Note: Descriptions are shown in the official language in which they were submitted.
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Method for Producing a Sheet or Strip from an Aluminum Alloy and a Sheet,
Strip or
Molded Part Produced Thereby
Technical Field
The invention relates to a method for producing a sheet or strip from an
aluminum
alloy and to a sheet, strip, or molded part produced thereby.
Prior Art
In order to adjust the strength and formability or ductility, more
particularly deep-draw-
ing formability in a 5xxx-aluminum alloy or aluminum alloy with an Al-Mg
basis, it is
known to provide the sheet or strip or more precisely the metal structure of
the alumi-
num alloy sheet or strip with a finer average crystal grain size, namely of 60
pm or,
according to EP0507411A1, of less than 50 pm. A finer crystal grain size of 60
pm or
less of this kind disadvantageously involves the risk of the occurrence of
type A
stretcher strain marks, namely LOders bands, on the surface of the plastically
de-
formed sheet or strip. Al-Mg-Mn alloys thus have only a limited suitability,
for example,
for outer shell components in vehicle body construction, which require ssf
quality
(stretcher strain free) or what is also known by its German abbreviation ffa
quality (ffa
= flief3figurenarme [low stretcher strain]), i.e. a freedom from or reduction
in type A
stretcher strain marks.
Disclosure of the Invention
The object of the invention, therefore, is to create a method for producing a
sheet or
strip from an aluminum alloy having Mg as one of the main alloying elements
and to
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create a sheet or strip of the type described above that has a comparatively
high
strength and formability and is of ssf quality or ffa quality The method
should also be
easy to use and reproducible.
The invention attains the stated object with regard to the method by means of
the
features of claim 1.
According to the invention, the sheet or strip in the method is composed of an
alumi-
num alloy, namely with the composition of from 2.0 to 5.5 wt% magnesium (Mg),
from
0.2 to 1.2 wt% manganese (Mn), optionally up to 0.45 wt% silicon (Si),
optionally up
to 0.55 wt% iron (Fe), optionally up to 0.35 wt% chromium (Cr), optionally up
to 0.2
wt% titanium (Ti), optionally up to 0.2 wt% silver (Ag), optionally up to 4 0
wt% zinc
(Zn), optionally up to 0.8 wt% copper (Cu), optionally up to 0.8 wt% zirconium
(Zr),
optionally up to 0.3 wt% niobium (Nb), optionally up to 0.25 wt% tantalum
(Ta), op-
tionally up to 0.05 wt% vanadium (V), and the remainder comprised of aluminum
and
inevitable production-related impurities, with up to at most 0.05 wt% of each
and all
together totaling at most 0.15 wt%.
The method has the following method steps
= casting of a rolling slab,
= hot rolling of the rolling slab into a hot-rolled sheet or strip;
= cold rolling of the hot-rolled sheet or strip to a final thickness;
= heat treatment of the sheet or strip that has been cold-rolled to the
final thick-
ness, including recrystallization annealing with subsequent accelerated cool-
ing;
Optionally, the method can have the following method steps:
= homogenization of the rolling slab;
= intermediate annealing of the sheet or strip in the cold rolling of the
hot-rolled
sheet or strip to a final thickness
= stabilization of the sheet or strip, which has undergone accelerated
cooling, in
the heat treatment;
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According to the invention, before the heat treatment, the sheet or strip that
has been
cold-rolled to the final thickness has at least one, more particularly
primary, interme-
tallic phase with first particles having an average particle size of 5 pm to
10 pm (meas-
ured using the ASTM E112 linear intercept method) ¨ this by means of the
method
steps preceding the heat treatment For example in that at least the casting
and the
cold rolling, more particularly after the intermediate annealing, are adjusted
relative
to each other in such a way that the sheet or strip has at least one
intermetallic phase
with first particles having an average particle size of 5 pm to 10 pm. These
first and
thus primary particles are relatively coarse. These particles of the primary
phase also
have a high stability ¨ even relative to a subsequent recrystallization
annealing or
relative to a subsequent heat treatment
With such a composition and microstructure, it is possible to produce a sheet
or strip
with a high strength and formability and of an ssf quality or ffa quality ¨
namely if after
the heat treatment, this sheet or strip that has been cold-rolled to the final
thickness
also has an average crystal grain size D of 5 60 pm (measured using the ASTM
E112
linear intercept method) and the average crystal grain size D in mm and the
number
A of first particles per mm2 in the aluminum alloy satisfy the condition -V75
* A > 1.8 ¨
for example in that the recrystallization annealing of the heat treatment is
performed
in such a way. Because of the different thermal expansion coefficients, an
accelerated
cooling following the recrystallization annealing causes internal stresses in
the struc-
ture to occur, namely between the aluminum matrix and the first particles of
the inter-
metallic phase, which ensures that there is a sufficient number of free
dislocations at
the first particles of the primary intermetallic phase As a result, LCiders
band disloca-
tions are not necessarily or inevitably produced during the forming of the
sheet or
strip. This is also true in the event of unfavorable deformations or complex
geometries
in the formed sheet or strip.
