U.S. patent application number 10/189176 was filed with the patent office on 2003-02-13 for product for a welded construction made of almgmn alloy having improved mechanical strength.
Invention is credited to Cottignies, Laurent, Hoffmann, Jean-Luc, Pillet, Georges, Raynaud, Guy-Michel.
Application Number | 20030031580 10/189176 |
Document ID | / |
Family ID | 27253029 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030031580 |
Kind Code |
A1 |
Raynaud, Guy-Michel ; et
al. |
February 13, 2003 |
Product for a welded construction made of AlMgMn alloy having
improved mechanical strength
Abstract
Rolled or extruded products for welded constructions made of
AlMgMn type aluminum alloy. These products contain, in % by weight,
3.0<Mg<5.0, 0.75<Mn<1.0, Fe<0.25, Si<0.25,
0.02<Zn<0.40, optionally one or more of the elements Cr, Cu,
Ti, Zr such that Cr<0.25, Cu<0.20, Ti<0.20, Zr<0.20,
other elements <0.05 each and <0.15 in total, wherein
Mn+2Zn>0.75. In the welded state, these products have improved
mechanical strength and resistance to fatigue without unfavorable
consequences with regard to toughness and corrosion resistance, and
are particularly suitable for naval construction, for industrial
vehicles and for bicycle frames made of welded tubes.
Inventors: |
Raynaud, Guy-Michel;
(Voiron, FR) ; Hoffmann, Jean-Luc; (Limoges,
FR) ; Cottignies, Laurent; (Poisat, FR) ;
Pillet, Georges; (Saint Cassin, FR) |
Correspondence
Address: |
DENNISON, SCHULTZ & DOUGHERTY
Suite 612
1745 Jefferson Davis Highway
Arlington
VA
22202
US
|
Family ID: |
27253029 |
Appl. No.: |
10/189176 |
Filed: |
July 5, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10189176 |
Jul 5, 2002 |
|
|
|
08875113 |
Jul 25, 1997 |
|
|
|
6444059 |
|
|
|
|
08875113 |
Jul 25, 1997 |
|
|
|
PCT/FR96/00279 |
Feb 21, 1996 |
|
|
|
Current U.S.
Class: |
420/541 |
Current CPC
Class: |
C22C 21/06 20130101 |
Class at
Publication: |
420/541 |
International
Class: |
C22C 021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 1995 |
FR |
95/02387 |
Oct 9, 1995 |
FR |
95/12065 |
Claims
What is claimed is:
1. Aluminum alloy sheet for a welded construction, consisting
essentially of, in % by weight: 3.0<Mg<5.0 0.5<Mn<1.0
0.02<Zn<0.40 Fe<0.25 Si<0.25 Cr<0.25 Cu<0.20
Ti<0.20 Zr<0.20 other elements <0.05 each and <0.15
total, remainder Al, wherein Mn+2Zn>0.75.
2. Sheet according to claim 1, wherein Mn+2Zn>0.8.
3. Sheet according to claim 1, wherein Cr<0.15.
4. Sheet according to claim 1, wherein Mg>4.3.
5. Sheet according to claim 4, wherein Mg>4.6.
6. Sheet according to claim 1, wherein 0.10.ltoreq.Zn<0.40.
7. Sheet according to claim 1, wherein Mn>0.8.
8. Sheet according to claim 1, wherein Fe<0.20.
9. Sheet according to claim 8, wherein Fe<0.15.
10. Sheet according to claim 1, wherein dispersoids are present in
a volumetric fraction greater than 1.2%.
11. Sheet according to claim 1, having a thickness >2.5 mm and
obtained directly by hot rolling.
12. Sheet according to claim 1, having, in an unwelded state,
fatigue resistance, measured by plane bending wherein R=0.1 in the
cross-longitudinal direction, higher than: 10.sup.5 cycles, with a
maximum stress >280 MPa; 10.sup.6 cycles with a maximum stress
>220 MPa; 10.sup.7 cycles with a maximum stress >200 MPa.
13. Sheet according to claim 1, having a fissure propagation rate
.DELTA.K, measured when R=0.1, higher than: 22 Mpa.check mark.m
when da/dn=5.times.10.sup.-4 mm/cycle; 26 Mpa.check mark.m when
da/dn=10.sup.-3 mm/cycle.
14. Sheet according to claim 1, welded by fusion to form a welded
zone, and having a hardness >80 Hv in the welded zone.
15. Sheet according to claim 1, having a yield stress, measured on
a standard DNV sample across an MIG butt welded joint, greater than
140 MPa.
16. Sheet according to claim 15, having a yield stress, measured on
a standard DNV sample across an MIG butt welded joint, greater than
150 MPa.
Description
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 08/875,113, filed Jul. 25, 1997, which was
filed under 35 USC 371 on the basis of PCT/FR96/00279, filed Feb.
