Note: Descriptions are shown in the official language in which they were submitted.
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ALUMINUM CASTING ALLOY
Field of the invention
The invention relates to the field of metallurgy, and specifically, to
aluminum-based alloys, and can be used in the production of castings of
complex shape by metal mold casting with the application of different
casting techniques, in particular pressure casting, low-pressure casting,
gravity casting, etc.
lo Summary of the prior art
Castings of complex shape, depending on their purpose, are produced from
non-heat-treatable and heat-treatable Al-Si alloys. Castings, which are
intended for the most critical parts, are usually used after a full T6 temper
heat treatment that includes water quenching and ageing to maximum
strength. The maximum strength of copper-free Al-Si alloys (for example,
AlSi7Mg alloys) in the T6 temper is usually up to 250-300 MPa for ultimate
tensile strength and 170-240 MPa for yield strength. Quenching makes the
casting production process considerably more difficult, since quenching
might cause geometrical distortions, changes in dimensions and cracks in
castings.
Non-heat-treatable alloys are usually characterized by low mechanical
strength properties. In particular, the AlSi 11 alloy, when cast into a metal
mold, has an ultimate tensile strength of no higher than 180-210 MPa; the
yield strength of such an alloy is about 70-80 MPa, and its elongation is
usually 6-15%. Low elongation values are due to the alloy's structure
characterized by a coarse eutectic silicon morphology; Al-Si alloys are
usually doped with various alloying components to increase elongation but it
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often causes an increase in porosity, which leads to deterioration of the
tightness of thin-walled castings.
The related art discloses an Al¨Ni¨Mn based alloy for aerospace and
automotive structural components, which is an alternative to Al-Si alloy
grades. The alloy has been developed by Alcoa and is disclosed in
US6783730B2 (publ. 31.08.2004). This alloy ¨ which includes about 2-6 wt.
% Ni, about 1-3 wt. % Mn, less than about 1 wt. % Fe, less than about 1 wt.
% Si, with incidental elements and impurities ¨ ensures production of
castings with a good combination of casting and mechanical properties. One
io of the drawbacks of this disclosure is that a high level of casting and
mechanical properties is ensured by the use of high-purity aluminum grades
and by a high nickel content, which considerably increases the production
cost of castings. Moreover, the proposed material is non-heat-treatable over
the whole concentration range, which places limitations on its application.
Furthermore, the corrosion resistance of castings significantly decreases in
the region of high nickel concentrations.
The related art also discloses Al--Ni and Al¨Ni¨Mn alloys and a method
for producing cast products out of these alloys, as disclosed in Alcoa's
invention US8349462B2 (publ. 08.01.2013). The invention proposes
compositions of alloys to be applied in the as-cast condition and a method of
their production to obtain a target structure ensuring reaching a required
level of mechanical properties and forming decorative anodized coatings.
The chemical composition of the proposed disclosure comprises the
following ranges of the alloy elements: about 6.6 to about 8.0 wt. % Ni;
about 0.5 to about 3.5 wt. % Mn; up to about 0.25 wt. % of any of Fe and Si;
up to about 0.5 wt. % of any of Cu, Zn, and Mg; up to about 0.2 wt. % of
any of Ti, Zr, and Sc, wherein one of B and C may be included up to about
0.1 wt. %. As in US6783730B2, the high level of casting and mechanical
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properties is ensured by the use of high-purity aluminum grades and by a
high nickel content, which considerably increases the production cost of
castings. Moreover, the high nickel content considerably reduces the
resistance of castings to corrosion. Furthermore, the corrosion resistance of
castings significantly decreases in the region of high nickel concentrations.
With a relatively low content of nickel and manganese, casting alloys have a
low level of strength.
In US8950465B2 (pub!. 10.02.2015) for aluminum alloys and a method of
to their production, Alcoa extended the concentration ranges of the alloy
elements, which are disclosed in US8349462B2. In the proposed disclosure,
castings in the as-cast condition may be produced from Al¨Ni and Al¨
Ni¨Mn alloys having the following concentration ranges of the alloy
elements: an Al¨Ni casting alloy comprising from about 0.5 wt. % to about
8.0 wt. % Ni; and an Al¨Ni¨Mn casting alloy comprising from about 0.5
wt. % to about 8.0 wt. % Ni and from about 0.5 wt. % to about 3.5 wt. %
Mn. One of the drawbacks of this disclosure is that the high level of casting
and mechanical properties is ensured by the use of high-purity aluminum
grades and by a high nickel content, which considerably increases the
production cost of castings.
