Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to aluminium casting
alloys.
The alloys of the present invention possess
a comprehensive range of enhanced properties and
are therefore suitable for a wide variety of
applications, among which may be mentioned brake
calipers and drums, piston/bore applications in
internal combustion engines and a number of other
. components in engines, compressors and electric
motors. A particular application of the alloys
of the invention is in alum;nium cylinder heads.
The alloys of the inventi.on have improved
properties and are characterized, in particular,
by possessing:
outstanding wear resistance, more specifically
- wear resistance under continued cycles of
compressive loads and under conditions of
sliding wear;
high tensile and compressive strengths as well
as stiffness at room temperature and at elevated
temperatures up to 250C for short periods;
a modulus of elasticity at room and elevated
temperature which is higher than is usual
for aluminium casting alloys;
a high degree of dimensional stability;
very good castability;
'
~ ~ ~5~
very good machinability;
excellent corrosion resistance;
a coefficient of thermal expansion which is
lower than normal for aluminium casting alloys.
The alloys of the invention may be used in
both the as-~cast and heat treated condition. While
the a]loys have good properties in the as-cast
condition, these properties may be *urther improved
by quite simple solution and ageing heat treatments.
The alloys of the present invention constitute
a range of novel aluminium alloy compositions in
which a number of known theories have been combined
in a novel and unique way to give a wide range of
excellent properties.
While there are a number of alloys which have
some, but not all, of the abovementioned favourable
properties, to our knowledge, there are none that
have all of these properties in one alloy.
The British alloy BS LM13, which is used for
pistons and comprises many o the elements used
- in the alloys of the present invention, does not
have excellent high temperature strength and is
not suited to applications requiring Yery high
wear resistance. The U.S. 390 alloys, which are
basically hypereutectic aluminium-silicon alloys,
have been used for cylinder blocks and brake drums
~7~
and possess reasonable high temperature strength
and ~ear resistance but poor casting and machining
properties. The Australian alloy 603 is a hypoeutectic
aluminium-silicon alloy and is currently being used
for the manufac-ture o disc brake calipers. It has
good machinability, castability and corrosion resistance
properties but compared to the alloys of the present
inventlon, has inferior wear resistance and strength
and stiffness at elevated temperatures. Other Australian
alloys (309, 3]3 and 601) are currently used for
cylinder heads but have poor wear resistance, especially
at elevated temperatures, and require inserts for
valve seats and guides.
Because the alloys of the pre.sent invention possess
a comprehensive range of enhanced properti`es, they
are suitable for a wide vari`ety o~ applications
These applications may require.only one or a combination
of the improved properti`es.. The e.xcellent elevated
temperature strength propertie.s and the hi`gh modulus
of.elasticity of the alloys of the i`nventi`on are
important properties for brake calipers. These.properti`es
together with the e~cellent wear resistance of the
alloys could also make them su;tab.le for brake drums.
The sliding wear resistance of the alloys when
in contact with other hard metal surfaces may make
them suitable for piston~bore appli.cations in two
--4--
and four-stroke motors, these applications also
taking advantage of the alloys' good dimensional
stability and low coefficient of thermal expansion.
The fineness of the microstructure also prevents
it from scoring or damaging sur-faces softer than
itself, and this is an advantage in many wearing
situations with items such as soft types of seals
and rotors.
The alloys of the invention could also be
used for a number of other components in engines,
compressors, pumps and electric motors where the
excellent combination of properties including
castability, machinability and corrosion resistance
are major advantages.
~ particular application of the alloys is in
aluminium cylinder heads which normally require
special steel/bronze inserts for valve guides and
valve seats. These special inserts constitute an
added manufacturing cost and hence the production
of alloys having improved properties, so that the
- need for special inserts can be mimimized and hope-
fully avoided altogether, has great benefit.
