Note: Descriptions are shown in the official language in which they were submitted.
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1
IMPROVED METHOD FOR MANUFACTURING A STRUCTURE COMPONENT
FOR A MOTOR VEHICLE BODY
Field of the invention
The invention relates to the field of motor vehicle
structure parts or components, also referred to as "body
in white", manufactured in particular by stamping
aluminium alloy sheets, more particularly alloys in the
AA6xxx series in accordance with the designation of the
Aluminium Association, intended to absorb energy
irreversibly at the time of an impact, and having
excellent compromise between high mechanical strength
and good behaviour in a crash, such as in particular
impact absorbers or "crashboxes", reinforcement parts,
linings, or other bodywork structure parts.
More precisely, the invention relates to the
manufacture of such components by stamping in a solution-
hardened, quenched and naturally aged temper state
followed by hardening by on-part ageing and a treatment
of baking the paint or "bake hardening".
Prior art
Aluminium alloys are increasingly used in
automobile construction in order to reduce the weight of
the vehicles and thus reduce fuel consumption and
discharges of greenhouse gases.
Aluminium alloy sheets are used in particular for
manufacturing many parts of the "body in white", among
which there are bodywork skin parts (or external bodywork
panels) such as the front wings, roofs, bonnet, boot or
door skins, and the lining parts or bodywork structure
components such as for example door, bonnet, tailgate or
roof linings or reinforcements, or spars, bulkheads,
load-bearing floors, tunnels and front, middle and rear
pillars, and finally the impact absorbers or
"crashboxes".
If numerous skin parts are already produced from
aluminium alloy sheets, the transposition of steel to
aluminium of lining or structure parts having complex
geometries proves to be trickier. Firstly, because of
the less good formability of aluminium alloys compared
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with steels and secondly because of the mechanical
properties that are in general inferior to those of
steels used for this type of part.
This is because this type of application requires
a set of properties, sometimes conflicting, such as:
- high formability in the delivery temper, temper
T4, in particular for stamping operations,
- a controlled tensile yield strength at the
delivery condition of the sheet in order to master the
spring back when shaping,
- good behaviour in the various assembly methods
used in automobile bodywork such as spot welding, laser
welding, adhesive bonding, clinching or riveting,
- high mechanical strength after cataphoresis and
baking of the paint in order to obtain good mechanical
strength in service while minimising the weight of the
part,
- good energy absorption capacity in the event of
impact for application to bodywork structure parts,
- good resistance to corrosion, in particular
intergranular corrosion, stress corrosion and filiform
corrosion of the finished part,
- compatibility with the requirements for recycling
of manufacturing waste or recycled vehicles,
- acceptable cost of mass production.
There do however now exist mass-produced motor
vehicles having a body in white consisting mainly of
aluminium alloys. For example, the Ford F-150 model 2014
version consists of A6111 structure alloy. This alloy
was developed by the Alcan group in the years 1980-1990.
Two references describe this development work:
- P. E. Fortin et al, "An optimized Al alloy for
auto body sheet applications", SAE technical conference,
March 1984, describes the following composition: Si:
0.85; Fe: 0.20; Cu: 0.75; Mn: 0.20 and Mg: 0.72.
- M. J. Bull et al, "Al sheet alloys for structural
and skin applications", 25th ISATA symposium, Paper
920669, June 1992.
The main property remains high mechanical strength,
even if it is initially designed to withstand indentation
for applications of the skin type: "A yield-strength of
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280 MPa is achieved after 2% pre-strain and 30 min at
177 C".
Moreover, other alloys in the AA6xxx family with
high mechanical characteristics have been developed for
aeronautical or automobile applications. Thus the alloy
of the type AA6056, the development of which dates from
the 1980s at Pechiney, has been the subject of many works
and numerous publications, either to optimise the
mechanical properties or to improve the resistance to
intergranular corrosion. This was the subject of a patent
application (WO 2004/113579 Al)
Alloys of the A76013 type have also been the subject
of numerous works. For example, at Alcoa, in the
application US 2002/039664 published in 2002, an alloy
comprising 0.6-1.15% Si; 0.6-1% Cu; 0.8-1.2% Mg; 0.55-
0.86 Zn; less than 0.19, Mn;
Cr and
approximately 0.2% Fe, used in the T6 temper, combines
good resistance to intergranular corrosion and an Rpo.2
of 380 MPa.
At Aleris, an application published in 2003, WO
03006697, relates to an alloy in the AA6xxx series with
0.2% to 0.45% Cu. The object of the invention is to
propose an alloy of the AA6013 type with a reduced Cu
level, targeting 355 MPa of Rm in the T6 temper and good
resistance to intergranular corrosion. The composition
claimed is as follows: 0.8-1.3% Si, 0.2-0.45% Cu; 0.5-
1.1% Mn; 0.45-0.1% Mg.