This method is also easy to use and has an extremely high reproducibility, for
example
due to a water cooling for the accelerated cooling, for producing a sheet or
strip in ssf
quality or ffa quality.
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The number of dislocations in the sheet or strip can be further increased in
the method
if al * A is > 2. More particularly, if NIT * A is > 2.5, then the sheet or
strip can satisfy
comparatively high quality requirements without having to also fear the
occurrence of
stretcher strain marks such as type A LOders bands on the surface of the
formed
sheet or strip, even in the case of comparatively complex geometries or
unfavorable
plastic deformations.
The method can be further improved in terms of reproducibility if in the heat
treatment,
the recrystallization annealing takes place by means of holding at a
temperature of
300 C (degrees Celsius) or more, more particularly up to 600 C. This can
improve
even more if the recrystallization annealing takes place at 450 C to 550 C. In
addition,
this annealing temperature can be enough to pre-stress the structure by means
of an
accelerated cooling sufficiently to produce the dislocations at the first
particles, which
subsequently make LOders band dislocations unnecessary.
This is more particularly the case if the heated sheet is cooled in an
accelerated man-
ner at a cooling rate of at least 10 K/s (Kelvin per second), more
particularly at least
20 K/s or at least 50 K/s, wherein this accelerated cooling can more
particularly be
carried out to below 180 C, more particularly to room temperature
It is possible to ensure that first particles are embodied as large enough in
the average
particle size if the rolling slab is solidified by maintaining a cooling rate
(or cooling
speed) of < 2.5 C/s This can be further improved if the cooling rate is < 2
C/s or <
1 C/s or < 0.75 C/s. In addition, this can counteract a possible reduction in
the aver-
age particle size by means of subsequent method steps, for example by means of
the
cold rolling, in order to ensure an average particle size of 5 pm to 10 pm
before the
heat treatment.
In addition, the optional homogenization can take place by means of holding at
450 C
to 550 C for at least 0.5 h.
The hot rolling can take place at 280 C to 550 C.
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The cold rolling to the final thickness can be carried out with a degree of
rolling reduc-
tion of from 10% to 65%, more particularly from 20% to 50%. More particularly,
it can
be advantageous if the cold rolling after the intermediate annealing is
carried out with
a degree of rolling reduction of from 10% to 65%, more particularly from 20%
to 50%,
in order to improve the reproducibility of the average particle size of 5 pm
to 10 pm
The optional intermediate annealing can take place by means of holding at 300
C to
500 C.
The optional stabilization can take place by means of holding at 80 C to 120 C
for at
least 0.5 h.
An average particle size of 5 pm to 10 pm before the heat treatment can more
partic-
ularly be assured if the product of the degree of rolling reduction in % after
the inter-
mediate annealing and the cooling rate in C/s satisfies the condition 10 <
degree of rolling reduction * cooling rate < 50, more
particularly 20 <
degree of rolling reduction * cooling rate < 45.
If the intermetallic phase has an Al-Mn basis, then it is possible to produce
the dislo-
cations in the aluminum alloy that enable stretcher strain marks to be avoided
in a
particularly reliable way. Preferably, the intermetallic phase is of the
A113(Mn,Fe)6 type
or of the Al15FeMn3Si2 type or of the Al12Mn type or of the AlsMn type. These
first
particles of the primary phase are a particularly stable phase. It is also
conceivable
for the primary phase to constitute the intermetallic phase in order, in
combination
with the heat treatment of the sheet or strip, to produce a sufficient number
of dislo-
cations.
