Note: Descriptions are shown in the official language in which they were submitted.
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HIGH TEMPERATURE ALUMINIUM ALLOY
The invention relates to an aluminium alloy of type
AlMgSi with good creep strength at elevated tempera
tures for the production of castings subject to high
thermal and mechanical stresses.
The further development of die sel engines with the aim
of achieving an improved combustion of the diesel fuel
and a higher specific output leads inter alia to a
higher explosion pressure and in consequence to a
pulsating mechanical load acting on the cylinder crank-
case that makes very high demands on the material.
Apart from a high fatigue strength, a good endurance
strength at high temperatures of the material is a
further precondition for its use in the production of
cylinder crankcases.
AlSi alloys are generally used today for comp onents
subject to high thermal stresses, this high -temperature
strength being achieved by the addition of Cu to the
=
alloy. Copper does, however, also increase the hot
shortness and has a negative effect on the castability.
Applications in which in particul ar high -
temperature
strength is demanded are primarily found in the area of
the cylinder heads of automotive engines, see e.g. F.J.
Feikus, "Optimierung von Aluminium -
Silicium-
Gussiegierungen ftir Zylinderkopfe" [Optimization of
Aluminium-Silicon Casting Al loys for Cylinder Heads],
Giesserei-Praxis, 1999, Volume 2, pp. 50-57.
A high-temperature AlMgSi alloy for the production of
cylinder heads is known from US -A-3 868 250. The alloy
contains, apart from the normal additives, 0.6 to 4.5%
w/w Si, 2.5 to 11% w/w Mg, of which 1 to 4.5% w/w free
Mg, and 0.6 to 1.8% w/w Mn.
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WO-A-96 15281 describes an aluminium alloy with 3.0 to
6.0% w/w Mg, 1.4 to 3.5% w/w Si, 0.5 to 2.0% w/w Mn,
max. 0.15% w/w Fe, max. 0.2% w/w Ti and aluminium as
remainder with further impuriti es of individually max.
0.02% w/w, and max. 0.2% w/w in total. The alloy is
suitable for the production of components where high
demands are made on the mechanical properties. Process -
ing of the alloy is preferably by pressure die casting,
thixocasting or thixoforging.
A similar aluminium alloy for the production of safety
components by pressure die casting, squeeze casting,
thixoforming or thixoforging is known from WO -A-
0043560. The alloy contains 2.5 - 7.0% w/w Mg, 1.0
3.0% w/w Si, 0.3 - 0.49% w/w Mn , 0.1 - 0.3% w/w Cr,
max. 0.15% w/w Ti, max. 0.15% w/w Ti, max. 0.15% w/w
Fe, max. 0.00005% w/w Ca, max. 0.00005% w/w Na, max.
0.0002 6 w/w P, further impurities of individually max.
0.02% w/w and aluminium as remainder.
A casting alloy of type AlMgSi know n from
EP -A-
1 234 893 contains 3.0 to 7.0% w/w Mg, 1.7 to 3.0% w/w
Si, 0.2 to 0.48% w/w Mn, 0.15 to 0.35% w/w Fe, max.
0.2% w/w Ti, optionally also 0.1 to 0.4% w/w Ni and Al
as remainder and manufacturing -related impurities of
individually max. 0.02% w/w and max. 0.2% w/w in total,
with the further condition that magnesium and silicon
in the alloy essentially exist in a ratio Mg : Si of
1.7 : 1 by weight, corresponding to the composition of
the quasi-binary eutectic with the solid phases Al and
Mg2Si. The a lloy is suitable for the production of
safety components in motor vehicles by pressure die
casting, rheocasting and thixocasting.
The object of the invention is to provide an aluminium
alloy with good creep strength at elevated temper atures
for the produ ction of components subject to high
thermal and mechanical stresses. The alloy should be
suitable in particular for pressure die casting, but
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also for gravity die casting, low -pressure die casting
and sand casting.
A specific object of the invention is th e provision of
an aluminium alloy for cylinder crankcases of internal
combustion engines, in particular of diesel engines,
produced by pressure die casting.
The components cast from the alloy should exhibit high
strength together with high ductility. The intended
mechanical properties in the component are defined as
follows:
Proof strength Rp0.2 > 170 MPa
Tensile strength Rm > 230 MPa
Elongation at break A5 > 6%
The castability of the alloy should be comparable with
the castability of the AlSiCu casting alloys currently
used, and the alloy should not show any tendency to hot
shortness.
The object is achieved with the solution according to
the invention in that the contents of the alloying
elements magnesium and silicon in % w/w in a Cartesian
coordinate system are limited by a polygon A with the
coordinates [Mg; Si] [8.5; 2,7] [8.5; 4,71 [6.3; 2,71
[6.3; 3.4] and that the alloy also contains
0.1 to 1% w/w manganese
max. 1% w/w iron
max. 3% w/w copper
max. 2% w/w nickel
max. 0.5% w/w chromium
max. 0.6% w/w cobalt
max. 0.2% w/w zinc
max. 0.2% w/w titanium
max. 0.5% w/w zirconium
max. 0.008% w/w beryllium
max. 0.5% w/w vanadium
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as well as aluminium as remainder with further elements
and manufacturing -related impurities of individually
max. 0.05% w/w and max. 0.2% w/w in total.