Structural parts for an automobile application made
from a 7xxx alloy as described for example in the
application EP 2 581 218 are also known.
Furthermore, for producing parts with a complex
geometry from aluminium alloy, such as for example a
door lining, which cannot be achieved by conventional
stamping with the aforementioned alloys, various
solutions have been envisaged and/or implemented in the
past:
- Getting round the difficulty relating to stamping
by producing this type of part by moulding and in
particular of the "under-pressure" type. The patent EP
1 305 179 B1 of Nothelfer GmbH under priority of 2000
testifies to this.
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- Carrying out a so-called "warm" stamping to
benefit from better suitability for forming. This
consists of heating the aluminium alloy blank, totally
or locally, to a so-called intermediate temperature,
that is to say 1500 to 350 C, in order to improve its
behaviour under the press, the tool of which may also be
preheated. The patent EP 1 601 478 El of the applicant,
under priority of 2003, is based on this solution.
- Modifying, via its composition, the suitability
for stamping of the alloy in the AA5xxx series itself;
it has in particular been proposed to increase the
magnesium content beyond 5 . But this is not neutral in
terms of corrosion resistance.
- Using composite sheets consisting of an alloy core
in the AA5xxx series, with an Mg content beyond 5% for
better formability, and a clad sheet made from an alloy
better resisting corrosion. However, the corrosion
resistance at the edges of the sheet, in punched zones
or more generally where the core is exposed, and
particularly in assemblies, may then prove to be
insufficient.
- Moreover, the document EP 1702995 Al describes a
method for producing a sheet of aluminium alloy, which
comprises the supply of a molten aluminium alloy having
a chemical composition, as a percentage by weight, Mg:
0.30 to 1.00%, Si: 0.30 to 1.20%, Fe: 0.05 to 0.50%, Mn:
0.05 to 0.50%, Ti: 0.005 to 0.10%, optionally one or
more from among Cu: 0.05 to 0.70% and Zr: 0.05 to 0.40%,
and the remainder: Al and unavoidable impurities: the
casting of the molten alloy in a plate having a thickness
of 5 to 15 mm by the double-strip casting method with a
cooling rate at 1/4 of the thickness of the plate of 40
to 150 C/s, coiling in the form of a reel, homogenisation
treatment, cooling of the resulting reel to a temperature
of 250 C at least at a cooling rate of 500 C/h or more,
followed by cold rolling, and then solution heat
treatment. This document does not mention on-part ageing
after forming.
- W02018/185425 invention relates to a method for
producing a stamped component of motor vehicle bodywork
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or body structure from aluminium alloy comprising the
steps of producing a metal sheet or strip of thickness
between 1.0 and 3.5 mm in an alloy of composition (96 by
weight): Si: 0.60-0.85; Fe: 0.05-0.25; Cu: 0.05-0.30; Mn:
5 0.05-0.30; Mg: 0.50-1.00; Ti: 0.02-0.10; V: 0.00-0.10
with Ti + V a 0.10. other elements each < 0.05, and <
0.15 in total, with the remainder aluminium, with Mg <
-2.67 x Si +2.87, dissolving and steeping, pre-tempering,
maturation for between 72 hours and 6 months, stamping,
tempering at a temperature of around 205 C with a hold
time between 30 and 170 minutes or tempering at a time-
temperature equivalent, painting and "bake hardening" of
the paints at a temperature of 150 to 190 C for 15 to 30
minutes. The invention also relates to a stamped
component of motor vehicle bodywork or body structure,
also called a "body in white" produced by such a method.
US20180119261 described 6xxx series aluminum alloys
with unexpected properties and novel methods of
producing such aluminum alloys. The aluminum alloys are
highly formable and exhibit high strength. The alloys
are produced by continuous casting and can be hot rolled
to a final gauge and/or a final temper. The alloys can
be used in automotive, transportation, industrial, and
electronics applications, just to name a few.
US20180171452 disclosed high-strength, highly
deformable aluminum alloys and methods of making and
processing such alloys. More particularly, disclosed is
a heat treatable aluminum alloy exhibiting improved
mechanical strength and formability. The processing
method includes casting, homogenizing, hot rolling,
solutionizing, pre-ageing and in some cases pre-
straining. In some cases, the processing steps can
further include cold rolling and/or heat treating.
Having regard to the increasing development of the
use of aluminium sheets for automobile bodywork
components and mass production, there still exists a
demand for further improved grades making it possible to
reduce thicknesses without impairing the other
properties so as always to increase lightening.