- In this respect our studies and extensive test
programmes have shown that the wear of valve seats
occurs by abrasion, valve rotation and continued
cycles of compressive load and that sliding wear
1 ~S~B~
is responsible for damage to valve guides. While a knowledge
of these wear mechanisms and the knowledge of properties re-
quired in other applications, was taken into careful account
when designing and developing the alloys of the present
invention, it should be understood that the use of the
alloys is in no way limited to the applications mentioned.
Broadly, the properties of the alloys are obtained by
novel alloy compositions and by careful control of the para-
meters of growth rate and temperature gradient at the liquid/
solid interface during the solidification process. These
specific compositions and solidification parameters are nec-
essary to produce the correct microstructure which in turn
is responsible for the wide range of excellent properties.
In general, the alloys of the invention have the
following compositions by weight:-
Si 12 - 15%
Cu 1.5 - 5.5%
Ni 1.0 - 3.0%
Mg 0.1 - 1.0%
Fe 0.1 - 1.0%
Mn 0.1 - 0.8%
Zr 0.01 - 0.1%
Silicon modifier 0~001 - 0.1%
Ti 0.01 - 0.1%
Al Remainder, apart from impurities.
The alloys have an essentially eutectic microstructure
containing not more than 10~ of primary alpha-aluminium
dendrites and substantially free from intermetallic par-
ticles exceeding 10 microns in diameter.
--6--
~,
~7S~t-l
In a preferred embodiment the invention also provides
primary alloys of the following compositions by weight:
Si 12 - 15
C~ 1.5 4
Ni 1.0 - 3.0~
Mg 0~4 - 1.0%
Fe 0.1 - 0.5%
Mn 0.1 ~ 0.8%
Zr 0.01 ~ 0.1%
Silicon modifier 5.01 - 0.05%
Ti 0.01 - 0.1%
Al Remainder, apart from impurities.
These alloys also have the eutectic microstructure
referred to above.
The silicon modifier preferably comprises strontium or
sodium.
In the following discussion and in the ~xamples
reference is made to the accompanying figures, wherein
Fig. 1 is a photomicrograph (X500l showing the
cast microstructure oE an alloy solidified at a growth
rate of lOO~ms 1 and at a G/R ratio of 9000Cs/cm .
Fig~ 2 is a photomicrograph (X500) showing the cast
microstructure of an alloy solidified at a growth rate
of llOO~ms 1 and at a G/R ratio of 450Cs/cm2.
Fig. 3 is a photomicrograph (XS00) showing the cast
microstructure of an alloy according to the invention,
solidified at a growth rate of 700~ms 1 and at a G/R
ratio of 1300Cs/cm2.
--7--
~,'',~.,'"'
,
Fig. 4 is a photomicrograph (X500) showing the cast
microstructure of an alloy according to the invention,
solidified at a growth rate of 600~ms 1 and at a C/R
ratio of 1500Cs/cm and heat-treated (solution treated
8 hours at 500C aged 16 hours at 160C)~
Fig. 5 is a photomicrograph (X500) showing a heat-treated
microstrueture, solution treated 8 hours at 470C, aged
16 hours at 160Co
Fig. 6 is a photomlerograph (X500) showing a heat treated
microstructure, solution treated 8 hours at 540C, aged
16 hours at 160C~
Fig. 7 is a diagrammatic representation of a simulative
test rig.
Fig. 8 shows the valve seat lives obtained as a function
of applied stress in the tests described in Example 3 below.
Flg. 9 is a photomicrograph (X500) showing a heat treated
microstructure /(solution treated 8 hours at 500C, aged
16 hours at 160C). The composition of this alloy is in
Table 7 , Alloy No. 9.
Fig. 10 (a), (b) and (c) show photomicrographs (X150)
comparing charaeteristie wear surfaees on aluminium alloys
which have undergone 500 hours of sliding wear against
soft seals and rotors.
Fig. 11 shows charaeteristie wear surface profiles on
aluminium alloys whieh have undergone 500 hours of sliding
wear against soft seals and rotors. Horizontal Mag. = 100,
Vertieal Mag. - 1000.
