PROCEDE DE FABRICATION D'UN DEMI-PRODUIT A PARTIR D'UN ALLIAGE D'ALUMINIUM ET ARTICLE OBTENU PAR CE PROCEDE

METHOD FOR PRODUCING HALF-FINISHED PRODUCTS MADE OF ALUMINIUM ALLOYS AND AN ARTICLE MANUFACTURED WITH THE AID OF SAID METHOD

Abrégé français

L'invention concerne un procédé de fabrication de demi-produits déformables à partir d'alliages d'aluminium et articles faits des ces demi-produits, qui se présentent comme des cloisons, ferrures, poutres, etc., destinés à être utilisés en industrie aérospatiale et dans des véhicules de transport. Le procédé de l'invention comprend les opérations suivantes: coulage d'un lingot, homogénéisation, forgeage du lingot, pressage d'une ébauche, trempage et déformation à froid en deux stades. Cette dernière comprend ce qui suit: 1) formage par étirage, avec une déformation résiduelle entre 1 et 5 %, 2) pliage volumique de l'ébauche, avec déformations plastiques simultanée par compression entre 1 et 20 % dans les zones de jonction des éléments de l'ébauche disposés sous un angle de 45 - 135 DEG les uns par rapport aux autres, vieillissement (1er palier: chauffage à une température de 90 à 120 DEG C pendant 5 à 24 heures; 2ème palier: chauffage à une température de 160 à 190 DEG C pendant 5 à 20 h). Le procédé de l'invention permet d'obtenir des demi-produits longs de forme complexe à partir d'alliages d'aluminium déformés présentant des caractéristiques de rigidité et une résistance au fissuration élevées ainsi qu'un faible niveau de contraintes résiduelles, ce qui permet d'obtenir lors d'un traitement mécanique des articles sans retrait ni ondulation.

Abrégé anglais

The present invention relates to the method of fabrication of wrought
semiproducts
from high strength aluminium-based alloys, and fabrication of articles from
such
semiproducts e.g frames, fittings, beams, etc. used in aerospace engineering
and
transportation facilities.
The suggested method comprises:
casting an ingot, homogenization, forging the ingot, extrusion of the wrought
billet, solution heat treatment, cold working in two steps:
1. stretching with 1-5% permanent set,
2. multi-axial shaping of the billet by bending while simultaneously
performing the
local plastic deformation of the billet by compressing (1-20 %) the joint
places of the
blank parts being disposed at an angle of 45-135° to each other;
two stage ageing: 1st stage = heating to 90-120°C for 5-24 hours;
2nd stage = heating to 160-190°C for 5-20 hours. The suggested method
allows to fabricate long, irregular-shaped semiproducts from wrought aluminium-
based
alloys having high strength and fracture toughness and low level of residual
stresses,
thereby providing the fabrication of products without any distortion or
buckling upon
machining.

Revendications

7
The embodiments of the invention in which an exclusive property or privilege
is
claimed are defined as follows:
1. A method of fabrication of a semiproduct from aluminium-based alloy, the
method comprising:
casting an ingot;
homogenizing;
forging an ingot;
extruding a forged billet into an extruded blank;
solution heat treating and quenching; and
cold working and ageing of the blank, wherein cold working after solution heat
treating
and quenching comprises the steps of:
stretching of the as-quenched extruded blank; and
multi-axial shaping of the blank by bending while simultaneously performing
local plastic deformation of the blank by compressing joint places of blank
parts,
wherein said parts are a longitudinal rib and a plate disposed at a
predetermined
angle to each other.
2. A method according to claim 1, wherein the stretching is performed with 1-
5%
permanent set without heating.
3. A method according to claim 1 or 2, wherein the multi-axial shaping of the
blank
is performed in a die without heating by bending, and wherein local
compression with
1-20% permanent set is provided.
4. A method according to any one of claims 1 to 3, wherein the ageing is
performed
in two stages:
wherein the first stage comprises heating to a temperature of 90-120°C
for 5-24 hours;
and
wherein the second stage comprises heating to a temperature of 160°C-
190°C for 5-20
hours.

