Field of the Invention
[0001] The present invention relates to creep-resistant magnesium-based alloys for applications
at high temperatures which exhibit good castability, particularly suitable for high-pressure
die casting, but advantageously used also in a processes comprising sand casting,
investment casting, permanent mold casting, as well as direct chill casting or twin-roll
casting.
Background of the Invention
[0002] The magnesium industry is experiencing dramatic growth, in part due to the demands
of the transportation industry to improve fuel economy and emissions. In addition,
a great progress in weight reduction has been made in consumer applications of magnesium
alloys such as power hand tools, lawn and garden equipment, electronic and optical
equipment, etc. In order to significantly expand the above applications, new advanced
alloys are required.
[0003] High pressure die casting (HPDC) is the dominant form of casting due to its productivity
and suitability for mass production. Currently, most common and new magnesium alloys
that are being used for HPDC process are Al containing alloys. However, these alloys
cannot serve at temperatures higher than 150-170°C under high stresses of 60-100 MPa.
US 6,193,817 describes magnesium-based alloys containing 0.1-2.0 wt% Zn, 2.1-5.0 wt% RE elements
(Ce based mishmetal) up to 0.4 wt% of a combination of at least two elements chosen
from the group consisting of Zr, Hf and Ti, and optionally up to 0.5 wt% Mn and up
to 0.5 wt% Ca. High-pressure die casting of the alloys results in low strength (TYS=120
MPa, UTS=165 MPa) and elongation (E= 2%).
[0004] EP 1866452 discloses magnesium based alloys containing 1.5-4.0% RE elements, 0.3-0.8% Zn, 0.02-0.1%
Al, 4-25 ppm Be and optionally up to 0.2% Zr, 0.3% Mn, 0.5%Y, and 0.1% Ca. The alloys,
under die cast conditions, exhibit low tensile strength (TYS=130 MPa, UTS=160 MPa)
and elongation (E= 1-3%).
[0005] WO 2009/086585 relates to magnesium based alloys containing 2-5% RE elements (primarily La and Ce,
wherein La content is higher than Ce content) and 0.2-0.8% Zn. In addition, the alloys
contain optionally Y, Gd, Zr, Mn, Ca, and Be. These alloys are also designated for
high-pressure die casting but exhibit very low values of elongation, TYS, and UTS.
[0006] SU 1,360,223 discloses Mg-based alloys containing 0.1-2.5% Zn, 0.3-1.0% Zr, 0.8-4.5% Nd, 0.5-5.0%
Y, 0.8-4.5% Gd, and 0.01-0.05% Mn. The alloys are intended for sand casting process
and exhibit optimal properties after full T6 treatment.
[0007] US 4,116,731 describes heat treated and aged magnesium based alloys containing 0.8-6.0 wt% Y,
0.5-4.0 wt% Nd, 0.1-2.2 wt% Zn, 0.3-1.1 wt% Zr, up to 0.05% Cu, and up to 0.2% Mn.
Due to relatively wide concentration ranges claimed by the above patent, the alloys
exhibit very diverse properties; in addition, they are designated only for sand casting
process
[0008] EP 1329530 discloses magnesium-based casting alloys containing 0.2-0.8 wt% Zn, 0.2-0.8 wt% Zr,
2.7-3.3 wt% Nd, 0.0-2.6 wt% Y, and 0.03-0.25% Ca. The alloys exhibit high strength
and high creep resistance after gravity casting and after full T6 heat treatment,
as well as after extrusion and forging. However, the HPDC is not addressed.
[0009] CN 1752251 describes magnesium alloys containing 0.35-0.8 wt% Zr, 2.5-3.6 wt% Nd, 0.0-0.4 wt%
Zn, 0.0-0.5 wt% Ca, and 0.0-0.02 wt% impurities. The alloys are prepared by a two-stage
process including a step of preparing intermediate master alloys Mg-Nd, Mg-Ca, and
Mg-Zr, and a step of alloying said master alloys by Nd, Ca, and Zr. The complexity
of the technology significantly increases the cost of the final alloy product.
[0010] EP 1641954 describes creep resistant alloys containing 2.0-4.5% Nd, 0.2-1.0% Zr, 0.2%-7.0% HRE
(Heavy Rare Earth Elements of atomic numbers 62-71), optionally up to 0.4% of other
RE elements, up to 0.5% Y, up to 1.3% Zn, up to 0.5% Mn, and up to 0.4% Hf or Ti.
The alloys are mainly designated for sand casting and, in addition, they are expensive
due to the use of heavy rare earth elements, such as Gd in amounts of 1.0-1.6%.
[0011] US 2009/0081313 relates to biodegradable magnesium alloys containing 1.5-5.0% Nd, 0.1-4.0% Y, 0.1-2.0%
Ca, and 0.1-1.0 % Zr. The alloys are designated for manufacturing medical implants
by extrusion. The high Ca content results in increased porosity, embrittlement and
hot cracking in HPDC processes.
