U.S. patent application number 14/624793 was filed with the patent office on 2015-06-11 for highly formable and intercrystalline corrosion-resistant aimg strip.
This patent application is currently assigned to Hydro Aluminium Rolled Products GmbH. The applicant listed for this patent is Henk-Jan Brinkman, Olaf Engler, Natalie Horster. Invention is credited to Henk-Jan Brinkman, Olaf Engler, Natalie Horster.
Application Number | 20150159250 14/624793 |
Document ID | / |
Family ID | 49084999 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150159250 |
Kind Code |
A1 |
Engler; Olaf ; et
al. |
June 11, 2015 |
Highly formable and intercrystalline corrosion-resistant AIMg
strip
Abstract
The invention relates to a cold-rolled aluminium alloy strip
made of an AlMg aluminium alloy as well as a method for producing
the same. Furthermore, corresponding components made from said
aluminium alloy strips are also proposed. The problem for the
invention of providing a single-layer aluminium alloy strip that is
sufficiently resistant to intercrystalline corrosion and is
nevertheless very formable so that even large-area deep-drawn
parts, e.g. interior parts of motor vehicle doors, can be made with
sufficient strength, is solved by an aluminium alloy strip made of
an AlMg aluminium alloy as described herein.
Inventors: |
Engler; Olaf; (Bonn, DE)
; Brinkman; Henk-Jan; (Bonn, DE) ; Horster;
Natalie; (Koln, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Engler; Olaf
Brinkman; Henk-Jan
Horster; Natalie |
Bonn
Bonn
Koln |
|
DE
DE
DE |
|
|
Assignee: |
Hydro Aluminium Rolled Products
GmbH
Grevenbroich
DE
|
Family ID: |
49084999 |
Appl. No.: |
14/624793 |
Filed: |
February 18, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2013/067487 |
Aug 22, 2013 |
|
|
|
14624793 |
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Current U.S.
Class: |
148/552 ;
148/439 |
Current CPC
Class: |
C22C 21/06 20130101;
C22F 1/047 20130101; C22C 21/08 20130101; C22C 21/00 20130101 |
International
Class: |
C22F 1/047 20060101
C22F001/047; C22C 21/08 20060101 C22C021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2012 |
EP |
12 181 356.2 |
Jul 11, 2013 |
EP |
PCT/EP2013/064736 |
Claims
1. Cold-rolled aluminium alloy strip composed of an AlMg aluminium
alloy, wherein the aluminium alloy comprises the following alloying
elements: Si.ltoreq.0.2 wt. %, Fe.ltoreq.0.35 wt. %, Cu.ltoreq.0.15
wt. %, 0.2 wt. %.ltoreq.Mn.ltoreq.0.35 wt. %, 4.1 wt.
%.ltoreq.Mg.ltoreq.4.5 wt. %, Cr.ltoreq.0.1 wt. %, Zn.ltoreq.0.25
wt. %, Ti.ltoreq.0.1 wt. %, the remainder being Al and inevitable
impurities, amounting to a maximum of 0.05 wt. % individually and
to a maximum of 0.15 wt. % in total, wherein the aluminium alloy
strip has a recrystallized microstructure, the grain size of the
microstructure ranges from 15 .mu.m to 25 .mu.m and the final soft
annealing of the aluminium alloy strip is performed in a continuous
furnace.
2. The Aluminium alloy strip according to claim 1, wherein the
aluminium alloy also has one or more of the following restrictions
to the contents of alloying elements: 0.03 wt. % Si.ltoreq.0.10 wt.
%, Cu.ltoreq.0.1, Cr.ltoreq.0.05 wt. %, Zn.ltoreq.0.05 wt. %, 0.01
wt. %.ltoreq.Ti.ltoreq.0.05 wt. %.
3. The Aluminium alloy strip according to claim 1, wherein the
aluminium alloy also has one or more of the following restrictions
to the contents of alloying elements: Cr.ltoreq.0.02 wt. %,
Zn.ltoreq.0.02 wt. %.
4. The Aluminium alloy strip according to claim 1, wherein the Fe
content is 0.10 wt. % to 0.25 wt. % or 0.10 wt. % to 0.2 wt. %.
5. The Aluminium alloy strip according to claim 1, wherein the Mn
content is 0.20 wt. % to 0.30 wt. %.
6. The Aluminium alloy strip according to claim 1, wherein the Mg
content is 4.2 wt. % to 4.4 wt. %.
7. The Aluminium alloy strip according to claim 1, wherein the
aluminium alloy strip has a thickness of 0.5 mm to 4 mm.
8. The Aluminium alloy strip according to claim 1, wherein the
aluminium alloy strip in the soft state has a yield point
R.sub.p0.2 of at least 110 MPa and a tensile strength R.sub.m of at
least 255 MPa.
9. A Method for producing an aluminium alloy strip according to
claim 1 comprising the following process steps: casting a rolling
ingot; homogenisation of the rolling ingot at 480.degree. C. to
550.degree. C. for at least 0.5 hours; hot rolling of the rolling
ingot at a temperature of 280.degree. C. to 500.degree. C.; cold
rolling of the aluminium alloy strip to the final thickness with a
degree of rolling of 40% to 70% or 50% to 60%; and soft annealing
of the finished-rolled aluminium alloy strip at 300.degree. C. to
500.degree. C. in a continuous furnace.
