Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02548788 2006-06-08
METHOD FOR PRODUCING AI-Mg-Si ALLOY SHEET
EXCELLENT IN BAKE-HARDENABILITY AND HEMMABILITY
TECHNICAL FIELD
The present invention relates to a production method for obtaining an AI-Mg-Si
alloy sheet that is abundant in hemmability while simultaneously having a high
age-hardening ability, by casting a thin slab by continuous casting of an AI-
Mg-Si alloy,
performing a homogenization treatment, then cold rolling, and performing a
solution
treatment in a continuous annealing furnace as needed. According to the
present method,
it is possible to produce, at a low cost as compared to the conventional art,
rolled sheets of
AI-Mg-Si alloy that are suitable for forming by bending, press forming and the
like of
automotive parts, household appliances and the like.
BACKGROUND ART
AI-Mg-Si alloys have the property of increasing in strength when heat is
applied
during processes such as coating after forming, so that they are well-suited
for use in
automotive panels or the like. Furthermore, the production of sheets of the
alloys by
continuous casting and rolling has been proposed to reduce costs by improved
productivity.
For example, Japanese Patent Application, First Publication No. S62-207851
discloses an aluminum alloy sheet for forming and method of production
thereof, obtained by
continuous casting of an aluminum alloy melt comprising 0.4-2.5% Si, 0.1-1.2%
Mg and one
or more among 1.5% or less of Cu, 2.5% or less of Zn, 0.3% or less of Cr, 0.6%
or less of
Mn and 0.3% or less of Zr, to form a 3-15 mm thick slab, cold rolling, then
performing a
solution treatment and quenching, characterized in that the maximum size of
intermetallic
compounds in the matrix is 5 ~m or less.
Japanese Patent Application, First Publication No. H10-110232 discloses an
AI-Mg-Si alloy sheet, obtained by preparing a direct cast rolled sheet of AI
alloy comprising
0.2-3.0% Si and 0.2-3.0% Mg, containing one or more of 0.01-0.5% Mn, 0.01-0.5%
Cr,
CA 02548788 2006-06-08
0.01-0.5% Zr and 0.001-0.5% Ti, and further containing 0-2.5% Cu, 0-0.2% Sn
and 0-2.0%
Zn, with Fe being limited to 1.0% or less and the remainder consisting of AI
and unavoidable
impurities, and further cold rolling, characterized in that the maximum
crystal size in the
metallic portion of the sheet is 100 ~m or less and the maximum length of
continuous Mg2Si
compounds on the surface layer portion is 50 ~m or less.
Additionally, Japanese Patent Application, First Publication No. 2001-262264
proposes an AI-Mg-Si alloy sheet excelling in ductility and bendability, the
aluminum alloy
comprising 0.1-2.0% Si, 0.1-2.0% Mg, 0.1-1.5% Fe or one or more further
elements chosen
from among 2% or less of Cu, 0.3% or less of Cr, 1.0% or less of Mn, 0.3% or
less of Zr,
0.3% or less of V, 0.03% or less of Ti, 1.5% or less of Zn and 0.2% or less of
Ag; wherein the
maximum size of intermetallic compounds is 5 ~m or less, the maximum aspect
ratio is 5 or
less and the average crystal grain size is 30 ~m or less.
Patent Document 1: Japanese Patent Application, First Publication No. S62-
207851
Patent Document 2: Japanese Patent Application, First Publication No. H10-
110232
I S Patent Document 3: Japanese Patent Application, First Publication No. 2001-
262264
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
Alloy sheets that are used as outer panels in automotive body sheets or the
like
require exceptional hemmability and bake-hardenability. For this reason, AI-Mg-
Si alloy
sheets that excel in bendability and age-harden when heated have been sought.
However,
sheets produced by continuous casting and rolling have the drawbacks of poor
hemmability
and insufficient bake-hardenability after coating.
The problem to be solved by the present invention is to obtain, at a low cost,
an
AI-Mg-Si alloy sheet for forming that suppresses GP zones that are deposited
during natural
ageing when left at room temperature, achieves a high level of bake-hardening
due to a
reinforcement phase being quickly deposited upon heating during coating and
baking, while
simultaneously having abundant bendability.
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CA 02548788 2006-06-08
Means for Solving the Problems
A thin slab of AI-Mg-Si alloy is continuously cast by a twin-belt casting
machine, the
cast thin slab is directly wound, subjected to a homogenization treatment
under appropriate
conditions, and cold rolled, then combined with a solution treatment in a
continuous
annealing furnace as needed, thereby fragmenting the compounds and raising the
hemmability while simultaneously enabling the procedure to be considerably
shortened.
