U.S. patent application number 12/093070 was filed with the patent office on 2009-05-28 for combination of casting process and alloy compositions resulting in cast parts with superior combination of elevated temperature creep properties, ductility and corrosion performance.
This patent application is currently assigned to MAGONTEC GMBH. Invention is credited to Per Bakke, Westengen Haakon.
Application Number | 20090133849 12/093070 |
Document ID | / |
Family ID | 37546955 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133849 |
Kind Code |
A1 |
Bakke; Per ; et al. |
May 28, 2009 |
COMBINATION OF CASTING PROCESS AND ALLOY COMPOSITIONS RESULTING IN
CAST PARTS WITH SUPERIOR COMBINATION OF ELEVATED TEMPERATURE CREEP
PROPERTIES, DUCTILITY AND CORROSION PERFORMANCE
Abstract
A process for casting a magnesium alloy consisting of 2.0-6.00%
by weight of aluminium, 3.00-8.00% by weight of rare earth metals
(RE-metals), the ratio of the amount of RE-metals to the amount of
aluminium expressed as % by weight being larger than 0.8, at least
40% by weight of the RE-metals being cerium, less than 0.5% by
weight of manganese, less than 1.00% by weight of zinc, less than
0.01% by weight of calcium less than 0.01% by weight of strontium
and the balance being magnesium and unavoidable impurities, the
total impurity level being below 0.1% by weight, wherein the alloy
is cast in a die the temperature of which is controlled in the
range of 180-340.degree. C., the die is filled in a time which
expressed in milliseconds is equal to the product of a number
between 5 and 500 multiplied by the average part thickness
expressed in millimeter, the static metal pressures being
maintained during casting between 20-70 MPa and is subsequently
intensified up to 180 MPa.
Inventors: |
Bakke; Per; (Porsgrunn,
NO) ; Haakon; Westengen; (Porsgrunn, NO) |
Correspondence
Address: |
RANKIN, HILL & CLARK LLP
38210 Glenn Avenue
WILLOUGHBY
OH
44094-7808
US
|
Assignee: |
MAGONTEC GMBH
Bottrop
DE
|
Family ID: |
37546955 |
Appl. No.: |
12/093070 |
Filed: |
September 19, 2006 |
PCT Filed: |
September 19, 2006 |
PCT NO: |
PCT/EP2006/009082 |
371 Date: |
August 18, 2008 |
Current U.S.
Class: |
164/113 |
Current CPC
Class: |
B22D 17/00 20130101;
C22C 23/06 20130101; B22D 21/007 20130101; C22C 23/02 20130101 |
Class at
Publication: |
164/113 |
International
Class: |
B22D 18/00 20060101
B22D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2005 |
EP |
05 077 583.2 |
Claims
1: A process for casting a magnesium alloy consisting of 2.0-6.00%
by weight of aluminum, 3.00-8.00% by weight of rare earth metals,
the ratio of the amount of rare earth metals to the amount of
aluminum expressed as a percentage by weight being larger than 0.8,
at least 40% by weight of the rare earth metals being cerium, less
than 0.5% by weight of manganese, less than 1.00% by weight of
zinc, less than 0.01% by weight of calcium, less than 0.01% by
weight of strontium, and the balance being magnesium and
unavoidable impurities, the total impurity level being below 0.1%
by weight, the process comprising: casting the alloy in a die, the
temperature of which is controlled in the range of 180-340.degree.
C., filing the die in a time which expressed in milliseconds is
equal to the product of a number between 5 and 500 multiplied by
the average part thickness expressed in millimeters, and
maintaining static metal pressures during casting between 20-70
MPa, with subsequent intensification up to 180 MPa.
2: The process according to claim 1, wherein the die temperature is
controlled to a temperature in the range between 200 and
270.degree. C.
3: The process according to claim 1, wherein the filling time of
the die expressed in milliseconds is equal to product of the
average part thickness expressed in millimeters multiplied by a
number between 5 and 20.
