U.S. patent application number 16/342096 was filed with the patent office on 2019-08-15 for thin sheets made of an aluminum-magnesium-scandium alloy for aerospace applications.
The applicant listed for this patent is CONSTELLIUM ISSOIRE. Invention is credited to Bernard BES, Jean-Christophe EHRSTROM, Gaelle POUGET.
Application Number | 20190249285 16/342096 |
Document ID | / |
Family ID | 58401638 |
Filed Date | 2019-08-15 |
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United States Patent
Application |
20190249285 |
Kind Code |
A1 |
BES; Bernard ; et
al. |
August 15, 2019 |
THIN SHEETS MADE OF AN ALUMINUM-MAGNESIUM-SCANDIUM ALLOY FOR
AEROSPACE APPLICATIONS
Abstract
The invention relates to a method for producing a wrought
product made of an aluminum alloy composed, in wt %, of Mg:
3.8-4.2; Mn: 0.3-0.8 and preferably 0.5-0.7; Sc: 0.1-0.3; Zn:
0.1-0.4; Ti: 0.01-0.05; Zr: 0.07-0.15; Cr: <0.01; Fe: <0.15;
Si<0.1; wherein the homogenization is carried out at a
temperature of between 370.degree. C. and 450.degree. C., for
between 2 and 50 hours, such that the equivalent time at
400.degree. C. is between 5 and 100 hours, and the hot deformation
is carried out at an initial temperature of between 350.degree. C.
and 450.degree. C. The invention also relates to hot-worked
products obtained by the method according to the invention, in
particular sheets with a thickness of less than 12 mm. The products
according to the invention are advantageous as they offer a better
compromise in terms of mechanical strength, toughness and
hot-formability.
Inventors: |
BES; Bernard; (Seyssins,
FR) ; EHRSTROM; Jean-Christophe; (Grenoble, FR)
; POUGET; Gaelle; (Grenoble, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONSTELLIUM ISSOIRE |
Issoire |
|
FR |
|
|
Family ID: |
58401638 |
Appl. No.: |
16/342096 |
Filed: |
October 17, 2017 |
PCT Filed: |
October 17, 2017 |
PCT NO: |
PCT/FR2017/052856 |
371 Date: |
April 15, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/047 20130101;
C22C 21/06 20130101 |
International
Class: |
C22F 1/047 20060101
C22F001/047; C22C 21/06 20060101 C22C021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2016 |
FR |
1660049 |
Claims
1. Method for producing a wrought product made of an aluminum alloy
comprising: a) Producing a molten metal bath having an aluminum
base, comprising, in wt %, Mg: 3.8-4.2; Mn: 0.3-0.8 and optionally
0.5-0.7; Sc: 0.1-0.3; Zn: 0.1-0.4; Ti: 0.01-0.05 and optionally
0.015-0.030; Zr: 0.07-0.15 and optionally 0.08-0.12; Cr: <0.01;
Fe: <0.15; Si<0.1; other elements <0.05 each and <0.15
combined, the remainder being aluminum; b) Casting an unwrought
product from said metal bath; c) Homogenizing said unwrought
product at a temperature that lies in the range 370.degree. C. to
450.degree. C., for a duration that lies in the range 2 to 50 hours
such that the equivalent time at 400.degree. C. lies in a range 5
to 100 hours, the equivalent time t(eq) at 400.degree. C. being
defined by formula: t ( eq ) = .intg. exp ( - 29122 / T ) dt exp (
- 29122 / T ref ) ##EQU00003## where T is the current temperature
expressed in Kelvin, which changes over time t (in hours) and Tref
is a reference temperature of 400.degree. C. (673 K), t(eq) being
expressed in hours, the constant Q/R=29122 K being derived from the
activation energy for the diffusion of Zr, Q=242000 J/mol, d)
Hot-working the unwrought product thus homogenized is hot worked
with an initial temperature in the range 350.degree. C. to
450.degree. C. and is optionally cold-worked; e) a flattening
and/or straightening process is optionally carried out; f) an
annealing process is optionally carried out at a temperature that
lies in the range 300.degree. C. to 350.degree. C.
2. Method according to claim 1, wherein the homogenization duration
lies in a range 5 to 30 hours.
3. Method according to claim 1, wherein working is carried out by
rolling in order to obtain a sheet metal and wherein a final
thickness of a sheet obtained is less than 12 mm.