Furthermore, microsegregation is reduced by a homogenization treatment, and
the cooling
rate after the homogenization treatment is raised, thereby reducing the
deposition of Mg2Si
while cooling, to obtain an aluminum sheet for automotive body sheets with
excellent
bake-hardenabiltiy and hemmability after a final anneal.
The present invention which solves the above problem relates to a method of
producing aluminum alloy sheets characterized by winding into thin slabs,
subjecting to a
homogenization treatment, cold rolling, then subjecting to a solution
treatment. Specifically,
as recited in claim 1, it is a method of producing aluminum alloy sheets
excelling in
bake-hardenability and hemmability, comprising steps of casting, by means of a
twin-belt
casting method, an alloy melt comprising 0.30-1.00 wt% of Mg, 0.30-1.20 wt% of
Si,
0.05-0.50 wt% of Fe, 0.05-0.50 wt% of Mn and 0.005-0.10 wt% of Ti, optionally
further
comprising at least one of 0.05-0.70 wt% of Cu or 0.05-0.40 wt% of Zr, the
remainder
consisting of AI and unavoidable impurities, to form a 5-15 mm thick slab at a
cooling rate of
40-150 °C/s at a quarter-thickness of the slab; winding into a coil;
subjecting to a
homogenization treatment; cooling to 250 °C or less at a cooling rate
of at least 500 °C/h;
cold rolling; then subjecting to a solution treatment (invention according to
claim 1 ).
In the above production method, the homogenization treatment preferably
involves
heating to 520-580 °C at a heating rate of at least 30 °C/h in a
batch furnace, then holding at
that temperature for 2-24 hours (invention according to claim 2).
The solution treatment preferably involves heating to 530-560 °C at a
heating rate
of at least 10 °C/s in a continuous annealing line, and holding for 30
seconds or less
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CA 02548788 2006-06-08
(invention according to claim 3).
Furthermore, in the invention according to claim 3 mentioned above, the
solution
treatment may be followed by steps of cooling to room temperature at a cooling
rate of at
least 10 °C/s, then subjecting to a restoration treatment by holding
for 30 seconds or less at
260-300 °C in a continuous annealing furnace, and cooling to room
temperature at a cooling
rate of at least 10 °C/s (invention according to claim 4).
Alternatively, in the invention according to claim 3 mentioned above, the
solution
treatment may be followed by steps of water-cooling to 250 °C or less
at a cooling rate of at
least 10 °C/s, then air-cooling to 60-100 °C at a cooling rate
of 1-20 °C/s, coiling up, and
subjecting to a preliminary ageing treatment by cooling to room temperature
(invention
according to claim 5).
Alternatively, in the invention according to claim 3 mentioned above, the
solution
treatment may be followed by steps of cooling to room temperature at a cooling
rate of at
least 10 °C/s, then subjecting to a restoration treatment by holding
for 30 seconds or less at
260-300 °C in a continuous annealing furnace, cooling to 60-100
°C at a cooling rate of at
least 1 °C/s, coiling up, and subjecting to a preliminary ageing
treatment by cooling to room
temperature (invention according to claim 6).
Effects of the Invention
According to the aluminum alloy sheet production method of the present
invention,
it is possible to obtain an aluminum alloy sheet with exceptional hemmability
and
bake-hardenability. Additionally, this production method is capable of
obtaining an
aluminum alloy sheet in an extremely short procedure and at low cost.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to a method of producing a rolled sheet of AI-Mg-
Si
alloy, characterized by casting a thin slab by a twin-belt casting method,
winding the slab
directly onto a coil, subjecting to a homogenization treatment, then cold
rolling, and further
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CA 02548788 2006-06-08
subjecting to a solution treatment.
In the present invention, an alloy melt consisting of the aforementioned
composition is cast into a slab 5-15 mm thick at a cooling rate of 40-150
°C/s at a quarter
thickness of the slab, using a twin-belt casting method, and after winding
into a coil, it is
subjected to a homogenization treatment and cooled to 250 °C or less at
a cooling rate of at
least 500 °C/s, then cold roiled, and subsequently subjected to a
solution treatment.
The twin-belt casting method is a method of casting thin slabs by pouring a
melt
between water-cooled rotating belts that oppose each other from above and
below, so as to
harden the melt by cooling through the belt surfaces. In the present
invention, slabs that
are 5-15 mm thick are cast by the twin-belt casting method. If the slab
thickness exceeds
mm, it becomes difficult to wind the thin slabs into coils, and if the slab
thickness is less
than 5 mm, there is a loss in productivity and it becomes difficult to cast
the thin slabs.