Problem posed
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The invention aims to obtain an excellent
compromise between formability in T4 temper and high
mechanical strength as well as good behaviour of the
finished component under riveting and in a crash, by
proposing a method for manufacturing such components
including forming in T4 temper after natural ageing at
ambient temperature, followed optionally by age
hardening on the formed part and baking of the paints or
bake hardening. One problem is also to achieve a short
and economically advantageous method and to improve
compared to a product made of alloy AA 6111.
These components must also have very good corrosion
resistance and good behaviour in the various assembly
processes such as spot welding, laser welding, adhesive
bonding, clinching or riveting.
Object of the invention
An object of the invention is a method for
manufacturing a rolled product for automobile bodywork
or body structure, also referred to as "body in white",
from an aluminium alloy, comprising the following
successive steps:
a. casting of an ingot with the following
composition (% by weight):
Si: 0.75 -1.10 ;
Fe: max 0.4 ;
Cu: 0.5 - 0.8 ;
Mn: 0.1 - 0.4 ;
Mg : 0.75 - 1 ;
Ti : max 0.15 ;
Cr : max 0.1 ;
V : max 0.1;
inevitable elements and impurities at maximum 0.05% each,
and total 0.15% maximum;
remainder aluminium,
b. homogenization of the ingot,
c. hot rolling of the ingot,
d. cold rolling into a sheet,
e. solution heat treatment, quenching of the sheet,
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f. pre ageing of the sheet,
g. natural ageing of the sheet.
Another object of the invention is a rolled product
obtainable by the method of the invention.
Another object of the invention is a part obtainable
by the method of the invention.
Another object of the invention is the use of the
part in in a car as bodywork skin parts (or external
bodywork panels) such as the front wings, roofs, bonnet,
boot or door skins, and the lining parts or bodywork
structure components such as for example door, bonnet,
tailgate or roof linings or reinforcements, or spars,
bulkheads, load-bearing floors, tunnels and front,
middle and rear pillars, and finally the impact absorbers
or "crashboxes".
Description of the figures
Figure 1 depicts the device for "three-point
bending test" consisting of two rollers R, and a punch
B of radius r, for carrying out the bending of the rolled
product T of thickness t.
Figure 2 depicts the rolled product T after the
"three-point bending" test with the internal angle p and
the external angle, the measured result of the test: a
is reported in the enclosed result. The maximum strength
during the test procedure is also reported.
Figure 3 depicts a specific embodiment for the
method:
1: uncoiler
2: coiler
3: sheet
4: solutionizing furnace
5: quenching unit
6: surface treatment machine
7: pre ageing oven
8: stored coil
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Description of the invention
Unless defined otherwise within this description,
the general terms are defined is the NF EN 12258-1. A
sheet is a flat rolled product of rectangular cross-
section with uniform thickness between 0,20 mm and 6 mm.
All aluminium alloys in question hereinafter are,
unless indicated to the contrary, designated by the
designations defined by the Aluminium Association in the
Registration Record Series that it publishes regularly.
All the indications relating to the chemical
composition of the alloys are expressed as a percentage
by weight based on the total weight of the alloy.
The definitions of the metallurgical temper are
indicated in the European standard EN 515 unless defined
otherwise herein.
The static tensile mechanical characteristics, in
other words the ultimate tensile strength R.., the tensile
yield strength at 0.2% elongation Rp0.2, and the
elongation at break A96, are determined by a tensile test
in accordance with NF EN ISO 6892-1.
The bending angles are determined by a three-point
bending test in accordance with NF EN ISO 7438 and the
procedures VDA 238-100 and VDA 239-200.
The bendability is also measured with the norm ASTM
E290-97a.
The inventors selected a set of composition of
aluminium alloys in conjunction with suitable methods
which offer to car manufacturer interesting properties
to produce parts.
The subject of the invention is a method for
manufacturing a rolled product for automobile bodywork
or body structure, also referred to as "body in white",
from aluminium alloy, comprising the following steps.
The casting of an ingot with the following composition:
(% by weight):
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Si: 0.75 -1.10. preferably the Si content
maximum is 1.0% and more preferably, the
maximum Si content is 0.95%.
Fe: max 0.4. Preferably the minimum Fe content
is 0.15% and/or the maximum Fe content is 0.30%.
Cu: 0.5 - 0.8. Preferably, the Cu maximum
content of the ingot is 0.70% and/or the Cu
minimum content is 0.55%. More preferably, the
maximum Cu content is 0.65%. Limiting the Cu
to 0.8%, 0.70% or even 0.65% is interesting
for economical reason as Cu is usually more
expensive than aluminium. It is also
advantageous to ease recyclability of the
material. It may also improve the corrosion
resistance. In another embodiment however the
Cu minimum content is 0.65 % in particular to
increase strength.