4: The process according to claim 1, wherein the static metal
pressure during casting is maintained between 30-70 MPa.
5: The process according to claim 1, wherein a cooling rate after
casting is in the range of 10-1000.degree. C./s.
6: The process according to claim 1, wherein the aluminum content
is between 2.50 and 5.50% by weight.
7: The process according to claim 1, wherein the rare earth metal
content is between 3.50 and 7.00% by weight.
8: The process according to claim 1, wherein the aluminum content
is between 3.6 and 4.5% by weight and the rare earth metal content
is between 3.6 and 4.5% by weight, and ratio of the amount of rare
earth metals to the amount of aluminum is larger than 0.9.
9: The process according to claim 1, wherein the aluminum content
is between 2.6 and 3.5% by weight and the rare earth metal content
is greater than 4.6% by weight.
10: The process according to claim 1, wherein the rare earth metals
are selected from the group consisting of cerium, lanthanum,
neodymium and praseodymium.
11: The process according to claim 10, wherein the amount of
lanthanum is at least 15% by weight of the total content of rare
earth metals.
12: The process according to claim 10, wherein the amount of
lanthanum is at most 35% by weight of the total content of rare
earth metals.
13: The process according to claim 10, wherein the amount of
neodymium is at least 7% by weight of the total content of rare
earth metals.
14: The process according to claim 10, wherein the amount of
neodymium is at most 20% by weight of the total content of rare
earth metals.
15: The process according to claim 10, wherein the amount of
praseodymium is at least 2% by weight of the total content of rare
earth metals.
16: The process according to claim 10, wherein the amount of
praseodymium is at most 10% by weight of the total content of rare
earth metals.
17: The process according to claim 10, wherein the amount of cerium
is greater than 50% by weight of the total content of rare earth
metals.
18: The process according to claim 10, wherein the amount of
calcium and/or strontium is a maximum of 0.01% by weight.
Description
[0001] The invention relates to a process for casting a magnesium
alloy consisting of [0002] 2.0-6.00% by weight of aluminium, [0003]
3.00-8.00% by weight of rare earth metals (RE-metals), [0004] the
ratio of the amount of RE-metals to the amount of aluminium
expressed as % by weight being larger than 0.8, [0005] at least 40%
by weight of the RE-metals being cerium, [0006] less than 0.5% by
weight of manganese, [0007] less than 1.00% by weight of zinc,
[0008] less than 0.01% by weight of calcium [0009] less than 0.01%
by weight of strontium [0010] and the balance being magnesium and
unavoidable impurities, the total impurity level being below 0.1%
by weight.
[0011] Magnesium-based alloys are widely used as cast parts in the
aerospace and automotive industries. Magnesium-based alloy cast
parts can be produced by conventional casting methods, which
include die-casting, sand casting, permanent and semi-permanent
mold casting, plaster-mold casting and investment casting.
[0012] Mg-based alloys demonstrate a number of particularly
advantageous properties that have prompted an increased demand for
magnesium-based alloy cast parts in the automotive industry. These
properties include low density, high strength-to-weight ratio, good
castability, easy machinability and good damping
characteristics.
[0013] Most common magnesium die-casting alloys such as
Mg--Al-alloys or Mg--Al--Zn-alloys are known to lose their creep
resistance at temperatures above 120.degree. C. Mg--Al--Si alloys
have been developed for higher temperature applications and offer
only a limited improvement in creep resistance. Alloys of the
Mg--Al--Ca and Mg--Al--Sr system offer a further improvement in
creep resistance, but a great disadvantage with these alloys is
problems with castability. This is particularly a problem with high
metal velocities impinging directly onto the die surface, the
so-called water hammer effect.
[0014] It is known that the alloy AE48 (4% AP, 2-3% RE) offers a
significant improvement in elevated temperatures properties and
corrosion.
