U.S. patent application number 08/875113 was filed with the patent office on 2001-12-13 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 | 20010050118 08/875113 |
Document ID | / |
Family ID | 26231789 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050118 |
Kind Code |
A1 |
RAYNAUD, GUY-MICHEL ; et
al. |
December 13, 2001 |
PRODUCT FOR A WELDED CONSTRUCTION MADE OF ALMGMN ALLOY HAVING
IMPROVED MECHANICAL STRENGTH
Abstract
The invention relates to rolled or extruded products for welded
constructions made of AlMgMn type aluminium alloy. These products
are composed (% by weight): 3.0<Mg<5.0 0.75<Mn<1.0
Fe<0.25 Si<0.25 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;
(ISSOIRE, FR) ; HOFFMANN, JEAN-LUC; (MOIRANS,
FR) ; COTTIGNIES, LAURENT; (GRENOBLE, FR) ;
PILLET, GEORGES; (SAINT CASSIN, FR) |
Correspondence
Address: |
DENNISON MESEROLE POLLACK & SCHEINER
1745 JEFFERSON DAVIS HIGHWAY SUITE 612
ARLINGTON
VA
22202
|
Family ID: |
26231789 |
Appl. No.: |
08/875113 |
Filed: |
July 25, 1997 |
PCT Filed: |
February 21, 1996 |
PCT NO: |
PCT/FR96/00279 |
Current U.S.
Class: |
148/439 ;
148/440; 420/542 |
Current CPC
Class: |
C22C 21/06 20130101 |
Class at
Publication: |
148/439 ;
148/440; 420/542 |
International
Class: |
C22C 021/06; C22C
021/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 1995 |
FR |
95/02387 |
Oct 9, 1995 |
FR |
95/12065 |
Claims
1. Product for a welded construction made of AlMgMn aluminium alloy
composed of (% by weight): 3.0<Mg<5.0 0.5<Mn<1.0
Fe<0.25 Si<0.25 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 and preferably >0.8%.
2. Product according to claim 1, characterized in that
Mg>4.3%.
3. Product according to one of claims 1 and 2, characterized in
that Mn>0.8%.
4. Product according to one of claims 1 to 3, characterized in that
Fe<0.20%.
5. Product according to claim 4, characterized in that
Fe<0.15%.
6. Product according to one of claims 1 to 5, characterized in that
the volumetric fraction of dispersoids is greater than 1.2%.
7. Sheet according to one of claims 1 to 6, characterized in that
it has a thickness >2.5 mm and is merely hot rolled.
8. Unwelded sheet according to any one of claims 1 to 7,
characterized in that it has 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.
9. Sheet according to any one of claims 1 to 8, characterized in
that it has a fissure propagation rate .DELTA.K, measured when
R=0.1, higher than: 22 Mpa{square root}{square root over (m)} when
da/dn=5.times.10.sup.-4 mm/cycle 26 Mpa{square root}{square root
over (m)} when da/dn=10.sup.-3 mm/cycle
10. Use of a product according to one of claims 1 to 9 in naval
construction.
11. Use of a product according to one of claims 1 to 9 for the
construction of industrial vehicles.
12. Use of extruded tubes according to one of claims 1 to 6 for the
manufacture of welded bicycle frames.
13. Sheet according to one of claims 1 to 9 welded by fusion and
having a hardness >80 Hv in the welded zone.
Description
TECHNICAL SPHERE
[0001] The invention relates to the sphere of rolled or extruded
products such as sheets, profiles, wires or tubes made of
AlMgMn-type aluminium 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.
STATE OF THE ART
[0002] The optimum dimensioning of welded structures made of
aluminium alloy leads to the use of 5,000 series AlMg alloys
according to the Aluminium 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.
[0003] 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.
[0004] 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.
OBJECT OF THE INVENTION
[0005] 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 unfavourable consequences for other parameters such as
toughness, corrosion resistance and cutting deformation, due to
internal stresses.
[0006] The invention relates to products for welded constructions
made of AlMgMn aluminium alloy composed of (% by weight):
[0007] 3.0<Mg<5.0
[0008] 0.5<Mn<1.0
[0009] Fe<0.25
[0010] Si<0.25
[0011] Zn<0.40
[0012] optionally one or more of the elements Cr, Cu, Ti, Zr such
that:
[0013] Cr<0.25
[0014] Cu<0.20
[0015] Ti<0.20
[0016] Zr<0.20
[0017] other elements <0.05 each and <0.15 in total, wherein
Mn+2Zn>0.75.
DESCRIPTION OF THE INVENTION
[0018] 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.
[0019] 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.
[0020] The magnesium is preferably kept >4.3%, because it has a
favourable 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 favourable to the yield stress, but Cr is
preferably kept <0.15% to maintain good resistance to
fatigue.
[0021] 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.
[0022] 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.
[0023] 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%.
[0024] 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.
[0025] 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:
[0026] 10.sup.5 cycles with a maximum stress >280 MPa
[0027] 10.sup.6 cycles with a maximum stress >220 MPa
[0028] 10.sup.7 cycles with a maximum stress >200 MPa.
[0029] The fissure propagation rate .DELTA.K, measured when R=0.1,
is >22 Mpa{square root}{square root over (m)} when
da/dN=5.times.10.sup.-4 mm/cycle and >26 Mpa{square root}{square
root over (m)} when da/dN=10.sup.-3 mm/cycle.
[0030] 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.
[0031] 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
[0032] Thirteen 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 O corresponds to a
conventional 5083 composition and reference 1 to a composition
slightly outside the invention. The 11 others (references 2 to 12)
have a composition according to the invention.
[0033] The compositions were as follows (% by weight):
1 Ref Mg Cu Mn Fe Cr Zn Ti Zr 0 4.40 <0.01 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 4.56 <0.01
0.83 0.12 0.13 0.01 0.01 3 4.60 <0.01 0.85 0.17 0.10 0.16 0.01 4
4.62 <0.01 0.96 0.10 0.05 0.02 0.01 5 4.80 0.09 0.80 0.11 0.03
0.02 0.01 6 4.72 <0.01 0.87 0.13 0.03 0.02 0.01 0.11 7 4.88 0.05
0.78 0.16 0.02 0.01 0.09 8 4.92 0.06 0.94 0.08 0.02 0.19 0.01 9
4.69 <0.01 0.72 0.07 0.02 0.10 0.01 10 4.71 <0.01 0.82 0.06
0.02 <0.01 0.01 11 4.73 <0.01 0.95 0.17 0.03 <0.01 0.01 12
4.70 <0.01 0.92 0.22 0.03 0.01
[0034] The samples all have, after rolling, a yield stress
R.sub.0.2>220 Mpa in the L direction.
[0035] 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.
[0036] 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 centre 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).
[0037] The volumetric fractions of manganese dispersoids was also
measured.
[0038] 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
302 150 1.4 3 300 146 1.6 4 310 158 1.7 5 309 149 1.4 6 305 155 1.5
7 315 166 1.3 8 318 164 1.9 9 310 153 1.5 10 312 150 1.5 11 315 153
1.6 12 315 151 1.5
[0039] 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.
[0040] The resistance to fatigue of unwelded sheets subjected to
plane bending wherein R=0.1 was also measured for references 0 to
5, 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{square root}{square root over (m)}).
[0041] 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 2 230 200 23 3 225 200 23 4 230 205 22 5 225 200 22
[0042] 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.
* * * * *