Note: Descriptions are shown in the official language in which they were submitted.
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Ultra High Strength 6xxx Forged Aluminium Alloys
[0001] The invention relates to ultra-high strength AA6xxx-series aluminium
alloy forgings
particularly suitable for automotive, rail or transportation structural
components, exhibiting an
ultimate tensile strength UTS typically higher than 400 MPa in T6 temper,
preferably higher than
450 MPa, and excellent corrosion resistance.
More particularly such forgings are produced through a manufacturing process
which, besides
including subsequent extrusion and forging steps, includes multiple
solutionising and quench steps
/o in order to achieve, after ultimate age hardening, high strength and
excellent corrosion resistance
on Cu-doped AA6xxx-series alloys.
[0002] Unless otherwise stated, all information concerning the chemical
composition of the
alloys is expressed as a percentage by weight based on the total weight of the
alloy. "6xxx aluminium
/5 alloy" or "6xxx alloy" designate an aluminium alloy having magnesium and
silicon as major alloying
elements. "AA6xxx-series aluminium alloy" designates any 6xxx aluminium alloy
listed in
"International Alloy Designations and Chemical Composition Limits for Wrought
Aluminum and
Wrought Aluminum Alloys" published by The Aluminum Association, Inc. Unless
otherwise
stated, the definitions of metallurgical tempers listed in the European
standard EN 515 will apply.
20 Static tensile mechanical characteristics, in other words, the ultimate
tensile strength R. (or UTS),
the tensile yield strength at 0.2% plastic elongation Rp0,2 (or YTS), and
elongation A% (or E%), are
determined by a tensile test according to NF EN ISO 6892-1.
[0003] Aluminium alloy compositions and tempers have been developed for
obtaining satisfying
25 strength and corrosion behavior in car components such as chassis-
suspension or body structure
parts, but also rail or transportation structural components in particular
when they are made from
forgings obtained from extruded rough products.
In order to achieve tensile properties in excess of 400 MPa in 6xxx alloys, it
is essential to maximise
both the ageing response through an adequate solutionising of solute elements,
predominantly Mg,
30 Si and Cu, while maximising retention of the fibrous structure through
minimal recrystallisation.
Date Recue/Date Received 2022-12-14
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Said recrystallisation is controlled through the addition of dispersoid
elements, typically Mn, Cr
and Zr and appropriate homogenisation temperatures. It is also controlled
through alloy processing
conditions, which arc defined so as to minimise stored-energy and thereby
maximise
rccrystallization temperature.
To achieve adequate solutionising, according to the prior art, highly alloyed
6xlm alloys are usually
separately solutionised and quenched after the ultimate hot forming step (in
this case forging). Such
a solution can be found in the patent application EP 2548933 Al by "Nissan
Motor Co". When
alloys are strongly alloyed it is often required to apply an extended
solutionising treatment (in excess
of 90min) at high temperature (530-560 C) in order to achieve excellent
solutionising. Such a case
to is described in the patent application JP2012-097321 by "Furukawa Sky
Aluminium-Corp". The
corollary to this is that extended recrystal ization will occur on highly
alloyed alloys (unless
significant dispersoid additions are made) as they are brought to a fully
solutionised temper and
the additional strength gained by improved solutionising shall be mitigated by
recovery and
recrystallisation.
[0004] The invention relates to forgings manufactured through a process
including, besides
subsequent extrusion and forging steps, multiple solutionising and quench
steps, to achieve
excellent solutionising and strong retention of the fibrous structure on 6xxx
type alloys, achieving
typically, after last step age hardening (T6 temper), an ultimate tensile
strength UTS higher than
400 MPa, and preferably higher than 450 MPa, and an excellent corrosion
resistance.
[0005] Solidus Ts is the temperature below which the alloy exhibits a solid
fraction equal to 1.
Solvus defines the temperature, which is the limit of solid solubility in the
equilibrium phase
diagram of the alloy. For high strength requirements, eutectic alloying
elements such as Si, Mg and
Cu should be added to form precipitated hardening phases. IIowever, the
addition of alloying
elements generally results in a decrease in the difference between solidus and
solvus temperatures.
When the content of eutectic alloying elements is higher than a critical
value, the solidus to solvus
range of the alloy becomes a narrow "window", with typically a solidus to
solvus difference lower
than 20 C, and consequently the solution heat treatment of the aforementioned
elements usually
achieved during extrusion cannot be obtained without observing incipient
melting. Indeed local
temperature gradients achieved during extrusion and forging, generally exceed
20 C implying that,
as solvus is reached, parts of the product will display temperatures in excess
of solidus Ts.