21, 1996.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to the sphere of rolled or extruded
products such as sheets, profiles, wires or tubes made of
AlMgMn-type aluminum alloy containing more than 3% by weight of Mg,
intended for welded constructions having a high yield stress, good
resistance to fatigue and good toughness for structural
applications such as ships, industrial vehicles or welded bicycle
frames.
[0004] 2. Description of Related Art
[0005] The optimum dimensioning of welded structures made of
aluminum alloy leads to the use of 5000 series AlMg alloys
according to the Aluminum Association nomenclature, in the
cold-worked temper (temper H1 according to the standard NF-EN-515)
or partially softened temper (temper H2), or stabilized temper
(temper H3), while maintaining high resistance to corrosion (temper
H116) rather than the annealed temper (temper O). However, the
improvement in the mechanical characteristics relative to the
temper O does not usually remain after welding, and certifying and
monitoring organizations generally recommend that only the
characteristics in temper O be taken into consideration for welded
structures. The resistance to fatigue and the fissure propagation
rate should also be taken into consideration for dimensioning.
[0006] In this sphere, research has concentrated mainly on the
implementation of the welding operation itself. There have also
been attempts to improve the corrosion resistance of the article by
appropriate thermomechanical treatments.
[0007] Japanese patent application JP 06-212373 proposes the use of
an alloy containing 1.0 to 2.0% of Mn, 3.0 to 6.0% of Mg and less
than 0.15% of iron to minimize the reduction in the mechanical
strength due to welding. However, the use of an alloy having such a
high manganese content leads to a reduction in the resistance to
fatigue and in the toughness.
SUMMARY OF THE INVENTION
[0008] The object of the invention is significantly to improve the
mechanical strength and fatigue resistance of welded structures
made of AlMgMn alloy, under predetermined welding conditions,
without unfavorable consequences for other parameters such as
toughness, corrosion resistance and cutting deformation, due to
internal stresses.
[0009] The invention relates to products for welded constructions
made of an AlMgMn aluminum alloy containing, in % by weight:
[0010] 3.0<Mg<5.0
[0011] 0.5<Mn<1.0
[0012] 0.02<Zn<0.40
[0013] Fe<0.25
[0014] Si<0.25
[0015] optionally one or more of the elements Cr, Cu, Ti, Zr such
that:
[0016] Cr<0.25
[0017] Cu<0.20
[0018] Ti<0.20
[0019] Zr<0.20
[0020] other elements <0.05 each and <0.15 in total, wherein
Mn+2Zn>0.75.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Contrary to earlier research which concentrated on the
welding process and the thermomechanical treatments, the inventors
have found a particular, range of composition for minor alloying
elements, in particular iron, manganese and zinc, leading to an
interesting set of properties combining static mechanical
characteristics, toughness, resistance to fatigue, resistance to
corrosion and cutting deformation, this set of properties being
particularly well adapted to the use of these alloys for naval
construction, utility vehicles or the welded frames of
bicycles.
[0022] This set of properties is obtained by combining a low iron
content, <0.25%, preferably <0.20%, and even 0.15%, and a
manganese and zinc content such that Mn+2Zn>0.75%, preferably
>0.8%. The Mn content should be >0.5%, preferably >0.8%,
to have adequate mechanical characteristics, but should not exceed
1% if a deterioration in toughness and fatigue resistance are to be
avoided. The addition of zinc combined with manganese has been
found to have a beneficial effect on the mechanical characteristics
of welded sheets and joints. However, it is better not to exceed
0.4% because problems can then be encountered in welding.
[0023] The magnesium is preferably kept >4.3%, because it has a
favorable effect on the yield stress and fatigue resistance, but
beyond 5% the corrosion resistance is less good. The addition of Cu
and Cr are also favorable to the yield stress, but Cr is preferably
kept <0.15% to maintain good resistance to fatigue.
[0024] The mechanical strength of the sheets depends both on the
magnesium content in solid solution and on the manganese
dispersoids. It has been found that the volumetric fraction of
these dispersoids, which is linked to the iron and manganese
contents, should preferably be kept above 1.2%. This volumetric
fraction is calculated from the average of the surface fractions
measured on polished cuts produced in three directions (length,
width and thickness) by scanning electron microscopy and image
analysis.
[0025] The products according to the invention can be rolled or
extruded products such as hot- or cold-rolled sheets, wires,
profiles or extruded and optionally drawn tubes.
[0026] The sheets according to the invention, which are assembled
by butt welding by a MIG or TIG process and with a bevel of the
order of 45.degree. over about 2/3 of the thickness have, in the
welded region, a yield stress R.sub.0.2 which can be at least 25
MPa higher than that of a conventional alloy having the same
magnesium content, that is a gain of about 20%.
