Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1
COMPACT ALUMINIUM ALLOY HEAT TREATMENT METHOD
FIELD OF THE INVENTION
The invention relates a method and a compact apparatus for the heat treatment
of an aluminium alloy strip.
BACKGROUND OF THE INVENTION
Aluminium alloys are used extensively for various purposes, such as automotive
components, structural components, and many other uses. Traditionally,
aluminium
alloys are either direct chill cast or continuously cast. Often, an ingot,
slab, or strip is
rolled to a final gauge that is deliverable to a customer (e.g., automotive
manufacturer
or part processing plant). In some cases, the aluminium alloy may need to
undergo
some sort of thermal treatment to achieve desirable temper properties. For
example,
annealing can improve formability of an aluminium article and solution heat
treatment
followed by a quench can improve strength of the aluminium article.
To achieve high volume throughput, aluminium alloy articles can be
continuously
annealed or solution heat-treated in large continuous processing line.
Traditionally,
such a continuous processing line occupies a very large building and requires
expensive and complicated equipment. For example, such a continuous annealing
solution heat-treatment line requires passing an aluminium alloy strip through
numerous sections to sufficiently raise the temperature of the aluminium strip
to keep it
at solution heat treatment temperature followed by quenching sometimes require
a
processing line of up to 130 meters or longer. As these continuous processing
lines
also include additional operations, such as entry sections, devices to stitch
or weld
strips together, loopers, tension controllers, degreasing before the annealing
or
solution heat treatment, and other metallurgical or surface treatment
operations after
quenching and final recoiling, the total developed length of these continuous
processing lines can reach up to 800 meters or longer. Low tension must be
maintained while the aluminium strip is moving at high temperatures and in the
quench
section, and to avoid surface defects the aluminium strip has to be maintained
without
contact with any surrounding equipment or structures in these sections. In
practice this
is achieved by the use of forced air applied on the two surfaces of the
aluminium strip
to keep it appropriately suspended in the air. If the aluminium strip makes
physical
contact with equipment or structures, it may damage the equipment or
structure, as
well as damage the surface of the aluminium strip, necessitating a shutdown
and
Date Recue/Date Received 2023-02-27
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
2
scrapping of the damaged aluminium strip, as well as any aluminium strip in
the up to
130 meter or longer annealing or solution heat treatment and quench sections
that is
affected and any aluminium necessary to start up a new processing ran (e.g.,
another
800 meters or more). Additionally, to maintain desired temperatures, the
forced air
used to suspend the aluminium strip must be heated as well in the annealing or
solution heat treatment section.
Annealing and solution heat treatment involves heating and cooling the
aluminium article to specific temperatures and holding at those temperatures
for
specific durations of time. The temperature-time profile of an aluminium
article can
greatly affect the resulting strength, ductility and other overall properties
(e.g.
resistance to crash for automotive body sheets) of the aluminium article. In
some
cases, for example for the AA6XXX and AATXXX-series aluminium alloys widely
used
in automotive and transportation applications, annealing or solution heat
treatment and
quenching of aluminum alloys can involve heating the article at a high
temperature
until alloying elements (mainly silicon and magnesium for the AA6XXX-series
alloys,
and zinc, magnesium and optionally copper for the AADOCX-series alloys) are
dissolved in solid solution in the metal article, then quenching the metal
article to lock
these elements in a supersaturated solid solution. After annealing or solution
heat
treatment and quench, the aluminium can he hardened by progressive
recombination
and precipitation of the alloying elements in the aluminium matrix. This
hardening can
take place at room temperature (e.g., naturally aged) for a duration, or
result from a
duration at a slightly elevated temperature (e.g., artificially aged or pre-
aged, typically
in the range of 70 C to 200 C), and/or from further processing (e.g.,
cleaning,
pretreatment, coating, or otherwise). The painting operation of an automotive
body and
its paint-curing-cycle is an example of such further processing step
contributing to
hardening of the aluminium alloy.
This solution heat treatment and quench is also of interest for aluminium
alloys
which do not harden by precipitation, for example the AA5XXX-series aluminium
alloys, which mainly harden by solid solution of magnesium, where the heating-
up
helps delivering and controlling a recrystallized structure, and the holding
at time and
temperature to control the size of the recrystallized grains. The degree of
recrystallization and the grain size directly impact mechanical properties,
surface
aspect, and the yield point elongation (YPE) in particular for AA5XXX-series
alloys.
