate preheating without
excessive oxidation. Once the first pass has
been accomplished, the reduction per pass canbe decreased, as is often desirable becauseroll-separating forces increase as the parts tobe rolled become thinner. However, the nonuniform stress distribution that builds up during asequence of very light passes can cause theweld to open up or “alligator.” Therefore, thereduction for subsequent passes is generally acompromise between applying excessive separating forces and “alligatoring.”
In pack roll welding, the parts to be welded
are completely enclosed in a pack that is sealed(typically by fusion welding) and often evacuated to provide a vacuum atmosphere. Thismay be accomplished by a frame that surrounds
the parts to be welded, which is sandwiched by
two lids, or may simply consist of two covers
formed to encapsulate the parts to be welded(Fig. 1). Semikilled or killed low-carbon steel
is a common material for the pack but is notsuitable for all alloy and temperature combinations. Although the preparation costs of packroll welding are significant, the process has
the following advantages:

temperature ranges. To overcome this problem,
titanium alloys that are pack rolled are sometimes encased in a steel envelope, or can. The
can is evacuated to minimize oxidation of thework metal, and it also serves to minimize heatloss to the relatively cold rolls upon deformation. The narrow working temperature rangeof titanium alloys makes the rolling of thesematerials labor-intensive. Rolling passes aredone by hand on relatively small pieces, andmany intermediate reheating steps are required.
Some b-titanium alloys, however, are continuously rolled on hot and cold strip mills.
Nonpack rolling, of course, can employ continuous strip rolling. A seldom-used hybrid version of roll welding is to seal the edges of theparts to be welded by fusion welding prior torolling. This method does not provide atmospheric protection to the outer surfaces, as inpack roll welding, but does occlude air fromthe more critical inner surfaces.
In roll welding, successful welding depends
not only on the total amount of deformation
but also on the pressure during rolling. A highisostatic pressure component during rolling is
promoted by large reductions per pass, large
roll diameters, and rough roll surfaces. A nonuniform distribution of normal stresses, referred Provides atmospheric protection, which may

be particularly important for reactive alloys
such as those of titanium, zirconium, niobium, and tantalum
 Permits welding of complex assemblies
involving several layers of parts.
A significant limitation of the process is thatpacks become difficult to process when theirlength exceeds several feet.
Titanium and titanium alloys are considerably more difficult to pack roll than are either
steels or copper and aluminum alloys because
most titanium alloys have very narrow working

Fig. 1 Pack used for roll welding. The top cover,which would be welded in place before
rolling, is not shown.

* Reprinted from R. Roper, Roll Welding, Welding, Brazing, and Soldering, Vol 6, ASM Handbook, ASM International, 1993, p 312–314

5264/7L/A0005620
2 / Solid-State Welding Processes
to as pressure hill effects, is caused by frictionaland mechanical restraint and results in lower
pressure near the outer edges of the parts beingrolled. Therefore, rolling conditions must be
such to ensure sufficient pressure near the edges
to avoid weak welds in these regions.
Copper, aluminum, and their alloys are often
cold roll welded. Hot rolling is applicable to awide spectrum of alloys. Typically, hot rollingis performed above recrystallization temperatures. In practice, weldability is often improvedby raising the temperature to the region where
oxygen mobility becomes significant to promoteoxide assimilation by diffusion. Also, welded
assemblies are often postheat treated to cause
recrystallization (in cold rolling), oxygen diffusion, and/or sintering. In welding dissimilar
metals, selection of temperatures for rolling andpostheating must take into consideration the possibility of intermetallic compound formation,
eutectic melting, and/or porosity due to Kirkendall diffusion. The most common metals thatare roll welded are low-carbon steels, aluminum
and aluminum alloys, copper and copper alloys,
and nickel. Low-alloy steels, high-alloy steels,
nickel-base alloys, and titanium and titanium
alloys have also been roll welded.

partial welding occurring during the first rolling
pass. The sandwich sometimes is heated prior tothis first rolling pass. Whether hot rolling or coldrolling is employed, the major reduction takes
place in this first pass (50 to 80%). Subsequently,
cold rolling may be employed to reduce the panel
to final gage. Also, panels are generally given a
postweld heat treatment. This heat treatment
results in an annealed part and, particularly inthe case of cold rolled panels, may improve theweld quality through recrystallization and diffusion. Finally, the passageways are formed byinflating them with air pressure while the sandwich is held between platens. The panel is thenready for trimming, additional forming, andpainting, as required for the application.
The process has been used to produce heatexchangers for refrigerators, solar panels, poultry
incubators, electronic equipment temperature
controllers, industrial heat exchangers, and special applications such as thermal control ofspacecraft. Modifications of the process permit
as many as six sheets to be welded at one timeand inclusion of passageways oriented along different principal directions at the different layers.
Also, it is possible to produce panels where thepassageways are expanded on one side only.