By casting a slab 5-15 mm thick using the twin-belt casting method, it is
possible to
make the cooling rate 40-150 °C/s at a quarter thickness of the slab.
The cooling rate is
15 computed by measuring the DAS (Dendrite Arm Spacing) by a line intersection
method from
observations of the microstructure in the slab at quarter thickness. When the
cooling rate is
less than 40 °C/s, the cast structure formed in the central portion of
the slab during
hardening becomes coarse, thus reducing the hemmability, while if the cooling
rate exceeds
150 °C/s, AI-Fe-Si crystals and AI-(Fe~Mn)-Si crystals become 1 ~m or
less and the size of
recrystallized grains becomes coarse at 30 pm or more.
After winding a thin slab, this coil is subjected to a homogenization
treatment under
appropriate conditions to fragment the AI-Fe-Si crystals and AI-(Fe-Mn)-Si
crystals that have
an adverse effect on hemmability, thus improving the hemmability. Furthermore,
it is
possible to obtain thin slabs in a state where relatively small Mg2Si crystals
that reside in the
cast structure are completely dissolved into the matrix, thus raising the
effectiveness of the
solid solution treatment after the cold rolling process.
The reason that the cooling after the homogenization treatment is performed at
a
rate of at least 500 °C/s and to 250 °C or less is in order to
suppress the deposition of
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CA 02548788 2006-06-08
relatively coarse Mg2Si as much as possible, and to dissolve the Mg and Si
into the matrix in
an oversaturated state.
After winding the thin slab, the coil is inserted into a batch furnace, and
heated at a
rate of at least 30 °C/h to 520-580 °C, at which temperature it
is held for 2-24 hours to
perform a homogenization treatment, after which the coil may be extracted from
the batch
furnace and forcibly air-cooled to room temperature at a cooling rate of at
least 500 °C/h.
This cooling can be performed, for example, by a fan while unwinding the coil.
The reason the heating rate to the homogenization temperature is limited to at
least 30 °C/h for the homogenization treatment following winding of the
thin slab is that if the
heating rate is less than 30 °C/h, at least 16 hours will be required
to reach the
predetermined homogenization temperature, thus raising costs.
The reason the homogenization temperature is within the range of 520-580
°C is
that if the temperature is less than 520 °C, the fragmentation of AI-Fe-
Si crystals and
AI-(Fe~Mn)-Si crystals is inadequate, and not enough to dissolve the Mg2Si
that crystallized
during casting into the matrix, and if the temperature exceeds 580 °C,
the metals with low
melting points will melt and cause burning.
Additionally, the reason that the homogenization treatment time is set to
within the
range of 2-24 hours is because if the treatment time is less than 2 hours, the
fragmentation
of AI-Fe-Si crystals and AI-(Fe~Mn)-Si crystals is inadequate, and not enough
to dissolve the
Mg2Si that crystallized during casting into the matrix, and if the treatment
time exceeds 24
hours, the Mg2Si that crystallized during casting is well-dissolved into the
matrix, and the Mg
and Si become saturated, resulting in cost increases.
The invention is characterized by further cold rolling this coil and
performing a
solution treatment. This solution treatment is preferably performed in a
normal continuous
annealing line (CAL).
A continuous annealing line (CAL) is an installation for performing continuous
solution treatments and the like of coils, characterized by comprising
inductive heating
devices for performing heat treatments, water tanks for water-cooling, air
nozzles for
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CA 02548788 2006-06-08
air-cooling, and the like.
As for the solution treatment, it should preferably be performed by heating at
a rate
of at least 10 °C/s to 530-560 °C by means of a continuous
annealing line, and holding for 30
seconds or less.
The reason the heating rate to the solution treatment temperature is limited
to at
least 10 °C/s in the solution treatment is that if the heating rate is
less than 10 °C/s, the coil
advancing speed becomes too slow, as a result of which the processing time
becomes long
and the cost mounts.
The reason the solution treatment temperature is set to be within the range of
530-560 °C is that if the temperature is less than 530 °C, it is
not sufficient to cause Mg2Si
that crystallized while casting or precipitated while being cooled after
homogenization to be
dissolved into the matrix, and if the temperature exceeds 560 °C, the
metals with low melting
points will melt and cause burning.
Additionally, the reason the solution treatment time is restricted to be
within 30
seconds is that in the case of treatment times exceeding 30 seconds, Mg2Si
that crystallized
while casting or precipitated while being cooled after homogenization is well-
dissolved into
the matrix, and the Mg and Si become saturated, thereby slowing the coil
advancement
speed, as a result of which the processing time is increased and the costs
mount.