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
3
Similarly, for aluminium alloys hardened by precipitation, AA2>O<X, AA6XXX and
AATXXX-series alloys for example, increasing the heat-up rate to annealing or
solution
heat treatment helps delivering and controlling a recrystallized grain
structure in the
aluminium strip, and the holding at time and temperature to control the size
of the
recrystallized grains. The degree of recrystallisation, the texture of the
material and the
size of the recrystallized grains directly impact the forming ability of the
aluminium
strip.
In practice with state of the art equipment for continuous heat treatment of
aluminium strips, the heat up speed to solution heat treatment is limited by
the fact that
the heating is done by the flow of air also suspending the moving aluminium
strip, thus
considerably reducing the possibility to accelerate this heat up speed.
Another issue associated with state of the art equipment for continuous heat
treatment of aluminium strips available is the tendency of the aluminium strip
to deform
during the solution heat treatment (or more generally treatment at elevated
temperature) in the sections of the furnace where heat up and mainly holding
at
maximum temperature take place. A typical pattern of deformation is a flat M-
like
shape or sea-gull shape along the transverse section, which may bring the
aluminium
strip in contact with the nozzles supplying the air which holds and suspends
the
aluminium strip in position during heat up and soaking at elevated
temperature. This
may create unacceptable defects on the surface of the aluminium strip and in
some
cases it may cause its breakage, generating major production stoppages.
In addition, this M-shape or other surface deformation occurring during
annealing
or solution heat treatment (or more generally treatment at elevated
temperature)
makes the quenching operation more difficult when the quenching operation
employs
water or any other liquid. A pocket or valley on the surface of the aluminium
strip will
create locally a potential accumulation of water or any other liquid making
the cooling
heterogeneous and enhancing aluminium strip deformation during the quenching
operation.
The rapid cooling after annealing or solution heat treatment also plays an
important role. A too slow cooling will allow a portion of the alloying
elements to leave
from the solid solution and no more contribute to the further hardening. These
may
also precipitate at the grain boundary and weaken the strength of the
aluminium alloy
by initiating premature failure at the grain boundary, therefore decreasing
the material
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
4
performance, its crash resistance in case of for example AA6XXX-series alloys.
From
that perspective, the cooling should be maximized, but with the state of the
art
equipment for continuous heat treatment of aluminium strips, maximizing the
cooling
means cooling the strip with a spray or a mist of water which creates
deformations of
the aluminium strip. This deformation is an issue as its amplitude may be big
enough
to create contact between the strip and the equipment such as the air nozzles
of the
devices supplying the air maintaining the aluminium strip in position in the
quench
section. The described deformation and risk of contact generally increase with
the
increase of cooling, obliging in practice to compromise between fast cooling
and
acceptable deformation.
From this it follows that the state of the art industrial equipment available
on the
market for continuous annealing or solution heat treatment and quenching of
aluminium strips do not provide full satisfaction. Due to the slow heat up
speed with
hot air, their annealing or solution heat treatment sections are long and
costly in
investment. The equipment is limited in their possibility to apply a quick
heat up to
annealing or solution heat treatment temperature as well as a high cooling
speed
during the quenching operation, both desirable for various metallurgical
reasons. They
also generate strip distortion which contribute to heterogenous quenching when
water
or another liquid is used, which may create surface defects due to strip
interaction with
the equipment and even major strip breaking in production. The operation of
such
continuous heat treatment lines remains in practice difficult and very costly.
Several improvements have been proposed in the art to remediate the
weaknesses of such lines.
Patent document WO-2016/037922-A1 discloses a method for the continuously
annealing of aluminium sheet of the AA6X>CX-series, wherein before or near the
entry
section of the continuous annealing furnace the aluminium sheet is pre-heated,
preferably inductively, to a temperature of 5 C to 100 C below the set
solution heat-
treatment temperature of 500 C to 590 C. Patent document WO-2016/091550-A1
discloses a method for the continuously annealing of aluminium sheet of the
AA7XXX-
series, wherein before or near the entry section of the continuous annealing
furnace
the aluminium sheet is pre-heated, preferably inductively, to a temperature of
5 C to
100 C below the set solution heat-treatment temperature of 370 C to 560 C.
Patent
document WO-2018/064228-A1 proposes a compact continuous heat treatment line
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
having a short heating zone for rapidly heating metal strip to a solutionizing
temperature using magnetic rotors, such as permanent magnetic rotors. The
magnetic
rotors can be used to levitate the metal strip within a gas-filled chamber.
And patent
document WO-2018/064145-A1 discloses a non-contact heating apparatus using a
5 series of rotating magnets to heat, levitate, and/or move metal articles
therethrough.