10. The Method according to claim 9, wherein after hot rolling
alternatively the following process steps are performed: cold
rolling of the hot-rolled aluminium alloy strip to an intermediate
thickness which is determined in such a way that the final degree
of cold rolling to the final thickness is 40% to 70% or 50% to 60%;
intermediate annealing of the aluminium alloy strip at 300.degree.
C. to 500.degree. C.; cold rolling of the aluminium alloy strip to
the final thickness with a degree of rolling of 40% to 70% or 50%
to 60%; soft annealing of the finish-rolled aluminium alloy strip
at 300.degree. C.-500.degree. C. in a continuous furnace.
11. The Method according to claim 9, wherein aluminium alloy strip
after soft annealing is cooled to a maximum temperature of
100.degree. C. and then coiled.
12. The Method according to claim 10, wherein the intermediate
annealing is performed in a batch furnace or in a continuous
furnace.
13. The Method according to claim 9, wherein the aluminium alloy
strip is cold rolled to a final thickness of 0.5 mm to 4 mm.
14. Method according to claim 9, wherein the soft annealing is
performed in the continuous furnace at a metal temperature of
350.degree. C. to 550.degree. C. for 10 seconds to 5 minutes.
15. A Component for a motor vehicle, composed of an aluminium alloy
strip according to claim 1.
16. The Component according to claim 15, wherein the component is a
body part or a body accessory of a motor vehicle.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application is a continuation of
PCT/EP2013/067487, filed Aug. 22, 2013, which claims priority to
European Application No. 12 181 356.2, filed Aug. 22, 2012, and
PCT/EP2013/064736, filed Jul. 11, 2013, the entire teachings and
disclosures of which are incorporated herein by reference
thereto.
FIELD OF THE INVENTION
[0002] The invention relates to a cold-rolled aluminium alloy strip
composed of an AlMg aluminium alloy and a method for the production
thereof. Furthermore, corresponding components produced from the
aluminium alloy strips will be proposed.
BACKGROUND OF THE INVENTION
[0003] Aluminium-magnesium-(AlMg-)-alloys of the AA 5xxx type are
used in the form of sheets or plates or strips for the construction
of welded or joined structures in ship, automotive and aircraft
construction. They are characterised by high strength which
increases as the magnesium content rises. AlMg-alloys of the AA
5xxx type with Mg contents of more than 3%, in particular more than
4%, have an increasing tendency towards intercrystalline corrosion,
when exposed to high temperatures. At temperatures of
70-200.degree. C., .beta.-AlsMg.sub.3 phases precipitate along the
grain boundaries, which are referred to as .beta.-particles and in
the presence of a corrosive medium can be selectively dissolved.
The result of this is that the AA 5182-type aluminium alloy (Al
4.5% Mg 0.4% Mn) having very good strength properties and very good
formability in particular cannot be used in heat-stressed areas,
where the presence of a corrosive medium such as water in the form
of moisture must be contended with. This concerns in particular the
components of a motor vehicle which normally undergo cathode dip
painting (CDP) and are then dried in a stoving process, as already
due to this stoving process, normal aluminium alloy strips can
become susceptible to intercrystalline corrosion. Furthermore, for
use in the automotive sector, forming during the manufacture of a
component and subsequent operational stressing of the component
must be taken into consideration.
[0004] The susceptibility to intercrystalline corrosion is normally
checked in a standard test (NAMLT test) according to ASTM G67,
during which the specimens are exposed to nitric acid and the mass
loss due to the intercrystalline corrosion is measured. According
to ASTM G67, the mass loss of materials which are not resistant to
intercrystalline corrosion, is more than 15 mg/cm.sup.2.
[0005] Sheet metal for the automotive industry, e.g. for internal
door parts, must have very good formability. Here, the requirements
are essentially determined by the stiffness of the component
concerned, with the strength of the material playing only a
subordinate role. The components often undergo multi-stage forming
processes, such as for example doors with integrated window frame
areas.
[0006] So, apart from the corrosion properties, the formability of
the AlMg aluminium alloy also has a major influence on the usage
possibilities for this material. For example, the materials known
so far have meant that it is not possible for the side walls of a
motor vehicle to be deep-drawn from a single sheet, making not only
reconstruction of the side wall but also additional process steps
for providing the side wall of a motor vehicle necessary.
[0007] The forming behaviour can, for example, be measured in a
stretch drawing trial by an Erichsen cupping test (DIN EN ISO
20482), in which a test piece is pushed against the sheet,
resulting in cold forming. During the cold forming, the force and
the force displacement of the test piece are measured, until a load
drop occurs, caused by the formation of a crack. The SZ32 stretch
drawing measurements quoted in the application were performed with
a punch head diameter of 32 mm and a die diameter of 35.4 mm with
the help of a Teflon deep-drawing film to reduce friction. Further
measurements of the deep drawability were performed using the
so-called plane-strain-cupping test using a Nakajima geometry
according to DIN EN ISO 12004 with a punch diameter of 100 mm. For
this, specimens with a specific geometry underwent drawing tests
until a crack appeared, with the depth until cracking being used as
a measure of the formability of the material.