4. Method according to claim 1, wherein working is carried out by
extrusion in order to obtain a profile.
5. Wrought product made of an aluminum alloy having the
composition, in wt %, Mg: 3.8-4.2; Mn: 0.3-0.8 and optionally
0.5-0.7; Sc: 0.1-0.3; Zn: 0.1-0.4; Ti: 0.01-0.05 and optionally
0.015-0.030; Zr: 0.07-0.15 and optionally 0.08-0.12; Cr: <0.01;
Fe: <0.15; Si<0.1; other elements <0.05 each and <0.15
combined, the remainder being aluminum, obtainable by the method
according to claim 1.
6. Wrought product in the form of a sheet having a thickness of
less than 12 mm, obtainable by the method according to claim 3,
wherein (a) the tensile yield stress thereof measured at 0.2%
elongation in the LT direction of at least 250 MPa, and optionally
of at least 260 MPa and/or (b) the tensile yield stress thereof
measured at 0.2% elongation in the L direction of at least 260 MPa,
and optionally of at least 270 MPa.
7. Wrought Product in the form of a Sheet according to claim 6,
wherein (c) the toughness K.sub.R60 thereof, measured on specimens
of type CCT760 in the L-T direction (where 2ao=253 mm), for an
effective crack growth .DELTA.a.sub.eff of 60 mm, of at least 155
MPa.sup. {square root over (m)}, and optionally of at least 165
MPa.sup. {square root over (m)} and/or (d) the toughness K.sub.R60
thereof, measured on specimens of type CCT760 in the T-L direction
(where 2ao=253 mm), for an effective crack growth .DELTA.a.sub.eff
of 60 mm, of at least 160 MPa.sup. {square root over (m)}, and
optionally of at least 170 MPa.sup. {square root over (m)}.
8. Method according to claim 1, wherein, at the end of f, forming
is carried out at a temperature that lies in the range 300.degree.
C. to 350.degree. C.
9. Aircraft fuselage element obtainable according to the method
according to claim 8, wherein (a) the tensile yield stress thereof
measured at 0.2% elongation in the LT direction of at least 250
MPa, and optionally of at least 260 MPa and/or (b) the tensile
yield stress thereof measured at 0.2% elongation in the L direction
of at least 260 MPa, and optionally of at least 270 MPa.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method for producing wrought
products made of an aluminum-magnesium alloy, also known as a SXXX
series aluminum alloy according to the Aluminium Association, more
particularly Al--Mg alloy products containing Sc having a high
mechanical strength, high toughness and good formability. The
invention further relates to products obtainable by said method, as
well as to the use of these products intended for transportation
and in particular for aircraft and spacecraft construction.
PRIOR ART
[0002] Wrought products made of an aluminum alloy are developed in
particular to produce structural elements intended for the
transportation industry and in particular for the aeronautics
industry and the aerospace industry. In these industries, product
performance must be constantly improved and new alloys are
developed in particular in order to provide a high mechanical
strength, low density, high toughness, excellent corrosion
resistance and very good formability. In particular, forming can
take place under heat, for example by creep forming, and the
mechanical properties must not deteriorate after this forming
process.
[0003] Al--Mg alloys have been extensively studied in the
transportation industry, in particular that of road and sea
transportation, due to the excellent properties thereof for use in
such industries, such as the weldability, corrosion resistance and
formability thereof, in particular in low-worked tempers such as
the 0 temper and Hill temper.
[0004] However, these alloys have a relatively low mechanical
strength for the aeronautics industry and aerospace industry.
[0005] U.S. Pat. No. 5,624,632 discloses an alloy composed of 3-7
wt % magnesium, 0.03-0.2 wt % zirconium, 0.2-1.2 wt % manganese, up
to 0.15 wt % silicon and 0.05-0.5 wt % of an element forming
dispersoids in the group consisting of scandium, erbium, yttrium,
gadolinium, holmium and hafnium.
[0006] U.S. Pat. No. 6,695,935 discloses an alloy composed, in wt
%, of Mg 3.5-6.0, Mn 0.4-1.2, Zn 0.4-1.5, Zr max. 0.25, Cr max.