The invention is characterized by cooling to room temperature at a rate of at
least
10 °C/s after the solution treatment. The reason the cooling rate after
the solution treatment
is at least 10 °C/s is that if the cooling rate is less than 10
°C/s, Si is deposited in the crystal
grain boundary during the cooling step, thus reducing the hemmability.
After performing the aforementioned homogenization treatment on the thin slab,
it
is further cold rolled, subjected to a solution treatment and cooled to room
temperature at a
rate of at least 10 °C/s, and after the coil is left at room
temperature, it may be held for 30
seconds or less at 260-300 °C in a continuous annealing line, then
cooled to room
temperature at 10 °C/s.
This solution treatment and restoration treatment are preferably performed in
a
CA 02548788 2006-06-08
normal continuous annealing line. A continuous annealing line (CAL) is an
installation for
performing continuous solution treatments and the like of coils, characterized
by comprising
inductive heating devices for performing heat treatments, water tanks for
water-cooling, air
nozzles for air-cooling, and the like. Due to the restoration treatment, it is
possible to
re-dissolve GP zones that appear due to natural ageing when left at room
temperature after
a solution treatment, thus enabling adequate strength to be obtained after
heating for coating
and baking.
Additionally, in order to obtain adequate strength after heating for coating
and
baking, it is left at room temperature after the solution treatment and
subjected to a
restoration treatment at 260-300 °C. If the restoration treatment
temperature is less than
260 °C, adequate bake-hardenability cannot be obtained, and if it
exceeds 300 °C, the
hemmability is reduced.
The reason the time over which the restoration treatment temperature is held
is
restricted to within 30 seconds is that if the treatment time exceeds 30
seconds, it is not
possible to adequately re-dissolve the GP zones that appear due to natural
ageing when left
at room temperature after the solution treatment, in addition to which the
coil advancement
speed is too slow, as a result of which the treatment time is long and the
costs mount.
After performing the aforementioned homogenization treatment on the thin slab,
it
can be further cold rolled, subjected to a heat solution treatment in a
continuous annealing
line, water-cooled to 250 °C or less at a cooling rate (first cooling
rate) of at least 10 °C/s,
then air-cooled to 60-100 °C at a cooling rate (second cooling rate) of
1-20 °C/s, coiled up
and cooled to room temperature.
This heat solution treatment and subsequent cooling are preferably performed
in a
normal continuous annealing line (CAL). During this heat solution treatment
and
subsequent cooling, a heat treatment (preliminary ageing) can be performed to
evenly
generate nuclei for (3" deposition in the matrix, to obtain adequate strength
after heating for
coating and baking.
After subjecting the thin slab to a homogenization treatment and further cold
rolling,
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it may be subjected to a solution treatment by heating to 530-560 °C at
a rate of at least
°C/s, then holding for 30 seconds or less, then cooled to room
temperature at a rate of at
least 10 °C/s, thereafter subjected to a restoration treatment by
holding within a range of
260-300 °C for 30 seconds, then cooled to 60-100 °C at a cooling
rate of at least 1 °C/s,
5 coiled up and subjected to a preliminary ageing treatment by cooling to room
temperature.
This solution treatment and subsequent cooling, and restoration treatment and
subsequent cooling are preferably performed in a normal continuous annealing
line (CAL).
With this production method, not only is it possible to re-dissolve GP zones
that appear due
to natural ageing when left at room temperature after the solution treatment,
but it is also
10 possible to perform a heat treatment (preliminary ageing) to generate
nuclei for (3" deposition,
thus further improving the resistance after coating and baking.
Next, the significance of the alloy ingredients of the present invention and
the
reasons for their limitations shall be explained. The essential element Mg is
dissolved in
the matrix after the heat solution treatment, and is deposited as a
reinforcing phase together
with Si upon heating for coating and baking, thereby improving the strength.
The reason
the Mg content is limited to 0.30-1.00 wt% is that the effect is small if less
than 0.30 wt%,
and if more than 1.00 wt%, the hemmability after the solution treatment is
reduced. A more
preferable range for the Mg content is 0.30-0.70 wt%.
The essential element Si is deposited together with Mg as an intermediary
phase
of Mg2Si known as (3" or an analogous reinforcing phase upon being heated for
coating and
baking, thereby increasing the strength. The reason the Si content is limited
to 0.30-1.20
wt% is that if less than 0.30 wt%, its effects are minimal, and if more than
1.20 wt%, the
hemmability is reduced after the heat solution treatment. A more preferable
range of Si
content is 0.60-1.20 wt%.