[0008] From JP 2011-052290 A, an aluminium alloy strip for can lids
is known, which is preferably load-resistant despite its small
thickness. Here, the strip has a recrystallized microstructure.
[0009] Further, from EP 2 302 087 A1, a chassis part is known made
from an aluminium composite material, which has aluminium alloy
layers as outer layers. Due to the alloying constituents, the Al
composite material is characterized by excellent strength values
with a high corrosion resistance at low weight.
[0010] Composite material solutions composed of AA5xxx aluminium
alloys with a high Mg content and outer aluminium alloy layers to
protect against corrosion, however, have the disadvantages that
manufacture is complex and additionally at joining points where the
aluminium composite material joins to other parts, for example at
cutting edges, drill-holes and breakouts, there is furthermore an
increased danger of corrosion.
SUMMARY OF THE INVENTION
[0011] The present invention is therefore concerned with
single-layer aluminium materials. On this basis, the object of the
invention is to provide a single-layer aluminium alloy strip,
having sufficient resistance to intercrystalline corrosion but
nevertheless having good formability, so that large-area,
deep-drawn parts, such as interior parts of motor vehicles doors,
with sufficient strength can be provided. Furthermore, a method
will be indicated with which single-layer aluminium alloy strips
can be produced. Finally, components produced from the aluminium
alloy strips according to the invention will be indicated.
[0012] According to a first teaching of the present invention, the
object indicated is achieved by a cold-rolled aluminium alloy strip
composed of an AlMg aluminium alloy, wherein the aluminium alloy
has the following alloying elements: [0013] Si.ltoreq.0.2 wt. %.
[0014] Fe.ltoreq.0.35 wt. %, [0015] Cu.ltoreq.0.15 wt. %,
0.2 wt. %.ltoreq.Mn.ltoreq.0.35 wt. %,
4.1 wt. %.ltoreq.Mg.ltoreq.4.5 wt. %,
[0015] [0016] Cr.ltoreq.0.1 wt. %, [0017] Zn.ltoreq.0.25 wt. %,
[0018] Ti.ltoreq.0.1 wt. %, the remainder being Al and inevitable
impurities, amounting to a maximum of 0.05 wt. % individually and a
maximum of 0.15 wt. % in total, wherein the aluminium alloy strip
has a recrystallized microstructure, the average grain size of the
structure ranges from 15 .mu.m to 30 .mu.m, preferably from 15
.mu.m to 25 .mu.m and the final soft annealing of the aluminium
alloy strip is carried out in a continuous furnace.
[0019] It has been found that within the specification of the
AA5182-type aluminium alloy, there is a specific, narrow, alloying
range which offers sufficient resistance to intercrystalline
corrosion and at the same time, by taking into account certain
constraints, such as for example the average grain size and the
type of final soft annealing, results in an exceptional forming
behaviour. In particular, the combination of the average grain size
with the claimed alloying elements of the aluminium alloy of the
aluminium alloy strip means that degrees of formability can be
achieved allowing the production of large-area design, deep-drawn
sheet aluminium products with sufficient strength. In particular it
has been found that the use of a continuous furnace rather than the
normal coil annealing performed in a chamber furnace provides a
further significant increase in formability.
[0020] According to a first configuration of the aluminium alloy
strip, the aluminium alloy also has one or more of the following
restrictions to the contents of alloying elements:
0.03 wt. % Si.ltoreq.0.10 wt. %,
[0021] Cu.ltoreq.0.1% preferably 0.04%.ltoreq.Cu.ltoreq.0.08%,
[0022] Cr.ltoreq.0.05 wt. %, [0023] Zn.ltoreq.0.05 wt. %,
0.01 wt. %.ltoreq.Ti.ltoreq.0.05 wt. %
[0024] Restricting the alloying content for copper to a maximum of
0.1 wt. % leads to an improvement in the corrosion resistance of
the aluminium alloy strip. A Cu content of 0.04 wt. % to 0.08 wt. %
ensures that the copper contributes to an increase in strength, but
that nevertheless the corrosion resistance is not reduced too
sharply. Silicon, chromium, zinc and titanium contents higher than
the values indicated lead to a worsening of the formability of the
aluminium alloy. The amount of silicon present in the alloy of 0.03
to 0.1 wt. %, in combination with the iron and manganese components
in the stated quantities, in particular leads to relatively evenly
distributed, compact particles of the quaternary
.alpha.-Al(Fe,Mn)Si-phase, increasing the strength of the aluminium
alloy, without negatively influencing other properties such as the
formability or corrosion behaviour.
[0025] Titanium is normally added during continuous casting of the
aluminium alloy as a grain refiner, for example in the form of
titanium boride wire or rods. Therefore in a further embodiment the
aluminium alloy has a Ti content of at least 0.01 wt. %.
[0026] A further improvement in the corrosion behaviour and the
formability of the aluminium alloy strip can be achieved by the
aluminium alloy also having one or more of the following
restrictions to the contents of alloying elements: [0027]
Cr.ltoreq.0.02 wt. %, [0028] Zn.ltoreq.0.02 wt. %
[0029] It has been found that chromium in contents below the
contamination threshold of 0.05 wt. % significantly influences the
formability of the aluminium alloy strip and therefore should be
contained in the smallest possible proportions in the aluminium
alloy of the aluminium alloy strip according to the invention. The
zinc content is set at below the contamination threshold of 0.05
wt. %, in order not to impair the general corrosion behaviour of
the aluminium alloy strip.