-- 8 --
Fig. 12 is a photomicrograph (X500) of a cast
microstructure of an alloy according to the invention
in which the Si has been modified with sodium. The
alloy was solidified at a growth rate of 700~ms 1 and
a G/P~ ratio of 1300Cs/cm .
The chemical composition of the alloys shown
in Figures 1 - 4 was as follows by weight:-
Si 14.2%
Fe 0.32%
Cu 2~60%
Mg o.51%
Zr 0.05%
Ni 2.25%
Mn
Ti 0~05%
Sr 0.03%
Al Remainder apart from impurities.
The chemical composition of the alloys shown inFigures 5 and 6 was as follows by weight:-
Si 14.3%
Fe 0.24%
- Cu 2.3~
Mg Q-.50%
Zr 0.05
Ni 2.26%
Mn 0.45%
Ti 0.06%
Sr 0.02%
Al Remainder apart from impurities.
Growth rate (R) is expressed in microns per
second (~ms 1) and temperature gradient at the interface
(G) expressed in C degrees per centimetre (Ccm 1).
Growth rate is the growth rate of the solid during
solidification of the casting. Temperature gradient
is the temperature gradient existing in the liquid
adjacent to the solid/liquid interface during solidification.
In order to achieve the desired properties in the
alloys of the invention, the microstructure must be
essentially eutectic. In practice, we have found that
up to 10% of primary alpha-aluminium dendrites can be
tolerated without an excessive decrease in properties.
We have found that the
-- 10 --
presence of exeesslve amounts of alpha-aluminium
dendrites results in zones of weakness in the
mierostrueture. In addition, the presenee of
large primary intermetallic par-~icles, of a size
above about 10 microns in diameter ean have a
very detrimental effect on properties and must
be avoided.
Having selected an alloy composition within
the specified ranges, the eorreet microstrueture,
as stated previously, depends on the choice of
suitable solidification eonditions. Grow-th rates
must not be less than 150 microns per second or
more than 1000 microns per second. The upper and
lower limits of these rates are governed by the
well established coneept of "eoupled growth". This
eoneept involves the seleetive use of growth rates
and temperature gradients whieh enable wholly
eutectic mierostruetures to be produeed with off-
euteetie alloy compositions. Below 150 microns
per seeond primary intermetallie partieles may
form and the size of the euteetie intermetallie
particles might become too large (Fig. 1). Ab~ve
1000 microns per seeond an exeess of dendrites
of the aluminium rieh alpha phase oceurs (Fig. 2).
Temperature gradients must be eontrolled sueh
that the G/R ratio (temperature gradient/growth
rate) is within the range of 500-8000Cs/em .
--11--
- ~ ~7~
With correct growth rates and G/R ratios the
correct microstructure (Fig. 3) is produced.
It should be noted tha-t in any casting of
large sectional thickness all properties will
vary from the surface to the interior. While
this may be critica] for some applications, in
situations requiring wear resistance it is
usually not necessary to produce the optimal
microstructure right across large sectional
thicknesses. Normally it will be sufficient to
do so over sectional thicknesses not exceeding
2cm, providing of course, that these include
the actual working portion of the components
concerned.
The composition of the alloys in the present
invention requiresthe careful selection of alloying
elements and the correct proportions of each.
In most cases the effect of one element depends
on others and hence there is an interdependence
of the elements within the composition. In general,
levels of alloying elements above the maximum
specified for the alloys of the invention give
rise to excessively coarse primary (as-cast)
intermetallics.