The essential element Fe, when coexisting with Si and Mn, generates many
AI-Fe-Si crystals and AI-(Fe~Mn)-Si crystals of a size of 5 ~m or less upon
casting, so that
re-crystallized nuclei are increased, as a result of which the recrystallized
grains are refined
and sheets of exceptional formability are obtained. If the Fe content is less
than 0.05 wt%,
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the effects are not very remarkable. If it exceeds 0.50 wt%, coarse AI-Fe-Si
crystals and
AI-(Fe~Mn)-Si crystals are formed upon casting, thus not only reducing the
hemmability but
also reducing the amount of Si dissolved in the thin slabs, as a result of
which the
bake-hardenability of the final sheets is reduced. Therefore, the preferable
range of Fe
content is 0.05-0.50 wt%. A more preferable range of Fe content is 0.05-0.30
wt%.
The essential element Mn is added as an element to refine the re-crystallized
grains. By keeping the size of the re-crystallized grains relatively small at
10-25 pm, it is
possible to form sheets with exceptional formability. If the Mn content is
less than 0.05 wt%,
the effect is not adequate, and if it exceeds 0.50 wt%, coarse AI-Fe-Si
crystals and
AI-(Fe~Mn)-Si crystals are formed upon casting, thus not only reducing the
hemmability but
also reducing the amount of Si dissolved in the thin slabs, as a result of
which the
bake-hardenability of the final sheets is reduced. Therefore, the preferable
range of Mn
content is 0.05-0.50 wt%. A more preferable range of Mn content is 0.05-0.30
wt%.
The essential element Ti will not inhibit the effects of the present invention
if it is
contained at 0.10 wt% or less, and it can function as a crystal grain refiner
for the thin slabs,
so as to reliably prevent casting defects of the slabs such as cracks or the
like. If the Ti
content is less than 0.005 wt%, the effects are not adequate, and if the Ti
content exceeds
0.10 wt%, coarse intermetallic compounds such as TiAl3 and the like are formed
during
casting, thus greatly reducing the hemmability. Therefore, the preferable
range of Ti
content is 0.005-0.10 wt%. A more preferable range for the Ti content is 0.005-
0.05 wt%.
The optional element Cu is an element that promotes age-hardening and raises
the
bake-hardenability. If the Cu content is less than 0.05 wt%, the effect is
small, and if it
exceeds 0.70 wt%, the yield strength of the sheets becomes high after a
preliminary ageing
treatment, and not only does the hemmability decrease, but the reduction in
corrosion
resistance is also marked. Therefore, the Cu content is preferably within a
range of
0.05-0.70 wt%. The Cu content is more preferably 0.10-0.60 wt%.
The optional element Zr is added as an element for refining the re-
crystallized
grains. If the Zr content is less than 0.05 wt%, the effect is not adequate,
and if it exceeds
0.40 wt%, coarse AI-Zr crystals are created during slab casting, thus reducing
the
CA 02548788 2006-06-08
hemmability. Therefore, the Zr content is preferably within a range of 0.05-
0.40 wt%. The
Zr content is more preferably within a range of 0.05-0.30 wt%.
As explained above, the present invention allows an AI-Mg-Si alloy sheet for
use in
automotive body sheets having exceptional bake-hardenablitiy and hemmability
after a final
anneal to be produced at low cost. While a restoration treatment or high-
temperature
winding is required to suppress natural ageing as with conventional methods,
the steps such
as facing, hot rolling and the like that precede these steps can be largely
simplified, thus
greatly reducing the total production cost.
Herebelow, the best modes of the present invention shall be described using
examples.
Example 1
In the below-given examples, the samples after cold rolling are not coils but
all cut
sheets. Therefore, in order to simulate the step of continuous annealing of a
coil in a
continuous annealing line (CAL), a solution treatment of the samples in a salt
bath and a
cold water quench or 85 °C water quench were employed.
After degassing melts having the compositions shown in Table 1, they were cast
into slabs 7 mm thick by means of a twin-belt casting method. The DAS
(Dendrite Arm
Spacing) was measured by an intersection method from observation of the
microstructures
at a quarter-thickness of the slab, and the cooling rate 75 °C/s was
computed. A
predetermined homogenization treatment was performed on the slabs which were
then
cooled to room temperature at a predetermined cooling rate, and cold rolled to
form sheets
of 1 mm thickness. Next, solution treatments were performed on these cold
rolled sheets in
a salt bath, and they were either 1 ) quenched in 85 °C water and
immediately inserted into
an annealer with a predetermined atmospheric temperature to perform a heat
treatment
under predetermined conditions, or 2) quenched in cold water, left at room
temperature for
24 hours, then subjected to a heat treatment under predetermined conditions.
Furthermore,
in order to simulate automobile coating steps, they were held for one week at
room
temperature after the heat treatment, and measured for 0.2% yield strength,
further baked at
180 °C for 30 minutes, and again measured for 0.2% yield strength.