But none of these solutions addresses in full the weaknesses of the state of
the
art equipment available on the market for continuous annealing or heat
treatment and
quenching of aluminium strips.
DESCRIPTION OF THE INVENTION
As will be appreciated herein below, except as otherwise indicated, aluminium
alloy and temper designations refer to the Aluminium Association designations
in
Aluminum Standards and Data and the Registration Records, as published by the
Aluminium Association in 2018 and are well known to the persons skilled in the
art.
The temper designations are laid down also in European standard EN515.
For any description of alloy compositions or preferred alloy compositions, all
references to percentages are by weight percent unless otherwise indicated.
The term "up to" and "up to about", as employed herein, explicitly includes,
but is
not limited to, the possibility of zero weight-percent of the particular
alloying
component to which it refers. For example, up to 0.25% Cu may include an
aluminium
alloy having no Cu.
It is an object of the invention to provide a compact method and a
corresponding
apparatus for the heat treatment of an aluminium alloy strip at an annealing
or solution
heat treatment temperature.
This and other objects and further advantages are met or exceeded by the
present invention providing a method for the continuous heat treatment of a
moving
aluminium alloy strip, the aluminium alloy strip has an upper-surface and a
lower-
surface, the method comprising moving or transporting the aluminium alloy
strip over
at least two rotating heating rolls, wherein the heating rolls comprise an
outer-surface
such that a surface of the aluminium alloy strip is in heat-transfer contact
with a part of
the outer-surface of the heating roll to induce heat into the aluminium alloy
strip to heat
the aluminium strip to an annealing temperature, and comprising moving the
aluminium alloy strip over a first rotating heating roll followed by moving
the aluminium
alloy strip over a second rotating heating roll such that alternating the
upper-surface
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
6
and the lower-surface of the aluminium alloy strip are in heat-transfer
contact with the
outer-surface of the rotating heating rolls. The aluminium alloy strip is heat
treated by
heating it to a predefined annealing temperature, by this is meant a
temperature at
which the aluminium sheet is annealed or solution heat treated.
The method of the invention requires a compact apparatus for the heat
treatment
of aluminium alloy strip. The aluminium alloy strip is moved over at least two
cylindrical
rotatable heating rolls to bring the aluminium alloy strip to a required and
predefined
annealing temperature and to control the soaking time at the annealing
temperature.
The method and the apparatus can be provided with speed control means (i.e.
the uncoiling speed of the aluminium alloy strip from a coil and the
rotational speed of
the heating rolls) and strip tension control means to control the heat
transfer from the
cylindrical rotatable heating roll to the aluminium alloy strip. The
rotational speed of
each cylindrical heating roll is individually adjustable.
To ensure that at least the upper-surface and the lower-surface of the
aluminium
alloy strip is brought into heat transfer contact with the outer-surface of
the heating
rolls at least two heating rolls are provided such that the aluminium alloy
strip moving
over a first heating roll such that the upper-surface of the aluminium alloy
strip is in
heat transfer contact with the first heating roll followed by moving the
aluminium alloy
strip over a second heating roll whereby the lower-surface of the aluminium
alloy strip
is in heat transfer contact with the outer-surface of the second heating roll
to ensure as
much as possible a fast and homogeneous heat-up of the aluminium sheet.
Alternatively, firstly the lower-surface is in contact with the first heating
roll followed by
the upper-surface of the aluminium alloy strip in contact with the outer-
surface of the
second heating roll. The first cylindrical heating roll is rotatable in a
first direction, i.e.
clockwise or counter-clockwise, and the second cylindrical heating roll is
rotatable in
an opposite second direction.
Moving or transporting an aluminium alloy strip over a cylindrical rotatable
roll
may result in some plastic deformation at the surface of aluminium alloy the
strip if the
stress seen at the surface of the strip exceeds the yield stress. The
advantage of
alternating the aluminium alloy strip over at least two rotatable heating
rolls moving in
opposite directions is also that the both surfaces of the aluminium alloy
strip are
deformed, the resultant is that the effect is symmetrical. Furthermore, it
results in
improved flatness control of the aluminium alloy sheet.
The heat-transfer to an aluminium alloy strip resulting from the direct
contact with
the outer-surface is much more effective than the heating of an aluminium
alloy strip
with heated air as is done in industrial scale continuous annealing lines.