[0012] WO 2010/038016 relates to magnesium alloys containing 2.0-4.0% Y, 0.5-4.0% Nd, 0.05-1.0% Zr, 0.0-5.5%
Gd, 0.0-5.5% Dy, 0-5.5% Er, 0.0-0.2% Yb, and 0.0-0.04% Sm. In addition, the total
content of Gd, Dy and Er is in the range of 0.3-12 wt.%. The alloy is dedicated for
sand casting, and it can also be used as a wrought alloy. The alloy is unsuitable
for HPDC process. Furthermore, the high content of heavy rare earth elements leads
to high cost of these alloys.
[0013] WO 2011/117628 describes magnesium alloys containing 0.0-10.0% Y, 0.0-5.0% Nd, 0.00-1.2% Zr, 0.0-0.3%
Gd, and 0.0-0.2% Sm, wherein the total content of Ho, Lu, Tm and Tb is in the range
of 0.5-5.5 %. The alloy is dedicated for manufacturing medical implants. Due to very
wide concentration ranges of Y, Nd, and heavy rare earth elements Ho, Lu and Tm, the
alloys exhibit very diverse properties. The alloys are not suitable for HPDC process
and are expensive.
[0015] It is therefore an object of this invention to provide magnesium alloys suitable
for high pressure die casting (HPDC) applications.
[0016] It a further object of this invention to provide magnesium-based alloys allowing
crack-free castings at HPDC applications.
[0017] It is also an object of this invention to provide magnesium-based alloys having a
superior combination of strength and ductility, as well as capability to operate at
a temperature of 200°C for a long time.
[0018] It is another object of the present invention to provide alloys which are also suitable
for sand casting, investment casting, and permanent mold casting, and which exhibit
excellent combination of castability, creep performance, and corrosion resistance.
[0019] It is a still further object of this invention to provide alloys which are also suitable
for direct chill casting and twin roll casting with subsequent plastic forming operations
such as rolling, forging and extrusion.
[0020] It is still another object of this invention to provide alloys which exhibit the
aforesaid behavior and properties, and have an affordable cost.
[0021] Other objects and advantages of the present invention will appear as the description
proceeds.
Summary of the Invention
[0022] The invention provides a lightweight alloy for high-pressure die casting (HPDC) process,
consisting of at least 94.8 wt% magnesium, 2.5 to 4.6 wt% neodymium, 0.05 to 0.40
wt% yttrium, 0.03 to 0.65 wt.% zirconium, optionally up to 0.02% Ca, and incidental
impurities. invention further The alloy according to the invention comprises essentially
no heavy rare earth (HRE) elements with the atomic number from 61 to 70. The alloy
according to the invention comprises essentially no cerium, lanthanum, and praseodymium.
The alloy according to the invention comprising essentially no zinc. In one embodiment,
the alloy according to the invention contains Nd and Y in an amount higher than 4.3
wt.%. Said incidental impurities usually comprise Si, Fe, Cu, and Ni in an amount
of up to 0.02 wt%. The lightweight alloy according to the invention is suitable for
prolonged operations at high temperatures of up to 200°C. The alloys for HPDC and
other applications according to the invention exhibit superior casting properties,
high strength, high creep resistance, high corrosion resistance, and the articles
manufactured from the alloys show superior performance at high temperatures. The alloy
according to the invention is usable for high pressure dies casting (HPDC), but it
may be also used for a process selected from the group consisting of sand casting,
investment casting, and permanent mold casting. The alloy according to the invention
are also usable for a process comprising either twin roll casting with subsequent
rolling, or direct chill casting with subsequent forging, extrusion or rolling.
[0023] In a preferred embodiment of the invention, the lightweight alloy is advantageously
used for HPDC. In one embodiment, the alloy suitable for HPDC contains 2.8 to 4.3
wt% Nd, 0.06 to 0.25 wt% Y, 0.05 to 0.4 wt% Zr, and 0.0 to 0.02 wt% Ca. In a preferred
embodiment of the invention, the alloy used for HPDC exhibits a tensile yield strength
(TYS) at 200°C of at least 153 MPa, a compression yield strength (CYS) at 200°C of
at least 152 MPa, a minimum creep rate of not more than 1.5x10
-10/s at 200°C under stress of 100 MPa, and a corrosion rate of not more than 2.65 mpy.
When measured in relative units characterizing oxidation resistance, fluidity, and
dies sticking, the alloy according to the invention preferably exhibits a castability
of at least 96%.
[0024] The invention relates to an article cast of the alloy containing 2.8 to 4.3 wt% Nd,
0.06 to 0.25 wt% Y, 0.05 to 0.4 wt% Zr, and 0.0 to 0.02 wt% Ca, the article exhibiting
a superior combination of strength and ductility after T5 treatment which includes
direct aging at 150-250°C for 1-10 h. In one embodiment, said article exhibits a superior
combination of strength and ductility after T5 treatment which includes direct aging
at 175-225°C for 1-6 h.