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The difference in yield strength before and after the baking treatment was
taken as
the bake-hardenability, and those exceeding 80 MPa were judged to have
excellent
bake-hardenability. In order to simulate hemmability, the sheets prior to
baking were
preliminarily warped by 5%, then bent into a U shape using a jig having a
radius r = 0.5 mm,
then 1 mm thick spacers were inserted and they were bent 180°. Those
which did not crack
were ranked O and those which cracked were ranked X. The detailed sheet
production
steps and evaluation results are shown in Table 2-6.
[Table 1 ]
TABLE 1 Alloy Composition
wt%
Allo M Si Fe Mn Cu Ar Ti
No.
A 0.5 0.7 0.2 0.2 - - 0.02
B 0.5 0.8 0.2 0.2 - - 0.02
C 0.6 0.8 0.2 0.2 - - 0.02
D 0.5 1 0.2 0.2 0.5 - 0.02
E 0.5 0.8 0.2 0.2 - 0.15 0.02
F 0.4 1.2 0.2 0.2 0.1 - 0.02
Table 2 shows the results for cases in which the homogenization conditions and
cooling rate after the homogenization treatment were changed. After the
homogenization
treatment, the slabs were cold rolled to a thickness of 1 mm, these cold
rolled sheets were
subjected to a solution treatment by holding for 15 seconds at a predetermined
temperature
by means of a salt bath, then quenched with 85 °C water, and
immediately inserted into an
annealer with an atmospheric temperature of 85 °C to perform a
preliminary ageing of 8
hours. Those falling within the scope of conditions of the present invention
(1-7) had
exceptional bake-hardenability and hemmability. Those that did not undergo a
homogenization treatment (8, 10) had poor bake-hardenability and hemmability.
Additionally, those which had a slow cooling rate after the homogenization
treatment had
poor bake-hardenability (9).
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[Table 2j
TABLE 2 Cooling Rate after Homogenization and Bake-Hardenability/Hemmability
Homo enization
Treatment
AlloyCast Heating Holding Holding Cooling
ID Type/
No. Slab Rate Tem Time Rate
Thick.
(mm) (Clh) (C) (h) (Clh)
1 A twin-belt30 560 5 1500
/ 7
2 B twin-belt50 560 6 1700
/ 7
P 3 B twin-belt50 550 5 500
/ 7
resent 4 C twin-belt30 530 10 1000
I / 7
ti
nven 5 D twin-belt40 530 10 1000
on / 7
6 E twin-belt40 530 10 1000
/ 7
7 F twin-belt50 550 6 1000
/ 7
C 8 A twin-beltNone
/ 7
omp. 9 B twin-belt50 560
E / 7 6 250
l
xamp 10 B twin-beltNone
e / 7
Cold Sol. Prelim Yield Str.Bake- Hem.
Roll
ID Sheet Treat. . fter Hard
before
Ageing ( j
Thick. Tem . Bakin M MPa
a
1 1 mm 550 C 85 C X 100/192 92 O
8 h
2 1 mm 550 C 85 C X 110/210 100 O
8 h
3 1 mm 530 C 85 C X 95/175 80 O
8 h
Present4 1 mm 540 C 85 C X 107/209 102 O
8 h
Invention
5 1 mm 550 C 85 C X 122/221 99 O
8 h
6 1 mm 550 C 85 C X 115/213 98 O
8 h
7 1 mm 550 C 85 C X 117/208 91 O
8 h
8 1 mm 550 C 85 C X 110/158 48 X
8 h
Comp.
9 1 mm 550 C 85 C x 90/145 55 O
le 8 h
Exam
p 10 1 mm 550 C 85 C X 92/160 68 X
8 h
Table 3 shows the results when the temperatures/times of the homogenization
treatment are changed. After the homogenization treatment, the slabs were cold
rolled to a
thickness of 1 mm, these cold rolled sheets were subjected to a solution
treatment by
holding for 15 seconds at a predetermined temperature by means of a salt bath,
then
quenched in 85 °C water and immediately entered into an annealer with
an atmospheric
temperature of 85 °C to perform a preliminary ageing of 8 hours. Those
falling within the
scope of conditions of the present invention (11-14) had exceptional bake-
hardenability and
hemmability. Those that had a low homogenization temperature (15) or had a
short holding
time (16) had poor bake-hardenability and hemmability.
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[Table 3J
TABLE 3 Homogenization Temperature/Time and Bake-Hardenabilit/Hemmability
Homo enization
Treatment
AlloyCast Heating Holding Holding Cooling
ID No. Type/ Rate Temp Time Rate
Sla
hjck.