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
7
A series of experiments have shown that for 1 mm sheet material of the AA6016-
series
the time to reach from ambient temperature a solution heat-treatment
temperature of
540 C is less than 30 seconds when heated from 1 side and about 10 to 15
seconds
when heated from both sides by keeping it in direct contact between two metal
blocks
having a temperature of 540 C. By increasing the heat input, for example by
using an
additional external heat source like induction heating, this heat-up time can
be reduced
to less than 10 seconds. Whereas in an industrial scale continuous annealing
time the
required heat-up time to this solution heat-treatment temperature is typically
in a range
of 45 to 55 seconds. This considerable reduction of heat up time in the method
of this
invention results amongst others in a better and more homogeneous grain
recrystallization due to the increased heat-up speed of the aluminium alloy
strip and to
a significant reduction in the size of the required equipment to achieve this
effect.
It is an important aspect of the invention that the aluminium alloy strip is
in direct
contact with the rotatable heating rolls, i.e. there is thermal contact
between the
aluminium alloy strip and the outer-surface of the rotatable heating roll. In
the prior art,
the direct contact of a moving aluminium alloy strip at elevated temperature
against
any static part of the equipment is to be avoided as it may lead to
undesirable surface
damaging of the aluminium alloy strip. However, in accordance with this
invention it
has been found that by selecting the right surface coating of the rotatable
heating roll
surface, damaging does not need to be an issue as there is tangent contact
without
any differential speed difference between the aluminium alloy strip and the
outer
surface of the rotatable heating roll other than the aluminium alloy strip
expansion
during heat-up.
Nevertheless, the number of cylindrical rotatable heating rolls in the method
of
this invention should be limited, and preferably two or three, but not more
than four,
heating rolls are employed to keep the system as compact as possible.
In an embodiment, the outer-surface of the rotatable heating rolls is coated
with
wear resistant material with a high thermal conductivity and a low coefficient
of friction.
In a preferred embodiment, the outer-surface of the rotatable heating rolls is
uniformly
coated with a composite diamond coating, for example the commercially
available
Composite Diamond Coatings of the Series-1100 from Endure Coatings can be
used.
The overall low coefficient of friction of 0.10 to 0.20 combined with a high
hardness of
more than 1,000 Vickers, and typically around 1,200 Vickers, contributes in
combination with strip tension and speed control, to limiting the occurrence
of surface
defects on the moving aluminium alloy strip.
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
8
This example of a suitable coating is non-limiting and the use of other
technologies, in particular thermal spraying, including high velocity oxygen
fuel
spraying (HVOF), to provide a heat conductive, wear resistant and highly
adhesive
coating onto the surface of the heating rolls is envisaged by this invention.
Other
suitable materials include ceramic coatings, such as titanium nitride,
tungsten carbide,
chromium nitride, and the like.
A rotatable heating roll is preferably manufactured from a metal selected from
the group of cast iron, steel, stainless steel, cemented carbides, copper,
copper-based
alloy, and aluminium based alloy, with a sufficient compressive strength and
wear
resistance so as to undergo only elastic deformations during the operation of
the
method. It can be heated by various heating means, for example by resistance
heating, e.g. with a set of heaters positioned inside the rotatable roll
together with
temperature measurement and temperature control means. The power supply can be
made for example via a connection through the axis of the cylindrical
rotatable heating
roll. The choice of the heating roll material can also be such as to obtain an
effective
heating via induction heating means. This can be of particular interest for at
least the
first rotatable heating roll in a set of heating rolls, where a significant
heat input is
required between the aluminium alloy strip and the rotatable heating roll.
This can be
achieved from the inside of the rotatable heating roll, but alternatively or
in addition
thereto also from inductors positioned perpendicular to the outer-diameter of
a
rotatable heating roll.
In an embodiment, the inductive heating means are provided contributing
directly
to the heating up of the aluminium alloy strip itself, or even before the
aluminium alloy
strip is in direct contact with the outer-surface of the heating roll. This
would result in
an effective and fast heat-up of the aluminium alloy strip and in reducing the
required
contact time with the outer-surface of the cylindrical rotatable heating
roll(s).
In an embodiment, the aluminium alloy strip is moving or transporting while
one
surface is in heat-transfer contact with a rotating heating roll and the other
surface of
the aluminium strip is facing a thermal shield or screen to modulate heat-
loss. The
thermal shield or screen consists of a wall(s) or a roof structure made from a
material
that is ideally reflective on the side facing the heating roll and the
aluminium sheet,
e.g., a stainless-steel plate. The thermal shield or screen is to reduce heat-
loss of the
moving aluminium alloy strip over the outer-surface of the rotating heating
roll by
reflecting the infra-red radiation of the aluminium alloy strip or by
adsorbing and re-
emitting infra-red radiation. The thermal shield or screen also prevents or
limits
uncontrolled temperature loss by preventing air currents around the moving
aluminium
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
9
sheet in the space or chamber defined by the rotating heating roll and the
thermal
shield or screen.
