U.S. patent application number 15/851154 was filed with the patent office on 2018-04-26 for method for coating a substrate and metal alloy vacuum deposition facility.
The applicant listed for this patent is ArcelorMittal. Invention is credited to Daniel Chaleix, Patrick Choquet, Bruno Schmitz, Eric Silberberg.
Application Number | 20180112305 15/851154 |
Document ID | / |
Family ID | 38370938 |
Filed Date | 2018-04-26 |
United States Patent
Application |
20180112305 |
Kind Code |
A1 |
Choquet; Patrick ; et
al. |
April 26, 2018 |
Method for Coating a Substrate and Metal Alloy Vacuum Deposition
Facility
Abstract
A vacuum deposition facility for continuously depositing
coatings formed from metal alloys having at least two metallic
elements on a running substrate is provided. The vacuum deposition
facility includes a vacuum deposition chamber, a substrate running
through the vacuum deposition chamber and an evaporation crucible
inside the vacuum deposition chamber. The evaporation crucible
includes a heater and a bath of molten metal alloy which has at
least two metallic elements in a predetermined and constant ratio.
The evaporation crucible evaporates the molten metal alloy into a
vapor. The vacuum deposition facility also includes a coater inside
the vacuum deposition chamber and connected to the evaporation
crucible. The coater sprays a face of the running substrate with
the vapor at a sonic velocity in order to deposit a coating on the
running substrate. The vapor includes the at least two metallic
elements in the predetermined and constant ratio.
Inventors: |
Choquet; Patrick;
(Longeville Les Metz, FR) ; Silberberg; Eric;
(Haltinne (Gesves), BE) ; Schmitz; Bruno;
(Nandrin, BE) ; Chaleix; Daniel; (Verny,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ArcelorMittal |
Luxembourg |
|
LU |
|
|
Family ID: |
38370938 |
Appl. No.: |
15/851154 |
Filed: |
December 21, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13870351 |
Apr 25, 2013 |
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15851154 |
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12532043 |
Dec 31, 2009 |
8481120 |
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PCT/FR2008/000347 |
Mar 19, 2008 |
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13870351 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 16/45563 20130101;
C23C 14/16 20130101; C23C 16/06 20130101; C23C 14/24 20130101; C23C
14/562 20130101 |
International
Class: |
C23C 16/06 20060101
C23C016/06; C23C 14/56 20060101 C23C014/56; C23C 14/16 20060101
C23C014/16; C23C 14/24 20060101 C23C014/24 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2007 |
EP |
07290342.0 |
Claims
1. A vacuum deposition facility for continuously depositing
coatings formed from metal alloys comprising at least two metallic
elements on a running substrate, comprising: a vacuum deposition
chamber; a substrate running through the vacuum deposition chamber;
an evaporation crucible inside the vacuum deposition chamber, the
evaporation crucible including a heater and a bath of molten metal
alloy including at least two metallic elements in a predetermined
and constant ratio, the evaporation crucible evaporating the molten
metal alloy into a vapor; a coater inside the vacuum deposition
chamber and connected to the evaporation crucible, the coater
spraying a face of the running substrate with the vapor at a sonic
velocity thereby depositing a coating on the running substrate, the
vapor including the at least two metallic elements in the
predetermined and constant ratio.
2. The vacuum deposition facility as recited in claim 1, wherein
the predetermined and constant ratio of the bath remains constant
during the depositing.
4. The vacuum deposition facility as recited in claim 1, further
comprising a furnace for melting metal.
5. The vacuum deposition facility as recited in claim 4, wherein
the furnace is outside the vacuum deposition chamber.
6. The vacuum deposition facility as recited in claim 4, further
comprising a recirculation pipe for continuously circulating the
bath, the recirculation pipe connecting the evaporation crucible to
the recharging furnace.
7. The vacuum deposition facility as recited in claim 4, wherein
the furnace and the evaporation crucible are adjacent one another
and have a common wall with at least one opening located beneath a
level of the metal alloy bath and above a bottom of the furnace and
of the evaporation crucible.
8. The vacuum deposition facility as recited in claim 4, wherein
the furnace includes a heater.
9. The vacuum deposition facility as recited in claim 4, wherein
the furnace supplies the molten metal alloy to the evaporation
crucible.
10. The vacuum deposition facility as recited in claim 4, further
comprising a metal ingot feeder connected to the furnace for
supplying metal ingots to the furnace for melting.