Similar processing is applied to many new
products, including electrical contacts, conductive springs, automotive windshield wiper sockets, automotive trim, clad cookware, wrap forunderground cable, and electromagnetic shielding (Table 1).
Essentially all combinations of ductile metals
and alloys can be clad by roll welding, although
the oxides of some metals may make welding

Fig. 2 Cross section of an aluminum solar collector
panel produced by the roll welding process

Roll-Welded Heat Exchangers
One of the more important applications ofroll welding is the fabrication of heat exchangers. This process is used to fabricate flat solar
collectors. In another method of heat-exchanger
fabrication, three plates are stacked, with the
middle plate containing the flow channels. The
stacked plates are initially held together by tackfusion welds or resistance spot welds. Thisapproach has been employed for both aluminum and steel heat exchangers. A second
important application of this process is in thecladding of sheet metal products.
A principal application of roll welding is the
production of heat-exchanger panels with flow
tubes as an integral part of the composite.
Millions of refrigerator evaporator plates havebeen formed by this process. A cross sectionof a similar application, solar collector panels,
is illustrated in Fig. 2. Roll-welded heatexchanger panels are most often made of aluminum, although copper and stainless steel panels
have also been produced commercially.
The first major step in the production of rollwelded heat exchangers is to thoroughly clean
the surfaces of the sheets to be joined by combinations of solvent cleaning, chemical cleaning, and wire brushing. Next, a stop-weld
pattern is reproduced on one of the sheets thatwill later form the passageways in the heatexchanger. This is accomplished by transferring
ink onto the surface by silkscreen processing.
These stop-off inks contain materials such asgraphite or titanium oxide.
The prepared plates are placed together andtemporarily joined by spot welding to form asandwich that is then roll welded, with at least

Cladding of Metals by Strip Roll
Welding
The common early application of strip rollwelding was the fabrication of bimetallic strips
for thermostats. This remains an important application, with thermostats taking many complex
forms and finding use in furnaces, color televisions, cars, and numerous industrial controls.
A key cladding application is the productionof coins by the U.S. Mint. Silver shortages in
the 1960s and 1970s resulted in the introductionof coins made from new materials. These coinsrequired a unique set of properties for acceptance by the general public and use in automatic vending machines. Copper clad withcupro-nickel was found to meet these requirements (Fig. 3). The cladding process is relatively simple, although stringent in its
requirement for surface preparation. Cladded
strips are produced by continuous rolling, withthe surfaces prepared just prior to rolling byprocesses such as wire brushing. Welding typically is accomplished in a single rolling pass.
Subsequent heat treatments may be employed
to improve the weld quality by processes suchas sintering, diffusion, and recrystallization.
The starting material for the U.S. quarter is
two outer layers of 75Cu-25Ni, each 1.2 mm(0.048 in.) thick, with an inner layer of purecopper that is 5.1 mm (0.20 in.) thick. To obtain
good bond strength, the surfaces are chemicallycleaned and wire brushed. The strips are thenroll welded to a combined thickness of 2.29
mm (0.090 in.) (Fig. 4). A second rolling operation reduces the final thickness 1.36 mm(0.0535 in.). The strips thus undergo a total
reduction of 82% (Ref 1).

Fig. 3 Metallographic cross section of the edge of acupronickel-clad copper coin

Fig. 4 Schematic showing 70% reduction in crosssection of a U.S. Mint quarter coin (composedof an inside layer of pure copper sandwiched between
two thin layers of cupronickel material) as it undergoes
an initial roll welding operation. A second rolling
operation further reduces the material to a final thicknessof 1.36 mm (0.0535 in.) for a total reduction of 82%.
Source: Ref 1

5264/7L/A0005620
Roll Welding and Laser Roll Welding / 3
compounds. In most cases, when a metal isnamed, alloys of that metal also apply.

