Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HIGH HARDNESS ALUMINIUM MOULDING PLATE AND METHOD FOR PRODUCING SAID PLATE
The invention relates to moulding plate of an aluminium wrought alloy. The
invention further relates to a method for producing said moulding plate.
In the tooling and moulding plate market for blow moulding and thermoforming
of rubbers and plastic, a sustained effort in reducing costs is made whilst
maintaining
satisfactory wear resistance and repair weldability. These types of tooling
plates are
also widely used in many other industrial applications, including components
produced
by various machining operations such as drilling, milling and turning.
Commonly used
tooling plates are made from selected alloys from the AA2000 series alloys,
the
AA6000 series alloys or the AA7000-series alloys.
High wear resistance in combination with good machinability are important
properties of alloys for moulding plate. In typical tooling plate wrought
alloys this wear
resistance is obtained by alloying with copper (such as in the AA2000 series)
or Zinc
(such as in the AA7000 series) or magnesium and silicon (such as in the AA6000
series) in combination with a thermo-mechanical treatment. In these heat
treatable
alloy classes, the typical way to achieve high hardness is via precipitation
hardening of
coherent phases. Additional hardening by relatively coarse particles, such as
primary
Si and incoherent Mg2Si is often considered inappropriate, because of the
related risks
of eutectic melting at elevated temperatures. Also additional hardening by a-
AI(Fe,Mn,Cu)Si dispersoids is not readily applied, since it is generally
believed that
they increase the quench sensitivity of the alloy. Increased quench
sensitivity is
considered a disadvantageous characteristic, in particular for thicker gauge
products.
Typically, with AA2000 and AA7000 alloys, higher hardness is achieved than
with AA6000 alloys. However, a disadvantage of the AA2000 series is the high
copper
content which makes the alloy expensive as well as very sensitive to the heat
treatment. Also, the weldability of the alloy is adversely affected by the
high copper
content. Similar arguments are made for the AA7000 series such as high
residual
stresses, and poor weldability and corrosion performance which cause
complications
with dimensional tolerances, repair weldability, and durability of the mould.
The wear
resistance of an AA6000 series alloy in a T6 temper, such as AA6010, AA6013,
AA6061, AA6066, AA6070 and AA6082 is usually adequate for normal industrial
applications. However, for high performance applications a higher wear
resistance is
desired, without adversely affecting weldability and costs.
CONFIRMATION COPY
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It is an object of the invention to provide a moulding plate of an aluminium
wrought alloy with an improved resistance to wear.
According to the invention, this object is reached by providing a moulding
plate
of an aluminium wrought alloy comprising, in weight percent:
- Si 1.4 - 2.1
- Mn 0.8-1.2
- Cu 0.45-0.9
- Mg 0.7-1.2
- Ti <0.15
- Zn <0.4
- Fe <0.7
- one or more of Zr, Cr, V each <0.25, total preferably < 0.35
- incidental elements and impurities, each <0.05, total <0.25,
- the balance aluminium, and having a thickness of more than 0.6 mm and in
T6 temper condition having a hardness of more than 105HB.
The increased hardness is reached by combining precipitation hardening of
Mg-Si-Cu phases, Fe- and Mn-containing intermetallics and dispersoids, which
are
known to actually reduce the age hardening effect in balanced AIMgSi(Cu)
alloys
through their effect on the quench sensitivity, with a high excess of Si,
which
decreases the Mg solute level, to minimise the negative effect of Mn-
containing
dispersoids on the quench sensitivity. The supersaturation level for Mg-Si
phases is
not yet so high that particularly high quench sensitivities already result
from the Mg-,
Si-, and Cu solute content. The balanced alloy composition according to the
invention
is believed to combine the strength increasing effect of a silicon addition
with
moderate amount of copper, magnesium and manganese. It was found that this
alloy
provides satisfactory weldability and a hardness of at least 105 HB. It should
be noted
that the hardness values are expressed in the Brinell scale and were measured
by a
ball having a 2.5 mm diameter loaded with a mass of 62.5 kg. The hardness
tests
were performed according to ASTM E10 (version 2002).
In a preferred embodiment of the invention the hardness in T6 temper
condition is at least 115HB, more preferably at least 120HB. These hardness
values
imply an increased machinability as well as wear resistance. The chemical
composition in combination with a heat treatment ensures that adequate
weldability
and thus reparability is maintained: surprisingly it has been found that for
Cu levels of
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up to 0.9% the plate alloy shows very good reparability with for instance a
common
4043 filler wire.