0.3, Ti max. 0.2, Fe max. 0.5, Si max. 0.5, Cu max. 0.4, and one or
more elements in the group: Bi 0.005-0.1, Pb 0.005-0.1, Sn
0.01-0.1, Ag 0.01-0.5, Sc 0.01-0.5, Li 0.01-0.5, V 0.01-0.3, Ce
0.01-0.3, Y 0.01-0.3, and Ni 0.01-0.3.
[0007] Patent application WO 01/12869 discloses an alloy composed,
in wt %, of 1.0-8.0 wt % Mg, 0.05-0.6 wt % Sc, 0.05-0.20 wt % Hf
and/or 0.05-0.20 wt % Zr, 0.5-2.0 wt % Cu and/or 0.5-2.0 wt % Zn
and additionally 0.1-0.8 wt % Mn.
[0008] Patent application WO2007/020041 discloses an alloy
composed, in wt %, of Mg 3.5 to 6.0, Mn 0.4 to 1.2, Fe<0.5,
Si<0.5, Cu<0.15, Zr<0.5, Cr<0.3, Ti 0.03 to 0.2,
Sc<0.5, Zn<1.7, Li<0.5, Ag<0.4, optionally one or more
elements forming dispersoids in the group consisting of erbium,
yttrium, hafnium, and vanadium, each <0.5 wt %. The products
described in these patents are not sufficient in terms of offering
a compromise between mechanical strength, toughness and
hot-formability. In particular, it is important that the mechanical
properties do not deteriorate after heat treatment at
300-350.degree. C., which is a typical temperature for forming.
[0009] There is thus a need for wrought products made of an Al--Mg
alloy with a low density and improved properties compared to those
of known products, in particular in terms of mechanical strength,
toughness and hot-formability. Moreover, such product must be
obtainable according to a reliable and cost-effective production
process that can be easily adapted to a conventional production
line.
PURPOSE OF THE INVENTION
[0010] The invention firstly relates to a method for producing a
wrought product made of an aluminum alloy wherein: [0011] a) a
molten metal bath having an aluminum base is produced, composed, in
wt %, of [0012] Mg: 3.8-4.2; [0013] Mn: 0.3-0.8; preferably
0.5-0.7; [0014] Sc: 0.1-0.3; [0015] Zn: 0.1-0.4; [0016] Ti:
0.01-0.05, preferably 0.015-0.030; [0017] Zr: 0.07-0.15, preferably
0.08-0.12; [0018] Cr: <0.01; [0019] Fe: <0.15; [0020]
Si<0.1; [0021] other elements <0.05 each and <0.15
combined, the remainder being aluminum; [0022] b) an unwrought
product is cast from said metal bath; [0023] c) said unwrought
product is homogenized at a temperature that lies in the range
370.degree. C. to 450.degree. C., for a duration that lies in the
range 2 to 50 hours such that the equivalent time at 400.degree. C.
lies in the range 5 to 100 hours, the equivalent time t(eq) at
400.degree. C. being defined by the formula:
[0023] t ( eq ) = .intg. exp ( - 29122 / T ) dt exp ( - 29122 / T
ref ) ##EQU00001## where T is the current temperature expressed in
Kelvin, which changes over time t (in hours) and Tref is a
reference temperature of 400.degree. C. (673 K), t(eq) being
expressed in hours, the constant Q/R=29122 K being derived from the
activation energy for the diffusion of Zr, Q=242000 J/mol, [0024]
d) the unwrought product thus homogenized is hot-worked with an
initial temperature in the range 350.degree. C. to 450.degree. C.
and is optionally cold-worked; [0025] e) a flattening and/or
straightening process is optionally carried out; [0026] f) an
annealing process is optionally carried out at a temperature that
lies in the range 300.degree. C. to 350.degree. C.
[0027] The invention secondly relates to a wrought product made of
an aluminum alloy having the composition, in wt %,
[0028] Mg: 3.8-4.2;
[0029] Mn: 0.3-0.8, preferably 0.5-0.7;
[0030] Sc: 0.1-0.3;
[0031] Zn: 0.1-0.4;
[0032] Ti: 0.01-0.05, preferably 0.015-0.030;
[0033] Zr: 0.07-0.15, preferably 0.08-0.12;
[0034] Cr: <0.01;
[0035] Fe: <0.15;
[0036] Si<0.1;
[0037] other elements <0.05 each and <0.15 combined, the
remainder being aluminum;
[0038] obtainable by the method according to the invention.