difficult and other combinations may suffer fromintermetallic compound formation on heating.
Most engineering metals and alloys can be processed into clad-laminate form, but some cannot(Table 2, Ref 2). One characteristic that makessome metals difficult or impossible to combine
by deformation is low ductility. Such metals cannot be co-reduced to the extent necessary toachieve a metallurgical bond. Another characteristic that can cause problems is the tendency ofsome metals to form a tenacious oxide film that
inhibits weld formation. Finally, some metals
are thermally unstable; they form brittle intermetallic compounds when heated above a certain
temperature. Those metals that are readily processed into clad laminates have opposite characteristics. They are ductile and easily cleaned ofoxides, and they form no intermetallic

Table 1

Laser Roll Welding
As noted, laser roll welding is a hybrid welding process—neither a fusion welding process
nor completely a solid-state welding process.
It is best described as a pressure welding process with a thin layer of melting from laser
heating on one side of a lap joint. Using a roller
and laser heating, it is typically used to joindissimilar-metal sheets. In the case of aluminum to steel with laser roll welding (Fig. 5),for example, the steel sheet is heated to1300  C (2370  F) so that aluminum melts only
near the interface with the steel.

The advantage of laser heating is the sharp
focusing of energy for fast heating and cooling.
Rapid heating and cooling minimizes the timefor formation of brittle intermetallics by diffusion processes. The process of combining laser
heating with roll bonding is intended to reachsufficient temperatures quickly, to form a bondwhile being pressed. Some basic process variables (Fig. 6) include laser power, travel speed,
and roll pressure. By control of welding speed,
laser power, and roll pressure, the interlayer
thickness and formation of brittle intermetallic
compounds can be minimized.
Different types of high-power lasers (on theorder of 2 kW) can be used for laser roll welding of dissimilar-metal joints. A schematic ofroll welding with a CO2 laser is illustrated
Fig. 5(a), and a setup with a fiber-optic laser

Typical properties of common roll-welded clad laminates
Thickness

Materials system

Width

Tensile strength

Yield strength

MPa

MPa

ksi

Elongation, %Applications

260(a) 38(a) 215(a)

31(a)

40(a)

420(b) 61(b) 250(b)

36(b)

35(b)

24

395

57

360

52

12

50–5102–20

180(c) 26(c)

12(c)

1.7

35(c)

0.014

305

12

393

57

195

28

35

0.20–2.41

0.008–0.095

25–64

1–2.5

...

...

310

45

40

0.10–0.15

0.004–0.006

12.7–150

0.5–6415(d) 60(d)

275

40

20(d)

0.38–1.52

0.015–0.060

610

24

455(e) 66(e)

435

63

16(e)

Typically used for commutators inelectric motors, replacing copper
10400. The lower conductivity ofsteel causes less heat loss during
welding, resulting in faster, betterquality welds. The added strength ofsteel allows thickness reduction.
Used in heat exchangers, replacing
brazing shim material. One-piece
manufacturing eliminates separate
shims and reduces assembly cost.
Because no ferrous surfaces are
exposed, no flux is needed.
Widely used for automotive body
moldings, drip rails, rocker panels,
and other trim components, often
replacing solid stainless steel oraluminum. Stainless steel provides
bright appearance; the hidden
aluminum base provides cathodic
protection, corroding sacrificially tothe body steel.
Developed specifically for transition
joints between copper and aluminum
in refrigeration equipment. Usuallyused in the form of deep-drawn
tubing.
Used in hydraulic tubing in vehicles,
replacing terne-coated carbon steel
tubing. The outer layer of carbon
steel cathodically protects thestainless core of the tube, extending
its life significantly.
Used in formed cans for transistor andbutton cell batteries, replacing solid
nickel at a lower cost.
Replaces heavier gapes of copper andbronze in buried communications
cable. The stainless steel provides
resistance to gnawing by rodents,
which is a serious problem inunderground installations.
Used in automotive applications, suchas windshield-wiper bearings. The
bronze provides the bearing qualities,
the steel provides strength, and thecopper aids tooling life and provides
corrosion resistance in service.

Composite ratio, %

mm

in.

mm

in.