[0027] The width of the thermally affected region is reduced by
about one third relative to a conventional 5083 alloy, and the
hardness of the welded joint increases from about 75 Hv to more
than 80 Hv. The welded joints also have a tensile strength
exceeding the minimum imposed by organizations monitoring unwelded
cold-worked crude sheets.
[0028] The sheets according to the invention have fatigue
resistance, measured by plane bending with a stress ratio wherein
R=0.1 on samples taken in the cross-longitudinal direction, higher
than:
[0029] 10.sup.5 cycles with a maximum stress >280 MPa;
[0030] 10.sup.6 cycles with a maximum stress >220 MPa;
[0031] 10.sup.7 cycles with a maximum stress >200 MPa.
[0032] The fissure propagation rate .DELTA.K, measured when R=0.1,
is >22 Mpa.check mark.m when da/dN=5.times.10.sup.-4 mm/cycle
and >26 Mpa.check mark.m when da/dN=10.sup.-3 mm/cycle.
[0033] The sheets according to the invention usually have a
thickness greater than 1.5 mm. With thicknesses greater than 2.5 mm
they can be obtained directly by hot rolling, without the need for
subsequent cold rolling and, furthermore, these hot-rolled sheets
are less distorted on cutting than cold-rolled sheets.
[0034] The products according to the invention have corrosion
resistance which is as good as that of normal alloys having the
same magnesium content, for example 5083 of common composition,
widely used in naval construction.
EXAMPLE
[0035] Eight samples of sheets were prepared by conventional
semi-continuous casting in the form of plates, were heated for 20 h
at a temperature >500.degree. C. and were then cold-rolled to
the final thickness of 6 mm. The reference 0 corresponds to a
conventional 5083 composition and reference 1 to a composition
slightly outside the invention. The others have a composition
according to the invention.
[0036] The compositions were as follows (% by weight):
1 Ref. Mg Cu Mn Fe Cr Zn Ti Zr 0 4.40 <.01 0.50 0.27 0.09 0.01
0.01 1 4.68 <0.01 0.72 0.12 0.05 <0.01 0.01 2 4.60 <0.01
0.85 0.17 0.10 0.16 0.01 3 4.62 <0.01 0.96 0.10 0.05 0.02 0.01 4
4.80 0.09 0.80 0.11 0.03 0.02 0.01 5 4.72 <0.01 0.87 0.13 0.03
0.02 0.01 0.11 6 4.92 0.06 0.94 0.08 0.02 0.19 0.01 7 4.69 <0.01
0.72 0.07 0.02 0.10 0.01
[0037] The samples all have, after rolling, a yield stress
R.sub.0.2>220 Mpa in the L direction.
[0038] The mechanical strength of the joints welded from these
sheets was measured under the following conditions: continuous
automatic MIG butt welding with a symmetrical bevel having an
inclination of 45.degree. to the vertical over a thickness of 4 mm
and filler wire of 5183 alloy.
[0039] The mechanical characteristics (tensile strength R.sub.m,
yield stress R.sub.0.2) were obtained by pulling over samples
standardized by the Norwegian monitoring organization DNV for naval
construction having a length of 140 mm and a width of 35 mm, the
weld bead with a width of 15 mm being in the center and the length
of the narrow portion of the sample being 27 mm, that is the sum of
the width of the bead and twice the thickness (15+22 mm).
[0040] The volumetric fractions of manganese dispersoids was also
measured.
[0041] The results are as follows (in MPa for resistances and % for
fractions):
2 Ref. R.sub.m R.sub.0.2 Fractions 0 285 131 0.62 1 292 144 1.2 2
300 146 1.6 3 310 158 1.7 4 309 149 1.4 5 305 155 1.5 6 318 164 1.9
7 310 153 1.5
[0042] It is found that the yield stress of samples welded
according to the invention increases by between 15 and 35 MPa
relative to the reference sample.
[0043] The resistance to fatigue of unwelded sheets subjected to
plane bending wherein R=0.1 was also measured for references 0 to
4, while determining the maximum stress (in MPa) corresponding to
10.sup.6 and 10.sup.7 cycles respectively, as well as the fissure
propagation rate .DELTA.K measured when da/dn=5.times.10.sup.-4
mm/cycle (in Mpa.check mark.m).
[0044] The results were as follows:
3 Ref. 10.sup.6 cycles 10.sup.7 cycles .DELTA.K 0 220 200 22 1 235
205 22 2 225 200 23 3 230 205 22 4 225 200 22
[0045] It is found that, despite the increase in the mechanical
strength, the sheets according to the invention have resistance to
fatigue which is at least as good as that of conventional 5083
sheets.
* * * * *