Mn: 0.1 - 0.4. Preferably the maximum Mn
content is 0.35% and / or the minimum Mn
content is 0.24% or preferably 0.25%. Addition
of Mn improves in particular the bending
behaviour.
Mg : 0.75 - 1, preferably, the minimum content
of Mg is 0.80% and/or the maximum Mg content
is 0.90%.
Ti : max 0.15, preferably the minimum Ti
content is 0.01% and/or the maximum Ti content
is 0.05%.
Cr : max 0.1 and preferably the Cr is an
inevitable element or an impurity.
V : max 0.1, and preferably the V is an
inevitable element or an impurity.
And the inevitable elements and impurities at
maximum 0.05% each, and total 0.15% maximum
and the remainder is aluminium.
The casting can be made with various casting
process. Continuous casting, which is usually a
horizontal casting, is possible. It is also
preferred to use a vertical semi continuous casting,
which is also known under the name of direct chill
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casting. The vertical semi continuous casting is
preferred because it more homogenous through the
thickness of the sheet.
5
The ingot is homogenised, hot rolled and cold rolled
into a sheet. The sheet is solution heat treated and
quenched. Preferably the homogenization treatment of the
ingot is at a temperature from 520 to 560 C during
preferably from 2 to 8 hours. Preferably the hot rolling
10 rolls the ingot to a rolled intermediate product having
a thickness from 3 to lOmm. Preferably the cold rolling
rolls the roiled intermediate product into a sheet having
a thickness from 1 to 4 mm. The sheet is then solution
heat treated typically at a temperature beyond the solvus
temperature of the alloy while avoiding incipient
melting. Preferably the solution heat treatment
temperature is from 530 C, preferably 540 C to 580 C
during preferably from is to 5 minutes. Quenching is
then applied to the sheet. Water quenching is suitable
with a temperature about 15 to 60 C, preferably 15 C to
40 C. A pre ageing is applied during preferably at least
8 hours with preferably a temperature from 50 to 120 C.
Natural ageing is then applied. Natural ageing is defined
in NF EN 12258-1 and room temperature is defined in NF
EN ISO 6892-1. Preferably the duration of the natural
ageing is from 72 hours to 6 months.
The pre ageing step is preferably achieved by
coiling of the sheet at a coiling temperature and cooling
it in open air at the room temperature.
A convenient continuous annealing line device to
realise the pre ageing is described by figure 3. The
sheet 3 is uncoiled by uncoiler 1 and goes through the
solutionizing furnace 4 and the quenching unit 5, then
the sheet 3 enters the surface treatment machine 6, which
is a very usual step for car body sheet, followed by a
pre ageing oven 7 and finally coiled on the coiler 8 in
open air. At the exit of pre ageing oven 7, the sheet is
therefore hot and the sheet is coiled on the coiler 2 at
a coiling temperature in open air. The coiled sheet 8 is
hot and is stored at ambient temperature in the plant
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and cools down to ambient temperature. Pre ageing occurs
during this cooling. Natural ageing starts after the end
the cooling of the coiled sheet 8, preferably the pre-
ageing duration is at least 8 hours.
Preferably, the pre ageing is obtained by coiling
the sheet at a coiling temperature from 50 to 120 C,
preferably from 60 to 120 C, followed by cooling the
coiled sheet in open air, and its duration is 8 hours at
least.
The rolled product of the invention comprises the
product obtainable with the above method from casting to
natural ageing. The temper of the rolled product after
natural ageing is T4.
T4 temper rolled product tensile yield strength
varies less than 5 MPa, preferably 3 MPa between the
tensile yield strength in the transverse and 45
directions within the same rolled product. The same
sheet is defined a rolled product made from the same
ingot, same homogenization, same hot and cold rolling,
same solution heat treatment, same quenching, same pre
aging, same natural aging and the tensile testing
samples are cut off from the rolled product as close as
possible. This is a useful property for part stamping.
The rolled product in T4 temper can be characterized
in 6 others specific tempers, TOA, TOC, TOD, T6B, T6C
and T8D, which estimate the material properties of the
part.
The T8A, T8C and T8D tempers are achieved by
applying on the T4 rolled product a 2% strain followed
each by a specific heat treatment. TBA temper uses a
bake hardening heat treatment of 20 minutes at a
temperature of 180 C. T8C temper uses a light and short
bake hardening heat treatment of 5 minutes at a
temperature of 160 C. T8D temper uses a light and long
bake hardening heat treatment of 20 minutes at a
temperature of 160 C.
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The T6B, T6C and T6D tempers are achieved by
applying on the T4 rolled product a specific heat
treatment. T6B temper uses a heat treatment at a
temperature of 225 C during 30 minutes. T6C temper uses
a light and short bake hardening heat treatment of 5
minutes at a temperature of 160 C. T6D temper uses a
light and long bake hardening heat treatment of 20
minutes at a temperature of 160 C.