[0025] The alloy according to the invention is also suitable for sand casting, investment
casting, permanent mold casting, and low pressure modifications thereof; in one embodiment,
the alloy contains 2.7 to 3.4 wt% Nd, 0.15 to 0.40 wt% Y, 0.3 to 0.6 wt% Zr, and 0.0
to 0.02 wt% Ca. The invention relates to an article cast of said alloy, the article
exhibiting a superior combination of performance properties after full T6 heat treatment
comprising solid solution heat treatment at 520-560°C for 1 to 16 hrs, followed by
cooling in a quenching medium and by subsequent aging at 200-270°C for 1 to 16 h.
In one embodiment, said article exhibits a superior combination of performance properties
after full T6 heat treatment comprising solid solution heat treatment at 535-545°C
for 3 to 5 hrs, followed by cooling in a quenching medium and by subsequent aging
at 225-250°C for 3 to 6 h.
[0026] The alloy according to the invention may be advantageously used for forging, extrusion,
and rolling; in one embodiment, the alloy contains 2.8 to 3.8 wt% Nd, 0.20 to 0.40
wt% Y, 0.35 to 0.60 wt% Zr, and 0.0-0.02 wt% Ca. The invention relates to an article
cast in said alloy, the article exhibiting a superior combination of performance properties
after T5 heat treatment comprising aging at 200-250°C for 1 to 16 h.
[0027] The present invention provides creep-resistant magnesium-based alloys designated
for applications at temperatures as high as 200-250°C, which exhibit good castability
and low susceptibility to hot tearing, which are strong and are corrosion resistant,
and have excellent ductility.
[0028] The invention provides a process for manufacturing a lightweight alloy for prolonged
operation at high temperatures of up to 200°C, comprising steps of i) alloying magnesium
with neodymium and zirconium at 765-785°C under intensive stirring; ii) settling the
melt for 20-40 minutes to allow iron to settle; iii) adding yttrium, while avoiding
intensive stirring to prevent the formation of Y-Fe intermetallic compounds; iv) optionally
adding calcium prior to settling; v) settling the molten alloy for 30-60 minutes;
and v) casting into desired form; wherein the steps are performed under a protective
atmosphere of CO
2 + 0.5% HFC134a till solidification; the amount of magnesium in the alloy being at
least 94.8 wt%, of neodymium from 2.5 to 4.6 wt%, of yttrium from 0.05 to 0.40 wt%,
of zirconium from 0.03 to 0.65 wt.%, and of calcium 0.00 to 0.02%. The lightweight
alloys thus manufactured are particularly suitable for high pressure die casting,
but can be advantageously employed in sand casting, investment casting, and permanent
mold casting.
[0029] The alloys according to the invention contain more than 94 wt% magnesium, from 2.5
to 4.6 wt% neodymium, from 0.05 to 0.40 wt% yttrium, from 0.03 to 0.65 wt% zirconium,
optionally calcium up to 0.02 wt%, and incidental impurities. The alloys usually contain
up to 0.007 wt% iron, up to 0.001 wt% nickel, up to 0.003 wt% copper, up to 0.015
wt% silicon, and eventually other incidental impurities. The alloys of the invention
exhibit an excellent combination of high tensile and compressive yield strength, and
high ductility. The great advantage of new alloys is related to their high creep rupture
stress, creep strength and low minimum creep rate, as well as low corrosion rate measured
under GM 9540 cyclic corrosion test. Thus, the alloys of the present invention combine
superior performance properties, good castability, and relatively moderate cost. Articles
according to the invention are preferably subjected to T5 or T6 heat treatments depending
on preceding casting process and plastic forming operations.
Brief Description of the Drawings
[0030] The above and other characteristics and advantages of the invention will be more
readily apparent through the following examples, and with reference to the appended
drawings, wherein:
- Fig. 1.
- is Table 1, showing chemical compositions of alloys for HPDC according to the invention
(Examples 1-7) and comparative alloys (Comparative Examples 1-7);
- Fig. 2.
- is Table 2, showing the results of die castability evaluation for alloys of Table
1;
- Fig. 3.
- is Table 3, showing mechanical and corrosion properties of the alloys of Table 1;
- Fig. 4.
- is Table 4, showing creep properties of the alloys of Table 1;
- Fig. 5.
- is Table 5, showing chemical compositions of alloys for sand casting according to
the invention (Examples 8-14) and comparative alloys (Comparative Examples 8-14);
- Fig. 6.
- is Table 6, showing mechanical and corrosion properties of the alloys of Table 5;
- Fig. 7.
- is Table 7, showing chemical compositions of alloys according to the invention after
forging (Examples 15-18) and comparative alloys (Comparative Examples 15-18);
- Fig. 8.
- is Table 8, showing mechanical properties of the alloys of Table 7; and
- Fig. 9.
- is a scheme showing GM 9540 cycling test procedure for the corrosion evaluation.
Detailed Description of the Invention
[0031] It was found that certain combinations of elements in magnesium based alloys comprising
neodymium, zirconium, yttrium, and optionally calcium, impart to the alloys superior
properties, particularly for high pressure die casting. These properties include excellent
combination of high tensile and compressive properties with high ductility, outstanding
corrosion resistance, and creep properties allowing to achieve service temperatures
up to 250°C.