T
n (C/h) (C) (h) (C/h)
m
11 B twin-belt30 _ 560 5 1500
/ 7
Present12 B twin-belt50 560 6 1500
/ 7
Invention13 C twin-belt50 550 5 1500
/ 7
14 C twin-belt30 530 10 1500
/ 7
Comp. 15 B twin-belt50 500 6 1500
/ 7
Example16 B twin-belt50 560 1 T 1500
/ 7
Cold Sol. Prelim. Yield Str.Bake- Hem.
ID Roll Treat. Ageing before/afterHard.
Sheet Tem . Bakin (Mpa)(MPa
Thick.
11 1 mm 550 C 85 C X 110/210 100 O
8 h
Present12 1 mm 550 C 85 C x 111/213 103 O
8 h
Invention13 1 mm 530 C 85 C x 107/209 102 O
8 h
14 1 mm 540 C 85 C x 112/215 103 O
8 h
Comp. 15 1 mm 550 C 85 C X 95/165 70 X
8 h
Example16 1 mm 550 C 85 C x 100/175 75 X
8 h
Table 4 shows the results when the homogenization conditions and restoration
conditions were changed. After the homogenization treatment, the slabs were
cold rolled to
a thickness of 1 mm, these cold rolled sheets are subjected to a solution
treatment by
holding for 15 seconds at a predetermined temperature by means of a salt bath,
then
quenched in cold water, and after leaving at room temperature for 24 hours,
subjected to a
restoration treatment by holding for 15 seconds at a predetermined
temperature. Those
falling within the scope of conditions of the present invention (17-20) had
exceptional
bake-hardenability and hemmability. Those that had a low restoration
temperature
(reheating temperature) (21 ) had poor bake-hardenability. Those whose
restoration
temperature (reheating temperature) was too high (22) had poor hemmability.
Furthermore,
even when the restoration conditions were within the scope of the present
invention, those in
which the homogenization temperature was low (23) or the holding time was
short (24) had
poor hemmability. Those in which the cooling rate after the homogenization
treatment was
slow (25) had poor bake-hardenability.
14
CA 02548788 2006-06-08
[Table 4)
TABLE 4 Homogenization Method/Reheat Temperature and Bake-
Hardenability/Hemmability
Homo enization
Treatment
AlloyCast Heating Holding Holding Cooling
ID No_ Type/ Rate Temp Time Rate
Sla(
TT
h?ck.
n (C/h) (C) (h) (Clh)
m
17 B twin-belt30 560 5 1500
/ 7
Present18 B twin-belt50 560 6 2000
/ 7
Invention19 C twin-belt50 550 5 1000
/ 7
20 C twin-belt30 530 10 2500
/ 7
21 B twin-belt50 560 6 __ 1500
/ 7
22 B twin-belt50 560 6 1500
7
Comp. 23 B ~ 50 500 6 500
l twin-belt
E 7
xamp 24 B twin-belt50 560 1 1000
e / 7
25 B twin-belt50 560 6 200
/ 7
Cold Sol. Yield Str.Bake-
Roll
Prelim Hem
. .
ID Sheet Treat. before/afterHard.
Ageing
Thick. Temp. Bakin M (MPa)
a)
17 1 mm 550 C 270 110/210 100 O
Present18 1 mm 550 C 270 111/213 103 O
Invention1 1 mm 530 C 290 107/209 102 O
g
20 1 mm 540 C 290 112/215 103 O
21 1 mm 550 C 240 95/170 75 O
22 1 mm 550 C 310 127/229 102 X
Comp.
23 1 mm 550 C 290 97/197 100 X
Exam
le
p
24 1 mm 550 C 280 90/160 70 X
25 1 mm 550 C 290 95/145 50 O
Table 5 shows the results when the homogenization conditions and cooling
pattern
after the solution treatment were changed. The cooling rate after the solution
treatment
was divided into two stages, with the cooling rate from the solution
temperature to an
intermediate temperature being defined as the first cooling rate and the
cooling rate from the
intermediate temperature to the coil-up temperature being defined as the
second cooling rate.
After the homogenization treatment, the slabs were cold rolled to a thickness
of 1 mm, and
these cold rolled sheets were subjected to a solution treatment by holding for
15 seconds at
a predetermined temperature by means of a salt bath, after which they were
cooled to the
intermediate temperature at the first cooling rate, then cooled to the coil-up
temperature at
the second cooling rate, and thereafter cooled to room temperature at 5
°C/h.
Those falling within the scope of the present invention (26-28) had
exceptional
bake-hardenability and hemmability. Those in which the first cooling rate
after the solution
CA 02548788 2006-06-08
treatment was slow (29), those in which the second cooling rate was slow (31 )
or those in
which the intermediate temperature was too high (30) had poor hemmability.