Copper 10300/lowcarbon steel

50:50

0.25–2.54

0.010–0.100

12.7–50

0.5–2

Deoxidized copper/
carbon steel/deoxidized copper

5:90:5, 10:80:10,
15:70:15

0.25–2.54

0.010–0.100

610

24

Type 434 stainless/5052
aluminum

40:60

0.56–0.76

0.022–0.030

610

Copper 11000/1100
aluminum

50:50

0.51–2.54

0.020–0.100

C1008 steel/type 347
stainless steel/ C1008
steel

43:10:45

0.36

Nickel 201/type 304
7.5:85:7.5
stainless steel/nickel
201
Copper 10300/type 430 17:66:17, 20:60:20,
stainless steel/ copper
33:34:33
10300

Phosphor bronze 51000/
carbon steel/copper

10:85:5ksi(a) In eighth-hard temper. (b) 10:80:10 material. (c) In three-quarter-hard temper. (d) 20:60:20 material. (e) In quarter-hard temper. Source: Ref 2

5264/7L/A0005620
4 / Solid-State Welding Processes
Table 2 Relative weldability of selected dissimilar metals and alloys roll welded into clad-laminate form
Base metal No. 2
Base metal No. 1

Ag

Al

Al alloys

Au

Carbon steel

Co

Cu

Mn

Mn-Ni

Nb

Ni

Pt

Stainless steel

Steel

Sn

Ta

Ti

U

Zr

Ag
Al
AlfesilBe
Carbon steel
Cu
Mn
Ni
Nb
Stainless steel
Steel
U

...
...
D
D
...
A
B
...
...
...
B
...

...
...
D
D
B
B
...
B
...
B
...
...

...
A
D
D
...
...
...
...
...
...
...
...

...
C
D
D
...
A
...
A
...
...
...
...

...
B
D
D
...
...
...
...
...
B
...
...

...
C
D
D
...
...
...
...
...
...
...
...

A
B
D
D
...
...
B
A
B
B
A
...

B
...
D
D
...
B
...
...
...
...
...
...

...
...
D
D
...
B
...
...
...
...
...
...

...
...
D
D
...
B
...
...
...
...
...
...

...
B
D
D
...
A
A
...
...
...
B
...

...
...
D
D
...
B
B
B
...
...
...
...

...
B
D
D
B
B
...
...
...
...
...
...

B
...
D
D
...
A
...
B
...
...
...
...

...
...
D
D
...
A
...
A
...
...
...
...

...
...
D
D
...
B
...
...
B
...
...
...

...
...
D
D
B
B
...
...
...
B
...
...

...
...
D
D
...
...
...
...
...
...
...
...

...
C
D
D
...
B
...
...
...
B
B
B

A, easy to weld; B, difficult but possible to weld; C, impractical to weld; D, impossible to weld. Source: Ref

(a)

(b)

CO2 laser head

Laser beam
Spring]Flat mirror

RollerSteel sheet
Table
Aluminium sheet

Direction of table travel

Fig. 5 Laser roll welding. (a) Schematic of laser roll welding process with aluminum and steel sheet. (b) Using a 2 kW fiber laser
is illustrated in Fig. 5(b). The diameter of thebeam spot is approximately 3 by 5 mm (0.12
by 0.2 in.) on the metal sheet and 10 mm (0.4in.) distance from the bottom of the roller. Incident angles of the laser beam were 45 min. CO2
laser and 30 min. fiber laser, respectively.

Laser Roll Welding of Dissimilar
MetalsSteel and Aluminum Sheet Joining
Fusion welding of aluminum to steel isimpractical, because brittle intermetallic compounds such as FeAl2, Fe2Al5, and FeAl3 canform during the melting and subsequent solidification. The reason for this is attributed to
the great difference between their melting
points (660  C, or 1220  F, for aluminum and1538  C, or 2800  F, for iron), almost zero solid
solubility in each other, and formation of brittle
intermetallic compounds.
In the iron-aluminum system (Fig. 7), intermetallic compounds are grouped as iron-richcompounds (FeAl and Fe3Al) and aluminumrich compounds (FeAl2, Fe2Al5, and FeAl3).
Mechanical properties of cast intermetallic
compounds under compressive test are shownin Fig. 8. While the aluminum-rich intermetallic compounds are brittle, iron-rich intermetallic compounds show slight ductility and highstrength. The objective is to minimize formation of the brittle intermetallic compounds.
Although the complete elimination of brittle
intermetallic compounds such as FeAl3, FeAl2,
and Fe2Al5 is not possible due to their low freeenergy, their formation can be suppressed tosome extent. Laser heating of the steel quickly
reaches the temperature of the interface suitable
to form ductile compounds such as FeAl andFe3Al (approximately 1250  C, or 2280  F).
This results in melting of a very thin layer ofaluminum—on the order of 10 mm—at theinterface. As this effect of laser heating is taking place, the heated zone is subjected to rollpressure to improve the contact area. This also
helps in increasing the cooling rate, preventing