[0030] It has furthermore been found that iron within the values
permitted according to the AA5182-type aluminium alloy in
conjunction with silicon and manganese contents as described above
has an effect on the formability. In combination with silicon and
manganese, iron contributes to the thermal stability of the
aluminium alloy strip, so that preferably the Fe-content of the
aluminium alloy strip according to a next configuration is 0.1 wt.
% to 0.25 wt. % or 0.10 wt. % to 0.20 wt. %.
[0031] The same also applies to the Mn content of a further
configuration of the aluminium alloy strip, which should preferably
be limited to 0.20 wt. % to 0.30 wt. %, in order to achieve optimum
formability of the aluminium alloy strip.
[0032] An especially good compromise between the provision of high
strength properties, good corrosion resistance to intercrystalline
corrosion and improved forming properties can be achieved according
to a further configuration of the aluminium alloy strip with an Mg
content of 4.2 wt. % to 4.4 wt. %.
[0033] In order to provide the strength properties necessary for
the areas of application, the aluminium alloy strip according to a
next embodiment has a thickness of 0.5 mm to 4 mm. The thickness is
preferably 1 mm to 2.5 mm, since most of the areas of application
of the aluminium alloy strip fall within this range.
[0034] Finally, in the automotive sector the aluminium alloy strip
according to the invention allows areas of application wherein the
aluminium alloy strip in the soft state has a yield point
R.sub.p0.2 of at least 110 MPa and a tensile strength R.sub.m of at
least 255 MPa. It has been found that aluminium alloy strips with
such yield points and tensile strengths especially are particularly
well-suited for use in the automotive sector.
[0035] According to a second teaching of the present invention the
object shown above is achieved by a method for producing an
aluminium alloy strip according to the embodiments described above,
wherein the method comprises the following process steps: [0036]
casting a rolling ingot preferably in the DC continuous casting
process; [0037] homogenisation of the rolling ingot at 480.degree.
C. to 550.degree. C. for at least 0.5 hours; [0038] hot rolling of
the rolling ingot at a temperature of 280.degree. C. to 500.degree.
C.; [0039] cold rolling of the aluminium alloy strip to the final
thickness with a degree of rolling of 40% to 70% or 50% to 60%; and
[0040] soft annealing of the finished rolled aluminium alloy strip
at 300.degree. C. to 500.degree. C. in a continuous furnace.
[0041] It has been found that with the indicated parameters in
conjunction with the stated aluminium alloying components an
aluminium alloy strip with average grain sizes of 15 .mu.m-30 .mu.m
can be produced, having sufficient resistance to intercrystalline
corrosion, providing sufficient strength properties and also having
very good forming properties, so that large-area, deep-drawn sheet
metal parts can be produced. Homogenisation of the rolling ingot
ensures a homogenous structure and a homogenous distribution of the
alloying elements in the hot rolling ingots to be rolled. The hot
rolling at temperatures of 280.degree. C.-500.degree. C. allows
recrystallization throughout during hot rolling, wherein the hot
rolling typically is performed up to a thickness of 2.8 mm-8 mm.
The final cold-rolling step is restricted to a degree of rolling of
40% to 70% or 50% to 60%, in both cases in order to ensure
recrystallization throughout the aluminium alloy strip during soft
annealing. The higher the degree of rolling of the aluminium alloy
strip, the lower the average grain sizes become, wherein it has
been found that above a 70% degree of rolling in the final soft
annealing an average grain size can result that is too low. At a
degree of rolling below 40% during soft annealing the average grain
sizes are on the other hand too large, so that despite the
resistance to intercrystalline corrosion increasing, the
formability is nevertheless reduced. Soft annealing of the
finish-rolled aluminium alloy strip takes place in a continuous
furnace, which will normally have a heat-up rate of 1-10.degree.
C./second and so unlike a chamber furnace, in which an entire coil
is heated, because of the rapid heating will have a marked effect
on the later properties of the structure of the aluminium alloy
strip. In particular, it has been possible to establish that during
soft annealing in the continuous furnace an improved formability of
the strip compared to variants annealed in the chamber furnace is
achieved.
[0042] Alternatively, according to a further embodiment of the
method, the aluminium alloy strip can also be produced with an
intermediate annealing. According to this alternative variant after
hot rolling alternatively the following process steps are
performed: [0043] cold rolling of the hot-rolled aluminium alloy
strip to an intermediate thickness which is determined in such a
way that the final degree of cold rolling to the final thickness is
40% to 70% or 50% to 60%; [0044] intermediate annealing of the
aluminium alloy strip at 300.degree. C. to 500.degree. C.; [0045]
cold rolling of the aluminium alloy strip to the final thickness
with a degree of rolling of 40% to 70% or 50% to 60%; [0046] soft
annealing of the finish-rolled aluminium alloy strip at 300.degree.
C. to 500.degree. C. in a continuous furnace.
[0047] The intermediate annealing of the aluminium alloy strip can
take place both in the chamber furnace and in the continuous
furnace. An effect on formability could not be determined. The
decisive factors here are the degree of rolling achieved in cold
rolling to the final thickness and if the soft annealing of the
strip takes place in the continuous furnace. This determines the
formability and corrosion resistance in conjunction with the
alloying composition, irrespective of the type of intermediate
annealing.