The following content ranges are preferred for the main
alloying elements, Mg and Si:
Mg 6.9 to 7.9% w/w, in particular 7.1 to 7.7% w/w
Si 3.0 to 3.7% w/w, in particular 3.1 to 3.6% w/w
Particularly preferred are alloys whose contents of the
alloying elements magnesium and silicon in % w/w in a
Cartesian coordinate system are limited by a polygon B
with the coordinates [Mg; Si] [7.9; 3,0] [7.9; 3,7]
[6.9; 3,0] [6.9; 317], in particular by a polygon C
with the coordinates [Mg; Si ] [7.7; 3.1] [7.7; 3,6]
[7.1; 3,1] [7.1; 3,6].
The alloying elements Mn and Fe allow sticking of the
castings to the mould to be avoided. A higher iron
content results in a higher high -temperature strength
at the expense of reduced elongation. Mn contribu tes
also significantly to red hardness. Depending on the
field of application, the alloying elements Fe and Mn
are therefore preferably balanced with one another as
follows:
With a content of 0.4 to 1% w/w Fe, in particular 0.5
to 0.7% w/w Fe, a content o f 0.1 to 0.5% w/w Mn, in
particular 0.3 to 0.5% w/w Mn, is set.
With a content of max. 0.2% w/w Fe, in particular max.
0.15% w/w Fe, a content of 0.5 to 1% w/w Mn, in
particular 0.5 to 0.8% w/w Mn, is set.
The following content ranges are preferred for t he
further alloying elements:
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Cu 0.2 to 1.2% w/w, preferably 0.3 to 0.8% w/w, in
particular 0.4 to 0.6% w/w
Ni 0.8 to 1.2% w/w
Cr max. 0.2% w/w, preferably max. 0.05% w/w
Co 0.3 to 0.6% w/w
Ti 0.05 to 0.15% w/w
Fe max. 0.15% w/w
Zr 0.1 to 0.4% w/w
Copper results in an additional increase in strength,
but with increasing contents leads to a deterioration
in the corrosion behaviour of the alloy.
The addition of cobalt allows the demoulding behaviour
of the alloy to be further improved.
Titanium and zirconium improve the grain refinement. A
good grain refinement contributes significantly to an
improvement in the casting properties and mechanical
properties.
Beryllium in combination with vanadium reduces the
formation of dross. With an addition of 0.02 to 0 .15%
w/w V, preferably 0.02 to 0.08% w/w V, in particular
0.02 to 0.05% w/w V, less than 60 ppm Be are
sufficient.
A preferred field of application of the aluminium alloy
according to the invention is the production of
components subject to high thermal a nd
mechanical
stresses by pressure die casting, mould casting or sand
casting, in particular for cylinder crankcases for
automotive engines produced by the pressure die casting
method.
The alloy according to the invention also satisfies the
mechanical pro perties demanded for structural compo
nents in automotive construction after a single -stage
heat treatment without separate solution annealing.
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In accordacne with one aspect of the present invetion,
there is provided a use of an aluminium alloy of type
AlMgSi with good creep strength at elevated temperatures
for the production of castings subject to high thermal and
mechanical stresses, consisting of the contents of the
alloying elements magnesium and silicon in % w/w in a
Cartesian coordinate system are limited by a polygon A with
the coordinates [Mg; Si] [8.5; 2,71 [8.5; 4,7] [6.3; 2,7]
[6.3; 3.4] and that the alloy also contains
0.1 to 1% w/w manganese
max. 1% w/w iron
max. 3% w/w copper
max. 2% w/w nickel
max. 0.5% w/w chromium
max. 0.6% w/w cobalt
max. 0.2% w/w zinc
max. 0.2% w/w titanium
max. 0.5% w/w zirconium
max. 0.008% w/w beryllium
max. 0.5% w/w vanadium
as well as aluminium as remainder and manufacturing
-related impurities of individually max. 0.05% w/w and max.
0.2% w/w in total, for components subject to high thermal
and mechanical stresses produced by pressure die casting,
mould casting or sand casting.
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Further advantage, features and properties of the
invention can be seen from the following description of
preferred exemplary embodiments and from the drawing
that shows in
Fig. 1 a diagram with the content limits for the
alloying elements Mg and Si
The polygon A shown in Fig. 1 defines the content range
for the alloying elements Mg and Si, the polygons 13 and
C re fer to preferred ranges. The straight line E
corresponds to the composition of the quasi -
binary
eutectic Al -Mg2Si. The alloy compositions according to
the invention thus lie on the side with an excess of
magnesium.
The alloy according to the invention was cast
into
pressure die cast plates with different wall
thicknesses. Tensile strength test specimens were
manufactured from the pressure die cast plates. The
mechanical properties proof strength (Rp0.2), tensile
strength (Rm) and elongation at break (A) we re
determined on the tensile strength test specimens in
the conditions
As cast
Water/F As cast, quenched in water after demoulding
F> 24 h As cast, > 24 h storage at room temperature
Water/F > 24 As cast, quenched in water after
demoulding, > 24 h storage at room temperature
and after various single-stage heat treatment processes
at temperatures in the range from 250 C to 380 C and
after long-term storage at temperatures in the range
from 150 C to 250 C.