Those in
which the coil-up temperature was too low (32) had poor bake-hardenability.
Conversely,
those in which the coil-up temperature was too high (33) had poor hemmability.
Furthermore, those in which the homogenization treatment temperature was too
low (34) or
the holding time was too short (35) had poor hemmability. Those in which the
cooling rate
after the homogenization treatment was too slow (36) had poor bake-
hardenability.
[Table 5]
TABLE 5 Homogenization Method/Coil-up Temperature and Bake-
Hardenability/Hemmability
Homo enization
Treatment
AlloyCast Type/Heating Holding Holding Cooling
ID Slab Thick.
No. Rate Tem Time Rate
mm (C/h) (C) (h) (Clh)
( )
P 26 B twin-belt30 560 5 1500
t / 7
resen 27 B twin-belt50 560 6 2000
Invention / 7
28 B twin-belt50 550 5 1000
/ 7
29 B twin-belt50 560 6 1500
/ 7
30 B twin-belt50 560 6 1500
/ 7
31 B twin-belt50 560 6 1500
/ 7
Comp. 32 B twin-belt50 560 6 1500
/ 7
Example33 B twin-belt50 560 6 2000
/ 7
34 B twin-belt50 500 6 1000
/ 7
35 B twin-belt50 560 1 1000
/ 7
36 B twin-belt50 560 6 200
/ 7
Cold Sol. First Sec. Coil
Int. YS b/a Bake- H
D Roll Treat.Cool Temp Cool ~p gak. Hard. a
Sheet Tem. Temp Temp Temp ( p ( )
Thick.(C) (C) ( (C) (C) ) MPa m
C) M a
Present26 1 mm 550 100 200 20 85 110/210101 O
Invention27 1 mm 550 100 200 20 70 105/207102 O
28 1 mm 530 100 200 20 90 101/211100 O
29 1 mm 550 5 200 20 80 106/20195 X
30 1 mm 550 100 300 20 80 101/19796 X
31 1 mm 550 100 250 1 80 102/19896 X
Comp. 32 1 mm 550 100 200 20 50 112/16553 O
Example33 1 mm 550 100 200 15 110 130/240110 X
34 1 mm 550 100 200 20 85 97/197 100 X
35 1 mm 550 100 200 20 85 104/19490 X
36 1 mm 550 100 200 20 80 89/134 45 O
Table 6 shows the results when the restoration treatment temperature
(reheating
temperature) after the solution treatment and coil-up temperature were
changed. After the
homogenization treatment, the slabs were cold rolled to a thickness of 1 mm,
these cold
16
CA 02548788 2006-06-08
rolled sheets are subjected to a solution treatment by holding for 15 seconds
at a
predetermined temperature by means of a salt bath, then quenched in cold
water, and after
leaving at room temperature for 24 hours, held for 15 seconds at a
predetermined
temperature (preheating temperature) and cooled to a predetermined coil-up
temperature at
10 °C/s, then further cooled to room temperature at 10 °C/h.
Those falling within the scope
of conditions of the present invention (37-40) had exceptional bake-
hardenability and
hemmability. Those in which the restoration treatment temperature (reheating
temperature)
was too high (41 ) had poor hemmability. Those in which the restoration
treatment
temperature (reheating temperature) was too low (42) had reduced bake-
hardenability.
Those in which the coil-up temperature was too low (43) had poor bake-
hardenability.
Those in which the coil-up temperature was too high (44) had poor hemmability.
[Table 6]
TABLE 6 Reheat Temperature/Coil-up Temperature and Bake-
Hardenability/Hemmability
Sol. Reheat Coil Yeld Str. Bake-
ID NllooyTreat. Temp Up before/afterHard. Hem.
Tem. (C) Temp Baking (MPa)
(C) (C) (Mpa)
37 B 550 270 85 121/231 110 O
Present38 B 550 270 90 125/237 114 O
Invention39 B 530 290 70 117/228 111 O
40 B 540 290 80 119/231 112 O
41 B 550 320 85 124/234 110 X
Comp. 42 B 550 250 80 111/198 87 O
Example43 B 550 260 40 110/185 75 O
44 B 550 290 120 131/249 118 X
I
Homogenization: 550 °C x 6 h Cooling Rate after Homogenization:
1000 °C/h
INDUSTRIAL APPLICABILITY
According to the present invention, rolled sheets of AI-Mg-Si alloy that are
suitable
for forming by bending, press forming and the like of automotive parts,
household appliances
and the like can be produced at a low cost relative to the conventional art.
17