[0048] In order to prevent a further change in the microstructural
state in the coiled condition following soft annealing, the
aluminium alloy strip according to a further configuration of the
method is cooled after soft annealing to a maximum temperature of
100.degree. C., preferably a maximum of 70.degree. C. and then
coiled.
[0049] As already stated above, the intermediate annealing can be
carried out in a further configuration of the method in a batch
furnace or in a continuous furnace.
[0050] If the aluminium alloy strip is cold-rolled to a final
thickness of 0.5 mm-4 mm, preferably to a final thickness of 1
mm-2.5 mm, this provides the typical areas of application, in
particular automotive construction, with sheet metal with very good
formability, and which can be deep-drawn with large surface areas
and at the same time provide high strength properties together with
sufficient corrosion resistance to intercrystalline corrosion.
[0051] The soft annealing is preferably performed in the continuous
furnace at a metal temperature of 350.degree. C.-550.degree. C.,
preferably at 400.degree. C.-450.degree. C. for 10 seconds to 5
minutes, preferably 20 seconds to 1 minute. This allows the cold
rolled strip to recrystallize sufficiently thoroughly and the
corresponding properties with regard to the very good formability
and the average grain size to be achieved reliably and
economically.
[0052] Finally, the object indicated above is achieved by a
component for a motor vehicle, composed of the aluminium alloy
strip according to the invention. The components are characterised
in that, as already stated, they can be deep-drawn with a large
surface area and therefore for example large-area components for
automotive construction can be provided. Furthermore, because of
the strength properties provided these also have the necessary
stiffness and the corrosion resistance required for use in
automotive construction.
[0053] It is conceivable, for example, for the component according
to a further configuration to be a motor vehicle body part or body
accessory, which apart from being subject to high strength
requirements is also heat-stressed. Preferably, the body-in-white
parts such as an internal door part or an internal tailgate part,
are made from the aluminium alloy strip according to the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] The invention is explained in more detail below with the
help of the drawing. The drawing shows as follows:
[0055] FIG. 1 shows a schematic flow diagram of an embodiment of
the production method of the aluminium alloy strip.
[0056] FIG. 2a shows a top view of the specimen geometry for the
plane-strain cupping test according to DIN EN ISO 12004.
[0057] FIG. 2b shows a side-view of the schematic test set-up for
the plane-strain cupping test according to DIN EN ISO 12004.
[0058] FIG. 3 shows a sectional view of the test setup for the SZ32
stretch drawing measurements in the Erichsen cupping test according
to DIN EN ISO 20482.
[0059] FIG. 4 shows a typical embodiment of a large-area,
deep-drawn sheet metal part according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0060] FIG. 1 shows the sequence of embodiments for the production
of aluminium strips.
[0061] The flow diagram of FIG. 1 is a schematic representation of
the various process steps of the production process of the
aluminium alloy strip according to the invention.
[0062] In step 1, a rolling ingot of an AlMg aluminium alloy with
the following alloying elements is cast, for example in DC
continuous casting: [0063] Si.ltoreq.0.2 wt. %. [0064]
Fe.ltoreq.0.35 wt. %, [0065] Cu.ltoreq.0.15 wt. %,
0.2 wt. %.ltoreq.Mn.ltoreq.0.35 wt. %,
4.1 wt. %.ltoreq.Mg.ltoreq.4.5 wt. %,
[0065] [0066] Cr.ltoreq.0.1 wt. %, [0067] Zn.ltoreq.0.25 wt. %,
[0068] Ti.ltoreq.0.1 wt. %, the remainder being Al and inevitable
impurities, amounting to a maximum of 0.05 wt. % individually and a
maximum of 0.15 wt. % in total.
[0069] Then the rolling ingot in process step 2 undergoes
homogenisation, which can be performed in one or more stages.
During homogenisation, temperatures of the rolling ingot of 480 to
550.degree. C. are reached for at least 0.5 hours. In process step
3 the rolling ingot is then hot rolled, wherein typically
temperatures of 280.degree. C. to 500.degree. C. are reached. The
final thicknesses of the hot-rolled strip are for example 2.8 to 8
mm. The hot-rolled strip thickness can be selected such that after
hot rolling only a single cold rolling step 4 takes place, in which
the hot-rolled strip, with a degree of rolling of 40% to 70%,
preferably 50% to 60%, has its thickness reduced to the final
thickness.
[0070] Then the aluminium alloy strip that has been cold-rolled to
its final thickness undergoes soft annealing. According to the
invention the soft annealing is performed in a continuous furnace.
In the embodiments shown in Table 1, the second route was applied
with an intermediate annealing. For this, the hot-rolled strip
after hot rolling according to process step 3 is passed for cold
rolling 4a, in which the aluminium alloy strip is cold rolled to an
intermediate thickness, which is determined in such a way that the
final degree of cold rolling to the final thickness is 40% to 70%
or 50% to 60%. In a subsequent intermediate annealing the aluminium
alloy strip preferably recrystallizes throughout. The intermediate
annealing was carried out in the embodiments either in the
continuous furnace at 400.degree. C. to 450.degree. C. or in the
chamber furnace at 330.degree. C. to 380.degree. C.