In the alloys of the invention the intermetallic
compounds which form part of the eutectic micro
-12-
-
~75~
structure are based principally on the aluminium-
silicon-copper-nickel system. The eutectic intermetallic
particles are principally silicon but copper-nickel-
aluminium, copper-iron-nickel aluminium and other
complex intermetallic phases are also present. Naturally
as particle size increases so does the propensity for
cracking under applied loads. ~or this reason the
intermetallic particles comprising the eutectic must
be fine (less than 10 microns in diameter), preferably
uniformly dispersed and preferably with an inter-
particle spacing not greater than 5 microns. In
order to have the desired silicon morphology and
dispersion, it is essential that the silicon be in
the modified form. In the abovementioned composition
strontium is shown as the preferred modifier but
it will be understood that the selection of any of
the other known modifying elements, such as, for
example, sodium, will always be well within the
competence of the expert.
In addition to the eutectic intermetallic particles~,
- the alloys of the invention comprise a dispersion
of intermetallic precipitates within the alpha aluminium phase
o~ the eutectic. Such dispersion reinforces the matrix
and helps the loads to be transmitted to the eutectic particles
-13-
5~
and increases the ability for load sharing if any
one eutectic particle cracks. In the present
alloys we believe that the elements magnesium and
copper are responsible for strengthening the matrix
by precipitation hardening and/or the formation of
solid solutions. Strengthening is further enhanced
by the presence of stable manganese and/or zirconium
containing particles. We also include these elements
to improve high temperature resistance.
Copper and magnesium levels are such that
suitable dispersions of precipitates can form not-
withstanding that copper is inevitably present in
the cast eutectic intermetallics. The copper to
magnesium ratios are preferably within the limits
of 3:1 to 8:1. Below this ratio unfavourable
precipitates may form. Copper levels beyond the
specified limits may reduce the corrosion resistance
of the alloy in the applications.
Nickel, iron and manganese are particularly
effective for improving elevated temperature properties
and form a number o~ compounds with each other.
These elements are interchangeable to a certain
degree as shown below:
0.2 < Fe + Mn < 1.5
1.1 < Fe + Ni c 3.0
1.2 < Fe + Ni + Mn < 4.0
-14-
Alloys of the invention may therefore be primary
alloys with the lower Fe content ox secondary alloys
where the Fe levels may reach the maximum of the
specification. The manganese and nickel content must be
adjusted accordingly.
Titanium, because it is a well known grain refiner,
is added to improve castability and to improve the
mechanical properties of the alloy. Its addition in the
established Ti-B form is preferred.
While the alloys of the present invention have
excellent properties in the as cast condition, the
compositions are such that most properties can be
improved by heat treatment. It is understood, however,
that heat treatment is optional.
For example the cast alloy may be directly subjected to an
artificial ageing treatment at 160 - 220C for 2 - 16 hours.
A variety of other heat treatment schedules may be
employed and may include solution treatment at 480-530C
for 5-20 hours. These solution treatments are selected
to provide a suitably supersaturated solution of elements
in aluminium, whilst still providing a preferred
dispersion of eutectic particles i.e. a microstructure in
which the eutectic particles are less than 10 microns in
~ diameter, preferably equiaxed, preferably uniformly
dispersed and preferably with an interparticle spacing
not greater than 5 microns. Fig. 4
- 15 -
shows such a microstructure whilst Figs. 5 and 6
show solution treatment microstructures which
are not as satisfactory.
The solution treatment may be followed, after quenching, by
artificial ageing at 140-250C for 2-30 hours.
A typical heat treatment schedule may be as follows: -
8 hours at 500C;
- quench into hot water;
artificially age at 160C for 16 hours.
The microstructure produced by this heat
treatment is shown in Fig. 4.
The following non-limiting examples illustrate
the superiority of the alloys of the invention:
Example 1
Alloys according to the invention were prepared
as cast-to-size tensile and compression samples.
The samples were of the following composition:
Si 14.2 ~t%
Fe 0.25 Wt%
Cu 2.0 wt%
rlg 0.5 wt%
Ni 2.5 wt%
~ln 0.4 wt%
Zr 0.05 wt%
Sr 0.01 wt%
Ti 0.04 wt%
Al - ~emainder, apart from impurities.