5264/7L/A0005620
Roll Welding and Laser Roll Welding / 5

Fig. 8 Stress-strain curve in compressive test of iron-aluminum intermetallic compounds. Source:

Ref 3

Fig. 6 Process parameter for laser roll welding. IMC, intermetallic compound
Aluminum, at. %
0

10

20

30

40

50

60

70

80

90

1600
1538 °C
L

1400
1394 °C
1310 °C(a Fe)

1232

1165 °C
1169 °C ~1160 °C

ε(g Fe)

1102°C

1000
912 °C
τC

FeAl3

800
770 °CFe2Al3FeAl
FeAl3Temperature, °C

1200

655 °C
600
(Al)

Fe3Al
400
0
Fe

10

20

30

40

50
Aluminum, wt%

60

70

80

90

combined sections consisting of steel sheet withaluminum or aluminum alloy sheet. Attempts to
use resistance spot welding with inserts for thispurpose have already been made (Ref 3), withthe major problem being the formation of brittle
intermetallic compounds such as FeAl3 andFe2Al5 in the interface layer. It has also beenreported that if the layer thickness of the intermetallic compound is limited to below 10 mm,
the joint strength is improved (Ref 4).
In an example of laser roll welding, a lowcarbon steel (JIS-SPCC, 0.12 C max, 0.5 Mnmax, 0.04 P max, S 0.045 max) with a sheet
100
thickness of 0.5 mm (0.02 in.) was joined witha 1 mm (0.04 in.) thick sheet of aluminum(A1050) and aluminum-magnesium alloy(A5052). A continuous-wave CO2 laser wasused to weld the steel sheet to the A5052 alloy,
while a pulsed CO2 laser was used to weld thesteel sheet to the unalloyed aluminum sheet(A1050).
A lap joint was used, and the steel wasplaced on top of the aluminum to absorb theheat from the incident laser beam without melting and to conduct the heat to the interface. The
overlap was 9 mm (0.36 in.), and the Gaussian
beam was defocused to give an elliptical spotof 2.5 mm (0.10 in.) minor and 3.5 mm (0.14in.) major diameter on the steel surface.
A spring was used to press the joint against
660,452 °Cthe table through the roll. Prior to joining, the faying surfaces of both sheets were cleaned ultrasonically to remove the hard aluminum oxidefilm, then treated with a brazing flux (KAlF4:K2AlF5H2O) to prevent further oxidation.
Laser roll welding was conducted with vary100
ing travel speed, laser power, and roll pressure.
Al
The range of conditions was as follows:

Fig. 7 Aluminum-iron phase diagram Laser power: 1.0 to 2.0 kW
 Travel speed: 1.0 to 3.2 m/min (3.3 to 10.5

ft/min)further diffusion at the interface. Such conditions restrict the intermetallic compound layer
thickness to thin levels. The existence of a thininterface layer containing some ductile compounds is favorable for improved joint strength.

Welding Uncoated Steel Sheet with Aluminum Sheet. Low-carbon steel and aluminumalloy sheet products are common in the automobile industry for structural components. For
weight reduction, one method is to use Beam spot diameter: 3 to 5 mm (0.12 to 0.2in.) Roll pressure: 100 to 200 MPa (14.5 to 29

ksi)

 Shielding method: Argon gas

5264/7L/A0005620
6 / Solid-State Welding Processes
cause melting of the steel sheet, and if itreaches low values, the heat input may not be
sufficient to produce a bond. As for the pressure, it is necessary to increase the contact area
for a short time after heating to allow the diffusion process to take place and help to increase
the cooling rate of the joint by heat conduction.
Figures 10 and 11 illustrate the effect oftravel speed on interface layer thickness andshear strength. By increasing the travel speed,
the interface layer thickness decreases at thesame time shear strength increases up to 33
MPa (4.8 ksi) for A1050 and to 56 MPa (8.1ksi) for A5052. With higher speeds, the percentage of ductile compounds is relatively high,but the shear strength drops for fast travel
speed, owing to insufficient temperature due tothe lack of heat energy at the interface layer.
To evaluate the formability of the joints, theErichsen test was carried out and evaluatedwith different speeds, as shown in Fig.12. The
cupping height increases with speed until itreaches a maximum value, then starts todecrease almost in the same manner as theshear strength analysis.
Welding Galvanized Steel Sheet with Aluminum Sheet. Laser roll welding of dissimilarmetal-joint zinc-coated steel with 6000-series
aluminum alloy (A6000) has also been