[0071] The intermediate annealing is shown in FIG. 1 by process
step 4b. In process step 4c according to FIG. 1 the
intermediately-annealed aluminium alloy strip is finally passed for
cold rolling to the final thickness, wherein the degree of rolling
in process step 4c is between 40% and 70%, preferably between 50%
and 60%. Then the aluminium alloy strip is again converted to the
soft state by soft annealing, wherein according to the invention
the soft annealing is carried out in the continuous furnace at
400.degree. C. to 450.degree. C. The annealings of the comparative
examples in table 4 were carried out in the chamber furnace (KO) at
330.degree. C. to 380.degree. C. During the various trials, apart
from the different aluminium alloys various degrees of rolling
after the intermediate annealing were set. The values for the
degree of rolling after the intermediate annealing are likewise
shown in Tables 1 and 4. The average grain size of the
soft-annealed aluminium alloy strip was also measured. To this end,
longitudinal sections were anodised according to the Barker method
and then measured under the microscope according to ASTM E1382 and
the average grain size determined from the average grain
diameter.
[0072] The aluminium alloy strips manufactured in this way had
their mechanical characteristics determined, in particular the
yield point R.sub.p0.2, the tensile strength R.sub.m, the uniform
elongation Ag and the elongation at rupture A.sub.80mm, Tables 2,
5. Apart from the mechanical characteristics of the aluminium alloy
strips measured according to EN 10002-1 or ISO 6892 in addition the
average grain sizes according to ASTM E1382 in .mu.m are given.
Furthermore, the corrosion resistance to intercrystalline corrosion
in accordance with ASTM G67 was measured, and in fact without
additional heat treatment in the initial state (at 0 h). In order
to simulate use in a motor vehicle, the aluminium alloy strips,
prior to the corrosion test, furthermore underwent various heat
treatments. A first heat treatment consisted of storage of the
aluminium strips for 20 minutes at 185.degree. C., in order to
model the CDP cycle.
[0073] In a further series of measurements the aluminium alloy
strips were also stored for 200 hours or 500 hours at 80.degree. C.
and then underwent the corrosion test. Since the forming of
aluminium alloy strips or sheets can also affect the corrosion
resistance, the aluminium alloy strips were stretched in a further
trial by approximately 15%, and underwent heat treatment or storage
at raised temperature and then a test for intercrystalline
corrosion according to ASTM G67, during which the mass loss was
measured.
[0074] Table 1 gives the alloying contents of a total of four
different aluminium alloys, which fall within the specification of
the AA5182-type aluminium alloy. The reference alloy is constituted
by the material used to date and is shown in comparison to variants
1, 2 and 3. Table 1 also contains details of the type of final
annealing, the final degree of rolling and the measured average
grain size (grain size diameter) in .mu.m. Variants 1 and 2 differ
here merely in terms of final degree of rolling, which leads to the
formation of a different grain size. Thus variant 2 differs from
variant 1 irrespective of the almost identical alloying elements
essentially in terms of the final degree of rolling of 57% at
identical continuous furnace conditions. The result was that
variant 2 had an average grain size of 18 .mu.m compared to 33
.mu.m for variant 1. The strips in Table 1 were heated in the
continuous furnace for 20 seconds to 1 minute to a temperature of
400.degree. C. to 450.degree. C., then cooled and coiled at less
than 100.degree. C. The specimens taken were then, as indicated in
Table 2, measured according to the corresponding DIN EN ISO
standards.
[0075] It is clear from Table 2 that variant 1 in terms of the
yield point does not reliably reach the value of 110 MPa and in the
diagonal measurement, identified by the D symbol, has a value of
less than 110 MPa. The measurement in the direction of rolling L
and transversally to the direction of rolling Q showed, however,
that variant 1 actually reached a yield point R.sub.p0.2 of 110
MPa. The reference and variants 2 and 3 were significantly above
this lower limit for the yield point. The embodiment according to
the invention in variant 2 reliably achieved the yield point value
of 110 M Pa in all tensile directions. It is clear to see that
variant 3 with the highest Mg content of 4.95 wt. % achieves the
highest yield point and tensile strength figures. It can also be
seen that the different degree of rolling between variants 1 and 2
not only markedly influences the grain size, but in particular
raises the yield point to a value of significantly higher than 110
MPa.
[0076] In particular the alloy according to the invention in
variant 2 has a lower anisotropy compared to the reference,
reflected in lower values of the planar anisotropy Ar. Here, the
planar anisotropy .DELTA.r is defined as 1/2*(r.sub.L+r.sub.Q-2
r.sub.D), wherein r.sub.L, r.sub.Q and r.sub.D correspond to the
r-values in the longitudinal, traversal and/or diagonal direction.
Here, the average r-value F, calculated from
1/4*(r.sub.L+r.sub.Q+2r.sub.D), does not differ significantly from
that of the reference material.
[0077] Table 3 gives the measured values recorded in relation to
the resistance to intercrystalline corrosion. It can be seen that
variant 2 according to the invention in terms of the measured
values of the reference, in particular in respect of the long-time
stressing, has comparable values both in the stretched state and in
the unstretched state. Here variant 2 and the reference are almost
identical. Variant 3, which despite the having the highest yield
point values and tensile strength values, nevertheless in the
corrosion test demonstrated that an excessive Mg content results in
an excessive mass loss, in particular in the long-time tests, which
apart from a short temperature cycle of 20 minutes at 185.degree.