DESCRIPTION OF THE INVENTION
[0039] Unless specified otherwise, all of the indications
concerning the chemical composition of the alloys are expressed as
a percentage by weight based on the total weight of the alloy. By
way of example, the expression 1.4 Cu means that the copper content
expressed in wt % is multiplied by 1.4. The designation of the
alloys is provided in accordance with the regulations of The
Aluminium Association, known to those skilled in the art.
[0040] The definitions of the tempers are indicated in European
standard EN 515 (1993). The tensile static mechanical properties,
in other words the ultimate tensile strength R.sub.m, the tensile
yield stress at 0.2% elongation R.sub.p0.2, and the elongation at
rupture A %, are determined by a tensile test according to standard
NF EN ISO 6892-1 (2009), whereby the sampling and the direction of
the test are defined by standard EN 485-1 (2016).
[0041] The plane strain toughness is determined by a curve of the
stress intensity factor KR as a function of the effective crack
growth .DELTA.a.sub.eff known as the R-curve, according to standard
ASTM E 561 (2010). The critical stress intensity factor K.sub.C, in
other words the intensity factor that makes the crack unstable, is
calculated from the R-curve. The stress intensity factor K.sub.CO
is also calculated by assigning the initial crack length to the
critical load, at the start of monotonic loading. These two values
are calculated for a specimen of the required form. K.sub.app
represents the factor K.sub.CO corresponding to the specimen that
was used to carry out the R-curve test. K.sub.eff represents the
factor K.sub.C corresponding to the specimen that was used to carry
out the R-curve test. K.sub.R60 corresponds to the value of KR for
an effective crack growth .DELTA.a.sub.eff=60 mm.
[0042] Within the scope of the invention, the grain structure of
the samples is characterized in the plane LxTC at mid-thickness,
t/2, and is quantitatively assessed after metallographic etching of
the anodic oxidation type under polarized light: [0043] the term
"essentially non-recrystallized" is used when the grain structure
has no or few recrystallized grains, generally less than 20%,
preferably less than 15% and more preferably less than 10% of the
grains are recrystallized; [0044] the term "recrystallized" is used
when the grain structure has a significant proportion of
recrystallized grains, generally more than 50%, preferably more
than 60% and more preferably more than 80% of the grains are
recrystallized.
[0045] Unless specified otherwise, the definitions of standard EN
12258-1 (1998) apply.
[0046] Within the scope of the present invention, a "structural
element" of a mechanical construction means a mechanical part for
which the static and/or dynamic mechanical properties are
particularly important to the performance of the structure and for
which a structural calculation is usually prescribed or carried
out. These are generally elements whose malfunction is likely to
jeopardize the safety of said construction, of its users or of
other persons. For an aircraft, these structural elements in
particular include the elements that comprise the fuselage (such as
the fuselage skin, fuselage stiffeners or stringers, bulkheads,
circumferential frames, wings (such as the upper or lower wing
skin), stringers or stiffeners, ribs, spars, floor beams and seat
tracks) and the tail unit in particular comprised of horizontal or
vertical stabilizers, as well as the doors.
[0047] The inventors hereof have observed that, for a composition
according to the invention, an advantageous wrought product can be
obtained by controlling the homogenization conditions, the
mechanical properties of which advantageous wrought product offer a
compromise between mechanical strength and useful toughness for the
aircraft construction industry, and the properties whereof are
stable after heat treatment corresponding to hot-forming
conditions.
[0048] According to the invention, a molten metal bath having an
aluminum base is produced composed, in wt %, of Mg: 3.8-4.2; Mn:
0.3-0.8, preferably 0.5-0.7; Sc: 0.1-0.3; Zn: 0.1-0.4; Ti:
0.01-0.05, preferably 0.015-0.030; Zr: 0.07-0.15, preferably
0.08-0.12; Cr: <0.01; Fe: <0.15; Si<0.1; other elements
<0.05 each and <0.15 combined, the remainder being
aluminum.
[0049] The composition according to the invention is noteworthy as
a result of the low quantity of added titanium from 0.01-0.05 and
preferentially from 0.015 to 0.030 wt % and preferably from 0.018
to 0.024 wt % and as a result of the absence of added chromium, the
content whereof is less than 0.01 wt %. The high static mechanical
properties (Rp0.2, Rm) are obtained despite these small additions,
as a result of the carefully-controlled homogenization conditions.
