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| United States Patent |
5,792,287
|
|
Heymes
, et al.
|
August 11, 1998
|
Al-Cu-Mg sheet metals with low levels of residual stress
Abstract
A metal sheet with a total thickness>0.5 mm comprising an AlCuMg aluminum
alloy consisting essentially of Al and, in percent by weight:
3.5<Cu<5.0
1.0<Mg<2.0
Si<0.25
Fe<0.25
Mn<0.55
all other elements: <0.25
with
0<Mn-2Fe<0.2,
optionally plated with another aluminum alloy with the thickness of the
plating being no more than 12% of the total thickness of the sheet, the
sheet having a recrystallization rate>50% at all points and a deviation in
recrystallization rate between surface and mid-thickness<35%, the sheet
having in the quenched and stretched state or in the quenched, stretched
and annealed state, a deflection after machining to mid-thickness of a bar
resting on two distant supports with a length l such that:
fe<0.14 1.sup.2,
where f is the deflection expressed in micrometers, e being the thickness
of the sheet in mm and l is the length of the bar in mm.
| Inventors:
|
Heymes; Fabrice (Saint-Marcellin, FR);
Lequeu; Philippe (Issoire, FR);
Raynaud; Guy-Michel (Issoire, FR)
|
| Assignee:
|
Pechiney Rhenalu (Paris, FR)
|
| Appl. No.:
|
663017 |
| Filed:
|
June 17, 1996 |
| Intern'l Class: |
C22C 021/00 |
| Field of Search: |
420/533,534,537,538,553
148/417,439
428/654
|
References Cited
U.S. Patent Documents
| 3826688 | Jul., 1974 | Levy | 148/417.
|
| Foreign Patent Documents |
| 58-8189353 | ., 0000 | JP.
| |
Other References
Translation of JP (97-2997).
|
Primary Examiner: Simmons; David A.
Assistant Examiner: Elve; M. Alexandra
Attorney, Agent or Firm: Dennison, Meserole, Pollack & Scheiner
Claims
What is claimed is:
1. A metal sheet with a total thickness>0.5 mm, comprising an AlCuMg
aluminum alloy consisting essentially of Al and, in % by weight:
3.5<Cu<5.0
1.0<Mg<2.0
Si<0.25
Fe<0.25
Mn<0.55
all other elements: <0.25
with
0<Mn-2Fe<0.2,
optionally plated with another aluminum alloy with the thickness of the
plating being no more than 12% of the total thickness of the sheet, said
sheet having a recrystallization rate>50% at all points and a deviation in
recrystallization rate between surface and mid-thickness<35%, said sheet
having in the quenched and stretched state or the quenched, stretched and
annealed state, a deflection after a machining to mid-thickness of a bar
resting on two distant supports with a length l such that:
fe<0.14 l.sup.2,
with f being the deflection expressed in micrometers, e being the thickness
of the sheet in mm and l being the length of the bar in mm.
2. The sheet according to claim 1, wherein
fe<0.09 l.sup.2.
3. The sheet according to claim 2, wherein
fe<0.06 l.sup.2.
4. A sheet according to claim 3 with a total thickness between 0.5 and 3 mm
and
fe<0.04 l.sup.2
which is plated and has in the quenched, stretched and annealed state a
yield strength>380 MPa.
5. A sheet according to claim 1 in which Fe<0.20.
6. A sheet according to claim 1 in which Si<0.17.
7. The sheet according to claim 6 in which Si<0.10.
8. A sheet according to claim 1 in which Cu<4.0.
9. A sheet according to claim 1 in which Mg<1.5.
10. A sheet according to claim 1, wherein Mn<0.4.
11. A sheet according to claim 1 having, between the bars machined to
half-thickness in the directions L and TL, an isotropy of deflection after
machining such that (bar deflection L)<1.5.times.(bar deflection TL).
12. A sheet according to claim 1, wherein it has in the quenched and
stretched state a yield strength in the direction TL>290 MPa.