C. also include long-time stressing of 200 hours at 80.degree.
C.
[0078] With regard to the measured values in Table 3 regarding the
formability it can be seen that in particular variant 2 was
superior in terms of the stretch forming properties in the SZ32
cupping test and in the plane-strain cupping test to the reference
alloy. The clear improvement in forming behaviour of the aluminium
alloy strip according to variant 2 compared to the reference
aluminium alloy strip shows that even with a reduced Mg content
comparable yield point values and tensile strength vales could be
achieved with the reference alloy, without major losses in
resistance to intercrystalline corrosion. This was demonstrated in
particular by the mass loss measurement performed according to ASTM
G67 in the NAML test. Significantly, with variant 2 an improvement
in the deep drawing behaviour in the Erichsen cupping test by 7%
and in the plane-strain cupping tests by approximately 10% was
found, demonstrating the additional forming potential of the
aluminium alloy strip according to the invention. This additional
forming potential can be used to produce deep-drawn, large-area
sheet metal parts, for example internal door parts of a motor
car.
[0079] A brief explanation of the test setup for the "SZ32 cupping"
test according to DIN EN ISO 20482 and the plane-strain cupping
test with Nakajima geometry according to DIN EN ISO 12004 is
provided below.
[0080] FIG. 2a shows the geometry of test piece 1. From a circular
sheet metal cut-out the tapered test piece 1 is cut such that the
web 4 has a width of 100 mm and the radii 2 at the waisted parts
are 20 mm. Dimension 3, which is 100 mm, represents the diameter of
the punch. FIG. 2b shows the test piece 1 clamped between two
holders 5, 6. The test piece 1, which was placed on a mount 8 and
via the holders 5, 6 pushed against the support, is pulled with a
punch 7, having a semi-circular tip with a radius of 100 mm, in the
direction of the arrow. The holders also have entry radii of 5 or
10 mm on their side facing the mount 8. The force with which the
cupping test is performed is measured during the forming and a
sudden drop in load, signalling the formation of a crack, leads to
the measurement of the corresponding punching depth.
[0081] The "SZ32 cupping" test according to Erichsen has a similar
setup, but no wasted test pieces are used, however. Here, a test
piece 9 is simply held between a holder 10 and a support 11 and
drawn with a punch 12 until likewise a drop is measured in the load
of the drawing force. Then, again, the corresponding position of
the punch is measured. The opening of the dies in FIG. 3 was 35.4
mm and the punch diameter 32 mm, meaning that the punch radius was
16 mm. A Teflon deep-drawing film was also used to reduce friction
in the SZ32 deep-drawing test.
[0082] In Tables 4 and 5, further embodiments and comparative
examples were created and measured according to their mechanical
characteristics and their resistance to intercrystalline corrosion.
It can be seen that the combination of using the continuous furnace
and a specifically selected grain size of 15 .mu.m-30 .mu.m,
preferably of 15 .mu.m-25 .mu.m results in a good compromise
between corrosion resistance and mechanical measured values. Thus,
for example, the embodiments according to the invention Nos. 3, 4,
7 and 11 have a satisfactory resistance to intercrystalline
corrosion and also exhibit the mechanical measured values
R.sub.p0.2 and R.sub.m necessary for use in the automotive sector,
so that these are ideal for the provision of large-area, deep-drawn
components.
[0083] FIG. 4 shows as an example a corresponding body-in-white
part in the form of an interior part of a door, which by using the
aluminium alloy strip of the present invention can be produced from
a single deep-drawn sheet. Here, the sheet thickness is preferably
1.0-2.5 mm. Furthermore, other parts of a motor vehicle are
conceivable in sheet metal shell construction, such as the interior
parts of tailgates, bonnets, and components in the vehicle
structure, which are subject to stringent requirements in terms of
formability and intercrystalline corrosion.