The T4 rolled product can then be formed, in
particular by press stamping, in order to obtain a shape.
Optionally, the shape is aged. The shape may be painted
and bake hardened into a part at a temperature from 150
to 190 C, and preferably from 170 to 190 C, during from
5 to 30 minutes, preferably from 15 to 30 minutes.
An object of the invention is a part obtainable
with the above method with the rolled product of the
invention. The part can be used in a car as bodywork
skin parts (or external bodywork panels) such as the
front wings, roofs, bonnet, boot or door skins, and the
lining parts or bodywork structure components such as
for example door, bonnet, tailgate or roof linings or
reinforcements, or, preferably, spars, bulkheads, load-
bearing floors, tunnels and front, middle and rear
pillars, and finally the impact absorbers or
"crashboxes".
In a first embodiment the coiling temperature is
from 50 C to 95 C, 95 C being excluded, preferably from
60 to 95 C, 95 C being excluded. The 14 temper rolled
product of this first embodiment is characterized by a
tensile yield strength lower than 165MPa, which can be
useful for customer formability at press stamping. The
16B temper rolled product of this first embodiment, as
described formally, has a minimum tensile yield strength
of 345 MPa and preferably a minimum tensile yield
strength of 350 MPa.
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A preferred composition for the method according to
the first embodiment is
Si: 0.75 -1.10 and more preferably less 0.95%;
Fe: max 0.4 and more preferably between 0.15%
and 0.30%;
Cu: 0.5 - 0.70 and preferably 0.5 - 0.65;
Mn: 0.1 - 0.4 ;
Mg : 0.75 - 1 ;
Ti : 0.01 - 0.05;
Cr : max 0.1 ;
V : as an impurity;
and the inevitable elements and impurities at
maximum 0.05% each, and total 0.15% maximum
and the remainder is aluminium.
With this preferred composition and with a coiling
temperature from 50 C to 95 C, 95 C being excluded,
preferably 60 to 95 C, 95 C being excluded, the
bendability of the 14 rolled product of the first
embodiment is 0.19 maximum. This is advantageous in part
forming.
A still more preferred composition of the first
embodiment is
Si: 0.75 -1.10 and more preferably less 0.95%;
Fe: max 0.4 and more preferably between 0.15%
and 0.30%;
Cu: 0.5 - 0.70 and preferably 0.5 - 0.65;
Mn: 0.24 - 0.30 and preferably minimum 0.25%;
Mg : 0.75 - 1 ;
Ti : 0.01 - 0.05;
Cr : max 0.1 ;
V : as an impurity;
and the inevitable elements and impurities at
maximum 0.05% each, and total 0.15% maximum
and the remainder is aluminium.
With this still more preferred composition, in
conjunction with a coiling temperature from 50 C to 70 C,
preferably from 60 to 70 C, the VDA angle of the 14
temper rolled product is greater than 125 . The
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bendability of the 14 rolled product is still smaller
than 0.19. This can be useful in some press stamping
application.
In another preferred method of the first embodiment
the coiling temperature is between 70 C and 95 C. With
this method, the T8A temper rolled product has a minimum
tensile yield strength of 275 MPa. In a more preferred
method of this embodiment, the T8A temper rolled product
has a minimum tensile yield strength of 280 MPa with a
coiling temperature between 70 C and 95 C and with a
composition of
Si: 0.75 -1.10 and more preferably less 0.90%;
Fe: max 0.4 and more preferably between 0.15%
and 0.30%;
Cu: 0.65 - 0.8;
Mn: 0.1 - 0.4 and more preferably less than
0.24% and 0,15% minimum;
Mg: 0.75 - 1 and more preferably less 0.95%;
Ti: 0.01 - 0.05;
Cr: max 0.1;
V: as an impurity;
and the inevitable elements and impurities at
maximum 0.05% each, and total 0.15-% maximum
and the remainder is aluminium.
In a second embodiment of the invention the coiling
temperature is from 95 C to 120 C and preferably from
95 C to 105 C with preferably the composition:
Si: 0.75 -1.10 and more preferably less 0.90%;
Fe: max 0.4 and more preferably between 0.15%
and 0.30%;
Cu: 0.5 - 0.70 and preferably 0.5 - 0.65;
Mn: 0.1 - 0.4
and preferably minimum 0.25%
and preferably less than 0,35%;
Mg: 0.75 - 1;
Ti: 0.01 - 0.05;
Cr: max 0.1;
V: as an impurity;
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and the inevitable elements and impurities at
maximum 0.05% each, and total 0.15% maximum
and the remainder is aluminium.