8
5. A method according to any one of claims 1 to 4, wherein the blank parts are
disposed at an angle of 45-135° to each other.
6. An aluminium-based alloy semiproduct fabricated by the method as defined in
any one of claims 1 to 5.
7. An aluminium-based alloy semiproduct as defined in claim 6, wherein the
semiproduct combines high strength and crack resistance with a low level of
residual
stress.
8. An article fabricated from the semiproduct as defined in claim 6 or 7,
wherein the
article is of irregular shape and has a length-to-width ratio > 2:1.

Description

CA 02417998 2008-12-08
Method For Producing Half-Finished Products Made Of Aluminium Alloys
And An Article Manufactured With The Aid Of Said Method
Field of the Invention
The present Invention relates to metallurgy, and more particularly it relates
to the
method of fabrication of wrought semiproducts from aluminium-based alloys and
the
articles made from said semiproducts. Such articles may be used in aerospace
engineering,
ship building, automotive and machine - building as frames, fittings, beams
and other
irregular-shaped long elements preferably having longitudinal and transverse
ribs. In such
articles the most important are: the low level of residual stresses and the
related distortion
and buckling during subsequent machining of semiproducts.
Background of the Invention
Well-known is the method of fabrication of semiproducts from high strength
aluminium-based alloy, which method comprising casting an ingot,
homogenization,
preferably extrusion of the billet, forging and hardening (solution heat
treatment +
quenching + aging) (US Patent 3.791.876 US Cl. 148/2 (publ. 24.10.72)) [1]. By
this
method it is possible to produce irregular-shaped semiproducts having high
strength but
their distortion is rather great. It leads to reduction (up to 40-50%) of
articles' output after
machining. When producing long regular-shaped semiproducts (e.g. sheets,
plates), there is
widely used stretching with 1-10% permanent set in order to relieve residual
stresses and to
prevent distortion (Kozlovskaya V.P., Kudryashov V.G., Bunnistrov V.I. et al,.
<<Technologiya Lyogkikh Splavov>>, 1976, .No 11, pp. 16-18) [2]; (Vladimirov
S.A.,
Vishnyakov Ya.D., Shadsky A.A. <<Technologiya Lyogkikh Splavov>>, 1977, N211,
pp. 18-
21) [3]. But this method is not applicable to complex- shaped semiproducts
because
stretching of such products doesn't reduce distortion to required degree owing
to
uncontrollable non-uniformity of deformation along stretching axis.
To relieve residual stresses and to reduce distortion of irregular-shaped
semiproducts it is known to use compressing with 1-6% permanent set (Bykov
L.N.,
Vladimirov S.A., Shadsky A.A. Technologiya Lyogkikh Splavov , 1982, Xol, pp.
25-29)
[4]. But this method also has essential restrictions because of the irregular
shape of the
product. In particular, the scheme of deformation by compressing is maximum
effective
when regular-shaped products having axial symmetry (cylindrical, circular,
rectangular)
are straightened.