[0015] Mg--Al alloys containing elements like Sr and Ca offer a
further improvement in creep properties, however at the cost of
reduced castability. Alloys of the Mg--Al--Ca and Mg--Al--Sr system
offer a further improvement in creep resistance, but a great
disadvantage with these alloys are problems with castability. This
is particularly a problem with high metal velocities impinging
directly onto the die surface, the so-called water hammer
effect.
[0016] In the annex FIGS. 1A and 1B there are schematically shown
cold chambers and hot chambers die castings machines respectively
each machine has a die 10, 20 provided with a hydraulic damping
system 11, 21 respectively. Molten metal is introduced into the die
by means of a shot cylinder 12, 22 provided with a piston 13, 23
respectively. In the cold chamber system an auxiliary system for
metering of the metal to the horizontal shot cylinder is required.
The hot chamber machine (FIG. 1 B) uses a vertical piston system
(12, 23) directly in the molten alloy.
[0017] To obtain the excellent performance of the Mg--Al--Re
alloys, it is mandatory that the alloys are cast under extremely
rapid cooling conditions. This is the case for the high pressure
die casting process. The steel die 10, 20 is equipped with an oil
(or water) cooling system controlling the die temperature in the
range of 200-300.degree. C. A prerequisite for good quality is a
short die filling time to avoid solidification of metal during
filling. A die filling time in the order of 10.sup.-2
S.times.average part thickness (mm) is recommended. This is
obtained by forcing the alloy through a gate with high speeds
typically in the range 30-300 m/s. Plunger velocities up to 10 m/s
with sufficiently large diameters are being used to obtain the
desired volume flows in the shot cylinder for the short filling
times needed. It is common to use static metal pressures 20-70 MPa
and subsequent pressure intensification up to 150 MPa. With this
casting method the resulting cooling rate of the component is
typically in the range of 10-1000.degree. C./s depending on the
thickness of the component being cast. For AE alloys this is a key
factor in determining the properties, both because of general high
cooling rate of the part, and in particular the extremely high
cooling rate of the surface layer. In the annexed FIG. 2 there is
shown the relationship between the solidification range and the
microstructure. On the horizontal axis there is shown the
solidification rate expressed as .degree. C./S and on the left hand
vertical scale the secondary dendrite arm spacings expressed in
.mu.m is shown, whereas the right hand vertical scale the grain
diameter expressed in .mu.m is shown. Line 30 indicates the grain
size obtained, whereas line 31 is the obtained value for the
secondary dendrite arm spacings.
[0018] With die casting grain refining is obtained by the cooling
rate. As mentioned above cooling rates in the range of
10-1000.degree. C./s is normally achieved. This typically results
in grain sizes in the range of 5-100 .mu.m.
[0019] It is well known that fine grain size is beneficial for the
ductility of an alloy. This relationship is illustrated in the
annexed FIG. 3, in which the relationship between grain size and
relative elongation has been shown. On the horizontal axis the
arrange grain size has been represented expressed in .mu.m, whereas
the vertical axis gives the relative elongation expressed in %. In
the graph there are shown two different composition, first pure Mg,
line 35 and a Mg-alloy designated AZ91, line 36.
[0020] It is also well known that fine grain size is beneficial for
the tensile yield strength of an alloy. This relationship
(Hall-Petch) is shown in the annexed FIG. 4. In the horizontal axis
there is represented the grain diameter, expressed as d (-0.5), in
which has been expressed in .mu.m, and in the vertical axis there
is shown the tensile yield strength expressed in MPa.
[0021] It is therefore evident that the fine grain size provided by
the very high cooling rates facilitated by the die casting process
is a necessity for obtaining tensile strength and ductility.
[0022] The castability term describes the ability of an alloy to be
cast into a final product with required functionalities and
properties. It generally contains 3 categories; (1) the ability to
form a part with all desired geometry features and dimensions, (2)
the ability to produce a dense part with desired properties, and
(3) the effects on die cast tooling, foundry equipment and die
casting process efficiency.