13. A sheet according to claim 1 having in the quenched, stretched and
annealed state a yield strength in the direction TL>400 MPa.
14. A plated sheet according to claim 1 having in the quenched and
stretched state a yield strength in the direction TL>270 MPa.
15. A sheet according to claim 1 which is plated and has in the quenched,
stretched and annealed state a yield strength>380 MPa.
16. A sheet according to claim 1 having a fatigue resistance such that the
maximum stress acceptable at a given number of cycles is respectively
greater than:
MPa for 10.sup.4 cycles
MPa for 10.sup.5 cycles
MPA for 10.sup.6 cycles
MPa for 10.sup.7 cycles.
17. A sheet according to claim 1 of total thickness>20 mm and having in the
quenched, stretched state a toughness K.sub.1c in the direction L-T>35
MPa.sqroot.m.
18. A sheet according to claim 1 of total thickness>20 mm and having in the
quenched, stretched state a toughness K.sub.1c in the direction T-L>32
MPa.sqroot.m.
19. The sheet according to claim 17 having in the quenched, stretched state
a toughness K.sub.1c in the direction L-T>40 MPa.sqroot.m.
20. The sheet according to claim 18 having in the quenched, stretched state
a toughness K.sub.1c in the direction T-L>35 MPa.sqroot.m.
21. A sheet according to claim 1 of total thickness>35 mm and having a
toughness K.sub.1c in the direction S-L>22 MPa.sqroot.m.
22. The sheet according to claim 21 having a toughness in the direction
S-L>24 MPa.sqroot.m.
23. A sheet according to claim 1 of total thickness>20 mm and having in the
quenched, stretched and annealed state a toughness K.sub.1c in the
direction L-T greater than 28 MPa.sqroot.m.
24. A sheet according to claim 1 of total thickness>20 mm and having in the
quenched, stretched and annealed state a toughness K.sub.1c in the
direction T-L>25 MPa.sqroot.m.
25. The sheet according to claim 23 having a toughness K.sub.1c in the
direction L-T>32 MPa.sqroot.m.
26. The sheet according to claim 24 having a toughness K.sub.1c in the
direction T-L>28 MPa.sqroot.m.
27. A sheet according to claim 23 of total thickness>35 mm and having in
the quenched, stretched and annealed state a toughness K.sub.1c in the
direction S-L>18 MPa.sqroot.m.
28. The sheet according to claim 27 having in the quenched, stretched and
annealed state a toughness in the direction S-L>20 MPa.sqroot.m.
29. A sheet with a thickness>20 mm according to claim 1 having a crack
velocity da/dn less than:
##EQU2##
30. A sheet according to claim 1 of total thickness<20 mm and having a
toughness K.sub.cb in the direction. T-L>110 Mpa.sqroot.m.
31. A sheet according to claim 1 with a thickness<12 mm and having a
roughness after chemical machining<6 micrometers.
32. A sheet with a thickness<4 mm according to claim 31 having a roughness
after chemical machining<3 micrometers.
33. An extruded, forged, or die-formed product comprising an AlCuMg alloy
consisting essentially of Al and, in % by weight:
3.5<Cu<5.0
1.0<Mg<2.0
Si<0.25
Fe<0.25
Mn<0.55
all other elements<0.25
with:
0<Mn-2Fe<0.2
having a recrystallization rate>50% at all points and a deviation in
recrystallization rate between surface and mid-thickness<35%, and having
in the quenched state or the quenched and annealed state a deflection f
after a machining to half-thickness of a bar resting on two distant
supports with a length l, such that:
fe<0.14 l.sup.2
with f being measured in micrometers, e being the average local thickness
of the product at the measurement point and l also being measured in mm.
34. The product according to claim 33 having in a quenched, de-stressed
state a yield strength R.sub.0.2 >290 MPa.
35. The product according to claim 33 having in a quenched, de-stressed and
annealed state a yield strength>400 MPa.