11. The vacuum deposition facility as recited in claim 4, further
comprising a pump between the evaporation crucible and the furnace
for continuously circulating the bath.
12. The vacuum deposition facility as recited in claim 6, further
comprising a second pipe for continuously circulating the bath, the
second pipe connecting the evaporation crucible to the recharging
furnace.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. application Ser. No.
13/870,351 filed on Apr. 25, 2013 which is a continuation of U.S.
application Ser. No. 12/532,043 filed Dec. 31, 2009, now U.S. Pat.
No. 8,481,120, the entire disclosures of which are hereby
incorporated by reference herein.
[0002] The present invention relates to a process for continuously
coating a substrate and to a vacuum deposition facility for
coatings formed from metal alloys, such as for example
zinc-magnesium alloys, said process being more particularly suited
for coating a steel strip, without in any way being limited
thereto.
BACKGROUND
[0003] Various processes for depositing metal coatings composed of
alloys on a substrate, such as a steel strip, are known. Among
these, mention may be made of hot-dip coating, electrodeposition
and also the various vacuum deposition processes, such as vacuum
evaporation and magnetron sputtering.
[0004] Thus, a vacuum evaporation process, described in WO 02/06558
is known that consists in co-evaporating two elements in a chamber
so as to mix the vapor of the two elements together before coating
the substrate.
[0005] However, industrial implementation of this process is
difficult and is not conceivable for production that must guarantee
a stable coating composition over long substrate lengths.
[0006] It is also possible for a layer of each of the constituent
elements of the alloy to be deposited in succession on the
substrate and then to carry out a diffusion heat treatment
resulting in the formation of an alloyed layer having the most
homogeneous composition possible. Thus, in particular
zinc-magnesium coatings may be produced which may advantageously be
used instead of coatings of pure zinc or other zinc alloys.
[0007] This successive deposition of each of the elements may in
particular be carried out by vacuum co-evaporation of each element
placed in a separate crucible, as described in EP 730 045, but also
by vacuum deposition of an element on a strip precoated with
another element by a conventional hot-dip process.
[0008] However, the subsequent diffusion heat treatment may prove
to be complicated and expensive as it involves the use of large
quantities of inerting gas in order to prevent any oxidation of the
coating at high temperature during the heat treatment. Furthermore,
to avoid any risk of oxidation between the magnesium coating and
the start of the diffusion treatment, it is necessary to perform
the two operations one immediately after the other, without
exposing the strip to the open air.
[0009] This heat treatment may also pose problems in the case of
certain materials that are not compatible with an excessively large
temperature rise. Mention may in particular be made of
bake-hardening steel strip which contains large amounts of carbon
in solid solution, which must not precipitate before the strip has
been formed by the user of the material.
[0010] Moreover, in this type of process, it is very tricky to
obtain a coating of constant composition over a long substrate
length as it is necessary for the thicknesses of each layer to be
very precisely controlled over the course of time.
[0011] Finally, the diffusion treatment does admittedly allow the
alloy to form, but it may also lead to the diffusion of elements
from the substrate to the coating, thus contaminating the interface
with the substrate.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is therefore to remedy
the drawbacks of the processes and facilities of the prior art by
providing a vacuum deposition facility for depositing coatings
formed from metal alloys and a process for manufacturing a metal
strip covered with a metal alloy layer, which allow simple
industrial implementation, in few steps, but which also allow a
coating of constant composition to be obtained, on various types of
substrates.
[0013] The present invention provides a process for coating a
substrate, whereby a metal alloy layer comprising at least two
metallic elements is continuously deposited on said substrate by
means of a vacuum deposition facility comprising a vapor jet coater
for spraying the substrate, at a sonic velocity, with a vapor
containing said at least two metallic elements in a constant and
predetermined relative content, said vapor being obtained by
evaporating a metal alloy bath containing said metallic elements in
a predetermined initial content, said initial content of the bath
being kept constant during the deposition.