[0006] According to the prior art, high strength forgings obtained from
extruded rough products,
and from 6xxx-series aluminium alloys characterised by a minimum Silicon
content of 0.7 /o and
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minimum Magnesium content of 0.6%, for example of the AA 6082, 6182, 6110, or
6056 type, are
produced by:
a) casting one of the following aluminium alloys AA6082, 6110, 6182 or 6056
acc. to AA standard
or to a restricted composition within AA standard;
b) homogenising,
c) cooling to room temperature;
d) heating a homogenised cast billet to a temperature 50 C to 100 C lower than
solidus
temperature (approx. 575 C);
e) extruding said billet through a die to produce a solid section profile with
an exit temperature
to (typically 500 C) lower than solidus (typically 550 C), in order to
avoid incipient melting due to
non-equilibrium melting of eutectic phases in profile hot-spots but still
allowing to dissolve part of
the constituent particles;
f) cooling to room temperature;
g) stretching;
h) heating cut-to-length extruded rod to forging temperature (400-520 C);
i) forging in heated mould (150-350 C);
j) separate solutionising at 530-560 C for durations between 30 min. and 90
min.;
k) water quenching the forged material down to room temperature;
1) room temperature ageing
m) ageing to T6 temper by a one-or multiple-step heat treatment at
temperatures ranging from 150
to 200 C for holding times ranging from 2 to 20 hours.
However, ultimate tensile strengths achieved with this processing route do not
exceed 450MPa.
Generally speaking, 400MPa is a maximum especially when ageing has to be
shifted away from
peak ageing T66 in order to guarantee minimum elongation values higher than 10
%.
[00071 The applicant decided to develop a novel combination of 6xxx-series
alloy and process
which secures an ultimate tensile strength higher than 400 MPa, preferably
higher than 450MPa,
and even higher than 480 MPa.
[0008] A first object of the invention is an aluminium alloy forged product
obtained by following
steps:
a) casting a billet from a 6xxx aluminium alloy comprising:
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Si: 0.7-1.3 wt. A; Fe : < 0.5 wt. %; Cu: 0.1-1.5 wt. %; Mn: 0.4-1.0 wt. A;
Mg: 0.6-1.2 wt. A; Cr: 0.05-
0.25 wt.%; Zr: 0.05-0.2 wt. A; Zn: < 0.2 wt.%; Ti: < 0.2 wt.% , the rest
being aluminium and inevitable
impurities;
b) homogenising the cast billet at a temperature TFI which is 5 C to 80 C
lower than solidus
temperature Ts, typically TH in the range of 500-560 C, for a duration between
2 and 10 hours to
ensure high level of dissolution of constituent particles while ensuring
precipitation and controlled
coarsening of dispersoid phases;
c) quenching said billet down to room temperature by using a first water
quench system;
d) heating the homogenised billet to a temperature Th between (Ts ¨ 5 C) and
(Ts - 125 C);
/o e) extruding said billet through a die to produce a solid section with
an exit temperature (typically
530 C) lower than Ts (typically 550 C), in order to avoid incipient melting
due to non-equilibrium
melting of eutectic phases in profile hot-spots but still allowing to dissolve
part of the constituent
particles, and with an extruding ratio of at least 8;
f) quenching the extruded product down to room temperature by using a second
water quench system;
g) stretching the extruded product to obtain a plastic deformation typically
between 0.5% and 10%,
preferably up to 5%;
h) heating cut-to-length extruded rod to forging temperature, typically
between 400 and 520 C;
i) forging in heated mould between 150 and 350 C;
j) separate solutionising at a temperature between 530 and 560 C for durations
between 2 min. and
1 hour;
k) water quenching the forged and solutionised material down to room
temperature;
1) room temperature ageing for a duration between 6 hours and 30 days;
m) ageing to T6 temper by a one-or multiple-step heat treatment at
temperatures ranging from 150 to
200 C for holding times ranging from 2 to 20 hours,
and the aluminium alloy forged product ultimate tensile strength is higher
than 400 MPa.
[0009] According to the invention, the aluminium alloy extruded product is
obtained by casting a
billet from a 6xxx aluminium alloy comprising: Si: 0.7-1.3 wt. %; Fe: < 0.5
wt. %; Cu: 0.1-1.5 wt. A;
Mn: 0.4-1.0 wt. A; Mg: 0.6-1.2 wt. A; Cr: 0.05-0.25 wt.%; Zr: 0.05-0.2 wt.