36. The product according to claim 33, wherein fe<0.09 l.sup.2.
Description
FIELD OF THE INVENTION
The invention relates to heavy (>12 mm thick), average (between 3 and 12 mm
thick), or light (between 0.5 and 3 mm thick) sheet metals made from a
high-strength Al-Cu-Mg aluminum alloy belonging to the 2000 series, in
accordance with the designations of the Aluminum Association of the United
States, which after quenching have a low level of residual stress, while
retaining high static mechanical properties (tensile strength, yield
strength and elongation), excellent damage tolerance, a low crack
propagation rate and good fatigue resistance, all of which properties are
particularly well adapted to their use in aircraft construction. These
sheets can be used uncoated or plated with another aluminum alloy having,
for example, better corrosion resistance.
DESCRIPTION OF RELATED ART
The residual stress present in age hardened aluminum sheets results from
the quenching which must be carried out in order to provide them with good
mechanical properties. The thermal shock caused by the rapid cooling from
high temperatures required for the natural aging of the alloying elements
produces extremely high internal stress.
This stress is troublesome because it causes substantial strain when the
sheets are machined, which is frequently the case in aircraft
construction. In order to reduce this stress, various processes for
relieving stress are used after quenching, for example a controlled
stretching or compression which makes it possible to reduce the internal
stress without affecting the properties of the product like a heat
treatment would. The research in this area has essentially consisted of
optimizing the stretching or compression operations required to ensure
effective stress relief.
In addition, much work has been done on the quenching operation itself.
This operation is generally carried out by means of immersion in or
spraying with cold water, and the cooling speeds obtained in this way are
often unnecessarily high. In effect, each alloy has a critical quenching
rate; if the cooling occurs more slowly than this critical rate, it causes
a decomposition of the solid solution which results in a substantial
reduction in the ultimate mechanical properties as well as the damage
tolerance. It must therefore be quenched faster than this critical rate,
but it is useless to go much beyond it) since it is known that the more
intense the cooling, the higher the internal stress.
Thus, a compromise must be found in order to optimize the quenching of the
sheets with a cooling which prevents any reduction in the ultimate
mechanical properties and minimizes the internal stress.
SUMMARY OF THE INVENTION
The object of the invention is to obtain, in sheet metals made from age
hardening alloys of the Al-Cu-Mg type, a reduced level of residual stress
after quenching, while maintaining static mechanical properties (tensile
strength, yield strength and elongation) and a fatigue resistance which
are as high as those in the current alloys, and while improving, in heavy
sheets, the toughness in the various directions and the crack velocity in
the long-transverse (L-T) and transverse-long (T-L) directions, without
changing anything in the procedures currently used for quenching and
relieving stress.
The subject of the invention is a sheet metal with a thickness of>0.5 mm
made from an aluminum alloy with the following composition (% by weight):
3.5<Cu<5.0
1.0<Mg<2.0
Si<0.25
Fe<0.25
Mn<0.55
all other elements<0.25
with
0<Mn-2Fe<0.2
possibly plated on 1 or 2 sides with another aluminum alloy having a total
thickness which does not exceed 12% of the total thickness of the plated
sheet, which sheet has a recrystallization rate>50% at all points and a
deviation between the recrystallization rate at the surface and that at
mid-thickness<35%, and has in the quenched and stretched state, or the
quenched, stretched and annealed state, a deflection f after a machining
to half-thickness of a bar resting on two distant supports with a length
l, such that:
fe<0.14 l.sup.2
preferably:
fe<0.09 l.sup.2
and even more preferably:
fe<0.06 l.sup.2
with f being measured in micrometers, e being the thickness of the sheet in
mm and l also being measured in mm.
For light sheets with a thickness of<3 mm, the deflection is such that:
fe<0.04 l.sup.2
Preferably, the iron content is less than 0.2%, the silicon content less
than 0.17% or even 0.10%, the copper content less than 4%, the magnesium
content less than 1.5%, and the manganese content less than 0.4%.