More preferably the thermal shield or screen further comprises active heating
means for improved temperature control of the moving aluminium alloy strip.
The
active heating can be done in various ways, in particular the heating is
selected from
the group consisting of infrared, radiant-tube, gas-fired heating, direct
resistance,
induction heating, and combinations thereof. In an embodiment, the active
heating
means are provided separate from the thermal shield to induce heat into the
aluminium
alloy strip in addition to the heat input from the aluminium alloy strip while
in heat-
transfer contact with the outer-surface of the heating roll.
To make the contact between the aluminium alloy strip and the outer-surface of
the rotatable heating roll(s) more effective, a leveller can be provided.
To control the tension of the moving aluminium alloy strip while in contact
with
the outer-surface of the rotating heating roll(s), a tension controller, e.g.
as in regular in
the art, can be provided between the leveller and the entry section of a first
rotatable
heating roll.
In an embodiment, and similarly as with regular industrial methods and
equipment for the continuous annealing and quench of aluminium alloy strips,
the entry
section of the apparatus or facility to perform the method of this invention
can be
equipped or provided with an un-coiler for handling the aluminium alloy strip
out of a
coil coming from the rolling mill; with one or more devices to join together
the ends the
aluminium alloy strips from different and successive coils, for example by
means of
stitching or friction stir welding; and with loopers sized to apply the
previous operations
without substantially lowering the overall speed of the heat-treatment line;
and also
with one or more degreasing sections removing prior to temperature heat up
residues
of rolling lubricant or rolling lubricant burn from the surface of the
aluminium alloy strip
to avoid that such residues would pollute the equipment and the surface of the
aluminium alloy strip.
In an embodiment, the aluminium alloy strip following the heat treatment is
rapid
cooled or quenched to below about 100 C, and preferably to below 50 C, and
more
preferably to ambient temperature.
The quenching can be achieved by conventional devices with the benefit that
the
aluminium strip exits the rotatable heating rolls substantially flat, making
the control of
the quenching and its homogeneity over the aluminium strip much easier than
current
industrial equipment for continuous annealing or solution heat-treatment and
quenching of aluminium alloy strips.
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
In an embodiment, the aluminium alloy strip following the heat treatment is
rapid
cooled or quenched to below about 100 C by moving the aluminium alloy strip
over at
least one rotatable cooling roll, and preferably a set of two or more
rotatable cooling
rolls, wherein the rotatable cooling roll comprises an outer-surface, such
that a surface
5 of the aluminium alloy strip is in heat-transfer contact with the outer-
surface of the
cylindrical rotatable cooling roll to remove heat from the aluminium alloy
strip to rapidly
cool the aluminium strip at a temperature below about 100 C, and preferably to
below
50 C, and more preferably to ambient temperature. The rotatable cooling
roll(s) can be
water cooled to achieve a high degree of heat transfer. The cooling rolls can
be made
10 from the same material and provided with the same or similar surface
coating as the
rotatable heating rolls. By using one or more rotatable cooling rolls, a more
homogenous cooling of the aluminium alloy strip is obtained resulting in
significantly
less distortion. Also the undesired formation of a so-called seagull shape or
M-like
shape across the width of the aluminium alloy strip is avoided. The cooling
speed of a
1 mm gauge AA6016 aluminium alloy strip is typically in a range of about 100-
200 C/sec from annealing temperature when using water cooled cooling rolls
made
from aluminium.
Optionally the aluminium strip is further cooled by actively spraying water,
water-
based emulsions, water mist, or another cooling medium on the surface of the
aluminium strip not in contact with the outer-surface of the cooling roll(s)
to accelerate
the heat removal. In a preferred embodiment, the spray of fine water droplets
mostly
evaporates at the surface of impact of the aluminium alloy strip. This
additional cooling
can be performed on the first cooling roll but can also be performed on the
second and
any further cooling rolls. In this way, rapid cooling speeds of for example
200-
400 C/sec be reached or even higher such that for example a 1 mm gauge
aluminium
alloy strip with minimum strip distortion is obtained. Minimum strip
distortion is here
defined as low enough to be fully removed by passing the strip through a
conventional
leveller.