The method can achieve high strength and formability while avoiding orange
peel and
stretcher strain marks if the aluminum alloy (with an Al-Mg-Mn basis) has from
4.0 to
5.0 wt% magnesium (Mg) and/or from 0 2 to 0.5 wt% manganese (Mn)
Particularly high strength can be achieved if the aluminum alloy also has from
2.0 to
4.0 wt% zinc (Zn) (Al-Mg-Zn basis). Optionally, this aluminum alloy can also
has up
to 0.8 wt% copper (Cu)
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The invention attains the stated object with regard to the sheet or strip by
means of
the features of claim 8.
If the sheet or strip is composed of an aluminum alloy, namely with the alloy
contents
from 2.0 to 5 5 wt% magnesium (Mg), from 0.2 to 1.2 wt% manganese (Mn),
optionally
up to 0.45 wt% silicon (Si), optionally up to 0.55 wt% iron (Fe), optionally
up to 0.35
wt% chromium (Cr), optionally up to 0.2 wt% titanium (Ti), optionally up to
0.2 wt%
silver (Ag), optionally up to 4.0 wt% zinc (Zn), optionally up to 0.8 wt%
copper (Cu),
optionally up to 0.8 wt% zirconium (Zr), optionally up to 0.3 wt% niobium
(Nb), option-
ally up to 0.25 wt% tantalum (Ta), and the remainder comprised of aluminum and
inevitable production-related impurities, with up to at most 0.05 wt% of each
and all
together totaling at most 0.15 wt%, then this provides an alloy composition
with which
it is possible to achieve a sufficiently high strength and
formability/ductility ¨ of the
kind that is required, for example, for outer shell components in vehicle body
con-
struction.
Freedom from orange peel and stretcher strain marks, among other things LOders
bands, in the formed sheet or strip can be achieved if this sheet or strip has
an aver-
age crystal grain size D of 5 60 pm (measured using the ASTM E112 linear
intercept
method) and at least one, more particularly primary, intermetallic phase with
first par-
ticles having an average particle size of 5 pm to 10 pm (measured using the
ASTM
E112 linear intercept method) and the average crystal grain size D in mm and
the
number A of first particles per mm2 in the aluminum alloy satisfy the
condition V15 *
A > 1.8. It is also necessary for the sheet or strip to have been subjected to
a heat
treatment, including recrystallization annealing with subsequent accelerated
cooling
and optionally a stabilization of the sheet or strip that has undergone
accelerated
cooling. As a result, dislocations are produced at the first particles in the
structure of
the sheet or strip. These first and thus primary particles are also stable
relative to the
heat treatment that is used to further adjust the microstructure of the sheet
or strip.
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Thus the average crystal grain size D of 60 pm according to the invention
results in
the fact that the comparatively fine crystal grain of the sheet or strip
enables achieve-
ment of a high strength and formability.
The latter, however, is not impaired by the presence of stretcher strain marks
on the
surface of the formed sheet or strip since according to the invention, the
first particles
that are present in the sheet or strip have a limited average particle size of
5 pm to
pm and the average crystal grain size D in mm and the number A of first
particles
per mm2 in the aluminum alloy satisfy the condition VD * A > 1.8
To be precise, if in the method for producing the sheet or strip, a heat
treatment is
performed by means of recrystallization annealing and subsequent accelerated
cool-
ing, then based on the composition and the resulting microstructure, this can
ensure
a sufficiently high number of dislocations in the sheet or strip. This
prevents the for-
mation of LOders band dislocations even with complex geometries. According to
the
invention, this produces a sheet or strip composed of an aluminum alloy,
preferably
with an Al-Mg basis (or with Mg as one of the main alloying elements) in ssf
quality or
ffa quality, which due to its sufficient strength and formability can also
excel when
used, for example, for outer shell components in vehicle body construction.