[0023] The German Patent Application 2122148 describes alloys of
the Mg--Al-RE type mainly Mg--Al-RE alloys with RE content <3 wt
%, although alloys with higher RE content are discussed as well. It
is known that the alloy AE42 (4% Al, 2-3% RE) offers a significant
improvement in elevated temperature properties and corrosion
properties. It is experienced that small RE additions to Mg--Al
alloys lead to a significant improvement in corrosion properties,
but a deterioration in the castability as problems with die
sticking occur more frequently. In the annexed FIG. 5 there is
shown the regions of excellent, poor and very poor castability in
the Mg--Al--Re system. In the horizontal axis the amount of Al
expressed as % by weight is shown, whereas in the vertical axis the
amount of RE expressed in % by weight is shown. The line 40 is the
line indicating the solubility of RE at 680.degree. C., whereas the
line 41 indicates the solubility of RE at 640.degree. C. The region
(dark) 42 represents the composition with very poor castability.
The region (intermediate) 43 represents the composition with poor
castability and the region 44 (light) represents the compositions
with excellent castability. As illustrated in FIG. 5, the
castability becomes worse as the RE content of the alloy increases.
However, as FIG. 5 indicates, there is a region with RE>3.5 wt %
(the upper limit restricted by the solubility of RE), Al in the
range 2.5% to 5.0% and furthermore described with a % RE/% Al ratio
greater than 0.8 where the high pressure die castability is
excellent.
[0024] It is therefore an object of the present invention to
provide relatively low cost magnesium-based alloys with improved
elevated-temperature performance and improved castability.
[0025] Due to the formation of AlxREy dispersoid phases, the
compositions of the present invention minimise the volume fraction
of the brittle Mg.sub.17Al.sub.2 phase (The RE/Al ratio in the
dispersoid phases increases with increasing % RE/% Al content in
the alloy). Due to the fact that the eutectic Mg.sub.17Al.sub.12
phase melts at around 420.degree. C., the conventional Mg--Al
alloys like AM50, AM60 and AZ91 will have a solidification range of
nearly 200.degree. C. as shown in the annexed FIG. 6. FIG. 6 shows
the fraction solid (expressed in % by weight) on the horizontal
axis versus the temperature (.degree. C.) on the vertical axis for
a number of alloys. The Mg--Al-RE alloys with the % RE/% Al ratios
as specified in the present invention will solidify completely at
around 570.degree. C., hence the solidification range is only
approximately 50.degree. C.
[0026] In general, increasing aluminium content in Mg--Al die
casting alloys improves the die castability. This is due to the
fact that Mg--Al alloys have a wide solidification range, which
makes them inherently difficult to cast unless a sufficiently large
amount of eutectic is present at the end of solidification. This
can explain the good castability of AZ91D consistent with the
cooling curves shown in FIG. 6. As the Al-content is reduced to 6,
5 and 2% in AM60, AM50 and AM20, respectively, the remaining
eutectic is decreasing to a level where feeding becomes difficult
during the final stages of solidification which means, for thick
walled parts, microporosity and even larger voids can be present.
For thin walled parts, the ability to feed during the final stages
is less important (while alloy fluidity becomes the significant
factor) since the volume shrinkage is partly taken up by thickness
reduction due to shrinkage from the die walls. The AE44 and AE35
alloys show very different cooling characteristics from Mg--Al
alloys. The solidification interval is significantly smaller,
indicating concentrated shrinkage porosity can be decreased during
solidification. These alloys have good fluidity during mold
filling, and can thus easily be cast into final products with less
casting defects. The castability of AE44 and AE35 is relatively
equal to that of AZ91D.
[0027] A further issue related to the narrow solidification
interval is the fact that the commonly observed inverse segregation
occurring in AZ91D as well as AM alloys will not occur. This is
illustrated by the fact that AE alloys with high RE contents have a
shiny surface without segregations of Mg--Al eutectic phase. The
surface layer solidifies during and immediately after die filling,
and the temperature will rapidly decrease below the solidus
temperature, thereby preventing molten metal to be forced towards
the die surface when shrinkage starts. This will be beneficial to
prevent reactions between the die wall and molten metal, which
could lead to die sticking.