In an embodiment the Si is in the range of 1.53 - 2.0 %, more preferably in
the
range of 1.55-1.9 %. It was found that this range of silicon provides a very
good
combination of the desirable properties, through hardening by coherent Mg-Si-
Cu
phases, and by primary Si, incoherent Mg2Si and a-AI(Fe,Mn,Cu)Si intermetallic
phases and dispersoids.
In an embodiment the Mn is in the range of 0.85 - 1.10 %. It was found that
this
range of manganese provides a very good combination of the desirable
properties, in
particular by stimulating the formation of a-AI(Fe,Mn,Cu)Si intermetallic
phases and
dispersoids. At high Si levels, the tendency to form the relatively brittle (3-
AIFeSi
intermetallic phase increases. However, by ensuring the presence of suitable
amounts
of Mn and Cu the more favourable a-AI(Fe,Mn,Cu)Si phase is stabilised.
In an embodiment the Cu is in the range of 0.5 - 0.7 %. It was found that this
range of copper provides a very good combination of the desirable properties
through
coherent Mg-Si-Cu phases and stabilised a-AI(Fe,Mn,Cu)Si, whilst keeping
alloying
cost down and ensuring good repair weldabiRy.
In an embodiment the Zn is below 0.3%, preferably in the range of 0.17 - 0.3
In an embodiment the Fe is preferably at least 0.2%, more preferably in the
range 0.2 - 0.5%, and even more preferably in the range 0.3 - 0.5% to ensure
the
formation of sufficient amounts of hardness increasing a-AI(Fe,Mn,Cu)Si
intermetallics.
In an embodiment the Zr, Cr, V are each preferably below 0.18%, more
preferably below 0.12% to further reduce the quench sensitivity.
In an embodiment the moulding plate has a machinability rating of "B" or
better
as defined in 'ASM Specialty Handbook - Aluminium and Aluminium Alloys (ed.
J.R.
Davis), ASM International 1993, page 328-331.
In an embodiment the moulding plate has a final thickness of 300 mm, in which
the claimed hardness values can still be met in the plate centre. Preferably
the final
thickness is in the range of between 5 to 300 mm, more preferably in the range
of
between 5 to 260 mm. These thickness ranges allow the application of the
moulding
plate for all practical application involving moulding plate.
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In an embodiment the moulding plate has been rolled to the final thickness by
hot rolling only.
According to a further aspect of the invention, a method is provided of
manufacturing a moulding plate comprising the subsequent steps of:
= casting an ingot having a composition comprising (in weight percent):
o Si 1.4 - 2.1
o Mn 0.8-1.2
o Cu 0.45 - 0.9
o Mg 0.7-1.2
o Ti <0.15
o Zn <0.4
o Fe <0.7
0 one or more of Zr, Cr, V each <0.25, total preferably < 0.35
o incidental elements and impurities, each <0.05, total <0.25, balance
aluminium, and with preferred compositional ranges as set out in the
description hereinabove.
= homogenising and/or preheating the ingot,
= working said plate to a final thickness, preferably by hot rolling and/or
cold
rolling, more preferably by hot rolling only,
= subjecting to heat treatment comprising solution heat treating followed by
rapid cooling,
= ageing,
wherein the cooling rate during said rapid cooling is chosen so as to obtain a
hardness of the moulding plate of at least 105 HB.
By manufacturing a moulding plate according to the invention a high hardness
product with a high content of chip-breaking intermetallics is obtained. The
cooling
rate during the rapid cooling after solution heat treating is important
because this
cooling rate determines the amount of solute content of Mg, Si and Cu which
were
dissolved during the solution heat treatment.
In an embodiment of the invention the heat treatment after hot rolling or hot
pressing is a T6-treatment.
In an embodiment the homogenisation temperature is at least 450 C,
preferably at least 500 C, more preferably between 500 and 595 C, preferably
for
between 1 to 25 hours, more preferably for between 10 to 16 hours. The pre-
heat
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temperature is at least 570 C, between about 300 C and 570 C, preferably
between
350 and 530 C, preferably for between 1 to 25 hours, more preferably for
between 1
and 10 hours.