The closest prior art is an aluminum-based alloy developed by the National
University of Science and Technology "MISiS" and disclosed in RF patent
2478131C2, pub!. 27.03.2013. This alloy comprises (in wt.%): 1.5-2.5%Ni,
0,3-0.7%Fe, 1-2%Mn, 0.02-0.2%Zr, 0.02%-0.12%Sc and 0.002-0.1%Ce.
Castings produced from this alloy after annealing (without quenching) are
characterized by an ultimate tensile strength of no less than 250 MPa and an
elongation of no less than 4%. The first drawback of this alloy is that it is
highly prone to forming localized porosity, which makes it difficult to
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produce high-quality, relatively large castings. The second drawback is
related to the necessity of using high casting temperatures, which is not
always possible at a casting facility.
Disclosure of the invention
The object of this invention is the development of a new aluminum alloy
that is intended for the production of shaped castings and meets a number of
target process and mechanical parameters ¨ first of all, elongation.
to The technical effect is to ensure a required combination of process and
mechanical properties of the alloy during casting.
The technical effect is achieved by the fact that the aluminum-based casting
alloy comprises iron, nickel, manganese, at least one element selected from
a group consisting of titanium and zirconium, such alloy elements have the
following concentrations, in weight %:
Iron 0.31-1.1,
Manganese 0.5-0.6,
Nickel 1.2-1.8,
zo Chromium 0.08-0.25,
Titanium 0.02-0.15,
Zirconium up to 0.24, and
Aluminum ¨ the remainder,
wherein the following conditions should be met: eutectic iron and nickel
should be represented mainly in the form of eutectic aluminides in the
amount of no less than 4% by weight.
An embodiment of this alloy allows producing castings, in which the
following tensile strength properties are achieved:
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- at a
ratio of 0.02<Zr+Ti<0.45: an ultimate tensile strength of no less
than 200 MPa and an elongation of no less than 15% in the as-cast
condition.
The amount of the eutectic component should be calculated with the use of
the Thermo-Calc software (TTAL5 database).
Zirconium may be redistributed between the solid solution and secondary
phases with a size of up to 20 nm and the L12 lattice type.
The alloy may comprise aluminum produced under an inert anode
electrolysis technology.
The above embodiments are not the only ones possible. Different
is modifications and enhancements are allowed, if they are not beyond the
scope of disclosure deftned by claim I.
Summary of the invention
The concentration of iron and nickel in the ranges claimed provides for the
required amount of eutectic aluminides in the amount of no less than 4 wt.
%, which, it its turn, ensures the required processability during casting
(first
of all, in terms of hot tearing tendency.) If the content of iron and nickel
is
lower than the amount claimed, the amount of eutectic phases will be lower
than required, and the required level of properties will not be ensured. If
the
content of iron and nickel is higher than the amount claimed, primary
crystals of the (Fe, Ni)-containing phases will be formed in the structure
during crystallization, which will lead to a reduction in the total level of
mechanical properties.
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Manganese in the range claimed is required to ensure solid solution
hardening in case of the as-cast condition and precipitation age hardening in
case of the heat-treated condition. A lower manganese concentration will not
be enough to ensure the required level of strength properties. A higher
concentration will likely lead to the formation of primary crystals of the
A16(Fe, Mn) phase, which will lead to a reduction in the level of mechanical
properties and casting processability.
Zirconium in the range claimed is required for solid solution hardening
io (when used in the as-cast condition) or the precipitation of the Al3Zr
secondary phase with the L12 lattice (in case heat treatment is used). If the
concentration is lower, the amount of the latter will not be enough to achieve
target strength properties; if the concentration is higher, it will be
required to
increase the casting temperature to make it higher than the target level.
Titanium in the range claimed is required to refine the aluminum solid
solution. Moreover, titanium can dissolve in the Al3Zr secondary phase with
the L12 lattice, which increases the effect of precipitation age hardening in
case heat treatment is used. If the concentration is higher, primary crystals
may appear in the structure and reduce the total level of mechanical
properties; if the concentration is lower, there will be no positive effect
from
this element.
Chromium in the range claimed is required to ensure solid solution
hardening for the as-cast condition and/or for precipitation age hardening for
the heat-treated condition. A lower chromium concentration will not be
enough to ensure the required level of strength properties. A higher
concentration will likely lead to the formation of primary crystals of the
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Al7Cr phase, which will lead to a reduction in the level of mechanical
properties.
The presence of silicon, as an impurity, in the amount of up to 0.15 wt.%
will ensure an additional effect from solid solution hardening. If the content
of silicon is higher, the crystallization interval will be considerably
longer,
which will reduce casting characteristics.