Optionally the cooling by means of the cylindrical rotatable cooling rolls can
be
supplemented by active cooling of the outer-surface of the aluminium alloy
strip not in
contact with the outer-surface of the cooling roll(s) via pressurised air,
e.g. using one
or more arrays of air-nozzles.
Following the cooling step, the usual processing steps can be applied similar
as
with the state of the art equipment for continuous annealing or solution heat
treatment
and quenching of aluminium strips. These operations include levelling, exit
looper,
shearing and recoiling. These can also include surface treatment (for example
in
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
11
sequences of degreasing, rinsing and etching), coating (for example a
passivation
layer can be applied), lubrication of the aluminium strip in perspective of
further
stamping and forming operations, and some dedicated thermal cycles like pre-
ageing.
The aluminium alloy strip may remain coiled or can be cut-to-length.
Next the heat-treated aluminium alloy strip can be formed in a forming
operation.
It can be any forming operation used to shape three-dimensional components,
and
includes in particular operations like stamping, deep drawing, pressing,
superplastic
forming, press forming, and roll forming, or combinations thereof.
In an embodiment, the annealing temperature is in a range of 400 C to 590 C.
As is well known to the skilled person, the annealing temperature is alloy
dependent.
For aluminium alloys of the AA5XXX-series the annealing temperature is
typically in a
range of about 400 C to 540 C, and preferably of about 470 C to 540 C. For
aluminium alloys of the AA6XXX-series the annealing temperature is typically
in a
range of about 500 C to 590 C, and preferably of about 510 C to 580 C. For
aluminium alloys of the AA7XXX-series the annealing or solution heat-treatment
temperature is typically in the range of about 400 C to 560 C. For the AA7XXX-
series
alloys having a purposive addition of Cu (i.e. Cu >0.25%) the temperature is
typically in
a range of about 400 C to 530 C, and preferably of about 450 C to 520 C, and
for the
AA7XXX-series alloys having no purposive addition of Cu (i.e. Cu<0.25%) the
temperature is typically in a range of about 400 C to 560 C, and preferably of
about
470 C to 530 C.
In an embodiment, the aluminium alloy sheet has a thickness in the range of
about 0.3 mm to 4.5 mm, preferably of about 0.7 mm to 4 mm, and more
preferably of
about 0.8 mm to 4 mm. The sheet width is typically in the range of about 600
to 2700
mm.
In an embodiment, the aluminium alloy strip has a composition within the
AA2XXX-, AA5XXX, AA6XXX- or AATXXX-series aluminium alloys. In a preferred
embodiment the aluminium alloy is within the AA6>O0cseries aluminium alloys,
and
includes, but is not limited to, 6005, 6009, 6010, 6111, 6014, 6016, 6022,
6029, 6451,
6061, 6181, 6082, and 6182. In another embodiment, the aluminium alloy is
within the
AA5>O0K-series aluminium alloys, and includes, but is not limited to, 5050,
5051, 5052,
5454, 5754, 5456, 5182, and 5083.
The aluminium alloy strip obtained by the method according to this invention
can
be used in automotive applications and other transportation applications,
including
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
12
aircraft and railway applications. For example, the disclosed resultant
aluminium alloy
products can be used to prepare automotive structural parts, such as bumpers,
side
beams, roof beams, cross beams, pillar reinforcements (e.g., A-pillars. B-
pillars, and
C-pillars), inner panels, outer panels, side panels, inner hoods, outer hoods,
or trunk
lid panels. The resultant aluminium alloy products and methods described
herein can
also be used in aircraft or railway vehicle applications, to prepare, for
example,
external and internal panels, including fuselage panels. Certain aspects and
features
of the present disclosure can provide metal articles with improved surface
qualities and
metallurgy, which can result in improved bonding capability and formability,
which may
be especially desirable for any of the applications mentioned herein, as well
as others.
The resultant aluminium alloy products and methods described herein can also
be
used in electronics applications. As non-limitative example, the resultant
aluminium
alloy products and methods described herein can be used to prepare housings
for
electronic devices, including mobile phones and tablet computers. In some
examples,
the resultant aluminium alloy products can be used to prepare housings for the
outer
casing of mobile phones (e.g., smart phones), tablet bottom chassis, and other
portable electronics.