[0028] An example with a wall thickness of about 3 mm showing three
layers with different microstructure in AE44 is given in the
annexed FIG. 7. The surface layer, having a thickness of approx. 50
.mu.m, consists of equiaxed grains with size about 10 .mu.m. This
is a fairly small grain size, which can be explained by the rapid
cooling conditions on the die wall. The intermediate layer is about
100 .mu.m thick and is extremely fine grained. The morphology is
different from the former and DAS in the range of 2-4 .mu.m is
observed. The change in equilibrium melting point due to pressure
may explain this observation. When the metal becomes pressurized
the equilibrium melting point increases, i.e., the metal suddenly
becomes undercooled. In theory, this is the same for all Mg alloys,
but there remains a significant difference in the solidification
characteristics among the alloys. The core consists of equiaxed
grains of .about.20 .mu.m. The solidification of the core is
restricted by the heat flow out of the core to the die. Both the
heat transport through the already solidified layer and the heat
transfer over the casting/die interface will give a slower cooling
rate than the skin and thus a coarser microstructure is formed.
[0029] When the RE content is low, or the % RE/% Al ratio is low
like in AE42 or AE63, there will be a possibility that eutectic
Mg--Al is present that could segregate to the surface, and lead to
sticking. This may explain why AE42 shows up with a poorer
castability.
[0030] In FIG. 8 there is shown a box die (upper) part of the
drawing. Micrographs of examples from node 3 (close to the gate)
for alloys AM60, AM40, AE63, AE44 and AE35 as shown below. Hot
cracks are observed in AM40 and AE63.
[0031] FIG. 8, have demonstrated that AE44 and AE35 are less
susceptible to hot tearing than AM alloys. This is explained from
the fairly rapid solidification of the surface layer resulting in
the relatively fine grained structure as described above.
[0032] Partly due to the fine grain structure and partly due to the
absence of the brittle Mg.sub.17Al.sub.12 phase this layer becomes
very ductile, and is therefore able to deform when thermal strains
are developing during solidifaction. A surface layer with coarser
grains, as would typically appear in alloys with larger
solidification interval, and/or a Mg.sub.17Al.sub.12 rich layer,
will have a much lower ductility and would tend to crack and form
hot tears rather than deform.
[0033] Testing of large (.about.1.5 m) thin walled parts (.about.3
mm thick) has shown that the die filling characteristics of AE44
and AE35 are excellent, and since long range feeding is not
necessary for thin walled parts as discussed above, this alloy is
expected to be a viable alternative for these types of components,
where die filling is of prime importance.
[0034] The properties of various AE alloys are explained from the
observations that Al alone provides the solid solution
strengthening while RE combines with Al forming dispersoid phases
in the grain boundary regions. In the alloys AE44 and AE35, the
dispersoid phase (mainly Al.sub.2RE) constitutes a continuous 3D
network, effectively preventing creep arising from thermal
activation and grain boundary sliding. This shown in FIG. 9 which
are SEM-BEC (Backscatter Electronic Composition) images showing the
die cast microstructure of (from left to right) AE44, AE35 and
AE63. While Al alone provides the solid solution strengthening, RE
combines with AL forming dispersoid phases in the grain boundary
regions.
[0035] A further enlargement of the SEM-BEC-images for AE 44 is
shown in FIG. 10, which also shows the lamellar structure of
Al.sub.xREy phases in AE44. As seen from FIG. 10 the dispersoid
AlxREy phases in the AE alloys consist of an extremely fine
lamellar structure. This structure of submicron lamellas are
stiffening the grain boundaries thereby preventing creep. On the
other hand, these lamellas are not brittle (or not as brittle as
the eutectic Mg--Al) as the die cast AE44 alloy experience a
ductility that is similar to AE42. In AE63, the network (mainly
Al.sub.11RE.sub.3) becomes fragmented and the grain boundary
regions are probably influenced by a substantial amount of eutectic
Mg--Al, reducing the ductility and the creep properties. In AE42
there is probably also a significant amount of eutectic Mg--Al that
limits the creep properties. The alloy AE35 has slightly lower
ductility than AE44, but still higher than AE63.