[0032] The above combination of properties can be realized at high-pressure die casting,
at sand casting, as well as at direct-chill casting or twin roll casting followed
by plastic forming processes such as forging, extrusion and rolling.
[0033] Magnesium-based alloys of the instant invention contain 2.5 to 4.6 wt% neodymium.
It was found by the inventors that if the Nd content is less than 2.5 wt%, the alloys
have insufficient strength at ambient and elevated, and their creep resistance is
not sufficient for serving at 250-300°C temperatures; Nd content higher than 4.6 wt%
results in low ductility due to excessive amount of intermetallic compounds which
are sources of cracks initiation and propagation. An alloy according to the present
invention contains 0.05 to 0.40 wt % yttrium. It was found that yttrium content less
than 0.05 wt% makes the alloy prone to oxidation and results in increased susceptibility
to burning during molten metal handling at 700-780°C. Contrary to
Aghion et al. (J. Mater. Sci. 2008, vol. 43, pp. 4870-4975), it was found that increasing the yttrium content to more than 0.40 wt% leads to
lower ductility, significantly deteriorated castability, while increasing the alloy
cost. Zirconium is mainly used to remove iron in the case of high pressure die casting
process. In the case of gravity casting (sand casting, investment casting, and permanent
mold casting) it also serves as a grain refiner. It has been found that 0.03 wt.%
of Zr is sufficient to ensure low iron content in the alloy, while at least 0.3 wt%
of zirconium is required for grain refining. The upper limit for the zirconium content
is about 0.65 wt% due to its limited solubility in Mg-Nd-Y alloys.
[0034] The alloys of the present invention contain substantially no zinc; it would deteriorate
creep resistance and corrosion performance due to the formation of Zn-Y-Nd-Zr coarse
intermetallics. Furthermore, the alloys of the instant invention do not contain rare
earth elements with low solubility in solid magnesium such as Ce and La. The presence
of those elements results in deterioration of mechanical properties, and particularly
of ductility, due to the formation of coarse intermetallic compounds. An admixture
of calcium in the alloys of the invention of up to 0.02% may improve oxidation resistance.
[0035] The Ca content is limited to 0.02% because higher Ca content leads to increased micro-porosity
and embrittlement of the alloys.
[0036] The alloys of instant invention also do not contain heavy rare earth elements with
atomic number higher than 60, they would increase the alloy price without remarkably
improving the alloy performance.
[0037] Surprisingly simple alloys of the invention are suitable for HPDC and other applications,
while exhibiting superior casting properties, high strength, high creep resistance,
high corrosion resistance, and the articles manufactured from the alloys show superior
performance at high temperatures.
[0038] The magnesium alloys according to the invention were examined along with comparative
alloys. The results show that the new alloys exhibit better oxidation resistance and
fluidity, as well as lower susceptibility to die sticking than comparative alloys.
Neither burning nor oxidation was observed on the surface of ingots made of alloys
according to this invention. In contrast, the preparation of comparative alloys was
sometimes accompanied by significant oxidation and undesirable losses of alloying
elements. The alloys according to the invention reached between 96 and 100% on the
relative castability scale, when evaluating oxidation resistance, fluidity, and die
sticking of the alloy on casting (see Examples below), in comparison with 73 and 83%
of comparative alloys whose composition differed more or less from the composition
of the invention.
[0039] Part of the ingots of both the new and the comparative alloys were then remelted
and high pressure die cast to produce different specimens for testing and examination.
Other ingots were remelted, grain refined and sand cast into different specimens for
testing. Tensile Yield Strength (TYS), Ultimate Tensile Strength (UTS), percent elongation
(%E), compressive strength (CYS) and different creep characteristics such as Creep
Strength, Creep Rupture Strength, and Minimum Creep Rate were then determined. Corrosion
behavior was evaluated by the GM 9540 cyclic test. The alloys according to the invention
surpassed the comparative alloys in creep stress to rupture, creep strength, and corrosion
resistance. They also exhibit better combination of strength and ductility, characterized
by elongation values, than comparative alloys.
[0040] The alloys according to the invention are very suitable for HPDC; it was found that
they develop excellent properties after direct T5 aging at 150-250°C for 1-10 h, preferably
at 175-225°C for 1-6 h. As for wrought alloys, it was found that the alloys according
to the invention achieve very good properties after direct aging at 200-250°C for
1-16 h. It was found that the alloys according to the invention also provide excellent
mechanical properties on sand casting after full T6 heat treatment; particularly,
good results were obtained when the heat treatment comprised solid solution heat treatment
at 520-560°C for 1 to 16 hrs, followed by cooling in a quenching media and by subsequent
aging at 200-270°C for 1 to 16 h, preferably after solid solution treatment at 535-545°C
for 3 to 5 hrs, followed by cooling in a quenching media and by subsequent aging at
225-250°C for 3 to 6 h.