Thus, surprisingly, recrystallisation can be prevented during the
hot-forming process with low quantities of added titanium and
without added chromium, while simultaneously procuring high static
mechanical properties, which were in particular possible to obtain
by adding high quantities of Cr and Ti, and a high toughness.
[0050] Mn, Sc, Zn and Zr must be added in order to obtain the
desired compromise between the mechanical strength, toughness and
hot-formability. The iron content is kept below 0.15 wt %, and
preferably below 0.1 wt %. The silicon content is kept below 0.1 wt
%, and preferably below 0.05 wt %. The presence of iron and silicon
in excess of the aforementioned maximum values has a negative
impact, in particular on toughness. The remaining elements are
impurities, i.e. elements whose presence is unintentional, the
presence whereof must be limited to 0.05% each and to 0.15%
combined and preferably to 0.03% each and to 0.10% combined.
[0051] According to the invention, said unwrought product is
homogenized at a temperature that lies in the range 370.degree. C.
to 450.degree. C., for a duration that lies in the range 2 to 50
hours such that the equivalent time at 400.degree. C. lies in the
range 5 to 100 hours, the equivalent time t(eq) at 400.degree. C.
being defined by the formula:
t ( eq ) = .intg. exp ( - 29122 / T ) dt exp ( - 29122 / T ref )
##EQU00002##
[0052] wherein T is the current temperature expressed in Kelvin,
which changes over time t (in hours) and Tref is a reference
temperature of 400.degree. C. (673 K), t(eq) being expressed in
hours, the constant Q/R=29122 K being derived from the activation
energy for the diffusion of the Zr, Q=242000 J/mol.
[0053] Preferably, the homogenization duration lies in the range 5
to 30 hours. Advantageously, the equivalent time at 400.degree. C.
lies in the range 6 to 30 hours.
[0054] A too low homogenization temperature and/or a too short
homogenization duration does not allow for the formation of
dispersoids to control recrystallisation. Surprisingly, when the
homogenization temperature is too high and/or when the
homogenization duration is too long, the properties obtained are
unstable at the conventional hot-forming temperature of
300-350.degree. C., in particular since the products
recrystallize.
[0055] Hot working can be carried out immediately after
homogenization without cooling to ambient temperature, whereby the
initial hot working temperature must lie in the range 350 to
450.degree. C. Alternatively, the unwrought product can be cooled
to ambient temperature after homogenization and then reheated to an
initial hot working temperature that lies in the range 350 to
450.degree. C. In the case of reheating, the equivalent time at
400.degree. C. during reheating must be kept low, generally less
than 10%, compared to the equivalent time at 400.degree. C. during
homogenization.
[0056] During hot working, the temperature of the metal can, in
some cases, rise, however the equivalent time at 400.degree. C.
during hot working must be kept low, generally less than 10%,
compared to the equivalent time at 400.degree. C. during
homogenization. In any case, the temperature during hot working
must preferably not exceed 460.degree. C. and preferentially not
exceed 440.degree. C. After hot working, cold working can be
carried out.
[0057] In a first embodiment, working is carried out by rolling in
order to obtain a sheet metal. In this first embodiment, the final
thickness of the sheet metal obtained is less than 12 mm.
[0058] In a second embodiment, working is carried out by extrusion
in order to obtain a profile.
[0059] In a first embodiment, hot working is generally carried out
until a thickness of about 4 mm is reached, then cold working is
carried out for a thickness that lies in the range 0.5 to 4 mm.
[0060] After the hot- and optionally cold-working process, a
flattening and/or straightening operation can advantageously be
carried out. During flattening and/or straightening operations, the
permanent set is generally less than 2%, preferably less than about
1%.
[0061] An annealing process is optionally performed at a
temperature that lies in the range 300.degree. C. to 350.degree. C.
The annealing time generally lies in the range 1 to 4 hours. The
main purpose of this annealing process is to stabilize the
mechanical properties such that they are not altered during a
subsequent forming process at a similar temperature. The products
according to the invention have the advantage of having very stable
mechanical properties at this temperature. Thus, for products whose
final thickness of 4 to 6 mm is obtained by hot rolling, the static
mechanical property variation is no greater than 10% and preferably
no greater than 6% after annealing between 300 and 350.degree. C.,
and for products whose final thickness of about 2 mm is obtained by
cold rolling, the static mechanical property variation is no
greater than 40% and preferably no greater than 30% after annealing
between 300 and 350.degree. C. Within the scope of the method
according to the invention, it is thus possible not to perform a
stabilizing annealing process and to immediately carry out forming,
in particular for products whose final thickness is obtained by hot
rolling. Thanks to the method of the invention, the products
according to the invention retain an essentially non-recrystallized
grain structure after annealing at between 300 and 350.degree.