[0036] Numerous examples of mechanical properties including
ductility, tensile strength, creep resistance and corrosion
properties of the AE alloys are shown later. The unique combination
of creep resistance and ductility compared to existing alloys is
illustrated in FIG. 11. In FIG. 11 the ductility (horizontal axis)
is shown as versus the creep resistance for a number of known
Mg-alloys. The zone 50 comprises AM-alloys, zones 51 AE-alloys,
zone 52 AZ91-alloy and zone 53 other high temperature alloys. The
AE alloys of the present invention are the only die casting alloys
that combine ductility and elevated temperature properties in this
way, and hence offer numerous new and unexplored opportunities for
constructors and designers particularly in the automotive
industry.
[0037] It is a more particular object to provide relatively low
cost die casting magnesium-aluminum-rare earth alloys with
excellent castability, good creep resistance and tensile yield
strength and bolt-load retention, particularly at elevated
temperatures of at least 150.degree. C.
SUMMARY OF THE INVENTION
[0038] The present invention therefore provides: [0039] the alloy
is cast in a die the temperature of which is controlled in the
range of 180-340.degree. C., [0040] the die is filled in a time
which expressed in milliseconds is equal to the product of a number
between 5 and 500 multiplied by the average part thickness
expressed in millimeter, [0041] the static metal pressures being
maintained during casting between 20-70 MPa and is subsequently
intensified up to 180 MPa.
[0042] By using the combination of a specified Mg--Al-RE alloy with
a special casting process, products could be obtained having
excellent creep resistance, at elevated temperature, high ductility
and generally good mechanical properties as well as corrosion
properties.
[0043] In general a number of RE-metals can be used as alloying
element, such as e.g. Ce, La, Nd and or Pr and mixtures thereof. It
is however preferred to use cerium in substantial amounts as this
metal gives the best mechanical properties. Mn is added to improve
the corrosion resistance but its addition is restricted due to
limited solubility.
[0044] Preferably the aluminium content is between 2.0 and 600% by
weight, more preferably between 2.60 and 4.50% by weight.
[0045] If higher amounts of aluminium are present, this can easily
lead to the formation of a Mg.sub.17Al.sub.12-phases which is
detrimental for the creep properties. Too low Al is negative for
the castability.
[0046] With respect to the RE-metals it is preferred that the
RE-content is between 3.50 and 7.00% by weight, the upper limit
being restricted by the solubility of RE in the Mg--Al-RE system as
indicated in FIG. 1.
[0047] If more than 3.50% RE by weight is present, this gives a
significant improvement of the creep properties. More than 7.00% by
weight is not practical because of the restricted solubility of
RE-metals in liquid magnesium-aluminium alloys.
[0048] Furthermore, it is preferred that the RE/Al ratio is larger
than 0.9.
[0049] For specific applications the composition of the alloy is
selected in such a way that the aluminium content is between 3.6
and 4.5% by weight and the RE-content is between 3.6 and 4.5% by
weight, with the additional constraint that the RE/Al ratio is
larger than 0.9.
[0050] This type of alloys can be used for applications up to
175.degree. C. while still showing excellent creep properties and
tensile strength. Moreover this alloy does not show any degradation
of its properties due to ageing and has a good castability.
[0051] For applications above 175.degree. C. the composition of the
alloy is such that the aluminium content is between 2.6 and 3.5% by
weight and the RE-content is greater than 4.6% by weight.
[0052] Apart from the excellent creep properties and tensile
strength this alloy does not show any degradation of properties due
to ageing.