%; Zn: < 0.2 wt.%; Ti: <
0.2 wt.%, the rest being aluminium and inevitable impurities. The aluminium
alloy according to the
invention is of the AlMgSi type, which, compared with other such as e.g.
AlZnMg alloys, provides an
excellent combination of high tensile strength and resistance to corrosion.
Date Recue/Date Received 2022-06-07
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[0009a] In accordance with one aspect there is provided an aluminium alloy
forged product
characterized in that the process to obtain the product comprises the
following steps:
a) casting a billet from a 6xxx aluminium alloy comprising:
Si: 0.7-1.3 wt. A; Fe: < 0.5 wt. /0; Cu: 0.6-1.0 wt. A; Mn: 0.4-1.0 wt. A;
Mg: 0.7-1.2 wt. A;
Cr: 0.05-0.25 wt%; Zr: 0.05-0.2 wt. %; Zn: < 0.2 wt.%; Ti: < 0.2 wt.% , the
rest being
aluminium and inevitable impurities;
b) homogenising the cast billet at a temperature TH which is 5 C to 80 C
lower than solidus
temperature Ts, for a duration between 2 and 10 hours to ensure high level of
dissolution of
constituent particles while ensuring precipitation and controlled coarsening
of dispersoid
io phases;
c) quenching said homogenised billet down to room temperature by using
water quench system;
d) heating the homogenised and quenched billet to a temperature Th between
(Ts ¨ 5 C) and
(Ts - 125 C);
e) extruding said billet of d) through a die to produce a solid section
with an exit temperature
lower than Ts, to avoid incipient melting due to non-equilibrium melting of
eutectic phases
in profile hot spots but still allowing to dissolve part of the constituent
particles and with an
extruding ratio of at least 8;
quenching the extruded product down to room temperature by using water quench
system;
g) stretching the extruded product to obtain a plastic deformation;
h) heating cut-to-length extruded rod to forging temperature;
i) forging in heated mould between 150 and 350 C;
i) separate solutionising at a temperature between 530 and 560 C for
durations between 2
minutes and 1 hour;
k) water quenching the forged and solutionised material down to room
temperature;
1) room temperature ageing for a duration between 6 hours and 30 days;
m) ageing to T6 temper by a one-or multiple-step heat treatment at
temperatures ranging from
150 to 200 C for holding times ranging from 2 to 20 hours;
and the aluminium alloy forged product ultimate tensile strength is higher
than 400 MPa.
Date Recue/Date Received 2022-01-20
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[0009b] In accordance with another aspect there is provided a process for
manufacturing an aluminium
alloy forged product described herein comprising the following steps:
a) casting a billet from a 6xxx aluminium alloy comprising:
Si: 0.7-1.3 wt. %; Fe: < 0.5 wt. /0; Cu: 0.6-1.0 wt. %; Mn: 0.4-1.0 wt. A;
Mg: 0.7-1.0 wt. %;
Cr: 0.05-0.25 wt.%; Zr: 0.05-0.2 wt. %; Zn: < 0.2 wt.%; Ti: < 0.2 wt.% , the
rest being
aluminium and inevitable impurities;
b) homogenising the cast billet at a temperature TH which is 5 C to 80 C
lower than solidus
temperature Ts, for a duration between 2 and 10 hours to ensure high level of
dissolution of
constituent particles while ensuring precipitation and controlled coarsening
of dispersoid
io phases;
c) quenching said homogenized billet down to room temperature by using
water quench system;
d) heating the homogenised and quenched billet to a temperature Th between
(Ts ¨ 5 C) and
(Ts - 125 C);
e) extruding said billet through a die to produce a solid section with an
exit temperature lower
than Ts lower than Ts, to avoid incipient melting due to non-equilibrium
melting of eutectic
phases in profile hot spots but still allowing to dissolve part of the
constituent particles and
with an extruding ratio of at least 8;
f) quenching the extruded product down to room temperature by using water
quench system;
g) stretching the extruded product to obtain a plastic deformation;
h) heating cut-to-length extruded rod to forging temperature;
i) forging in heated mould between 150 and 350 C;
j) separate solutionising at a temperature between 530 and 560 C for
durations between 2 mm.
and 1 hour;
k) water quenching the forged and solutionised material down to room
temperature;
1) room temperature ageing for a duration between 6 hours and 30 days;
m) ageing to T6 temper by a one-or multiple-step heat treatment at
temperatures ranging from
150 to 200 C for holding times ranging from 2 to 20 hours.