The number of dislocations in the sheet or strip can be further increased if
VD * A is
> 2. More particularly, if -0* A is > 2.5, then the sheet or strip can satisfy
compara-
tively high quality requirements without having to also fear the occurrence of
stretcher
strain marks such as type A Luders bands on the surface of the formed sheet or
strip,
even in the case of comparatively complex geometries or unfavorable plastic
defor-
mations.
A sufficient number of dislocations in order to avoid stretcher strain marks
in the
formed sheet or strip can be achieved if the crystal structure has more than
200, more
particularly more than 400, dislocations at each first particle This can be
achieved if
the sheet or strip has been heat treated by heating and subsequent accelerated
cool-
ing in such a way that the crystal structure has more than 200, more
particularly more
than 400, dislocations at each first particle.
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Preferably, the number A of first particles is ?. 10 particles/mm2, which can
enable a
sufficient distribution of the dislocations in the sheet or strip in order to
avoid stretcher
strain marks. This is more particularly the case if the number A of first
particles is
25 particles/mm2, preferably 35 particles/mm2.
If the intermetallic phase has an Al-Mn basis, then it is possible to produce
the dislo-
cations in the aluminum alloy that enable stretcher strain marks to be avoided
in a
particularly reliable way. Preferably, the intermetallic phase is of the
A113(Mn,Fe)6 type
or of the Al15FeMn3Si2 type or of the Al12Mn type or of the AlsMn type. These
first
particles of the primary phase are a particularly stable phase. It is also
conceivable
for the primary phase to constitute the intermetallic phase in order, through
the sub-
sequent heat treatment of the sheet or strip, to achieve a sufficient number
of dislo-
cations.
The method can achieve high strength and formability while avoiding orange
peel and
stretcher strain marks if the aluminum alloy has from 4 0 to 5.0 wt% magnesium
(Mg)
and/or from 0 2 to 0.5 wt% manganese (Mn).
Particularly high strength can be achieved if the aluminum alloy also has from
2.0 to
4.0 wt% zinc (Zn) (with an Al-Mg-Zn basis). Optionally, this aluminum alloy
can also
has up to 0 8 wt% copper (Cu).
The sheet or strip according to the invention can also be particularly well-
suited for
producing a molded part, more particularly a vehicle part, preferably a
vehicle body
part, by means of sheet-metal-forming. Preferably, the sheet or strip is used
to pro-
duce a sheet bar in order to be able to perform a sheet-metal-forming process.
In general, it should be mentioned that the average crystal grain size and the
average
particle size are measured using the ASTM E112 linear intercept method
Preferably, the aluminum alloy has an Al-Mg basis.
In addition, the sheet or strip can have an average crystal grain size D of 5
50 pm,
5. 40 pm, or 5 30 pm.
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In addition, the cooling rate (or cooling speed) can be < 2 4 C/s, < 2.3 C/s,
< 2.2 C/s, < 2.1 C/s, < 2.0 C/s, < 1.9 C/s, < 1 8 C/s, < 1 7 C/s, < 1 6 C/s, <
1 5 C/s,
< 1.4 C/s, < 1.3 C/s, < 1.2 C/s, < 1.1 C/s, < 1.0 C/s, < 0.9 C/s, < 0.8 C/s, <
0.7 C/s,
or < 0 6 C/s.
In general, it should be mentioned that the strip can be cut into a slit strip
or cut into
sheets or also sheet bars can be cut out from the sheet or strip in order to
form these
semi-finished products, for example by means of sheet-metal-forming. The
forming
can be a deep-drawing, roll profiling, etc.
In general, it should be mentioned that the aluminum alloy can, for example,
be of the
EN AVV-5083 or EN AVV-5086 or EN AVV-5182 or EN AVV-5454 or EN AVV-5457 or EN
AVV-5754 type.