[0053] Preferably the RE-metals are selected from the group cerium,
lanthanum, neodymium and praseodymium.
[0054] The RE-metals are contributing to the ease of alloying, but
also increase the corrosion resistance, the creep resistance and
improve the mechanical properties.
[0055] Preferably the amount of lanthanum is at least 15% by weight
and more preferably at least 20% by weight of the total content of
RE-metals, Preferably the amount of lanthanum is less than 35% by
weight of the total content of RE-metals.
[0056] Preferably the amount of neodymium is at least 7% by weight
and more preferably at least 10% by weight of the total content of
RE-metals. Preferably the amount of neodymium is less than 20% by
weight of the total content of RE-metals.
[0057] Preferably the amount of praseodymium is at least 2% by
weight and more preferably at least 4% by weight of the total
content of RE-metals. Preferably the amount of praseodymium is less
than 10% by weight. Of the total content of RE-metals.
[0058] Preferably the amount of cerium is greater than 50% by
weight of the total content of RE-metals, preferably between 50 and
55% by weight.
[0059] It is known that calcium and strontium give an increase in
creep resistance, and the addition of at least 0.5% weight of
calcium will improve the tensile strength.
[0060] However, Ca and Sr should be avoided because even at very
small concentrations these elements lead to considerable sticking
problems thereby influencing the castability of the alloy.
[0061] The present invention is described in more detail with
reference to the following example which are for purposes of
illustration only and are not to be understood as indicating or
implying any limitation on the brood invention described
herein.
EXAMPLE 1
[0062] In order to compose the influence of the alloying elements
and a number of Mg-alloys have been prepared with the compositions
as given in table 1.
[0063] Of each alloy purposes a number of test bars has been made
to do the testing described in the following examples. The
performed tests are the following [0064] Tensile strength and
ductility [0065] Test-bars of 6 mm in accordance to ASTM have been
made, and the following [0066] Test conditions has been used:
[0067] 10 kN Instron machine [0068] Room temperature to 210.degree.
C. [0069] At least 5 parallels at each temperature [0070] Strain
rate [0071] 1.5 mm/min up to 0.5% strain, [0072] 10 mm/min above
0.5% strain [0073] Testing in accordance with ISO 6892 [0074]
Tensile creep testing [0075] For this text the following test
material is used [0076] Diameter: 6 mm [0077] Gauge length: 32.8 mm
[0078] Radius of curvature: 9 mm [0079] Grip head diameter: 12 mm
[0080] Total length: 125 mm [0081] The testing is done in
accordance with ASTM E 139 [0082] Stress relaxation testing [0083]
Test material [0084] 12 mm diameter, 6 mm length [0085] Cut from
arbitrary end of creep bars [0086] Testing in accordance with ASTM
E328-86 [0087] Corrosion Properties [0088] The corrosion is tested
according to ASTM 117.
EXAMPLE 2
[0089] For a number of compositions the strength has been measured
as a function of the temperature.
[0090] The results are shown in FIGS. 12, 13 and 14. In these
figures the y-axis is representing the tensile strength expressed
in MPa, whereas the x-axis is representing the temperature
expressed in degrees Celsius.
EXAMPLE 3
[0091] For a number of compositions the Creep strain has been
measured as a function of the time.
[0092] The results are shown in FIGS. 15 and 16. In FIG. 15 the
measurement is done at 175.degree. C. whit a 40 MPa-force, and in
FIG. 16 the measurement is done at 150.degree. C. with a 90
MPa-forces.
[0093] In these figures the y-axis is representing the creep strain
expressed in percentage, whereas the x-axis is representing the
time expressed in hours.
EXAMPLE 4
[0094] For a number of compositions according to table 1 the stress
relaxation has been defined, expressed as the remaining load versus
the time. The results are shown in FIGS. 17, 18 and 19.
[0095] In these figures the y-axis is representing the remaining
load expressed in percentage of initial load, whereas the x-axis is
representing the time expressed in hours.