Date Recue/Date Received 2022-01-20
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[0010] The process according to the invention consists in particular in
replacing conventional
homogenising followed by slow cooling, heating and extruding followed again by
slow cooling of
AA6xxx alloy billets, by high temperature homogenising and quenching followed
by heating,
extruding and quenching again, and does not comprise a separate post-extrusion
solution heat
treatment, because, as a result of steps b) and c), most part of the alloying
elements which
contribute to the formation of hardening particles are in solid solution in
the lattice of the extrudate.
[0011] The present invention therefore provides a process to manufacture a
range of 6xxx alloys
with superior mechanical properties, especially if applied to a sufficiently
copper-doped AlMgSiCu,
to with strength levels in excess of 400 MPa and even 450 or 480 MPa,
hitherto not achieved through
a conventional route. In addition, good extrudability and forgeability is
maintained because the
limitation with extrusion speed due to premature speed cracking resulting from
incipient melting
is minimised due to a higher level of dissolution of constituent particles
while ensuring precipitation
and controlled coarsening of dispersoid phases prior to extrusion.
[0012] According to the invention, a billet is provided resulting from casting
a 6xxx aluminium
alloy, ie. an aluminium alloy having magnesium and silicon as major alloying
elements. Preferably,
this aluminium alloy is a high-strength 6xxx aluminium alloy, such as AA6082,
AA6182, AA6056,
AA6110 or any copper-doped alloy derived from the said AA6xxx aluminium
alloys.
[0013] This alloy has preferably a high Cu content, typically between 0.1 and
1.5 wt. Vo, more
preferably between 0.4 and 1.2 wt. Vo, even more preferably between 0.6 and
1.0 wt. Vo. Dispersoid
elements, Mn with a content of 0.4-1.0 wt. Vo, Cr with a content of 0.05-0.25
wt. % and Zr with a
content of 0.05-0.2 wt. Vo, are added to control recrystallization and
maximize the retention of
fibrous structure of the extrudate and the forged component.
[0014] Si and Mg content are defined so as to ensure high level of dissolved
Mg2Si while
minimising presence of undissolved Mg2Si in the forged component after
ultimate solutionising
step, with a maximum content of 0.5 wt.%. For example, when solutionising at
550 C is applied at
the ultimate step of the invention, the content of dissolved Mg is 0.623 wt.%,
dissolved Si is 0.977
wt.% and undissolved Mg2Si 0.45wt.%.
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[00151 Si is combined with Mg to form Mg2Si. The precipitation of Mg2Si
contributes to
increasing the strcngth of the final aluminium alloy forged product.
If the Si content is less than 0.7 wt.%, the final product does not have a
sufficiently high strength,
it means a tensile strength not higher than 400 MPa. If it is lower than 0.9
wt.%, tensile strength
will be at most 450 MPa and with less than 1.1wt.% it will be lower than 480
MPa.
On the other hand, if the Si content is more than 1.3 wt.%, the level of
undissolved Mg2Si is too
high and extrudabi]ity is reduced as well as corrosion resistance and
toughness of the resultant final
forged product.
to [0016] Mg is combined with Si to form Mg2Si. Therefore Mg is
indispensable for strengthening
the product of the present invention. If the Mg content is lower than 0.7
wt.%, the effect is too
weak. On the other hand, if the Mg content is higher than 1.2 wt.%, the billet
becomes difficult to
be extruded and the extruded bar to be forged. Moreover, a large amount of
Mg2Si particles tends
to precipitate during quenching process after the solution treatment. In
addition, the Mg content
is preferably between 0.7 wt.% and 1.1 wt.% and more preferably between 0.8
wt.% and 1.0 wt.%.
[0017] Fe is an impurity and combines with other elements to form
intermetallic compounds.
These precipitated particles lower fracture toughness and fatigue strength of
the final forged
product. Especially, if the Fe content is higher than 0.5 wt.% it is difficult
to obtain an aluminium
alloy forged product with both high strength and high toughness as required
for automotive
structure and suspension applications. Preferably, its content is lower than
or equal to 0.3 wt.%
and more preferably, lower than or equal to 0.2 wt.%.
[0018] Mn also combines with Al to form intermetallic compounds which control
recrystallisation. However, if the Mn content is less than 0.4 wt.%, the
effect is not sufficient. On
the other hand, if the content of Mn is higher than 1.0 wt.%, coarse
precipitated particles are
formed and both the workability and the toughness of the aluminium alloy are
reduced. The Mn
content is preferably between 0.5 wt.% and 0.9 wt.% and more preferably
between 0.5 wt.% and
0.7 wt.%.