The sheets have a yield strength R.sub.0.2 in the transverse-long direction
greater than 290 MPa in the quenched state, and greater than 400 MPa in
the annealed state. As for plated sheets such as, for example, those used
in the manufacture of aircraft fuselages, they are generally plated on two
sides with an aluminum alloy which is not very loaded and has good
corrosion resistance, and each layer of plating can represent between 4
and 6% of the total thickness in the lightest sheets, and up to 2 to 4% of
the total thickness of sheets>1.6 mm thick, which means that the total
thickness of the plating never exceeds 12% of this total thickness. For
these plated sheets, the yield strength in the L-T and T-L directions is
greater than 270 and 380 MPa, respectively.
The sheets have a fatigue resistance, measured on flat test bars with a
stress concentration factor K.sub.t =2.3 with a ratio R between the
minimum and the maximum stress of 0.1, such that the stress acceptable for
a given number of cycles is greater than:
295 MPa for 10.sup.4 cycles
160 MPa for 10.sup.5 cycles
100 MPA for 10.sup.6 cycles
100 MPa for 10.sup.7 cycles
The heavy sheets>20 mm thick, made of an alloy with less than 0.2% Fe have
a toughness in the quenched and stretched state, measured by the critical
stress intensity factor under plane strain K.sub.1c, in the L-T and T-L
directions which is respectively greater than 35 and 32 MPa.sqroot.mm, and
preferably greater than 40 and 35 MPa.sqroot.m.
In the quenched, stretched and annealed state, this toughness is
respectively greater than 28 and 25 MPa.sqroot.m, and preferably greater
than 32 and 28 MPa.sqroot.m.
The toughness measured in the S-L direction for sheets>35 mm thick is
greater than 22 and preferably 24 MPa.sqroot.m in the quenched, stretched
state, and greater than 18 and preferably 20 MPa.sqroot.m in the quenched,
stretched and annealed state. The heavy sheets also have, in the L-T and
T-L directions, a crack velocity da/dn, for a loading with R=0.1, which is
less than:
##EQU1##
The orientation code for the L-T, T-L and S-L directions is defined in the
ASTM E 399 standard related tests for the toughness of metallic materials.
The sheets with a thickness of less than 20 mm have a toughness measured by
the critical stress intensity factor under plane strain K.sub.cb, in the
T-L direction, greater than 110 MPa.sqroot.m. It is measured on a test bar
with a width of 405 mm, a notch length of 100 mm and a thickness equal to
that of the sheet up to 6 mm and a thickness of 6 mm beyond that, which
thickness is obtained after symmetrical surfacing.
DESCRIPTION OF THE INVENTION
In contrast with the research trends of the prior art, the inventors have
researched the reduction of residual stress at the level of the
metallurgic parameters involved before quenching.
Since the possibilities for deviating from the compositions of the existing
alloys are limited, for the major alloying elements (Cu and Mg) because of
the high mechanical properties which must be obtained, the inventors
sought modifications in the contents of the minor alloying elements, and
found that the best results in terms of reducing residual stress, and thus
in terms of machining stability, were obtained when the contents of iron
and manganese by weight were such that:
Mn<0.55% Fe<0.25% and
0<Mn-2Fe<0.2%
This indicates that the lower the iron content, the more the manganese
content must be reduced. The iron content of Al-Cu alloys has a tendency
to be lowered regularly, for example as evidenced by the evolution, over
the last 20 years, of the compositions registered with the Aluminum
Association for the alloys 2024, 2124, 2224 and 2324, whereas in these
successive compositions, the Mn content has not changed. Adjusting the
outlet temperature of the hot rolling obtains, with the compositions
according to the invention, a largely recrystallized microstructure with a
recrystallization rate which is always higher than 50% and a
recrystallization gradient between the surface and the core of the sheet
which is always less than 35%. This is particularly remarkable in heavy
sheets which, at mid-thickness, have a structure which is substantially
more recrystallized than the sheets of the prior art with the same
composition in terms of major elements.