In a further aspect of the invention there is provided an apparatus or
facility for
carrying out the method as herein described and claimed, the apparatus
comprising:
a heating-section comprising two or more rotatable heating rolls adapted to
move or transport in use an aluminium alloy strip while in heat-transfer
contact with the
outer-surface of the rotatable heating roll to induce heat into the aluminium
alloy strip
to heat the aluminium alloy strip at an annealing temperature;
- a rapid cooling or quenching section for rapid cooling or quenching of
the
aluminium alloy strip from the annealing temperature to below 100 C, and
preferably
comprising at least one rotatable cooling roll;
- optionally one of more heat shields or screens with an interior
reflective
surface to modulate the heat-loss of a moving aluminium alloy strip and being
positioned to face the side of the aluminium alloy strip that is not in heat
transfer
contact with the outer-surface of a rotatable heating roll;
- optionally one of more heating means to induce heat into the aluminium
alloy strip in addition to the heat input into the aluminium alloy strip while
in heat-
transfer contact with the outer-surface of a rotatable heating roll;
- optionally a tension controller is leveller is provided; and
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
13
optionally a tension controller is provided between the leveller and the
entry section of a first rotatable heating roll.
DESCRIPTION OF THE DRAWING
The invention shall now be described with reference to the appended drawings,
in which:
Fig. 1 is a schematic representation of the principle of this invention;
Fig. 2 is a schematic representation of an exemplary method and apparatus;
Fig. 3 is a schematic representation of another exemplary method and
apparatus; and
Fig. 4 is a schematic representation of another exemplary method and the
apparatus.
Fig. 1 is a schematic representation of the principle of the method according
to
the invention. An aluminium alloy strip 1 is moving or transported in the
direction of the
arrows and is heat treated by bringing it in heat-transfer contact with the
outer-surface
of in this case three rotatable heating rolls 6,7,8. The required diameter of
the rotatable
heating rolls can be first order estimated by the following guidelines where:
v is the speed (m/sec) of the moving aluminium alloy strip;
Tc is the time (sec) of the required contact between the aluminium alloy strip
1
and the outer-surface of the heating rolls to heat-up the aluminium alloy
strip to the
required annealing or solution heat-treatment temperature and the required
soaking
time at this temperature. This is aluminium alloy dependent and can be
established by
simple experiments or thermodynamic computer modelling calculations by the
skilled
person;
Lc is the total length (m) of the required contact;
Di is the diameter (m) is heating toll number i;
Ki is the contact factor (dimensionless) of heating roll number i. Depending
on
the relative positions of the heating rolls and the position of the aluminium
alloy strip,
Ki is the ratio between the perimeter of heating roll i in contact with the
strip divided by
the total perimeter of said heating roll;
N is the number of rolls;
Lc = v.Tc or Lc = Z Di.Ki.rr;
If it is assumed for this model calculation that all rolls have the same Ki
and the
same diameter, then this can be simplified to:
Le = N.D. K and consequently D = Tc.v / (N.u.K)
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
14
To provide a first order of magnitude where Tc is 15 sec, v is 1 m/sec, N is 3
and K is
0/5, this would result in a heating roll diameter of 2.12 meter for each of
three heating
rolls.
The skilled person will immediately recognise that this concerns a mere model
calculation and that various variations are possible or required while using
the same
principles.
In practice the diameter of a set of heating rolls can be varied within this
set, but
typically the diameter of each heating roll is in a range of about 1 meter to
3 meters.
Fig. 2 is a schematic representation of an embodiment of the method according
to the invention and the apparatus employed therein. In this configuration,
aluminium
alloy strip 1 with a lower-surface 2 and an upper-surface 3 is being uncoiled
from a coil
4 and moved or transported to a heating section comprising three cylindrical
rotatable
heating rolls 6,7,8 and followed by a rapid cooling section comprising of
cylindrical
three rotatable cooling rolls 9,10,11 and subsequently re-coiled into a coil
5. In the
heating section, the upper-surface 3 of the aluminium alloy strip 1 is brought
into heat-
transfer contact with the outer-surface of heating roll 6 to induce heat into
the
aluminium strip to heat the aluminium strip to an annealing temperature. While
progressively moving the lower-surface 2 of the aluminium alloy strip 1 is
brought into
heat-transfer contact with the outer-surface of heating roll 7, followed by
bringing the
upper-surface 3 of the aluminium alloy strip 1 into heat-transfer contact with
the outer-
surface of heating roll 8. Both heating rolls 7 and 9 are rotatable in a first
direction, i.e.
clockwise or counter-clockwise, and heating roll 8 is rotatable in an opposite
second
direction. By adjusting the transport speed or line speed of the moving
aluminium alloy
strip 1 it receives a heat treatment by soaking for a certain time at a pre-
defined
annealing temperature sufficient to achieve annealing required for the subject
aluminium alloy. Soaking times are typically in a range of up to 1 minute, and
preferably up to 30 sec. To enhance the heat input into the aluminium alloy
strip 1, it
can be pre-heated prior to being brought into contact with the first rotatable
heating
roll. The pre-heat can be achieved by various heating means, for example by
using an
inductive heating device 13. To assist in the temperature control of the
aluminium alloy
strip and to modulate heat-loss of the strip, heat shields 12 or screens 12
can be used.