Embodiments of the invention
EMBODIMENT 1
The alloy compositions as per Table 1 were prepared under laboratory
conditions. The alloys were prepared in an induction furnace in graphite
crucibles with the use of aluminum (grade AA1085), nickel (cathode nickel)
and master alloys A1-10Cr, A1-10Mn, and AI-5Ti. The casting temperature
was 750 C for the alloys. The prepared alloys were poured into a rod-type
metal mold to assess the mechanical properties and analyze the
microstructure. The casting properties were assessed based on the hot
tearing tendency (HT) with the use of the "ring sample", where the best
parameter is a ring with the minimum section of the wall solidified without a
crack. Using a computational method, the phase composition and the content
of the eutectic phase in the alloys were analyzed. The results are given in
Table 2. For alloy 5 in Table 1, no calculation was made because of an
incorrect calculation of the eutectic phase due to the presence of primary
crystals.
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The analysis of the results in Table 1 and 2 shows that alloys 2-5 in the
claimed concentration ranges provide for a good level of casting
characteristics. Alloy composition 1 is characterized with an unsatisfactory
level of casting properties (based on the hot tearing tendency) - first of
all,
due to a low eutectic content. In the structure of alloy 5, primary crystals
of
the ferrous phase were found, which had a negative effect on the mechanical
properties and, first of all, on elongation (Table 3). The mechanical
properties were defined based on a casting produced by gravity casting with
an average cooling rate of about 10 K/sec. The tensile strength test was run
o with the use of separately-cast test bars with a diameter of 10 mm and a
calculated length of 50 mm. The traverse speed was 10 mm/min.
Table 1 - Chemical composition and Eutectic content
Chemical composition, wt.% Eutectic content, wt.%
Fe Ni Mn Cr Zr Ti Al Al3Ni Al9FeNi Total
1 0.01 0.5 0.1 0.01 - 0.001 base 2.18 0.13 2.31
2 1.1 1.2 0.5 0.25 - 0.02 base - 5.46 5.46
3 0.31 1.8 0.6 0.08 0.24 0.15 base 5.84 6.19 12.03
4 0.1 2.2 2.5 0.02 0.30 0.1 base 9.49 2.10 11.59
5* 0.8 3.1 2.0 0.3 - 0.1 base -
Table 2 - Hot tearing tendency and Microstructure analysis
Alloy No. HT, Microstructure analysis
mm
1 10 (Al)**, eutectic ((A1)+ A13Ni+Al9FeNi)
2 3 (Al), eutectic ((Al+Al9FeNi)
3 3 (Al), eutectic ((A1)+Al3Ni+Al9FeNi)
4 3 (Al), eutectic ((A1)+ Al3Ni+Al9FeNi)
5 3 (Al), eutectic ((A1)+Al3Ni+Al9FeNi), primary crystals
of the Al9FeNi phase
* - see Table 1; ** - (Al) - aluminum solid solution,
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The formation of eutectic aluminides with favorable morphology in the
structure is an essential prerequisite for achieving a high level of
elongation.
A typical structure ensuring a good level of elongation is shown in Fig. 1.
The composition of alloys 2 and 3 (Table 1) is the most preferable
composition for use in the as-cast condition.
Table 3 ¨ Tensile strength testing (Gravity casting)
Alloy No.* Condition** YS, MPa
UTS, MPa Elongation, %
2 F 85 161 18.0
3 F 104 164 24.3
4 F 121 189 16.2
5 F 124 197 4.5
* - see Table 1; ** - F - as-cast condition;
EMBODIMENT 2
From the composition of alloys 2 and 3 in Table 1, castings were produced
by High-Pressure Die Casting (HPDC). The results are given in Table 4.
Table 4 ¨ Tensile strength testing (Gravity casting)
Alloy No.* Condition** YS, MPa
UTS, MPa Elongation, %
2 F 96 175 17.0
3 F 126 201 15.5
* - see Table 1; ** - F - as-cast condition
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Table 4 shows that the claimed alloys, provided the eutectic content is
higher than 4, ensure the required hot tearing tendency.
EMBODIMENT 3
From the composition of alloys 2 and 3 in Table 1, castings were produced
by High-Pressure Die Casting (HPDC). The results are given in Table 5.
Table 5 ¨ Tensile strength testing (Gravity casting)
Alloy No.* Condition** YS, MPa UTS,
MPa Elongation, %
2 96 175 17.0
3 F 126 201 15.5
* - see Table 1; ** - F - as-cast condition
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