In addition to these parameters, pulsed laser
welding is used to weld the unalloyed aluminum A1050, which enables more control of
the heating and cooling rates by changing thepulse.
The joints were cut transversely to observe
the macrostructure and microstructure. Macrostructure examples are shown in Fig. 9. Specimens were used to identify and estimate theintermetallic compounds through the interface
layer by electron probe microanalysis (EPMA)
with wavelength-dispersion analysis. Based on
the EPMA results, the thickness of the interface
layer was divided into ductile compounds (FeAland Fe3Al) and brittle compounds (FeAl3 andFe2Al5). The EPMA analysis showed that theinterface layer consisted of brittle intermetallic
compounds (FeAl3 and Fe2Al5) on the aluminum side and ductile ones (FeAl and Fe3Al)
on the steel side. As the travel speed increased,
the total thickness of the interface layer
decreased with increasing thickness of the ductile compounds.
Thickness of the interface layer could becontrolled by changing pressure values andinterface temperature (by varying the laser
power or travel speed). Increasing the power
has the same effect as decreasing the speed,
but if the power reaches high values, it will

evaluated. Like the uncoated steel sheet, thefollowing conclusions were observed:
 Increase in the travel speed of the table led

to decrease in the thickness of the intermetallic compound layer at the interface.
Increase in travel speed led to lowering of
the peak temperature and shortening of theholding time more than 500  C (900  F) at
the interface.
 It is suggested that the intermetallic compound layer formed is mainly brittle FeAl3.
Because the travel speed is faster than 0.6
m/min (2.0 ft/min), zinc is confirmed in thealuminum alloy.
 When the intermetallic compound layer wasless than 10 mm, failure of the specimen
occurred at the base metal of the zinc-coatedsteel in tensile shear test.

Steel and Titanium Sheet Joining

Fusion welding of steel and titanium is difficult because of generating the brittle intermetallic compound, but laser roll welding allows
some control over the formation of intermetallic compounds. In the case of laser roll weldingof titanium to steel, the eutectic phase between
titanium and TiFe intermetallic compound isformed from the liquid phase at the interface
above 1180  C (2155  F). The melting interface(a)(b)
and interlayer should be controlled to obtain aductile phase at the interlayer.
Pure titanium sheet (JIS H4600-TP340C) andlow-carbon steel (JIS SPCC) sheet were used
for joining. The dimension of the titanium sheet
and the steel sheet were 40 by 200 by 0.5 mm
0.5 mm
0.5 mm (1.6 by 8 by 0.02 in.).
Process parameters are shown in Table 3.
Travel speed varied from 1.2 to 1.7 m/min
Fig. 9 Macrostructure samples from joints after laser roll welding of low-carbon steel sheet (JIS-SPCC) with (a) A1050 (3.9 to 5.6 ft/min). The steel surface exposed
aluminum and (b) aluminum-magnesium alloy A5052. Laser power, welding speed, and roll pressure were: (a)1.5 kW, 1.5 m/min (4.9 ft/min), and 150 MPa (22 ksi) for A1050, and (b) 1.5 kW, 2.2 m/min (7.2 ft/min), and 200 MPa to the laser beam was coated with graphite(29 ksi) for A5052
to increase the absorption of the laser beam.

(a)

(b)
Travel speed, ft/min
4.9

7.4

13.1

Travel speed, ft/min

19.7
3.9

% Thickness of (FeAl+Fe3Al)

7.6% Thickness of (Fe2Al5+FeAl3+Al)

16.0

12.0
92.4

17.9

8.0
34.8
40.6

82.1

4.0

65.2
59.4
0.0

Average interface layer thickness, μm

Average interface layer thickness, μm

20.0

4.9

5.2

5.9

% Thickness of (FeAl+Fe3Al)% Thickness of (Fe2Al5+FeAl3)

12Roll pressure 150 MPa

23
8
26
77

28

4
74

72

35
65

51
49

1.8

2.0

0
1.5

2.25

4

Travel speed, m/min

6

6.6

16

1.2

1.5

1.6
Travel speed, m/min

Fig. 10 Composition of intermetallic compounds in the interface layer. (a) SPCC-A1050 at 1.5 kW, 150 MPa (22 ksi). (b) SPCC- A5052 at 1.5 kW, 150 MPa (22 ksi)