[0014] The process according to the invention may also comprise
various features, taken by themselves or in combination, as
follows: [0015] the metallic elements are zinc and magnesium;
[0016] the metal alloy layer contains no iron-zinc intermetallic
phases; [0017] the metal alloy layer predominantly consists of a
Zn.sub.2Mg phase; [0018] a layer of a zinc-based metal alloy having
a predetermined magnesium content of between 4% and 20% by weight
is continuously deposited on the substrate by evaporating a bath of
a zinc-based metal alloy initially having a predetermined magnesium
content of between 30% and 55% by weight of magnesium, the initial
content being kept constant during the deposition; [0019] a layer
of a zinc-based metal alloy having a predetermined magnesium
content of between 4% and 18% by weight is continuously deposited
on the substrate by evaporating a bath of a zinc-based metal alloy
initially having a predetermined magnesium content of between 30%
and 50% by weight of magnesium, the initial content being kept
constant during the deposition; [0020] the metallic elements have
evaporation temperatures differing by no more than 1 oooc at the
selected evaporation pressure; [0021] a metal alloy layer is
deposited with a thickness of between 0.1 and 20 .mu.m; [0022] the
substrate is a metal strip and preferably a steel strip; [0023] the
metal strip is made of a bake-hardening steel; and [0024] the metal
alloy layer consists predominantly of a Zn.sub.2Mg phase.
[0025] The present invention also provides a vacuum deposition
facility for continuously depositing coatings formed from metal
alloys comprising at least two metallic elements on a running
substrate, comprising a vacuum deposition chamber and means for
running the substrate through this chamber, the facility further
comprising: [0026] a sonic vapor jet coater; [0027] means for
feeding said coater with vapor comprising said at least two
metallic elements in a predetermined and constant ratio; [0028]
means for evaporating a bath of metal alloy comprising said
metallic elements, which will feed said coater; and [0029] means
for adjusting the composition of the metal alloy bath, enabling it
to be kept constant over the course of time.
[0030] The facility according to the invention may also comprise
the following variants, taken in isolation or in combination:
[0031] the means for adjusting the composition of the metal alloy
bath comprise means for feeding the evaporation means with a molten
metal alloy of controlled composition; [0032] the evaporation means
consist of an evaporation crucible provided with heating means and
said means for feeding said evaporation crucible with a molten
metal alloy of controlled composition comprise a recharging furnace
which is connected to metal ingot feed means and is provided with a
heating system, said recharging furnace being connected to the
evaporation crucible that it feeds; [0033] the facility further
includes means for continuously circulating the bath, in the form
of a recirculation pipe connecting the evaporation crucible to the
recharging furnace; [0034] the evaporation crucible is placed in
the vacuum chamber and the recharging furnace is placed outside the
vacuum chamber; [0035] the recharging furnace and the evaporation
crucible are placed side by side and have a common wall pierced by
at least one opening located beneath the level of the metal alloy
bath but above the bottom of the furnace and of the crucible; and
[0036] the evaporation crucible is placed in a confined chamber and
the recharging furnace is placed outside the confined chamber.
[0037] The present invention further provides an ingot based on
zinc containing 30 to 55% magnesium by weight, preferably 30 to 50%
magnesium by weight, and able to be used for implementing the
process according to the invention or in a facility according to
the invention.
[0038] The present invention includes depositing a metal alloy of
given composition on a substrate by a sonic vapor jet coating
process.
[0039] Owing to the pressure difference created between a closed
evaporation crucible and the deposition chamber, it is possible to
generate, through a narrow slot, a metal vapor jet of possibly
sonic velocity, see for example, WO 97/47782, hereby incorporated
by reference herein for a fuller description of the details of this
type of device.
[0040] The vapor feeding the JVD (Jet Vapor Deposition) device
comes from the direct vacuum evaporation of a bath of the alloy
itself, the composition of the bath being kept constant over the
course of time.
[0041] Now, taking the example of a zinc-based alloy containing
magnesium, each of these two elements has a different vapor
pressure. The composition of the layer deposited will therefore not
be the same as that of the ingot used as raw material for the
evaporation. Thus, as may be seen in FIG. 1, which shows the
magnesium content in wt % in the coating plotted on the y-axis as a
function of the magnesium content in wt % in the bath plotted on
the x-axis, to obtain a magnesium content of 16% in the coating it
is necessary to have 48% magnesium in the metal bath.
[0042] Because of this difference in the vapor pressures of the
alloy elements, the composition of the alloy bath used for the
evaporation and, in fact, the corresponding vapor flux will vary
over the course of time, with in the case of zinc-magnesium a
progressive enrichment with magnesium.