The alloys examined are summarized in Table 1. The
letter A indicates alloys with copper additive, the
letter B alloys without copper additive.
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Table 2 shows the results of the mechanical properties
determined on tensile strength test specimens of the
alloys in Table 1.
An alloy not included in Tables 1 and 2 with good creep
strength at elevated temperatures exhibited the
following composition (in % w/w):
3.4 Si, 0.6 Fe, 0.42 Cu, 0.32 Mn, 7.4 Mg, 0.07 Ti, 0.9
Ni, 0.024 V and 0.004 Be
The results of the long -term tests underline the good
creep strength at elevated temperatures of the alloy
according to the invention. The mechanical properties
after a single-stage heat treatment at 350 C and 380 C
for 90 minutes indicate furthermore that the alloy
according to the invention also satisfies the demands
made for structural components in automotive
construction.
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Table 1: Chemical composition of the alloys in % w/w
___________________________________________________________________ ,
1
Alloy Wall Si Fe Cu Mn Mg Ti V Be
1
' variant thickness
1
of flat
specimen
1 3mm 3.469 0.1138 0.787 7.396
0.106 0.0221 0.0025
1A 3 mm 3.4 0.117 0.527 0.781 7.151 0.119 0.0223
0.0019
2 2 mm 3.366 0.0936 0.774 7.246 0.117 0.0263
0.0024
2A 2 mm 3.251 0.0841 0.507 0.76 7.499 0.1 0.0246
0.0023
3 4 mnn 3.352 0.0917 0.774 7.221 0.118 0.026
0.0024
3A 4 mm 3.198 0.0848 0.522 0.747 7.351 0.101 0.0255
0.0023
4 6 mm 3.28 0.0921 0.766 7.024 0.119 0.0268
0.0024
4A 6 mm 3.181 0.862 0.535 0.745 7.273 0.1 0.0257
0.0023
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Table 2: Mechanical properties of the alloys
1 __________________________________________ I i
Alloy Initial state Heat treatment Rp0.2 Rm A5 I
variant [MPa] [MPa] [%]
F 210 359 8.6
Water/F 181 347 9.6
F>24 h 204 353 8.9
Water / F>24 h 176 347 13.4
250 C/10 min 216 352 7.4 I
=
250 C/20 min 218 352 6.8
250 C/90 min 207 349 10.8 _
350 C/10 min 154 315 12.5
1 350 C/20 min 158 315 10.6
350 C/90 min 147 306 11.4 _
F>24 h 380 C/10 min 145 304 14.1
380 C/20 min 139 299 13.9
1
380 C/90 min 137 299 16.7
150 C/100 h 221 365 9.4
180 C/100 h 214 346 6
200 C/100 h 211 354 9.4
250 C/100 h 184 336 11.7 :
150 C/500 h 223 353 6
180 C/500 h 216 357 9.7
200 C/500 h 202 349 9.2
250 C/500 h 170 327 12.3 ,
1A F 234 345 4.2
Water/F 170 319 4.9
F>24 h 205 355 7.1
Water / F>24 h 188 340 5.6
F>24 h 250 C/10 min 227 355 6.6
250 C/20 min 217 354 7.5
250 C/90 min 213 350 7.9
350 C/10 min 157 328 10.4
350 C/20 min 151 317 9.3
350 C/90 min 142 312 12.1
380 C/10 min 141 315 12.6
380 C/20 min 137 312 12.4 _
380 C/90 min 133 309 12.2
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I
150 C/100 h 248 370 , 5
180 C/100 h 249 373 , 6.3
200 C/100 h 215 346 _ 6.2
250 C/100 h 185 329 7.6
150 C/500 h 239 368 6.5
180 C/500 h 227 352 6.9
200 C/500 h 215 350 7.8
250 C/500 h 162 317 8.9
212 364 10.7 .
2 F>24 h 250 C/90 min 223 358 9.9
350 C/90 min 152 312 13.9
380 C/90 min 139 297 , 17.9
241 394 7.8
2A F>24 h 250 C/90 min 234 375 8.5
,
350 C/90 min 163 332 9
380 C/90 min 144 328 , 13.7
158 321 9.9
3 F>24 h 250 C/90 min 164 324 , 10.4
350 C/90 min 143 307 12
380 C/90 min 129 292 16.4
173 326 6
3A F>24 h 250 C/90 min 181 325 5.9
350 C/90 min 151 315 6.9
380 C/90 min 137 312 , 9.5
138 304 8.2
4 F>24 h 250 C/90 min 145 309 , 9
350 C/90 min 133 297 8.4
380 C/90 min 123 286 , 12.7
152 284 4.3
4A F>24 h 250 C/90 min 163 278 3.7
350 C/90 min 139 286 _ 5.2
380 C/90 min 131 285 5.7