The advantage of this second embodiment is in
5 particular the low sensitivity of the yield strength of
the part to a variation of the bake hardening treatment.
The bake hardening conditions are dependent on the
location inside the car body assembly, parts having a
low sensitivity to bake hardening conditions are thus
10 favourable because the car manufacturer has more
flexibility. This low sensitivity can be assessed by
comparing properties in T6C temper to those in T6D temper
and/or properties in T8C temper to those in T8D temper
which are obtained from the same 34 temper rolled product.
15 With rolled product obtained with the method of the
second embodiment, the tensile yield strength of the
rolled product in T8C and 38D tempers and made from the
same rolled product in 34 temper, differ by less than 5
MPa. The T8C and T8D rolled product samples differs only
by the duration of the bake hardening, the temperature
of which is 160 C.
The T6C and T6D rolled product samples differs only
by the duration of the bake hardening the temperature of
which is 160 C. With rolled product obtained with the
method of the second embodiment, the tensile yield
strength of the rolled product in T6C and T6D tempers
and made from the same rolled product in 34 temper,
differ by less than 5 MPa.
More generally, the rolled product can be heat
treated with a temperature from 150 to 190 C, and
preferably from 170 to 190 C, during from 5 to 30 minutes,
preferably from 15 to 30 minutes. The yield strength of
the rolled product, heat treated at a given temperature
in the above temperature ranges, during any duration in
the above duration ranges, varies by less than 15 MPa,
preferably 10 MPa and more preferably 5 MPa.
More generally, the 2% strained rolled product can
be heat treated with a temperature from 150 to 190 C,
and preferably from 170 to 190 C, during from 5 to 30
minutes, preferably from 15 to 30 minutes. The yield
strength of the 2% strained rolled product, heat treated
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at a given temperature in the above temperature ranges,
during any duration in the above duration ranges, varies
by less than 15 MPa, preferably 10 MPa and more
preferably 5 MPa.
With the second embodiment, the 14 temper rolled
product has a maximum tensile yield strength of 190 MPa.
With the second embodiment, the T6B temper rolled product
has a minimum tensile yield strength of 340 MPa. With
the second embodiment, the T8A temper rolled product has
a minimum tensile yield strength of 280 MPa, preferably
of 290MPa.
Recyclability of any alloy is an important
technical and economical parameter. Reducing the range
any element is useful in order to strengthen recycling
process as it gives predictability of the future melt.
Reducing the maximum of the addition element is also
advantageous as they can be more expensive than aluminium.
Reducing Si content is advantageous for recycling
because in many alloys, this element is not only an
impurity but also detrimental to aluminium product
properties. Therefore, an advantageous embodiment of the
invention is to reduce the Si content to maximum of 0.95-6.
It is also an advantageous embodiment to reduce Fe
maximum to 0.30% and/or to increase the Fe minimum to
0.15%. Another advantageous embodiment is to reduce the
Cu maximum to 0.70% and preferably to 0.65% and/or to
increase the Cu minimum to 0.55%. Another advantageous
embodiment is to reduce the Mn maximum content to 0.35%
and more preferably to 0.30% and/or to increase its
minimum content to 0.15% and more preferably to 0.25%.
Another embodiment is also to reduce the Ti maximum
content to 0.05% and/or to increase the minimum content
to 0.01 . Another embodiment is to classify the V as an
impurity with a maximum of 0.05%
All those combinations of alloys composition and
coiling temperature of the invention gives many
possibilities for the car manufacturer with different
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forming properties. The car manufacturer can also
optimize its processing and the design of its part. The
shape ageing allows a high strength part but it requires
a specific heat treatment of the shape ageing. High
strength alloys are useful to lightweight part. If the
part does not require high strength material, the car
manufacturer can avoid the shape ageing, which is
advantageous to simplify the production. Hence, the
invention gives flexibility to car manufacturer.
Examples
Preamble
Table 1 summarises the chemical compositions (% by
weight) of the alloys used during tests. The proportion
of the others inevitable elements and impurities were
lower than 0.05%, the total lower is than 0.1525, and the
remainder is aluminium. Alloy G is an exemplary A716111
alloy and alloy H is an exemplary of a modified AA6056.
Alloy Si Fe Cu Mn Mg Ti Cr V
A 0.81 0.21 0.68 0.20 0.7 0.04 <0.05 <0.05
0.81 0.21 0.70 0.20 0.8 0.03 <0.05 <0.05
0.81 0.20 0.58 0.20 0.7 0.03 <0.05 <0.05
0.80 0.20 0.58 0.20 0.9 0.04 <0.05 <0.05
0.83 0.19 0.56 0.29 0.8 0.03 <0.05 <0.05
0.82 0.20 0.58 0.29 0.9 0.10 <0.05 0.07
0.70 0.20 0.65 0.20 0.7 0.04 <0.05 <0.05
0.81 0.20 0.85 0.20 0.7 0.05 <0.05 <0.05
Table 1
The rolling ingots of these various alloys were
obtained by vertical semi-continuous casting. After
scalping, these various ingots underwent homogenisation
heat treatment at 540 C during about 4 hours directly
followed by the hot rolling to a 5mm intermediate rolled
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product. The 5 mm intermediate rolled product was cold
rolled to obtain sheets with a thickness of 2mm.