Ways to Implement the Invention
To demonstrate the achieved effects, cold-rolled semi-finished products,
namely thin
sheets composed of an aluminum alloy with an Al-Mg-Mn basis and thin sheets
com-
posed of and aluminum alloy with an Al-Mg-Zn-Mn basis were produced. The
follow-
ing aluminum alloys were used, which were composed of
Mg Mn Fe Si Zn
Alloy
wt% wt% wt% i wt% wt%
Cl 4.57 0.41 019 012
C2 4.71 041 0.23 0.12
C3 4.88 0.41 0 18 0.12
C4 4.74 0.44 0.24 0.12
D1 4.70 0.45 0.23 0.13 3.5
Table 1: Different aluminum alloys
and the remainder comprised of aluminum and inevitable production-related
impuri-
ties, with up to at most 0.05 wt% of each and all together totaling at most
0.15 wt%
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The production of these thin sheets was carried out with the following process
param-
eters:
Casting Hot rolling Cold rolling
Cooling Starting Degree of Intermediate
rate temperature rolling re- annealing
Heat
Sheets Alloy [ C/s] [ C] duction after
treatment
the interme-
diate an-
nealing
0.7 530 C 63% 385 C 500 C
Al Cl
2h VVQ
1 8 530 C 15% 385 C 500 C
A2 C2
2h VVQ
1 8 530 C 18% 385 C 500 C
A3 C3
2h VVQ
1.8 530 C 25% 385 C 500 C
A41 C4
2h VVQ
1.8 530 C 25% 385 C 370 C
A4.2 04
2h AC
1.8 530 C 63% 385 C 500 C
AS 04
2h VVQ
1.8 530 C 18% 385 C 500 C
A6.1 D1
2h VVQ
1 8 530 C 63% 385 C 500 C
A62 D1
2h VVQ
Table 2: Overview of the production processes
VVa Water quenching (as an example of an accelerated cooling)
AC: Cooling in stationary air
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These thin sheets were used to produce sheet bars ¨ i e sheet blanks ¨ which
were
formed, namely sheet-metal-formed, specifically deep-drawn, to produce a
vehicle
body part, namely a hood.
Grain size \ID A -\/ID. A 1 Stretcher strain
Sheets Alloy
D [pm] [mmo 5] [mm-2] [mm-15] marks
Al Cl 15 0.12 44 5.4 No
A2 02 35 0.19 12 2.24 No
A3 03 29 0.17 14 2.38 No
A4.1 04 32 018 12 214 No
A4.2 04 32 0.18 12 2.14 Yes
A5 04 10 010 12 1.2 Yes
A6 1 D1 28 0.17 14 2.34 No
A6.2 D1 10 0.1 14 1.4 Yes
Table 3. Overview of the deep-drawn thin sheets
Exemplary Embodiment 1:
An alloy of the AA5182 type (AI-Mg-Mn basis) with the chemical composition Cl
was
used to produce a thin sheet Al with a sheet thickness of 1.2 mm. The
production of
the rolling slab was solidified at a comparatively reduced cooling rate (or
cooling
speed) and the rolling steps in the hot rolling and cold rolling were carried
out in ac-
cordance with the standard scheme. The last rolling reduction pass in the cold
rolling
amounted to 63% (from 3 25 mm to 1.2 mm) and the final heat treatment was
carried
out at 500 C with subsequent water quenching. The average crystal grain size
or final
grain size of the thin sheet Al was 15 pm (measured using the ASTM E112 linear
intercept method) and in the primary intermetallic phase, there were 44 first
particles
per mm2 having an average particle size of 5 pm to 10 pm (measured using the
ASTM
E112 linear intercept method) These primary particles were also embodied as
com-
paratively coarse. In addition, with the product of the cooling rate after the
intermedi-
ate annealing and the degree of rolling reduction of 44, the condition 10 <
degree of rolling reduction * cooling rate < 50 is satisfied.
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With a .\11:)*A value of 5.4, the criterion (\ILYA > 1.8) is satisfied. A
tensile test did not
show any Leiders bands on the surface of the thin sheet Al. The intermetallic
phase
according to the invention with the first particles was therefore able to
provide a suffi-
cient number of dislocations to prevent the occurrence of LOders bands during
the
forming.
Exemplary Embodiment 2:
An alloy of the AA5182 type with the chemical composition 02 was used to
produce
a thin sheet A2 with a sheet thickness of 1.2 mm The rolling slab was
solidified at a
cooling rate (or cooling speed) of 1 8 C/s and the rolling steps in the hot
rolling and
cold rolling were carried out in accordance with the standard scheme. The last
rolling
reduction pass in the cold rolling amounted to 15% (from 1.41 mm to 1.2 mm)
and the
final heat treatment was carried out at 500 C with subsequent water quenching
In
addition, with the product of the cooling rate after the intermediate
annealing and the
degree of rolling reduction of 27, the condition 10 < degree of rolling
reduction *
cooling rate < 50 is satisfied.