[0043] To keep the composition of the evaporation flux constant
over the course of time, it is necessary to provide a device
enabling the composition of the bath to be kept constant if it is
desired to be able to deposit this type of coating in the context
of industrial implementation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] Other features and advantages of the invention will become
apparent on reading the following detailed description given solely
by way of example, with reference to the appended figures in
which:
[0045] FIG. 1 shows the magnesium content in wt % in a ZnMg coating
as a function of the magnesium content in wt % in the liquid metal
bath before evaporation;
[0046] FIG. 2 shows a first embodiment of a facility according to
the invention;
[0047] FIG. 3 shows a second embodiment of a facility according to
the invention; and
[0048] FIG. 4 shows the microstructure of a 5 .mu.m coating of ZnMg
alloy deposited on a cold-rolled low-carbon steel.
DETAILED DESCRIPTION
[0049] The description that follows will refer to a coating of a
zinc alloy containing magnesium, but it is quite obvious that the
facility according to the invention is not limited thereto and that
it is possible to deposit many other coatings based on metal
alloys.
[0050] A first embodiment of a facility according to the invention
is shown more particularly in FIG. 2, which shows a facility 1
comprising a vacuum deposition chamber 2. This chamber 2 is
preferably kept at a pressure of between 10.sup.-8 and 10.sup.-4
bar, for example. It has an entry load-lock and a exit load-lock
between which a substrate S, such as for example a steel strip,
runs.
[0051] The substrate S may be made to run by any suitable means,
depending on the nature and the shape of said substrate. A rotary
support roller on which a steel strip can bear may in particular be
used.
[0052] Placed opposite the face of the substrate S which has to be
coated there is a small extraction chamber 7 provided with a narrow
slot, the length of which is close to the width of the substrate to
be coated. This chamber may for example be made of graphite and may
be mounted, directly or otherwise, on an evaporation crucible 3
that contains the liquid metal to be deposited on the substrate S.
The evaporation crucible 3 is continuously recharged with liquid
metal via a pipe 4 connected to a melting furnace 5 which is placed
beneath the extraction chamber 7 and is at atmospheric pressure. An
overflow pipe 6 also connects the evaporation crucible 3 directly
to the recharging furnace 5. The elements 3, 4, 5 and 6 are heated
to temperatures high enough for the metal vapor not to condense or
the metal not to solidify on their respective walls.
[0053] The evaporation crucible 3 and the liquid metal recharging
furnace 5 are advantageously provided with an induction heater 30,
50, respectively which has the advantage of making the stirring and
the composition homogenization of the metal alloy bath easier.
[0054] When it is desired to operate the facility 1, the
composition of the metal alloy that it is desired for deposition on
the substrate is first determined. Then the composition of the bath
for obtaining, in equilibrium with this bath, a vapor having the
composition of the intended coating is determined. Ingots L of a
metal alloy having this precise composition are produced, and are
then introduced continuously into the recharging furnace 5.
[0055] Once the ingots L have melted, the evaporation crucible 3
and the pipe 6 are heated and then a vacuum is created in the
evaporation crucible 3. The liquid metal contained in the
recharging furnace 5 then fills the evaporation crucible 3. During
the operation of the device, a constant level of liquid metal is
maintained in the evaporation crucible 3 by adjusting the height
between the evaporation crucible 3 and the recharging furnace 5, or
by activating a liquid metal pump P. A circulating pump installed
on the overflow 6 makes it possible to permanently replenish the
liquid metal in the evaporation crucible 3 so as to minimize the
accumulation of impurities which, after a certain time, would
greatly reduce the rate of evaporation of the metal.
[0056] The bath is thus continuously replenished and therefore
always has the required composition at any point, while still
minimizing the amount of material needed to coat the substrate.
[0057] The evaporation crucible 3 is itself provided with heating
means enabling the vapor to form and to feed a JVD coater including
the extraction chamber 7, which sprays a sonic vapor jet onto the
running substrate S.
[0058] Surprisingly, it has been found that spraying a sonic metal
vapor jet onto a substrate makes it possible to obtain a coating of
an AB alloy with nanoscale mixing of the elements A and B. This
result is extremely important in terms of corrosion resistance as,
in this case, no micro-cell can form on the surface of the AB alloy
coating when this is in contact with liquid condensates.
[0059] The sonic jet outlet orifice may have any suitable shape,
such as a slot having dimensions that can be adjusted lengthwise
and widthwise for example to accommodate the desired range of
evaporation. This process thus makes it possible for the width of
the vapor outlet orifice to be easily adapted so as to maintain a
sonic jet within a wide range of evaporated metal surface
temperatures and therefore a wide range of evaporation rates.