EXAMPLE 5
[0096] For a number of compositions the corrosion properties have
been defined in accordance to ASTM B117. In this test a great
amount of data has been incorporated in order to define the
influence of the RE-contest versus the Al-contest. The results are
shown in FIG. 20.
[0097] In this figure the y-axis is representing the RE-content
expressed in % by weight whereas the x-axis is representing the
Al-content also expressed in % by weight.
[0098] The border lines between the zones with different shades are
representing lines of equal corrosion resistances.
[0099] From these test results it is clear that a process for
casting a magnesium alloy has been provided whereby products are
obtained with a superior combination of elevated temperature creep
properties, ductility and corrosion performance.
TABLE-US-00001 TABLE 1 Alloy Al Mn Zn Si Ce La Nd Pr RE Type wt %
wt % wt % wt % wt % wt % wt % wt % wt % Ce/RE La/RE Nd/RE Pr/RE
AZ91D 8.93 0.17 0.73 AS21B 2.11 0.08 1.01 0.09 AE35-24 3.23 0.29
2.49 1.73 0.94 0.28 5.44 45.77 31.80 17.28 5.15 AE42-15 3.89 0.15
1.31 0.79 0.37 0.16 2.64 49.85 30.08 14.15 5.92 AE44-24 4.12 0.29
2.11 1.53 0.75 0.23 4.62 45.67 33.12 16.23 4.98 AE63-4 6.31 0.18
1.42 1.35 0.40 0.13 3.30 43.03 40.91 12.12 3.94 ACe44 3.70 3.90
3.90 100.00 ANd44 3.90 2.50 2.50 100.00 ALa44 3.70 0.38 3.00 3.00
100.00 ALaCe431 3.70 0.45 0.90 2.30 3.20 28.10 71.90 ALaCe413 4.00
0.28 2.40 0.90 3.30 72.70 27.30 ALaNd431 3.90 0.46 2.60 0.80 3.40
76.50 23.50 ALaNd413 3.70 0.42 1.10 1.60 2.70 40.70 59.30 ACeNd431
4.70 0.27 2.60 0.80 3.40 76.50 23.50 ACeNd413 4.40 0.32 0.90 1.00
1.90 47.40 52.60 ACeNd422 3.60 1.50 1.50 3.00 50.00 50.00
TABLE-US-00002 TABLE 1 Alloy Al Mn Zn Si Ce La Nd Pr RE Type wt %
wt % wt % wt % wt % wt % wt % wt % wt % Ce/RE La/RE Nd/RE Pr/RE
AZ91D 8.93 0.17 0.73 AS21B 2.11 0.08 1.01 0.09 AE35-24 3.23 0.29
2.49 1.73 0.94 0.28 5.44 45.77 31.80 17.28 5.15 AE42-15 3.89 0.15
1.31 0.79 0.37 0.16 2.64 49.85 30.08 14.15 5.92 AE44-24 4.12 0.29
2.11 1.53 0.75 0.23 4.62 45.67 33.12 16.23 4.98 AE63-4 6.31 0.18
1.42 1.35 0.40 0.13 3.30 43.03 40.91 12.12 3.94 ACe44 3.70 3.90
3.90 100.00 ANd44 3.90 2.50 2.50 100.00 ALa44 3.70 0.38 3.00 3.00
100.00 ALaCe431 3.70 0.45 0.90 2.30 3.20 28.10 71.90 ALaCe413 4.00
0.28 2.40 0.90 3.30 72.70 27.30 ALaNd431 3.90 0.46 2.60 0.80 3.40
76.50 23.50 ALaNd413 3.70 0.42 1.10 1.60 2.70 40.70 59.30 ACeNd431
4.70 0.27 2.60 0.80 3.40 76.50 23.50 ACeNd413 4.40 0.32 0.90 1.00
1.90 47.40 52.60 ACeNd422 3.60 1.50 1.50 3.00 50.00 50.00
* * * * *