The average crystal grain size or final grain size of the thin sheet Al after
the heat
treatment was 35 pm and in the primary intermetallic phase, there were 12
first parti-
cles per mm2 having an average particle size of 5 pm to 10 pm With a :AM value
of
2.24, the criterion (iD*A > 1.8) is satisfied A tensile test did not show any
LOders
bands on the surface of the thin sheet A2. The intermetallic phase according
to the
invention with the first or primary particles was therefore able to provide a
sufficient
number of dislocations to prevent the occurrence of LOders bands during the
forming.
Exemplary Embodiment 3:
An alloy of the AA5182 type with the chemical composition 03 was used to
produce
a thin sheet A3 with a sheet thickness of 1.2 mm The rolling slab was
solidified at a
cooling rate (or cooling speed) of 1.8 C/s and the rolling steps in the hot
rolling and
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cold rolling were carried out in accordance with the standard scheme. The last
rolling
reduction pass in the cold rolling amounted to 18% (from 1.46 mm to 1.2 mm)
and the
final heat treatment was carried out at 500 C with subsequent water quenching
The
average crystal grain size or final grain size was 29 pm and in the primary
intermetallic
phase, there were 14 first particles per mm2 having an average particle size
of 5 pm
to 10 pm. In addition, with the product of the cooling rate after the
intermediate an-
nealing and the degree of rolling reduction of 32, the condition 10 <
degree of rolling reduction * cooling rate < 50 is satisfied
With a .VD*A value of 2.38, the criterion (VID*A > 1.8) is satisfied. A
tensile test did not
show any LOders bands on the surface of the thin sheet A3 The intermetallic
phase
according to the invention with the first or primary particles was therefore
able to pro-
vide a sufficient number of dislocations to prevent the occurrence of LOders
bands
during the forming.
Exemplary Embodiment 4:
An alloy of the AA5182 type with the chemical composition C4 was used to
produce
two thin sheets A4.1 and A4.2 with a sheet thickness of 1.2 mm The rolling
slab was
solidified at a cooling rate (or cooling speed) of 1.8 C/s and the rolling
steps in the hot
rolling and cold rolling were carried out in accordance with the standard
scheme. The
last rolling reduction pass in the cold rolling amounted to 25% from 1 60 mm
to 1.2
mm). The final heat treatment of the thin sheet A4 1 was carried out at 500 C
with
subsequent water quenching. By contrast, the final heat treatment of the thin
sheet
A4.2 was carried out at 370 C with subsequent cooling in stationary air.
The average crystal grain size or final grain size of both of the thin sheets
A4.1 and
A4 2 was 32pm and in their primary intermetallic phase, there were 12 first
particles
per mm2 having an average particle size of 5 pm to 10 pm. With a -\/Di*A value
of 2.14,
the criterion (\trA > 1.8) is satisfied by both thin sheets A4.1 and A4 2.
In addition, with the product of the cooling rate after the intermediate
annealing and
the degree of rolling reduction of 45, the condition 10 < degree of rolling
reduction *
cooling rate < 50 is satisfied by both thin sheets A4 1 and A4.2
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By contrast with the thin sheet A4.1, the thin sheet A4.2 exhibits LOders
bands after
the deep-drawing. In the thin sheet A4.2, despite having the same composition
and
microstructure, because of the slower cooling in stationary air, it was not
possible for
a sufficient number of dislocations in the structure to form in order to
prevent the oc-
currence of alders bands. In other words, the accelerated water cooling of the
thin
sheet A4.1 resulted in the fact that the intermetallic phase with the first or
primary
particles was able to provide a sufficient number of dislocations to prevent
the occur-
rence of LOders bands during the forming.