Furthermore, the possibility of adapting its length to the width of
the substrate to be coated makes it possible to minimize the loss
of evaporated metal.
[0060] In a second embodiment as shown in FIG. 3, a facility 11
comprises a vacuum deposition chamber 12 similar to the chamber 2.
An evaporation crucible 13 is placed under the vacuum chamber 12
and is connected via a pipe 14 thereto.
[0061] A recharging furnace 15 is placed alongside the evaporation
crucible 13, the two components sharing a common wall 16 pierced by
a communication opening 19 placed below the level of the metal
alloy bath but above the bottom of these components so as to
prevent any impurities that settle at the bottom of the recharging
furnace 15 from being introduced into the evaporation crucible
13.
[0062] The evaporation crucible 13 is moreover placed in a confined
chamber 18, placed outside the vacuum chamber 12.
[0063] The pipe 14 feeds a JVD coater 17, similar to the coater
7.
[0064] In the same way as described above with respect to FIG. 2,
the composition of the coating which it is desired to obtain on the
substrate is first determined and then deduced from this is the
composition of the metal bath that has to be present in the
evaporation crucible 13, and therefore the composition of the metal
ingots L with which the recharging furnace 15 has to be fed.
[0065] The ingots are placed in the recharging furnace 15, which is
provided with an induction heating system. As they melt, the metal
alloy passes from the recharging furnace 15 to the evaporation
crucible 13 via the opening 19. The evaporation crucible 13 is
itself provided with an induction heating system that enables a
metal alloy vapor having the required composition to be generated.
This vapor is then conveyed to the JVD coater 17 via the pipe 14,
which is advantageously provided with a valve V for regulating the
vapor flow rate.
[0066] By having a communication opening 19 between the recharging
furnace 15 and the evaporation crucible 13 it is possible to feed
the evaporation crucible 13 and provide a constant circulation
between these two components, thereby ensuring that a constant
composition is maintained at all points in the bath contained by
the evaporation crucible 13.
[0067] The process according to the invention applies more
particularly, but not solely, to the treatment of metal strips,
whether precoated or bare. Of course, the process according to the
invention may be employed for any coated or uncoated substrate,
such as for example aluminum strip, glass strip or ceramic
strip.
[0068] The process will more particularly be applied to substrates
liable to suffer a deterioration in their properties during a
diffusion heat treatment, such as bake-hardening steel strip that
contains large amounts of carbon in solid solution, which must not
precipitate before the steel has been formed by drawing or any
other suitable process. By implementing the process according to
the invention it thus makes it possible to make metal alloy
deposition compatible with most metallurgies.
[0069] A further object of the present invention includes obtaining
zinc-magnesium coatings. However, the process is not limited to
these coatings, but preferably encompasses any coating based on a
metal alloy the elements of which have evaporation temperatures not
differing by more than 100.degree. C., as controlling their
respective relative content is then facilitated.
[0070] For example, mention may thus be made of coatings made of
zinc and other elements, such as chromium, nickel, titanium,
manganese and aluminum.
[0071] Moreover, although the process and the facility according to
the invention are more particularly intended for the deposition of
binary metal alloys, the process and facility can be adapted to the
deposition of ternary metal alloys, such as Zn--Mg--Al, or even the
deposition of quaternary alloys, such as for example
Zn--Mg--Al--Si.
[0072] In the case of zinc-magnesium deposition, the thickness of
the coating will preferably be between 0.1 and 20 .mu.m. This is
because below 0.1 .mu.m, there would be a risk that the corrosion
protection of the substrate would be insufficient. The coating
thickness does not exceed 20 .mu.m as it is unnecessary to go
beyond this thickness in order to have a level of corrosion
resistance which is required, in particular, in the automotive or
construction field. In general, the thickness may be limited to 5
.mu.m, for example, for automotive applications.
[0073] By carrying out industrial trials it has been shown that
deposition by this process advantageously achieves a high
deposition rate of 5 .mu.m ZnMg alloy coating that can be deposited
on a line running at 10 m/min, with a material yield greater than
98% thanks to the targeted orientation of the jet.
[0074] Furthermore, the density of the coating layers obtained may
be advantageous, due to a higher vapor energy. FIG. 4 thus shows
the microstructure of a 5 .mu.m ZnMg alloy coating deposited on a
cold-rolled low-carbon steel.
* * * * *