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When long articles having complex geometry (having ribs, curved elements,
different thicknesses) e.g. fittings, frames, etc, are to be straightened, one
can't use the
method of compressing because it is not possible to provide uniformity of
plastic
deformation and to eliminate distortion and buckling during subsequent
machining.
Well-known is the method of production of semiproducts from wrought
aluminium-based alloys, which method comprising:
-casting a billet,
-homogenization of as-cast billet,
-forging of as-cast billet,
-extrusion of the forged billet,
-solution heat treatment and quenching from 470 C,
-cold working by compressing in one direction with 1,5-5,0% set and then in
another direction normal to the first one with the same -set,
-aging 108 C, 7 hours+163 C, 7 hours (Japan Application No 04187747 (publ.
22.11.90) Int. Cl. C22F 1/04) [5].
The shortcoming of this method is the impossibility to produce long, irregular-
shaped semiproducts with length-to-width ratio>2:1, free from quenching
stresses, that
means it is impossible to produce long products of high quality. Besides that,
in said
method relieving of residual stresses is achieved by compression with 1,5-5,0%
set in one
direction and then in another direction normal to the first one, with the same
set, but the
required change in billet shaping is not achieved. Therefore in order to
provide the required
shape, the subsequent step is needed which causes the additional residual
stresses which in
turn lead to distortion and to quality reduction during the subsequent
machining.
Description of Invention
The object of the present invention is to provide the method of fabrication of
long,
irregular-shaped semiproducts from wrought aluminium-based alloys with
enhanced
strength properties and crack resistance, and reduced level of residual
stresses, which
method allows to fabricate distortion free products during machining.
Accordingly, there is
provided method comprising:
-casting an ingot,
-homogenization of as-cast billet,
-forging the as-cast billet,
-extrusion of the forged billet,

CA 02417998 2003-02-03
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-solution heat treatment and quenching,
-cold working in two steps:
-the first step comprises stretching of the as-quenched extruded billet;
-the second step comprises multi-axial shaping of the billet by bending while
simultaneously performing the local plastic deformation of the billet by
compressing the
joint places of the blank parts, said parts being disposed at a predetermined
angle to each
other,
-ageing. Stretching is performed with 1,0-5,0% permanent set without heating.
Multi-axial shaping of the billet by bending is performed in a die without
heating,
but providing local compression with 1-20% permanent set of the joint places
of the blank
parts (e.g. ribs and plates). Ageing of the resulted blank is performed in two
stages:
1S` stage - heating to 90-120 C for 5-24 hours;
2 a stage - heating to 160-190 C for 5-20 hours. More preferably, method of
the
invention is applicable to semiproducts consisting of the following parts: a
longitudinal rib
and a plate which are disposed at an angle of 45-135 to each other.
By suggested method it is possible to fabricate such long products as
fittings,
frames, beams, etc., which products have enhanced strength and crack
resistance and have
no distortion or buckling after machining.
The suggested method differs from prior art methods in possibility to change
the
blank shape after solution heat treatment and quenching by multi-axial shaping
by bending
in a die without heating while simultaneously relieving the residual stresses
by performing
the local plastic deformation by compressing (with 1-20% permanent set ) the
joint places
of the blank parts being disposed at an angle to each other, that is why it
becomes possible
to eliminate distortion and buckling during subsequent machining. Besides
that, in the
suggested method the blank parts, namely ribs and plates, are disposed at an
angle of 45-
135 to each other, and length-to-width ratio is > 2:1. The above-said angle
range
embraces all possible structural designs of semiproducts.
Embodiments of the present invention will now be described by way of example.
Examplel
A long fitting blank having an irregular shape: cross- shaped section of
variable
thickness (40-100 mm), asymmetric deflection of blank parts relative to
longitudinal axis,
and angle between ribs and a plate changing from 75 to 105 , was fabricated
from high-