Exemplary Embodiment 5:
An alloy of the AA5182 type with the chemical composition 04 was used to
produce
a thin sheet A5 with a sheet thickness of 1.2 mm. The rolling slab was
solidified at a
cooling rate (or cooling speed) of 1.8 C/s and the rolling steps in the hot
rolling and
cold rolling were carried out in accordance with the standard scheme. The last
rolling
reduction pass in the cold rolling amounted to 63% (from 3.25 mm to 1.2 mm)
and the
final heat treatment was carried out at 500 C with subsequent water quenching.
The
average crystal grain size or final grain size was 10 pm and in the primary
intermetallic
phase, there were 12 first particles per mm2 having an average particle size
of 5 pm
to 10 pm.
With a -Nil:VA value of 1.2, the criterion for freedom from LOders bands (-
\/D*A > 1 8) is
not satisfied. In addition, with the product of the cooling rate after the
intermediate
annealing and the degree of rolling reduction of 113, the condition 10 5_
degree of rolling reduction * cooling rate < 50 is not satisfied. After the
deep-drawing,
LOders bands were detected The intermetallic phase with the first or primary
particles
was therefore not able to provide a sufficiently high number of dislocations
to prevent
the occurrence of LOders bands during the forming
Exemplary Embodiment 6.1:
An alloy with an Al-Mg-Zn-Mn basis and the chemical composition D1 was used to
produce a thin sheet A6.1 with a sheet thickness of 1 2 mm The rolling slab
was
solidified at a cooling rate (or cooling speed) of 1 8 C/s and the rolling
steps in the hot
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rolling and cold rolling were carried out in accordance with the standard
scheme. The
last rolling reduction pass in the cold rolling amounted to 18% (from 1.46 mm
to 1 2
mm). The final heat treatment was carried out at 500 C with subsequent water
quenching. After the accelerated cooling, a stabilization was carried out at
100 C for
3 h. The average crystal grain size or final grain size was 28 pm and in the
primary
intermetallic phase, there were 14 first particles per mm2 having an average
particle
size of 5 pm to 10 pm. With a =NlID*A value of 2.34, the criterion (\iLD*A > 1
8) is satisfied
In addition, with the product of the cooling rate after the intermediate
annealing and
the degree of rolling reduction of 32, the condition 10 < degree of rolling
reduction *
cooling rate < 50 is satisfied.
A tensile test did not show any LOders bands on the surface of the thin sheet
A6.1
The intermetallic phase according to the invention with the first or primary
particles
was therefore able to provide a sufficient number of dislocations to prevent
the occur-
rence of Luders bands during the forming.
Exemplary Embodiment 6.2:
An alloy with an Al-Mg-Zn-Mn basis and the chemical composition D1 was used to
produce a thin sheet A6.2 with a sheet thickness of 1 2 mm The rolling slab
was
solidified at a cooling rate (or cooling speed) of 1.8 C/s and the rolling
steps in the hot
rolling and cold rolling were carried out in accordance with the standard
scheme The
last rolling reduction pass in the cold rolling amounted to 63% (from 3.25 mm
to 1.2
mm) and the final heat treatment was carried out at 500 C with subsequent
water
quenching The average crystal grain size or final grain size was 10 pm and in
the
primary intermetallic phase, there were 14 first particles per mm2 having an
average
particle size of 5 pm to 10 pm With a \11-3*A value of 1 4, the criterion for
freedom from
LOders bands (\/D*A > 1.8) is not satisfied. In addition, with the product of
the cooling
rate after the intermediate annealing and the degree of rolling reduction of
113, the
condition 10 < degree of rolling reduction * cooling rate 5 SO is not
satisfied.
After the deep-drawing, LOders bands were detected. The intermetallic phase
with the
first or primary particles was therefore not able to provide a sufficiently
high number
of dislocations to prevent the occurrence of LUders bands during the forming
CA 03128294 2021-07-29
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All of the exemplary embodiments according to the invention, namely Al, A2,
A3,
A4.1, and A6.1 share the fact that their crystal structure has more than 200,
more
particularly more than 400, dislocations at each first particle.
In general, it should be noted that the German expression "insbesondere" can
be
translated into English as more particularly." A feature that is preceded by
more
particularly" is to be considered an optional feature that can be omitted and
therefore
does not constitute a limitation, for example of the claims. The same applies
to the
German term "vorzugsweise,"which is translated into English as "preferably."