5264/7L/A0005620
Roll Welding and Laser Roll Welding / 7(a)(b)
Travel speed, ft/min

Travel speed, ft/min
19.7

26.2
20.0
Average shear strength, MPa

Shear strength, MPa (Ksi)Interface thickness, μm
40.00
(6.0)

15.0

30.00
(4.0)

10.0

20.00
(3.0)
5.0
10.00
(1.5)
0.00
0.0

2.0

4.0

6.0

8.0

3.3
80.0
(12.0)

4.9

8.2

9.8
16.0

Average shear strength, MPa
Average interface thickness, μm

60.0
(9.0)

12.0

40.0
(6.0)

8.0

20.0
(3.0)

4.0

0.0
1.0

0.0

6.6

Average interface layer thickness, μm

13.1

Shear strength, MPa (Ksi)

4.6

Average interface layer thickness, μm

0.0
50.00
(7.0)

0.0
1.5

2.0

2.5

3.0

Travel speed, m/min

Travel speed, m/min

Fig. 11 Effect of travel speed on shear strength. (a) SPCC- A1050. (b) SPCC-A5052
Travel speed, ft/min

19.7

6.00

0.24

4.00

0.16

2.00

0.08
1.5 k W, 150 MPa

0.00
0.0

2.0

4.0

6.0

0.0
10

26.2
0.32

0
8.0

Travel speed, m/min

Cupping height, mm

13.1

Cupping height, in.

Cupping height, mm

6.6

6.6

13.1

19.7

26.2

32.8

39.4
0.40

8

0.32

6

0.24

4

0.16

2
0

2.0 k W, 175 MPa
0

2

4

6

8

10

0.08
0
12

Travel speed, m/min

Cupping height, in.

Travel speed, ft/min
0.0
8.00

Table 3 Process parameters in laser rollwelding of commercially pure titanium withsteel sheet
Type of laser
Laser power
Duty cycles
Frequency
Travel speed
Overlap width
Roll pressure
Center shielding gas
Side shielding gas

Pulsed CO2 laser
1.6–2.0 kW
80%
150 Hz1.2–1.7 m/min (3.9–5.6 ft/min)
3 mm (0.12 in.)
76–128 MPa (11–18.5 ksi)
Ar: 25 L/min
Ar: 25 L/min

Fig. 12 Results of Erichsen test performed on laser roll-bonded joints. (a) A1050 at 1.5 kW, 150 MPa (22 ksi), 1.5 m/
min (4.9 ft/min). (b) A5052 at 2.0 kW, 175 MPa (25 ksi), 2.0 m/min (6.6 ft/min)Fig. 13 Effect of power and speed on interlayer
thickness

The faying surface was polished and degreased.
Argon gas at the flow rate of 25 L/min was used
for shielding of joints.
The effect of laser power and travel speed oninterlayer thickness is shown in Fig. 13. Interlayer thickness decreases significantly from170 to 10 mm as the travel speed is increased
from 1.3 to 1.5 m/min (4.3 to 4.9 ft/min) at alaser power of 1.8 kW.
A tensile shear test was done to investigate
the performance of the welded joint. Tensile
shear specimens after testing of laser rollwelded joints are shown in Fig. 14. Some

specimens were broken at the interface (Fig.
14a), and others were broken in the base metalof the steel sheet (Fig. 14b). When the interlayer thickness was less than 25 mm, failure of
the specimen occurred in the base metal of thesteel sheet.

REFERENCES
1. S. Kalpakjian, Manufacturing Processes forEngineering Materials, Addison-Wesley,
1984, p 703–704

5264/7L/A0005620
8 / Solid-State Welding Processes
2. R.G. Delagi, “Designing with Clad Metals,”
Metallurgical Materials Division of Texas
Instruments, Inc.
3. M. Yasuyama, K. Ogawa, and T. Taka, Spot
Welding of Aluminum and Steel Sheet with
Insert of Aluminum Clad Steel Sheet—Part 1, J. Jpn. Weld. Soc., Vol 14 (No. 2),
1996, p 314–320
4. C.E. Albright, The Fracture Toughness of
Steel-Aluminum Deformation Welds, Weld.
J., Vol 60 (No. 11), 1981, p 207s–214sFig. 14 Tensile shear specimens from steel-titanium

joint after laser roll welding. (a) Failure atinterface. (b) Failure in base metal of SPCC