[0041] The invention will be further described and illustrated in the following examples.
Examples
[0042] The alloys of the present invention were prepared in 150 l crucible made of low carbon
steel. The mixture of CO
2 + 0.5% HFC134a was used as a protective atmosphere. The raw materials used were as
follows:
Magnesium (Mg) - pure magnesium, grade 9980A, containing at least 99.8% Mg.
Neodymium (Nd) - commercially pure Nd (less than 0.5% impurities).
Zirconium (Zr) - Zr95 Tablets, containing at least 95% Zr.
Yttrium (Y) - commercially pure Y (less than 1% impurities).
Calcium (Ca) - pure Ca (less than 0.1% impurities).
[0043] Contrary to the alloying procedure described in
CN1752251, where intermediate Mg-Nd , Mg-Ca and Mg- Zr master alloys were used, the alloys
of the present invention have been prepared using pure Nd and pure Ca that significantly
simplifies the process, reduces its duration and markedly lowers the alloy cost. Neodymium
and zirconium were added typically at 770-780°C with intensive stirring of the melt.
After addition of zirconium, the melt was held for 20-40 minutes to allow iron to
settle. Yttrium was added after the iron settling, without intensive stirring, to
prevent the formation of Y-Fe intermetallic compounds, which leads to excessive loss
of yttrium. A strict temperature control was provided during the alloying in order
to insure that the melt temperature will not increase above 785°C, thus preventing
an excessive contamination by iron from the crucible walls, and to ensure that the
temperature will not decrease below 765°C, thus preventing an excessive loss of zirconium.
Calcium was added prior to settling. After obtaining the required compositions, the
alloys were held for 30-60 minutes for homogenization, and settling of iron and non-metallic
inclusions, and then they were cast into the 15 kg ingots. The casting was performed
with gas protection of the molten metal during solidification in the molds by CO
2 + 0.5% HFC134a mixture. The die casting trials were carried out using an IDRA OL-320
cold chamber die casting machine with a 345 ton locking force.
[0044] The castability was evaluated based on observed fluidity, oxidation resistance and
die sticking or soldering. The casting temperature was 710°C. Each of the properties
(fluidity, oxidation resistance, die sticking) was evaluated by assigning from 0 to
10 points on a relative scale, the higher the better (see Table 2). The sum of the
points for an alloy divided by 30 and multiplied by 100 provides "castability coefficient",
a relative assessment having a value between 0 and 100%, which characterizes the overall
suitability of an alloy for die casting. The alloys according to the invention had
castability coefficient between 96 and 100%, while comparative examples, even if differing
only slightly from the new alloys of the invention, had castability coefficient between
73 and 83%.
[0045] Tensile and compression testing at ambient and elevated temperatures were performed
using an Instron 4483 machine. Tensile Yield Strength (TYS), Ultimate Tensile Strength
(UTS), percent elongation (%E) and Compression Yield Strength (CYS) were determined.
The SATEC Model M-3 machine was used for creep testing. Creep tests were performed
at 200°C and 250°C for 200h or until rupture under various stresses. Creep resistance
was estimated by measuring rupture strength and creep strength. Creep strength is
usually defined as the stress, which is required to produce a certain amount of creep
at a specific time and temperature. It is a common practice to report creep strength
as the stress, which produces 0.2% creep strain at a given temperature for 100 hours.
This parameter is used by design engineers for evaluating the load-carrying ability
of a material for limited creep strain in prolonged time periods. Creep rupture stress
is the stress resulting in specimens rupture at a selected testing temperature for
a certain time, usually 100 h. In addition, minimum creep rate at a steady state (MCR)
was used to evaluate creep performance.
[0046] Corrosion behavior was evaluated as per GM9540 cyclic test for 40 days (Fig.9). The
test procedure includes three main stages, combining both wet-dry transition and short
sprays of light electrolyte solution. In this test a gradual increase of temperature
is applied during the cycle. The die cast plates with dimensions of 140x100x3 mm were
used. The plates were degreased in acetone and weighed prior to the test. Five replicates
of each alloy were tested. At the end of the test the corrosion products were stripped
in a chromic acid solution (180 g CrO
3 per liter solution) at 80°C about three minutes and the weight loss was determined.
The weight loss was used to determine the average corrosion rate in mpy (milli-inch
per year).
[0047] Tables 1 to 4 illustrate chemical compositions, castability parameters, and properties
of alloys for HPDC according to the invention and of comparative alloys. The new alloys
of the invention demonstrate significantly better die castability evaluated by tendency
to oxidation, fluidity and susceptibility to die sticking (Table 2), reflected by
a castability coefficient of minimally 96%. As can be seen from Table 3, the new alloys
are superior in tensile yield strength (TYS) and compressive yield strength(CYS) over
the comparative alloys at both ambient and elevated temperatures. The same is true
for UTS values. For example, TYS values of the new alloys according to the invention
at 200°C are 150 MPa or more, usually 153 MPa or more, whereas the comparative alloys
have lower values. Furthermore, new alloys exhibit much better combination of strength
and elongation than comparative alloys. Corrosion resistance of the new alloys determined
under GM 9540 cyclic test conditions (Fig. 9) also surpasses that property of the
comparative alloys; the corrosion rate of the new alloys is less than 2.9 mpy, usually
less than 2.7 mpy, such as 2.65 mpy or less (Tab. 3). In addition, new alloys also
exhibit excellent creep resistance in the temperature range 200-250°C, outperforming
the comparative examples (Table 4). The creep rupture strength of the new alloys for
HPDC is typically about 200 MPa or more at 200°C, and about 105 MPa or more at 250°C.