C.
[0062] Sheet metal having a thickness of less than 12 mm obtained
by the method of the invention is advantageous, preferably having
the following characteristics:
[0063] (a) a tensile yield stress measured at 0.2% elongation in
the LT direction of at least 250 MPa, and preferably of at least
260 MPa and/or
[0064] (b) a tensile yield stress measured at 0.2% elongation in
the L direction of at least 260 MPa, and preferably of at least 270
MPa, whereby these properties are achieved even in the case wherein
the optional annealing step at a temperature in the range
300.degree. C. to 350.degree. C. is carried out.
[0065] Advantageously, sheet metal having a thickness of less than
4 mm obtained by the method of the invention has a tensile yield
stress measured at 0.2% elongation in the LT direction of at least
300 MPa, and preferably of at least 320 MPa, whereby these
properties are achieved even in the case wherein the optional
annealing step at a temperature in the range 300.degree. C. to
350.degree. C. is carried out.
[0066] The sheet metal according to the invention preferably has
advantageous toughness properties, in particular:
[0067] (c) a toughness K.sub.R60, measured on specimens of type
CCT760 in the L-T direction (where 2ao=253 mm), for an effective
crack growth .DELTA.a.sub.eff of 60 mm, of at least 155 MPa.sup.
{square root over (m)}, and preferably of at least 165 MPa.sup.
{square root over (m)} and/or
[0068] (d) a toughness K.sub.R60, measured on specimens of type
CCT760 in the T-L direction (where 2ao=253 mm), for an effective
crack growth .DELTA.a.sub.eff of 60 mm, of at least 160 MPa.sup.
{square root over (m)}, and preferably of at least 170 MPa.sup.
{square root over (m)}.
[0069] Preferably, for the products according to the invention, the
toughness KR in the T-L direction is greater than that in the L-T
direction.
[0070] Preferably, the toughness Kapp, measured on specimens of
type CCT760 in the T-L direction (where 2ao=253 mm), is at least
125 MPa, and preferably at least 130 MPa. The products according to
the invention can be formed at a temperature that lies in the range
300.degree. C. to 350.degree. C. in order to obtain structural
elements for an aeroplane, preferably fuselage elements.
[0071] Aircraft fuselage elements according to the invention are
advantageous because they have [0072] (a) a tensile yield stress
measured at 0.2% elongation in the LT direction of at least 250
MPa, and preferably of at least 260 MPa and/or [0073] (b) a tensile
yield stress measured at 0.2% elongation in the L direction of at
least 260 MPa, and preferably of at least 270 MPa.
EXAMPLES
Example 1
[0074] A plurality of slabs with a thickness of 400 mm were cast,
the composition whereof is provided in Table 1.
TABLE-US-00001 TABLE 1 Composition in wt % (analyzed by spark
optical emission spectrometry, S-OES). Si Fe Cr Mn Mg Zn Ti Zr Sc A
0.02 0.05 <0.01 0.62 4.05 0.28 0.023 0.10 0.19 B 0.02 0.04
<0.01 0.59 3.99 0.29 0.038 0.10 0.19
[0075] The slab made of alloy A was homogenized for 5 h at
445.degree. C., whereas the slab made of alloy B was homogenized
for 15 h at 515.degree. C. The slabs thus homogenized were hot
rolled immediately after homogenization with a hot-rolling starting
temperature of 415.degree. C. for slab A and 480.degree. C. for
slab B, in order to obtain 4 mm thick sheets.
[0076] The tensile static mechanical properties of the sheet made
of alloy A remained high, both in the hot-rolled temper (HR) and in
the annealed temper (annealing treatment for 4 h at 325.degree.
C.), whereas those of the sheet made of alloy B deteriorated after
annealing.