[0019] The cast billet according to the invention is homogenised for a
duration between 2 and
10 hours at a temperature between 5 C and 80 C lower than solidus, and then
water quenched.
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[0020] The homogenised and quenched cast billet to be extruded is heated to a
soaking
temperature Th below the solidus temperature Ts, between Ts-5 C and Ts-125 C.
For example,
solidus temperature is near 575 C for alloys AA6082 and AA6182. The billets
are preferably heated
and held at the soaking temperature during ten seconds to several minutes.
[00211 The billet is then introduced in the extrusion press and extruded
through a die to form a
solid extruded product or extrudate. The extrusion speed is controlled to have
an extrudate surface
exit temperature lower than solidus temperature Ts, respectively 530 and 550 C
approximately.
The exit temperature should be high enough to merely avoid precipitation.
Practically, the targeted
to extrudate surface temperature is commonly ranging from 530 C to 550 C,
to have an extrusion
speed compatible with a satisfying productivity and avoid incipient melting
due to non-equilibrium
melting of eutectic phases in profile hot-spots but still allowing to dissolve
part of the constituent
particles. The extrusion ratio (starting cross-sectional area divided by final
cross-sectional area) is
at least 8 to maximize the fibrous structure of the extrudate.
[0022] The extruded product is then water quenched at the exit of the
extrusion press, i.e. in an
area located between 500 mm and 5 m of the exit from the die. It is cooled
down to room
temperature with an intense cooling device, for example a device projecting
sprayed water or a
water based cooling liquid on the extrudate.
[0023] The extrudate is then stretched to obtain a plastic deformation
typically between 0.5%
and 10%, preferably up to 5%, in order to have stress-relieved straight
profiles.
[0024] The extruded bar is then cut to length, heated to forging temperature,
typically between
400 and 520 C, and then forged in a heated mould typically between 150 and 350
C.
10025] After forging, parts undergo a separate solutionising at a temperature
between 530 and
560 C for a duration comprised between 2 min. and 1 hour and then water
quenched with an
intense cooling device, for example a device projecting sprayed water or a
water based cooling
liquid, down to room temperature.
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The product is then aged at room temperature for a duration between 6 hours
and 30 days , after
which artificial ageing is applied to achieve T6 temper by a one-or multiple-
step heat treatment at
temperatures ranging from 150 to 200 C for holding times ranging from 2 to 20
hours.
[0026] The process according to the invention allows to obtain forged products
made from Cu-
doped 6xxx alloys, which were until now very difficult to solutionise because
of their very narrow
solv-us-solidus temperature window and the risk of recrystallization during
ultimate separate
solutionising prior to final age-hardening treatment. The process and chemical
composition of the
invention permits to obtain a forged product displaying a near to fully
wrought structure by
to retaining the wrought structure generated during extrusion in parts of
the forged component
submitted to limited or no deformation during forging and by limiting the
extent of recrystallization
occurring during the ultimate separate solutionising step. This process is
particularly well suited to
alloys with Mg2Si content comprised between 1.2 wt. % and 1.6 wt. %, Si excess
up to 0.7%,
particularly if comprised between 0.2 wt. % and 0.7 wt. %, and especially if
copper content lies
between 0.4 wt.% and 1.5 wt.%, which gives a solv-us to solidus temperature
difference
approximately equal to or even lower than 10 C, and renders such alloy almost
impossible to
extrude when processed according to the prior art route.
[0027] As this alloy comprises, further to Mn, additional dispersoid elements
zirconium, between
0.05 and 0.2 wt. %, and Cr, between 0.05 and 0.25 wt. %, the microstructures
of the extrudates
show a strong fibrous retention providing an additional strengthening
contribution, considered
important in meeting such high mechanical property values. After having
applied the process
according to the invention to Cu doped AlMgSiCu aluminium alloys, the
applicant was able to
obtain forged components having at T6 temper ultimate tensile strengths higher
than 450 MPa,
even higher than 480 MPa.
[0028] Mechanical properties achieved in T6 temper on invention forgings after
manufacturing
according to the aforementioned process were significantly higher than by
using conventional
process on AA 6082 and displayed a far higher tolerance to solutionising
conditions i.e. increased
ease of solutionising at low temperature and soaking time and high resistance
to recrystallization.