The rolling steps were followed by a solution heat
treatment followed by quenching. The solution heat
treatment was at a temperature beyond the solvus
temperature of the alloy while avoiding incipient
melting. In this non limitating example the
solutionizing temperature was 570 C. The solutionized
sheet was then water quenched in a 20 C water. The sheet
samples were coiled with 3 coiling temperatures of 100 C,
80 C and 60 C for a pre ageing of 8 hours followed by a
natural ageing. Two natural ageing were used: 7 days and
30 days at room temperature to obtain T4 temper rolled
products.
The T4 rolled products were transformed into a IRA
temper with a 2% strain and then heat treatment with a
typical bake hardening heat treatment of 180 C during 20
minutes. T8A samples were then characterized.
The 74 rolled product were also heat treated into
a 765 temper with a heat treatment of 225 C during 30
minutes. T65 samples were then characterized.
Tests results
Tensile tests at ambient temperature were carried
out in accordance with NF EN ISO 6892-1
with non-proportional test pieces, with a geometry
widely used for sheets, and corresponding to the type of
test piece 2 in table B.1 of Appendix B of said standard.
These test pieces in particular have a width of 20 mm
and a calibrated length of 120 mm. Tensile tests were
done on rolled product in T4, 18A and 165 temper. The
results obtained with a coiling temperature of 80 C and
30 days of naturel ageing are presented in Table 2. The
results obtained with a coiling temperature of 60 C and
30 days of naturel ageing are presented in Table 3. The
results obtained with a coiling temperature of 60 C,
80 C and 100 C and 7 days of naturel ageing are
presented in Table 4.
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Coiling temperature 80 C +30 days natural ageing
Measures in long transverse direction
three-point
Tensile Yield strength, Bending radius
bending test
T4
T4
T4 TBA T6B radius T4 14
Alloy Angle a
MPa MPa MPa WRAP dt
Fmax N
mm
A 140 268 336 0.3 0.15 127
5303
B 152 288 356 0.4 0.20 118
4911
C 138 255 339 0.2 0.10 121
4316
D 152 275 355 0.3 0.14 123
4972
E 149 279 353 0.3 0.15 122
4800
F 151 278 353 0.4 0.20 115
4766
G 129 254 325 0.3 0.14 129
4924
H 148 270 344 0.4 0.16 115
5453
Table 2
Coiling temperature 60 C +30 days natural ageing
Measures in long transverse direction
three-point
Tensile Yield strength, Bending radius
bending test
T4
T4
T4 T8A T6B radius 14 14
Reference Angle a
MPa MPa MPa WRAP r/t Fmax N
mm
A 140 230 334 0.3 0.15 133
5928
B 149 248 352 0.4 0.20 113
5295
C 138 238 337 0.2 0.10 128
4687
D 150 245 356 0.3 0.14 120
4826
E 150 241 351 0.3 0.15 135
5852
F 154 244 354 0.4 0.20 110
5080
G 135 221 326 0.3 0.14 133
5281
H 152 342 0.4 0.16 116
5679
Table 3
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Coiling temperature +7 days
Alloy
natural ageing
60 C 80 C 100 C
Tensile Yield Strength MPa
Measures in long transverse
direction, T4 temper
A 142 137
148 149
133 136
146 149
154 147 174
152 149
124 125
149 146 170
Table 4
The coiling temperature is an important parameter
5 for 14 temper tensile yield strength. At 60 and 80 C it
allows to limit the T4 tensile yield strength below 165
MPa which can be advantageous for car manufacturer if it
is needed to maintain stamping easiness.
10
Example alloys B, D, E and F, have a tensile yield
strength minimum of 350 MPa in T8B temper. Those example
alloys have a tensile yield strength minimum of 275 MPa
in T8A temper.
Reducing the range of Ti to maximum 0.05%, the V to
15 an impurity of 0.05% maximum and reducing Cu to less
than 0.65'6 is also advantageous as exemplified by alloy
E and D because it reduces the bendability to 0.15, which
eases the manufacturability of the component
independently of the coiling temperature.
20 In addition to the above reduced range of V, Ti and
Cu, the optimized range of Mn from 0.25 to 0.35% offers
with the 60 C coiling temperature a very advantageous 3
points bending test with a high VDA angle which is good
for formability. This is exemplified by alloy E with
coiling temperature of 60 C.