Contrary to what the metallurgist specializing in high-strength aluminum
alloys might expect, this highly recrystallized structure and the low Mn
contents, which participate in the age hardening of the alloy due to the
fine precipitates of Al.sub.2 OCu.sub.2 Mn.sub.3 and AlMn.sub.6, do not
affect the static mechanical properties of the sheet in any significant
way. Moreover, it has been determined that the fatigue properties are also
preserved, whereas a reduction in fatigue resistance might have been
expected.
Furthermore, in the case of heavy sheets>20 mm thick, the inventors
unexpectedly determined that a largely recrystallized structure would lead
to greater toughness in all directions, as measured by the critical stress
intensity factor under plane strain K.sub.1c in accordance with the ASTM E
399 standard.
Finally, these heavy sheets with a largely recrystallized structure have
lower crack-velocities in the L-T and T-L directions than the sheets of
the prior art with the same composition in terms of major elements. Thus,
they make it possible to obtain an advantageous compromise between the
static mechanical properties and the damage tolerance properties
(toughness and crack velocity).
For light sheets, the inventors determined that the composition according
to the invention had a positive influence on the elongation in the
transverse-long direction of the sheet, in contrast to the generally
accepted idea that high Mn and Fe contents have a favorable effect on this
elongation, since the fines precipitated from the manganese make it
possible to homogenize the strain by limiting the formation of bands of
strain. Likewise, it was generally accepted by metallurgists that for
light or average sheets, an extremely recrystallized and fine-grained
structure, which was recognized to be beneficial to elongation, was
preferably obtained with high Mn and Fe contents.
Thus the reduction in the Mn-2Fe content below the 0.2% threshold, in light
sheets as well as heavy sheets, leads not only to a reduction in residual
stress which results in better machining stability, but also to a set of
usage properties which are particularly advantageous for aircraft
construction. It is not desirable, however, for the value of Mn-2Fe to
become negative, since in that case a degradation of the mechanical
properties is observed without any additional gain in the reduction of
internal stress.
The sheets according to the invention have, in the quenched and stretched
state or in the quenched, stretched and annealed state, a level of
residual stress such that the deflection f measured after a machining-to
half-thickness of a bar resting on two distant supports with a length 1 is
such that:
fe<0.14 l.sup.2
with f being measured in micrometers, and the thickness e of the sheet and
the length l being expressed in mm.
This deflection is measured in the following way. Two bars are taken from
the sheet with the thickness e: one called the direction L bar, which has
a length b in the direction of the length of the sheet (direction L), a
width of 25 mm in the direction of the width of the sheet (direction TL)
and a thickness e which corresponds to the full thickness of the sheet
(direction TC); the other, called the direction TL bar, has 25 mm in the
direction L, b in the direction TL and e in the direction TC.
Each bar is machined to half-thickness and the deflection is measured at
the mid-length of the bar. This deflection represents the level of
internal stress of the sheet and its ability not to be deformed during
machining.
For heavy sheets with a thickness greater than 20 mm, the length b of the
bars is 5e+20 mm. The machining is a progressive mechanical machining in 2
mm passes. The deflection at mid-length is measured to the nearest
micrometer with the aid of a comparator, at the center of the bar, which
is positioned between two distant knives with l=5e, which bar extends 10
mm beyond both sides of the knives.
For sheets with a thickness of<20 mm, the length b of the bar is 400 mm and
the length 1 used to measure the deflection is set at 300 mm.
For thicknesses between 8 and 20 mm, the machining is a mechanical
machining in 1 mm passes. Below 8 mm, the machining is a chemical one in a
soda bath. One side of the bar is protected by means of a flexible plastic
mask put in place before the test. The sample is removed from the etching
bath and its thickness is checked every 15 minutes.