The screen is reflective at least on the side facing the heating roll and the
moving
aluminium sheet and reflects the infra-red radiation of the moving aluminium
alloy strip
or by adsorbing and re-emitting infra-red radiation. The thermal shield or
screen also
prevents or avoids uncontrolled temperature loss by preventing air currents
around the
CA 03147396 2022-01-13
WO 2021/024062 PCT/IB2020/056809
moving aluminium sheet in the space or chamber defined by the rotating heating
roll
and the thermal shield or screen. Optionally, the heat shield or reflective
screen can be
provided further with active heating means (not shown). Following the heat-
treatment,
the aluminium alloy strip 1 is rapidly cooled or quenched in a quenching
section by
5 moving
or transporting the aluminium strip over cylindrical rotatable cooling rolls
9,10,11, wherein the rotating cooling rolls comprises an outer-surface, such
that a
surface of the aluminium strip is in heat-transfer contact with the outer-
surface of the
rotating cooling rolls to remove heat from the aluminium strip and to cool the
aluminium strip to a temperature below 100 C, and preferably to about ambient
10
temperature. In this set-up, the aluminium alloy strip 1 is also further
cooled by actively
spraying water or water-mist via spray nozzles 14 onto either surface 2,3 of
aluminium
alloy strip to enhance the cooling rate of the strip material. Alternative
approaches
have been described herein.
15 Fig. 3
is a schematic representation of another embodiment of the method
according to the invention and the apparatus used therein. In this
configuration,
aluminium alloy strip 1 is being uncoiled and via a cylindrical transfer roll
or support roll
15 moved or transported to a heating section comprising three cylindrical
rotatable
heating rolls 6,7,8 of the same diameter and next transported to a rapid
cooling or
quenching section (not shown). All three rotatable heating rolls are provided
with heat
shields 12 or reflective screens 12. In this configuration, rotatable heating
rolls 6 and 7
are heated via an external induction source 16, whereas rotatable heating roll
8 is
heated by means of electric resistance heating (not shown).
Fig. 4 is a schematic representation of another embodiment of the method
according to the invention and the apparatus used therein. Also in this
configuration
aluminium alloy strip 1 is being uncoiled and via a cylindrical transfer roll
or support roll
15 moved or transported to a heating section comprising three cylindrical
rotatable
heating rolls 6,7,8 and next transported to a rapid cooling section (not
shown). All three
rotatable heating rolls 6,7,8 are heated by means of electric resistance
heating.
Optionally the moving aluminium alloy strip 1 can be pre-heated by means of
induction
heating using induction device 13. In this configuration the aluminium alloy
strip 1 while
in heat transfer contact with the outer-surface of the first heating roll 6 is
further heated
by means of induction heating using induction source 16. Such additional
induction
heating of the aluminium alloy strip 1 can be applied at one rotatable heating
roll, but
also at or near more of the rotatable heating rolls.
CA 03147396 2022-01-13
WO 2021/024062 PCT/1B2020/056809
16
This kind of arrangement would be particularly suitable for processing high-
strength alloys, for example but without limiting to these examples, aluminium
strips
from AA2X.XX-series aluminium alloys for aircraft applications or AATXXX-
series
aluminium alloys for aircraft or automotive applications, as these aluminium
alloys
contain high amounts of alloying elements requiring a longer soaking time at
solution
heat treatment temperature. With the current regular industrial equipment
available for
continuous annealing and quenching of aluminium alloy strips, this longer
soaking time
obliges to severely reduce the speed of the line (exit speed of the strip),
typically by up
to about 70% compared to the line speeds used for AA6XXX-series aluminium
alloys,
making these continuous annealing lines very costly to operate for
manufacturing
these high-strength aluminium alloys. In the approach of this invention, this
can be
done very much easier and more cost effective by increasing the diameter of
the
heating rolls or by adding one or more heating rolls while maintaining a high
line speed
of the moving aluminium alloy strip.
The invention is not limited to the embodiments described before, and which
may
be varied widely within the scope of the invention as defined by the appending
claims.