The MCR values of the new alloys are 1.5x10
-10/s or less at 200°C and 100 MPa, usually 1.0x10
-10/s or less; the comparative alloys have higher values even if differing only slightly
in composition from the new alloys (Tab. 4).
[0048] The excellent combination of these properties along with low susceptibility to hot
tearing makes the alloys of the instant invention the most promising candidates for
high pressure die casting of moving parts serving at high temperatures of 200-250°C
where low moment inertia and correspondingly low vibration are required.
[0049] Tables 5-6 demonstrate chemical compositions and properties of alloys for sand casting
according to the invention and of comparative alloys subjected to full T6 heat treatment.
The alloys of the instant invention exhibit superior combination of TYS and Elongation
in comparison with comparative examples. The compressive strength of new alloys is
also higher both at ambient and elevated temperatures. Furthermore a great advantage
of the alloys of this invention is that they combine excellent mechanical properties
with outstanding corrosion resistance which outperforms corrosion resistance of comparative
alloys.
[0050] Tables 7-8 illustrate chemical composition and mechanical properties of forged alloys
of instant invention. The alloys of present inventions and comparative alloys were
direct chilled cast, homogenized, forged and T5 heat treated. The forged alloys of
the present invention exhibit higher TYS and UTS values than comparative alloys at
both ambient temperature and 200°C. It is important that they the alloys according
to the invention have also superior elongation and significantly higher compressive
yield strength.
[0051] While this invention has been described in terms of some specific examples, many
modifications and variations are possible. It is therefore understood that, within
the scope of the appended claims, the invention may be realized otherwise than as
specifically described.
1. A lightweight alloy for high-temperature applications, consisting of
i) at least 94.8 wt% magnesium,
ii) 2.5 to 4.6 wt% neodymium,
iii) 0.05 to 0.40 wt% yttrium,
iv) 0.03 to 0.65 wt% zirconium,
v) optionally up to 0.02 wt.% calcium, and
vi) incidental impurities.
2. A process of making a magnesium alloy ingots comprising 2.5 to 4.6 wt% Nd, 0.05 to
0.40 wt% Y, 0.03 to 0.65 wt% Zr, and optionally 0.0 to 0.02 wt% Ca and the balance
being magnesium and unavoidable impurities, wherein Nd added under intensive stirring
at 770-780°C while Y is added after settling at these temperatures under gentle agitation.
3. An alloy according to claim 1, usable for a process selected from the group consisting
of high pressure die casting (HPDC), sand casting, investment casting, and permanent
mold casting.
4. An alloy according to claim 1, usable for a process comprising either twin roll casting
with subsequent rolling, or direct chill casting with subsequent forging, extrusion
or rolling.
5. A lightweight alloy for high-temperature applications according to claim 4 usable
for HPDC.
6. A high pressure die casting process of a magnesium alloy comprising 2.5 to 4.6 wt%
Nd, 0.05 to 0.40 wt% Y, 0.03 to 0.65 wt% Zr, and optionally 0.0 to 0.02 wt% Ca and
the balance being magnesium and unavoidable impurities, wherein an alloy exhibits
castability of at least 96%, when measured in relative units characterizing oxidation
resistance, fluidity, and susceptibility to die sticking
7. An alloy according to claim 5, which contains 2.8 to 4.3 wt% Nd, 0.06 to 0.25 wt%
Y, 0.05 to 0.4 wt% Zr, and 0.0 to 0.02 wt% Ca.
8. An article cast of an alloy according to claim 5, exhibiting a superior combination
of strength and ductility after T5 treatment which includes direct aging at 150-250°C
for 1-10 h.
9. An article according to claim 8, exhibiting a superior combination of strength and
ductility after T5 treatment which includes direct aging at 175-225°C for 1-6 h.
10. An alloy according to claim 3 suitable for sand casting, investment casting, permanent
mold casting, and low pressure modifications thereof, containing 2.7 to 3.4 wt% Nd,
0.15 to 0.40 wt% Y, 0.3 to 0.6 wt% Zr, and 0.0 to 0.02 wt% Ca.
11. An article cast of an alloy according to claim 10, exhibiting a superior combination
of performance properties after full T6 heat treatment comprising solid solution heat
treatment at 520-560°C for 1 to 16 h followed by cooling in a quenching medium and
by subsequent aging at 200-270°C for 1 to 16 h.