In an embodiment the solution heat-treating temperature is at least 500 C,
preferably at least 520 C and more preferably at least 540 C. In an
embodiment the
cooling rate after solution heat-treating from the solution heat-treating
temperature to
below 250 C, preferably to below 150 C and more preferably to below 100 C, is
at
least 1 C/s, preferably at least 2 C/s more preferably 5 C/s, even more
preferably at
least 10 C/s. It should be noted that the cooling.rate of the product during
quenching
is dependent on the location within the product. The centre of the product
cools down
more slowly than the surface of the product. Consequently, since the final
hardness is
dependent on the cooling rate, the hardness will be lower if the local cooling
rate
during quenching is lower. The critical point in the product is defined as the
point
where the cooling rate during quenching is the lowest. The abovementioned
cooling
rates relate to the cooling rate at the critical point.
In a further embodiment, the ageing process comprises natural ageing for a
maximum duration of 28 days, preferably for a maximum duration of 14 days,
more
preferably for a maximum duration of 7 days, even more preferably for a
maximum
duration of 2 days, followed by an artificial ageing treatment equivalent to
ageing at
about 180'to 200 C for about 1-10 hours. It is known to the skilled person
that time
and temperature of an annealing are usually not chosen independently. The
ageing
process is thermally activated, resulting in the situation that a high
temperature
coupled with a short time is equivalent to a lower temperature and a longer
time, i.e.
the same metallurgical state is reached after the ageing treatment.
In an embodiment of the invention the working step comprises a rolling or
pressing step. In a further embodiment the rolling step comprises a hot
rolling and/or a
hot pressing step and/or cold-rolling step. Preferably, the working step
comprises hot
rolling and/or hot pressing only.
In an embodiment of the invention the casting step is a near-net shape casting
step, wherein the dimensions of the cast product approximates the final
product.
A particular embodiment of the invention will now be explained by the
following
non-limitative examples and figure. It should be noted that the chemical
composition of
the alloys was varied by mixing cuttings of a brazing alloy, consisting mostly
of an
AA3000-series core alloy clad with a Si-rich AA4000-series alloy with
technical purity
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Al 99.0 after which Cu and/or Mg and/or other elements can be added to obtain
the
final chemistry.
Table 1. Average composition of tested alloys and hardness in T6-condition.
Alloy Si Fe Cu Mn Mg Zn Ti HB content brazing
alloy (%)
Al 99.0 0.4 0.6 0.03 0.03 0.03 0.07 - - 0
Brazing alloy 2.0 0.4 0.5 1.0 0.40 0.25 0.05 - 100
Example 1 1.72 0.37 0.61 0.77 0.97 0.21 0.05 124 82
Example 2 1.70 0.39 0.91 0.95 0.85 0.21 0.05 124 81
Example 3 2.10 0.38 0.50 1.03 0.88 0.25 0.05 124 100
Example 4 1.68 0.41 0.40 0.78 0.98 0.21 0.05 123 80
Example 5 1.71 0.43 0.51 0.76 0.70 0.21 0.05 122 82
Example 6 1.59 0.38 0.61 0.81 0.98 0.10 0.03 123 75
Example 7 1.60 0.39 0.64 0.95 0.91 0.02 0.05 Fig.1 80
These alloys were homogenised at a temperature above 510 C, optionally hot
rolled, solution heat treated at 550 C, cooled down with at least 10 C/s to
maximise
the solute content of Mg, Si and Cu, stored for 14 days at room temperature,
and
aged following an ageing treatment equivalent to 190 C for 2-6 hours. In this
way, a
high-hardness T6-temper product with a high content of chip-breaking
intermetallics is
obtained, leading to a hardness of at least 120 HB. Example 7 was solution
heat
treated at 530 C and stored at room temperature for a period of 1 day, the
remainder
of the process conditions being as given above for the other alloys.
The hardness profiles of plates with the composition according to Example 7
with thicknesses of 80, 100 or 150 mm are shown in Fig. 1. Along the X-axis
the
distance (L) to the centre of the plate in the thickness direction in mm is
given, and
along the Y-axis the hardness in HB values is given at different locations
over the
thickness of the plate. All measured values show a hardness value of at least
120 HB
at every location over the thickness of the plate.
It is of course to be understood that the present invention is not limited to
the
described embodiments and examples described above, but encompasses any and
all
embodiments within the scope of the description and the following claims.