For light sheets with a thickness of<2 mm, the method is slightly
different. The measurement of the deflection is carried out with the bar
placed on its side (length, half-thickness) on a sheet of paper marked in
millimeters, which is itself placed on a horizontal surface, making it
possible to measure the deflection to the nearest 0.5 mm, by eliminating
the influence of the dead weight of the bar and the force of the
comparator on the deflection at mid-length.
The inventors also determined that the isotropy of strain could be
improved. Thus, in the sheets according to the invention, the deflection
measured on the bars in the long direction and in the direction transverse
to the rolling were such that:
(direction L deflection)<1.5 (direction TL deflection)
For light and average sheets<12 mm thick, it was determined that the
roughness after chemical machining was less than 6 micrometers, and for
sheets less than<4 mm thick, less than 3 micrometers.
The invention also applies to aluminum alloy products other than sheet
metals, for example extruded, forged, or die-formed products. In this
case, the thickness e of the bar is the local thickness of the piece, and
if this thickness is not constant, a surfacing can be carried out in order
to produce a bar of constant thickness for the measurement of the
deflection.
These products have a yield strength>290 MPa in the quenched and
de-stressed state, and>400 MPa in the quenched, de-stressed and annealed
state.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 through 10 represent the comparative results mentioned in the three
examples so as to show the improvements in the properties obtained by the
sheets according to the invention.
FIGS. 1 and 2 show the improvement in machining stability in the long
direction (L) and in the traverse-long direction (TL) for heavy sheets.
FIG. 3 shows the improvement in the isotropy of the machining stability for
these sheets in the directions L and TL.
FIGS. 4, 5 and 6 show, for these same sheets, the improvement in toughness
in the directions L-T, T-L, and S-L.
FIG. 7 illustrates the results in terms of fatigue resistance.
FIG. 8 shows the relative improvement in crack velocity.
FIG. 9 shows the improvement in elongation in the direction T-L in light
sheets.
FIG. 10 shows the improvement in machining stability for light sheets.
FIGS. 11 and 12 illustrate the results related to machining stability and
crack velocity for average sheets.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Example 1
The inventors carried out several semi-continuous castings of plated sheets
made from different alloys of the 2024 type, in the nomenclature of the
Aluminum Association. All of the plates had the same dimensions and were
cast using the same procedures. They were subjected to a standard
transformation sequence for heavy sheets, that is: reheating after
homogenization, hot rolling, natural aging, quenching with cold water by
spraying, controlled stretching in accordance with the EN 515 standard
between 1.5 and 3%, age hardening at an ambient temperature. In this way,
sheets were obtained which had a thickness of 55 mm in the T351 state, in
the nomenclature of the Aluminum Association. The compositions of the cast
alloys were the following:
__________________________________________________________________________
Alloy
Si Fe Cu Mn Mg Cr Zn Ti Zr
__________________________________________________________________________
A1 0.11
0.23
4.32
0.63
1.43 0.022
0.11
0.02
0.014
A2 0.08
0.17
4.52
0.52
1.40 0.008
0.10
0.02
0.002
A3 0.08
0.16
4.48
0.51
1.41 0.007
0.08
0.02
0.002
A4 0.08
0.15
4.32
0.37
1.29 0.005
0.05
0.02
0.001
A5 0.08
0.16
4.44
0.54
1.30 0.008
0.08
0.02
0.002
__________________________________________________________________________
The following measurements were carried out on these sheets:
deflection after machining according to the method described above. It was
noted that the deflection obtained in the sheets made from the alloys A2,
A3 and A4 according to the invention is lower, particularly in the
direction L, than for those made from the alloys A1 and A5 outside the
invention.
static mechanical properties (tensile strength R.sub.m, 0.2% yield strength
R.sub.0.2, elongation at rupture A) in the directions TL (transverse to
the rolling) and TC (transverse-short).
toughness measured in the directions L-T, T-L and S-L in accordance with
the ASTM E399 and B645 standards. The improvement appears in FIGS. 4
through 6.
recrystallization rate at the surface, at quarter thickness and at
mid-thickness, measured from micrographs. All of the above results are
arranged in Table 1.