12. An article according to claim 11, exhibiting a superior combination of performance
properties after full T6 heat treatment comprising solid solution heat treatment at
535-545°C for 3 to 5 h, followed by cooling in a quenching medium and by subsequent
aging at 225-250°C for 3 to 6 h.
13. An alloy according to claim 4, suitable for forging, extrusion, and rolling, which
contains 2.8 to 3.8 wt% Nd, 0.20 to 0.40 wt% Y, 0.35 to 0.60 wt% Zr, and 0.0-0.02
wt% Ca.
14. An article cast of an alloy according to claim 13, exhibiting a superior combination
of performance properties after T5 heat treatment comprising aging at 200-250°C for
1 to 16 h.
1. Leichtlegierung für Hochtemperaturanwendungen, bestehend aus
i) mindestens 94,8 Gew.-% Magnesium,
ii) 2,5 bis 4,6 Gew.-% Neodym,
iii) 0,05 bis 0,40 Gew.-% Yttrium,
iv) 0,03 bis 0,65 Gew.-% Zirkonium
v) gegebenenfalls bis zu 0,02 Gew.-% Calcium und
vi) zufällige Verunreinigungen.
2. Verfahren zur Herstellung eines Magnesiumlegierung-Barren, umfassend 2,5 bis 4,6 Gew.-%
Nd, 0,05 bis 0,40 Gew.-% Y, 0,03 bis 0,65 Gew.-% Zr und gegebenenfalls 0,0 bis 0,02
Gew.-% Ca und wobei der Rest Magnesium und unvermeidbare Verunreinigungen sind, wobei
Nd unter intensivem Rühren bei 770 - 780°C zugegeben wird, wohingegen Y nach Absenken
bei diesen Temperaturen unter leichter Bewegung zugegeben wird.
3. Legierung nach Anspruch 1, verwendbar für ein Verfahren ausgewählt aus der Gruppe
bestehend aus Hochdruck-Druckguss (HPDC), Sandguss, Feinguss und Kokillenguss.
4. Legierung nach Anspruch 1, verwendbar für ein Verfahren, umfassend entweder Doppelwalzenguss
mit anschließendem Walzen oder direkten Kokillenguss mit anschließendem Schmieden,
Extrudieren oder Walzen.
5. Leichtlegierung für Hochtemperaturanwendungen nach Anspruch 4 verwendbar für HPDC.
6. Hochdruck-Druckguss-Verfahren einer Magnesiumlegierung umfassend 2,5 bis 4,6 Gew.-%
Nd, 0,05 bis 0,40 Gew.-% Y, 0,03 bis 0,65 Gew.-% Zr und gegebenenfalls 0,0 bis 0,02
Gew.-% Ca und wobei der Rest Magnesium und unvermeidbare Verunreinigungen sind, wobei
eine Legierung Gießbarkeit von mindestens 96% aufweist, wenn gemessen in relativen
Einheiten kennzeichnend Oxidationsbeständigkeit, Fließvermögen und Empfänglichkeit
gegenüber Formkleben.
7. Legierung nach Anspruch 5, die 2,8 bis 4,3 Gew.-% Nd, 0,06 bis 0,25 Gew.-% Y, 0,05
bis 0,4 Gew.-% Zr und 0,0 bis 0,02 Gew.-% Ca umfasst.
8. Gegenstand gegossen aus einer Legierung nach Anspruch 5, der eine außergewöhnliche
Kombination von Festigkeit und Verformbarkeit nach T5-Behandlung aufweist, die direktes
Altern bei 150 - 250°C für 1 - 10 h einschließt.
9. Gegenstand nach Anspruch 8, der eine außergewöhnliche Kombination von Festigkeit und
Verformbarkeit nach T5-Behandlung aufweist, die direktes Altern bei 175 - 225°C für
1 - 6 h einschließt.
10. Legierung nach Anspruch 3, geeignet für Sandguss, Feinguss, Kokillenguss und Niederdruckmodifikationen
davon, enthaltend 2,7 bis 3,4 Gew.% Nd, 0,15 bis 0,40 Gew.% Y, 0,3 bis 0,6 Gew.% Zr
und 0,0 bis 0,02 Gew.-% Ca
11. Gegenstand gegossen aus einer Legierung nach Anspruch 10, der eine außergewöhnliche
Kombination von Leistungseigenschaften nach vollständiger T6-Wärmebehandlung aufweist,
umfassend eine Mischkristall-Wärmebehandlung bei 520 - 560°C für 1 bis 16 h, gefolgt
von Abkühlen in einem Abschreckmedium und von anschließendem Altern bei 200 - 270°C
für 1 bis 16 h.
12. Gegenstand nach Anspruch 11, der eine außergewöhnliche Kombination von Leistungseigenschaften
nach vollständiger T6-Wärmebehandlung aufweist, umfassend Mischkristall-Wärmebehandlung
bei 535 - 545°C für 3 bis 5 h, gefolgt von Abkühlen in einem Abschreckmedium und von
anschließendem Altern bei 225 - 250°C für 3 bis 6 h.