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strength alloy of AI-Zn-Mg-Cu system by the following method: casting of an
ingot 0 870
mm, homogenization of as-cast billet at 460 C for 24 hours, forging the ingot
at all sides at
410 C, extrusion of the cross-shaped blank at 400 C with reduction ratio 1:10.
Solution
heat treatment of the extruded blank from 470 C and water quenching at 20 C.
Stretching
the quenched blank with 1,9% permanent set for residual stress relieving,
multi-axial
shaping of the blank by bending without heating in a die while simultaneously
performing
the local plastic deforrnation by compressing (with 2 % permanent set) the
joint places of
longitudinal ribs and plate thus finally shaping the blank, and ageing at 120
C for 5 hours
+160 C for 15 hours.
Example 2.
From the same alloy as in Example 1, a long blank having cross-shaped section
of
variable thickness (30-80 mm), was fabricated. The blank had more asymmetric
deflection
of axis and plate as compared with Example 1, and angle between ribs and a
plate changed
from 45 to 135 .
In this example the following method was used: casting and homogenization of
an
ingot 0 650 at 460 C for 12 hours; forging an ingot at all sides at 450 C;
extrusion of the
cross-shaped blank at 390 C with reduction ratio 1:10. Solution heat treatment
of the
extruded blank was performed at 470 C with subsequent water quenching at 20 C.
After
quenching the blank was stretched with 2,8% permanent set. Then it was
performed multi-
axial shaping of the blank by bending combined with simultaneous local plastic
deformation by compressing (with 20 % permanent set) the joint places of
blank's ribs and
a plate, without heating, in a die. Ageing was performed as follows: 120 C 24
hours +
190 C 5 hours.
Example 3. A long beam blank with T-shaped cross-section and of variable
thickness (30-65 nun), with asymmetric deflection relative to longitudinal
axis, the angle
between a rib and a plate changing from 60 to 110 , was fabricated from the
alloy B93n*q
(of AL-Zn-Mg-Cu systems) according to the following schedule:
casting and homogenization of an ingot 0 650 at 450 C for 5 hours; forging an
ingot at all sides at 410 C; extrusion of the forged blank at 390 C with
reduction ratio
1:12. Solution heat treatment of the extruded blank at 475 C, water quenching
at 20 C.
After quenching the blank was stretched with 5% permanent set. Then it was
performed
multi-axial shaping of the blank by bending combined with simultaneous local
plastic
deformation by compressing (with 10 % permanent set) the joint places of the
blank's ribs

CA 02417998 2003-02-03
and a plate, in a die without heating. Ageing was performed as follows: 110 C
8 hours +
165 C 12 hours.
Example 4. From the alloy of AI-Zn-Mg-Cu system, a long cross-shaped fitting
blank identical to that of Example 1, having variable (55-110mm) cross-section
thickness,
5 was fabricated according to the method described in Japan Application No
04187747:
casting and homogenization of an ingot 0 870 at 460 C for 24 hours; forging
the as-
cast ingot at all sides at 390 C with reduction ratio 1:8. The hardening of
the wrought billet
included solution heat treatment at 475 C, water quenching at 20 C.
Straightening of the
billet was performed by compressive deformation with 5% permanent set in one
direction
and then in another one normal to the first, with the same set.
Shaping of the final blank was performed by bending in a die without heating.
Ageing was performed as follows: 110 C 8 hours + 165 C 12 hours.
The samples for mechanical properties' and crack resistance determination were
cut
from final semiproducts. The rest semiproducts were machined, and the
deviations of the
blank's dimensions as compared to drawings' requirements, were determined. The
material
utilization index (MUI) was also determined.
The Table below shows the comparative properties of semiproducts obtained by
the
practices of the present invention and disclosed in Japan Application No
04187747.
The data given in the Table evidently show that practice of the present
invention
allows to fabricate long, complex-shaped semiproducts and articles from
aluminium-based
alloy having a pronounced high level of strength and fracture toughness (K ic)
combined
with a reduced level of residual stresses thereby providing the fabrication of
products
without any distortion or buckling upon machining, increase of the material
utilization
index by 1,5 times and avoiding of faulty production related to impermissible
deviations
from the dimensions pointed out in the drawing.
The described method of the invention allows to fabricate long, irregular-
shaped
products such as fittings, frames, beams, etc. used in aerospace engineering
and
transportation facilities.

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6
Table 1
Mechanical properties and data of efficiency of semiproducts fabrication from
high
strength alloy of AI-Zn-Mg-Cu system
Example UTS, MPa YTS, MPa E1, % Kic, Max. MUI*, % Faulty
MPa~m distortion, production
mm through
distortion,
%
1 550 490 13 46 3,0 40 0
2 510 460 14 49 2,0 48 0
3 540 470 14 47 1,8 60 0
4 prior art 520 460 13 39 18,3 25 46
15
25