TABLE-US-00001 TABLE 1 Final degree Material [wt. %] Final of
rolling (cold Grain Si Fe Cu Mn Mg Cr Zn Ti Impurities annealing
rolling) size [.mu.m] min. 0.20 4.0 Individually max. AA 5182 0.20
0.35 0.15 0.50 5.0 0.10 0.25 0.10 0.05 in total max. max. 0.15
Reference 0.07 0.24 0.036 0.3 4.57 0.005 0.007 0.016 0.05 BDLO 46
15 0.15 Var. 1 0.06 0.16 0.004 0.27 4.37 0.008 0.002 0.013 0.05
BDLO 21 33 0.15 Var. 2 0.06 0.16 0.004 0.27 4.38 0.008 0.003 0.013
0.05 BDLO 57 18 0.15 Var. 3 0.05 0.17 0.023 0.26 4.95 0.008 0.003
0.026 0.05 BDLO 57 17 0.15
TABLE-US-00002 TABLE 2 Test R.sub.p0.2 Rm Ag Ag (elong) A.sub.80 mm
A.sub.80 mm (Hand) Z-value piece Pos. N/mm.sup.2 N/mm.sup.2 % % % %
% n-value r-value .DELTA.r r Ref. L 137 284 21.3 20.7 24.5 25.2 69
0.316 0.827 0.197 0.754 T 133 276 22.2 21.4 25.2 25.8 72 0.306
0.704 D 133 277 21.9 21.6 25.5 26.3 71 0.305 0.779 Var. 1 L 110 262
21.2 21.9 25.9 26.4 71 0.335 0.668 -0.363 0.779 T 107 256 24.7 23.0
27.7 28.7 72 0.338 0.870 D 111 259 22.0 21.2 24.6 25.7 65 0.332
0.708 Var. 2 L 128 266 23.2 22.7 26.8 27.7 67 0.332 0.724 0.035
0.693 T 127 261 23.1 22.2 26.2 27.0 67 0.332 0.685 D 128 262 23.9
22.5 26.5 27.6 66 0.333 0.681 Var. 3 L 141 290 24.1 23.5 28.4 29.1
70 0.335 0.697 -0.12 0.710 T 140 286 22.6 23.4 27.0 27.8 68 0.336
0.740 D 141 286 22.6 23.3 27.1 27.7 65 0.335 0.663 DIN EN ISO
6892-1:2009 DIN EN ISO DIN EN ISO 10113:2009 10275:2009
TABLE-US-00003 TABLE 3 IK-mass losses Formability Not 20 min
185.degree. C. 15% stretched 15% stretched SZ32 Plane-strain
thermally 20 min. plus 200 h 17 h 20 min. 20 min. 185.degree. C.
plus cupping cupping Variant treated 185.degree. C. 80.degree. C.
130.degree. C. 185.degree. C. 200 h 80.degree. C. [mm] [mm] Limit
2.0 4.0 35.0 50.0 15.0 45.0 Reference 1.2 2.1 29.8 48.8 10.4 42.1
14.2 27.9 Var. 1 (comp.) 1.2 1.7 10.4 21.3 4.4 12.9 14.5 30.3 Var.
2 (inv.) 1.2 2.4 33.7 42.2 13.5 40.1 14.6 30.7 Var. 3 (comp.) 1.3
5.3 41.7 55.0 30.4 53.5 14.6 31.6
TABLE-US-00004 TABLE 4 Grain Degree of Final size No Alloy rolling
[%] annealing [.mu.m] Si Fe Cu Mn Mg Cr Zn Ti 1 III 46 KO 16 0.07
0.24 0.040 0.30 4.50 0.005 0.007 0.016 3 II 57 BOLO 18 0.06 0.16
0.004 0.27 4.35 0.008 0.002 0.013 4 I 45 BOLO 18 0.03 0.13 0.002
0.25 4.15 0.001 0.004 0.021 6 I 45 KO 21 0.03 0.13 0.002 0.25 4.15
0.001 0.004 0.021 7 III 30 BOLO 22 0.07 0.24 0.040 0.30 4.50 0.005
0.007 0.016 11 III 25 BOLO 27 0.07 0.24 0.040 0.30 4.50 0.005 0.007
0.016 13 I 32 BOLO 29 0.03 0.13 0.002 0.25 4.15 0.001 0.004 0.021
15 III 30 KO 30 0.07 0.24 0.040 0.30 4.50 0.005 0.007 0.016 16 I 25
BOLO 31 0.03 0.13 0.002 0.25 4.15 0.001 0.004 0.021 18 II 21 BOLO
33 0.06 0.16 0.004 0.27 4.35 0.008 0.002 0.013 20 I 20 BOLO 34 0.03
0.13 0.002 0.25 4.15 0.001 0.004 0.021
TABLE-US-00005 TABLE 5 IK-mass loss, Mechanical IK-mass loss,
unstretched** 15% stretched** characteristics, 20 min. 20 Min.
185.degree. C. + 20 Min. 185.degree. C. + 20 Min. 20 Min.
185.degree. C. + soft state No Start (O h) 185.degree. C. 200 h
80.degree. C. 500 h/80.degree. C. 185.degree. C. 200 h 80.degree.
C. R.sub.p0.2 Rm Ag A.sub.80 mm Result 1 III 15.4 16.6 25.7 26.9
18.8 33.6 135 279 20.7 25.2 Comparison 3 II 1.2 2.4 33.7 36.7 13.5
40.1 128 262 23.9 26.5 Invention 4 I 1.3 1.9 17.8 22.2 1.6 20.1 117
258 22.8 25.3 Invention 6 I 8.2 10.8 18.6 22.1 9.6 20.7 106 250
23.8 26.7 Comparison 7 III 1.1 1.7 18.0 24.5 3.3 25.1 119 276 20.3
24.9 Invention 11 III 1.1 1.6 14.3 17.7 2.8 19.8 116 275 20.2 24.4
Invention 13 I 1.1 1.2 13.3 16.7 2.1 17.4 104 251 22.2 24.8
Comparison 15 III 2.8 3.0 7.9 10.9 6.4 18.0 125 281 19.5 23.6
Comparison 16 I 1.1 1.3 10.8 13.1 1.9 14.2 103 252 21.6 26.1
Comparison 18 II 1.2 1.7 10.4 12.5 4.4 12.9 109 259 22.0 24.6
Comparison 20 I 1.1 1.2 8.3 11.1 1.7 12.4 101 251 20.8 25.1
Comparison
* * * * *