13. Legierung nach Anspruch 4, geeignet zum Schmieden, Extrudieren und Walzen, die 2,8
bis 3,8 Gew.-% Nd, 0,20 bis 0,40 Gew.-% Y, 0,35 bis 0,60 Gew.-% Zr und 0,0 - 0,02
Gew.-% Ca enthält.
14. Gegenstand gegossen aus einer Legierung nach Anspruch 13, der eine außergewöhnliche
Kombination von Leistungseigenschaften nach T5-Wärmebehandlung aufweist, umfassend
Altern bei 200 - 250°C für 1 bis 16 h.
1. Alliage léger pour applications haute température, constitué de
i) au moins 94,8 % en poids de magnésium,
ii) de 2,5 à 4,6 % en poids de néodyme,
iii) de 0,05 à 0,40 % en poids d'yttrium,
iv) de 0,03 à 0,65 % en poids de zirconium,
v) facultativement jusqu'à 0,02 % en poids de calcium, et
vi) des impuretés accidentelles.
2. Procédé de fabrication de lingots en alliage de magnésium comprenant de 2,5 à 4,6
% en poids de Nd, de 0,05 à 0,40 % en poids d'Y, de 0,03 à 0,65 % en poids de Zr,
et facultativement de 0,0 à 0,02 % en poids de Ca et le reste étant du magnésium et
des impuretés inévitables, dans lequel le Nd est ajouté sous agitation intense à 770
à 780 °C tandis que l'Y est ajouté après sédimentation à ces températures sous agitation
douce.
3. Alliage selon la revendication 1, utilisable pour un procédé choisi dans le groupe
constitué de la coulée sous haute pression (HPDC), de la coulée en sable, du moulage
en cire perdue et de la coulée en moule permanent.
4. Alliage selon la revendication 1, utilisable pour un procédé comprenant soit une coulée
entre cylindres avec laminage ultérieur, soit une coulée semi-continue avec forgeage,
extrusion ou laminage ultérieur(e).
5. Alliage léger pour applications haute température selon la revendication 4 utilisable
pour HPDC.
6. Procédé de coulée sous haute pression d'un alliage de magnésium comprenant de 2,5
à 4,6 % en poids de Nd, de 0,05 à 0,40 % en poids d'Y, de 0,03 à 0,65 % en poids de
Zr, et facultativement de 0,0 à 0,02 % en poids de Ca et le reste étant du magnésium
et des impuretés inévitables, dans lequel un alliage présente une coulabilité d'au
moins 96 %, lorsqu'elle est mesurée en unités relatives caractérisant la résistance
à l'oxydation, la fluidité, et la tendance au collage.
7. Alliage selon la revendication 5, qui contient de 2,8 à 4,3 % en poids de Nd, de 0,06
à 0,25 % en poids d'Y, de 0,05 à 0,4 % en poids de Zr, et de 0,0 à 0,02 % en poids
de Ca.
8. Article coulé d'un alliage selon la revendication 5, présentant une combinaison supérieure
de résistance et de ductilité après un traitement T5 qui inclut un vieillissement
direct à 150 à 250 °C pendant 1 à 10 h.
9. Article selon la revendication 8, présentant une combinaison supérieure de résistance
et de ductilité après un traitement T5 qui inclut un vieillissement direct à 175 à
225 °C pendant 1 à 6 h.
10. Alliage selon la revendication 3 adapté à une coulée en sable, un moulage en cire
perdue, une coulée en moule permanent, et des modifications de ceux-ci à basse pression,
contenant de 2,7 à 3,4 % en poids de Nd, de 0,15 à 0,40 % en poids d'Y, de 0,3 à 0,6
% en poids de Zr, et de 0,0 à 0,02 % en poids de Ca.
11. Article coulé d'un alliage selon la revendication 10, présentant une combinaison supérieure
de propriétés de performance après un traitement thermique T6 complet comprenant un
traitement thermique en solution solide à 520 à 560 °C pendant 1 à 16 h suivi d'un
refroidissement dans un milieu de trempe et d'un vieillissement ultérieur à 200 à
270 °C pendant 1 à 16 h.
12. Article selon la revendication 11, présentant une combinaison supérieure de propriétés
de performance après un traitement thermique T6 complet comprenant un traitement thermique
en solution solide à 535 à 545 °C pendant 3 à 5 h, suivi d'un refroidissement dans
un milieu de trempe et d'un vieillissement ultérieur à 225 à 250 °C pendant 3 à 6
h.
13. Alliage selon la revendication 4, adapté au forgeage, à l'extrusion et au laminage,
qui contient de 2,8 à 3,8 % en poids de Nd, de 0,20 à 0,40 % en poids d'Y, de 0,35
à 0,60 % en poids de Zr, et de 0,0 à 0,02 % en poids de Ca.
14. Article coulé d'un alliage selon la revendication 13, présentant une combinaison supérieure
de propriétés de performance après un traitement thermique T5 comprenant un vieillissement
à 200 à 250 °C pendant 1 à 16 h.