TABLE-US-00002 TABLE 2 Static mechanical properties obtained for
the different sheet in the hot-rolled temper (HR) and in the
annealed temper (4 h at 325.degree. C.). Alloy A sheet Alloy B
sheet Thickness 4 mm Thickness 4 mm HR Annealing HR Annealing Rp0.2
L, MPa 303 289 287 233 Rm L, MPa 400 393 364 352 A L, % 14.5 16.2
14.8 17.6 Rp0.2 LT, MPa 311 292 276 238 Rm LT, MPa 396 387 361 349
A LT, % 17.7 19.5 18.2 23.0 Kapp MPa m L-T 129.9 129.1 128.5 Kapp
MPa m T-L 134.9 134.0 125.8 Kr60 MPa m L-T 172.9 171.5 171.2 Kr60
MPa m T-L 178.9 177.1 164
[0077] The 4-mm sheets were cold rolled to a thickness of 2 mm by
three passages, without intermediate heat treatment, then underwent
flattening. Different heat treatments were carried out after cold
rolling. The tensile mechanical test results are shown in table
3.
TABLE-US-00003 TABLE 3 Static mechanical properties obtained for
the different cold-rolled sheets having undergone annealing under
different conditions. Alloy A sheet Alloy B sheet Annealing
Thickness 2 mm Thickness 2 mm after cold Rp02 Rp02 rolling (LT) Rm
(LT) A % LT (LT) Rm (LT) A % LT -- 417 466 9.95 358 422 10.5 2 h
275.degree. C. 349.5 415 19 256 355 18.2 2 h 325.degree. C. 333 405
21.7 168 311 23.0 2 h 375.degree. C. 297.5 393 21.4 156 301
23.1
[0078] The grain structure of the sheets was observed after
metallographic etching of the anodic oxidation type under polarized
light after cold rolling (CR) or after cold rolling and annealing
for 2 h at 325.degree. C.
[0079] A qualitative assessment of the microstructure was carried
out:
[0080] Table 4 shows the results of the microstructural
observations of the sheets of compositions A and B in the unwrought
cold rolling temper and after annealing treatment (2 h at
325.degree. C.).
TABLE-US-00004 TABLE 4 Microstructure (plane LxTC, at
mid-thickness) of the sheets Alloy Reference Microstructure A CR
Appreciably non-recrystallized 2 h 325.degree. C. Appreciably
non-recrystallized B CR Appreciably non-recrystallized 2 h
325.degree. C. Recrystallized
[0081] Alloy A according to the invention has excellent
recrystallisation resistance.
Example 2
[0082] This example studied the effect that the homogenization
conditions before hot working have on the mechanical properties.
Blocks made of alloy A of dimensions 250.times.180.times.120 mm
were hot rolled under different conditions until obtaining a
thickness of 8 or 12 mm. The conditions are described in Table
5.
TABLE-US-00005 TABLE 5 Transformation conditions of the different
blocks made of alloy A Homogenization Initial rolling Final Final
rolling temperature Homogenization T(eq) temperature thickness
temperature (.degree. C.) duration (h) at 400.degree. C. (.degree.
C.) (mm) (.degree. C.) CD2 450 15 298 440 12 329 CD3 400 15 15 390
12 319 CD4 450 15 298 440 8 325 CF1 450 5 99 440 8 330 CF2 450 5 99
12 327 CF3 400 5 5 405 12 320 CF4 515 17 9341 8 325
[0083] The mechanical properties were measured on the sheets having
undergone rolling or a treatment. The results are presented in
Table 6.
TABLE-US-00006 TABLE 6 Static mechanical properties obtained for
the different sheets in the hot rolled temper (HR) and in the
annealed temper (4 h at 325.degree. C.). Annealing for 4 h HR at
325.degree. C. Rp0.2 Rm A Rp0.2 Rm A block direction MPa MPa % MPa
MPa % CD2 L 251 377 15.4 243 370 16.0 CD3 L 286 398 14.5 278 391
15.4 CD4 L 260 371 13.6 252 366 16.7 CF1 L 275 381 16.1 267 373
17.1 CF2 L 268 390 12.9 262 382 13.8 CF3 L 288 399 14.8 280 392
15.4 CF4 L 223 341 15.7 209 339 17.3
[0084] The products obtained by the method according to the
invention (CD3, CF1, CF2, CF3) have advantageous mechanical
properties, in particular Rp0.2 in the L direction of at least 260
MPa after hot rolling and after annealing for 4 h at 325.degree.
C.
* * * * *