[00291 Moreover a forged product manufactured according to the invention also
displays a
limited sensitivity to intergranular corrosion as assessed according to ISO
11846B and opposed to
what the copper level would lead a corrosion expert to expect.
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[00301 Such forged products arc particularly suitable as automotive body
structure or chassis-
suspension parts and especially suspension arms.
EXAMPLE
[0031] Forged suspension arms were made from two 6xxx aluminium alloys, the
first one being
of the AA6082 type, the other one according to the invention, starting from
extruded round bars
with a diameter of 40 mm.
to Said bars were extruded by following two different process routes: the
current prior art route for
AA6082 alloys and the route according to the invention for others.
The chemical compositions of these alloys are shown on Table I in weight %.
Si Fe Cu Mn Mg Cr Ni Zn Ti Pb V Zr
AA6082 1.112 0.197 0.061 0.744 0.807 0.193 0.003 0.012 0.029 0.001
Invention 1.3 0.16 0.74 0.53 0.89 0.1
0.04 0.008 0.019 0.0011 0.011 0.13
Table I
I Iomogenised cast billets having a diameter of 308 mm and a length of 1200 mm
were heated,
introduced into an extrusion press and pressed to form 40 mm in diameter bars.
Forged suspension arms were obtained by following a conventional route for
AA6082 alloys:
a) homogenising the cast billet at a temperature TH close to 480 C, for a
duration of 5 hours;
b) cooling said billet down to room temperature;
c) heating the homogenised billet to a temperature Th close to 500 C;
c) extruding said billet through a die to produce round bars with an exit
temperature close to 530 C;
d) cooling the extruded product down to room temperature;
e) stretching the extruded product to obtain a plastic deformation close to
1%;
f) heating cut-to-length extruded rod to forging temperature, close to 500 C;
g) forging in mould heated close to 300 C;
h) separate solutionising at a temperature close to 530 C for 30 min.;
i) water quenching the forged material with an intense cooling device down to
room temperature;
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j) room temperature ageing for a duration of 1 day;
k) ageing to T6 temper by a one-step heat treatment at 175 C for 8 hours.
Forged suspension arms were obtained by following the route according to the
invention for other
ones ("Invention"):
a) homogenising the cast billet at a temperature TH close to 520 C, for a
duration of 5 hours;
b) quenching said billet down to room temperature by using water quench
system;
c) heating the homogenised billet to a temperature Th close to 500 C;
d) extruding said billet through a die to produce round bars with an exit
temperature close to
to 530 C;
e) quenching the extruded product down to room temperature by using water
quench system;
f) stretching the extruded product to obtain a plastic deformation close to
1%;
g) heating cut-to-length extruded rod to forging temperature close to 500 C;
h) forging in heated mould close to 300 C;
i) separate solutionising at a temperature close to 550 C for 30 min.;
j) quenching the forged material with an intense cooling device down to room
temperature;
k) room temperature ageing for a duration of lday;
1) ageing to T6 temper by a one-step heat treatment at 170 C for 8 hours.
[0032] Tensile test specimens were machined in the suspension arms. Table 2
shows the ultimate
tensile strength (u-Ts), the yield strength (YS) and the elongation of forged
products.
Rm Rp0,2 A
Alloy Solutionising Ageing Temper
[MPa] [MPa] ryd
AA 6082 530 C/30 min. 175 C/8h T6 378 358 11
AA 6082 530 C/30 min. 175 C/8h T6 376 354 12.5
Invention 550 C/30 min. 170 C/8h T6 481 452 13
Invention 550 C/30 min. 170 C/8h T6 484 456 12
Table 2
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[0033] The results of table 2 show that the process routc according to the
invention enables the
manufacture of aluminium alloy forged products having significantly higher
strength (UTS and YS)
than products obtained by a conventional route, and similar elongation.
[0034] Corrosion tests were performed using the ISO 11846B test for 24 hours
of exposure time
on suspension arms as above, the ones obtained from AA6082 alloy following the
prior art route,
the other ones according to the invention.
[0035] Figure 1 shows no significant difference for products according to the
invention, with a
maximum surface attack depth of 310 microns and a maximum end grain attack
depth of 380
microns for the product according to the invention compared to respectively
390 and and 320
microns for AA6082 alloys processed through a prior art route.
[0036] These results show that the process route according to the invention
enables the
manufacture of aluminium alloy extruded products having simultaneously better
strength (UTS
and YS) and equivalent corrosion resistance than products obtained by a
conventional route.