fatigue life measured in the directions L and T-L according to the ASTM
E466 standard, for sample No. 3 (the alloy A1 outside the invention) and
sample No. 9 (the alloy A4 according to the invention). The test bars are
3 mm flat test bars taken from the sheets at quarter thickness. The
machining of a central hole makes it possible to have a stress
concentration factor K.sub.t =2.3. The loading is with a ratio R of
minimum stress to maximum stress of 0.1. The results, indicated in Table
2, are roughly identical in the directions L and T-L. They are shown in
FIG. 7, and quite similar results are noted for the two alloys.
crack velocity da/dn, also for samples No. 3 and 9, measured in the
directions T-L and L-T in accordance with the ASTM E647 standard, with a
ratio R =0.1, for values of AK between 10 and 25 MPa.sqroot.m. The test
bars are CT 35 test bars taken from the sheets at quarter thickness. The
results, indicated in Table 3, are quite similar in both directions. It is
noted in FIG. 8 that the crack velocities are lower in sample No. 9 than
in sample No. 3.
Example 2
Plates made from an alloy of the 2024 type were cast semi-continuously,
then subjected to a standard transformation sequence for light plated
sheets, namely: reheating, simultaneous hot-rolling with two plating
sheets made from the alloy 1070, cooling, cold rolling, natural aging,
quenching with cold water, finishing by pass rolling and controlled
stretching, age hardening at an ambient temperature. In this way, sheets
with a thickness of 1.6 mm in the T351 state were obtained which had, on
each side, a plating thickness representing 5% of the thickness of the
sheet.
The compositions of the alloy 2024 were the following:
__________________________________________________________________________
Alloy
Si Fe Cu Mn Mg Cr Zn Ti Zr
__________________________________________________________________________
A6 0.09
0.19
4.38
0.63
1.50 0.013
0.10
0.024
0.014
A7 0.079
0.17
4.36
0.52
1.30 0.012
0.013
0.022
__________________________________________________________________________
The following properties were measured in these sheets:
the deflection after machining according to the method described above. It
is noted that in the alloy A7 according to the invention, this deflection
was clearly reduced, both in the direction L and in the direction TL,
relative to the alloy A6 outside the invention, and that it verifies the
relation: fe<0.04 l.sup.2.
the static mechanical properties in the direction TL (an average of 2 test
bars taken in the direction transverse to the rolling and an average of 4
sheets per alloy).
The results are summarized in Table 4. An improvement in the elongation in
the direction TL of the alloy A7 relative to A6 is noted in FIG. 9, and a
reduction in the deflection during machining of A7 relative to A6 is noted
in FIG. 10.
Example 3
Plates with the same dimensions were cast semi-continuously, using the same
casting procedure. These plates were subjected to a standard
transformation sequence for average sheets, that is: reheating, hot
rolling, natural aging, quenching with cold water, controlled stretching,
age hardening at an ambient temperature. In this way, sheets with a
thickness of 12 mm in the T351 state were obtained, which had the
following composition:
__________________________________________________________________________
Alloy
Si Fe Cu Mn Mg Cr Ni Zn Ti Zr
__________________________________________________________________________
A8 0.08
0.17
4.45
0.53
1.46
0.007
0.005
0.06
0.02
0.002
__________________________________________________________________________
The following properties were measured in these sheets:
the deflection after machining according to the procedure described above,
the static mechanical properties in the direction TL (transverse to the
rolling),
the recrystallization rate on the surface, at quarter thickness and at
mid-thickness.
The results are presented in Table 5 and illustrated in FIGS. 11 and 12.
TABLE 1
__________________________________________________________________________
DEFLECTION
RECRYSTALLIZATION MECHANICAL PROPERTIES
SHEET (micrometers) Surface/Mid-th.
TL TC TOUGHNESS
No.
e. (mm)
Alloy
fL fTL Surface
Quarter
Mid-th.