Example 2
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Rolled products manufactured with alloy E, with coiling
temperatures 80 C and 100 C and after 7 days of natural
ageing were used for others trials. Samples at both
coiling temperature were split in 2 groups: in the first
group a strain of 2% was applied and the second group
there was not any strain. Then a bake hardening
temperature of 160 C was applied, with two different
durations of 5 and 20 minutes.
Those results, provided in Table 5 for a coiling
temperature of 80 C and Table 6 for a coiling
temperature of 100 C, show another advantageous
embodiment: with a coiling temperature of 100 C, the
rolled product tensile yield strength is nearly
independent from bake hardening duration. This is an
advantageous behaviour for parts which can be installed
in the car body assembly either at the surface or deep
inside a multiple parts assembly because their yield
strength remains similar. This offer flexibility for
part design for car manufacturer.
Coilling temperature 80 C
Alloy temper 1 C Tps, min
Strain (%) Rp0,2 (MPa) Rm (MPa)
T4 147
293
T6C 160 5 0 169
310
T8C 160 5 2 215
321
T6D 160 20 0 194
326
T8D 160 20 2 235
333
Table 5
Coiling temperature 100 C
Alloy temper 1 C Tps, min
Strain (%) Rp0,2 (MPa) Rm (MPa)
T4 174
317
T6C 160 5 0 203
336
T8C 160 5 2 249
349
T6D 160 20 0 204
337
T8D 160 20 2 247
346
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Table 6
Example 3
A ingot of the following composition was cast
An ingot with the chemical composition in table 7
(% by weight) was cast using a vertical semi continuous
casting. The proportion of the others inevitable
elements and impurities were lower than 0.05%, and the
total is lower than 0,15%, the remainder is aluminium.
Si Fe Cu Mn Mg Cr Ti
0.86 0.21 0.66 028 0.85 0A01
0.04
Table 7
The rolling ingot were heated at 554 C during 4
hours. The ingot was directly hot rolled. The
temperature of the ingot just before the start of hot
rolling was 540 C. The thickness at the end of hot
rolling was 5mm. The thickness at the end of cold
rolling was 2mm. The sheet was split in three in order
to solutionize at three different temperatures, 535 C,
544 C and with each a different duration above 525 C:
20s, 45s and 68s. The sheets were quenched in 22 C
water. The sheets were pre aged by coiling the sheets
at a temperature of 96 C and cooling in open air
followed by a natural ageing at room temperature about
20 C during 3 days to obtain T4 temper rolled products.
The T4 rolled products were transformed into a TOA
temper with a 2% strain and then heat treatment with a
typical bake hardening heat treatment of 180 C during 20
minutes. T8A samples were then characterized.
The T4 rolled product were also heat treated into
a 36B temper with a heat treatment of 225 C during 30
minutes. T63 samples were then characterized.
Tensile tests were done in the rolling direction
(L), in the transverse direction to the rolling
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direction (T) and direction at 450 the rolling
direction (450).
Solution YS,
HT'C Direction Temper 1\413a UTS,N4Pa Ag% A%
535 L T4 183 309 22 26
535 T T4 171 304 25 27
535 450 T4 172 302 25 27
535 L T8A 303 369 17 21
535 T T8A 293 361 17 21
535 450 T8A 297 362 17 21
535 L T66 356 380 7 11
535 T T66 345 376 8 12
535 450 T6B 346 375 8 11
544 L T4 180 308 21 27
544 T T4 168 301 24 26
544 45 T4 170 300 25 28
544 L T8A 307 373 17 21
544 T T8A 300 366 17 21
544 450 T8A 304 367 17 21
544 L T66 356 380 8 11
544 T T6B 344 376 8 11
544 450 T66 344 376 8 12
559 L T4 183 312 22 27
559 T T4 172 304 24 26
559 45' T4 175 304 26 28
559 L T8A 305 371 17 21
559 T T8A 298 366 17 21
559 45' T8A 302 366 17 21
559 L T6B 360 382 8 11
559 T T66 350 381 8 12
559 450 T66 349 379 8 11
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Table 8
Table 8 shows the solution heat treatment is
reliable to process variation about temperature or
duration to obtain the mechanical properties.
14 temper tensile yield strength shows an
anisotropy of less than 3 MPa between the tensile yield
strength in the T and 45 directions within the same
rolled product as it can be seen in table 8.
Bending radius was also measured on 16B temper to
check the crash behaviour of the rolled product.
Results are disclosed in table 9.
Solution Bending
HT C Direction Temper radius r/t
535 L T6B 0,889
544 L T6B 0,889
559 L T6B 1,016
Table 9.
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