Deviation
Rm R0.2
A %
Rm R0.2
A %
L-T
T-L
S-L
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1 55 A1 210
120 478
351
13.6
431
306
5.9
2 55 " 231
55 468
342
15.7
432
306
6.1
3 55 " 207
79 79 58 30 49 470
341
15.3
432
306
6.2
37.1
32.2
22.2
4 55 A2 57 43 99 95 71 28 461
330
16.5
419
315
7 44.4
38.1
5 55 " 46 33 100 95 69 31 462
329
17.2
417
314
6.3
44 40.9
6 55 " 42 31 100 96 68 32 462
329
16.9
422
312
7.1
45.3
38.5
7 55 A3 57 62 97 84 63 34 468
343
17.7
421
320
5.4
8 55 " 100
70 96 68 62 34 481
358
14.7
422
315
4.9
43.2
37.2
26.1
9 55 A4 49 73 99 93 70 29 463
332
14.4
425
299
8.5
51.8
43.8
29.6
10 55 A5 156
9 95 82 64 31 470
344
16.5
425
312
6.1
11 55 " 128
1 96 86 62 34 468
336
17.4
418
314
5.1
12 55 " 150
25 99 88 70 29 469
338
16.1
418
314
6
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TABLE 2
______________________________________
Fatigue results in sheet Nos. 3 and 9
(Kt = 2.3, R = 0.1)
Max. stress Endurance
Direction (MPa) (No. of cycles)
______________________________________
Sheet No. 3
TL 260 21000
L 260 20000
TL 230 31000
L 230 33000
TL 230 33000
L 230 35000
TL 230 35000
TL 210 47000
L 210 51000
TL 180 131000
L 180 140000
TL 160 279000
L 160 150000
TL 150 15553000
TL 170 147000
L 170 173000
TL 160 420000
L 160 256000
TL 170 121000
L 170 139000
TL 160 234000
Sheet No. 9
TL 300 10700
L 300 15400
TL 280 23200
L 280 22500
TL 260 25600
L 260 22600
TL 240 30200
L 240 33000
TL 222 58800
L 210 60800
TL 200 95100
TL 190 101600
L 190 110000
TL 180 182800
L 180 190000
TL 160 332000
L 160 700000
TL 150 589700
L 150 434000
TL 140 9567000
L 140 7834500
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TABLE 3
______________________________________
Delta K
da/dn
(MPa.sqroot.m)
(mm/cycle)
______________________________________
Sheet No. 3
10 1.0E-04
15 4.0E-04
20 7.0E-04
25 2.5E-03
Sheet No. 9
10 2.0E-05
15 1.0E-04
20 6.0E-04
25 2.0E-03
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TABLE 4
______________________________________
MECHANICAL
DEFLECTION
PROPERTIES TL
SHEET (micrometers)
Rm R0,2
Sheet No.
Alloy e. (mm) fL fTL (MPa) (MPa) A %
______________________________________
13 A6 1.6 4000 3000 440 305 20.05
14 A6 1.6 3000 4000 440.5 301.5 20.95
15 A6 1.6 4000 3500 441 298.5 21.55
16 A6 1.6 3500 3000 443 301 21.25
Average 3625 3375 441.1 301.5 21.0
17 A7 1.6 500 0 439.5 294 24.55
18 A7 1.6 1500 1500 438.5 277.5 24.4
19 A7 1.6 2000 1500 440 290 23.85
20 A7 1.6 1000 0 441 289.5 25
Average 1250 750 439.8 287.8 24.5
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TABLE 5
__________________________________________________________________________
DEFLECTION MECHANICAL PROPERTIES
SHEET (micrometers)
RECRYSTALLIZATION TL
Sheet No.
e. (mm)
Alloy
fL fTL Surface
Quarter
Core
Surface-Core Deviation
Rm (MPa)
R.02 (MPa)
A %
__________________________________________________________________________
21 12 A8 240
480 90 90 67 23 465 335 15
22 12 A8 710
90 100 99 97 3 470 339 15
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