--16--
: ' :
and were solidified at a growth rate of approximately
200~ms 1 and G/R ratlos of approximately 1300C s/cm .
Mechanical properties of -the as-cast and heat
treated samples at ambient and elevated temperatures
were determined and are shown in Tables 1 and 2.
The ambien-t temperature ultimate tensile
strength, hardness, 0.2% compressive yield strength
and Young's modulus are superior to most aluminium
casting alloys. We believe that the coefficient
of thermal expansion and the high temperature
properties are equal to the best that can be obtained
with the known, highest strength aluminium alloys
(Table 3).
~5~8~
T E_
,_ _ _
Temper As cast T5 T7 T6
(5hrs at Solution treated Solution treated
190C) for 8hrs at for 8hrs at
520C, quenched 520C, quenched
into hot water into hot water
(~60C)and then (>60C) and then
aged for 5hrs. a~ed for 16hrs.
at 220C. at 160C.
__ _.. __ . ._ __ .... _ _
Ultimate
Tensile 225 265 310 375
(k~a)
~__ _. _ _ ._ _ __
Hardness
(BHN) 110 125 135 155
_ _ . _ .. _ _ ~
0.2%
Compressive
Yield 245 320 365 445
Strength
(k~a)
. __ _ .
Young's
Modulus
Elasticity 8.3x104 _ _ 8.3x104
. . . __ _. , .
Coeff. Of
Thermal
Expans. 6
(mm/mm/C in ~9.5xlO- _ _ l9.0xlO-
the temp.range
20-100C)
~___ _ . _ . _ _
-18-
TABLE _
. _
Ultimate Tensile Strength (MPa)
TestingHours at
Temp . Temp As- Cast ~ T~ T6
150 1 235 245 290 355
_ 1000 235 2~5 280 310
200 1 230 230 260 325
1000 200 205 23~ 225
250 1 200 185 220 235
1000 145 155 150 145
~,
-- 19 --
I
-
~t7~
~ ~ __ o _ _ x o,
~ ~ ~ ~ ~ r~
:~OE~ _ _ ~
.
_ ~: t- ~ $ l l
!
l O O O O O
3 ~:) `S) ~ .r) ~`J X
C~ ~ ~ ~ r~ ~
~lEo~ ~
~l 00~~0 ~ _ ~
;~ . U~ O O
-Cl ~ ~: ~o C~ ~0 l ~`I O
_ _ _
~ ~ol
JC: ~C) u~ ~1 Ul ~ ~X
O ' ~-~) ~ ~ ~ ~1 O
S~r~ I Xl O~
~ _ _ _ ~ _ .
_ ~ o o
' '1: ~C~' ~ u~ ~ ~0 ~ X X
_ C _ . o~ a~
J r. ~ ~
0 h O 0 e
E
~ E- ~ _~ 3 ~ _ ~
:.~ Ll )~ ~ ~4 O o E E -
o E ~ Cr ~ ~ ~ o ~,
~ ~~ _~ oo ~ C~ _ ~ . U~ ~ o
E-E C--~ --a~ ~ e ~ ~ ~ - ~ o
. C ~ ~ ~ 5: ~ :~ C C ~ I
~ C, ._, - ~ ~ . .~ ,~ o ~ ~ o X C: o
--
Example 2
Alloys of the invention were compared with
other aluminium casting alloys in terms of dimensional
stability, castability, machinability and corrosion
resistance ~Table 4).
The dimensional stability o the present alloys
is considered better than the common hypoeutectic
Al Si alloys and similar to the excellent stability
of the hypereutectic 390 alloy. After 1000 hours
of service at 200C the dimensional change for the
as-cast alloys of the present invention is less
than 0.9%, for the alloys in the T6 temper is
less than 0~04% and for the alloys in the T5 and
T7 tempers is less than 0.02%.
The casting characteristics of the alloys of
the invention are also very good and have the
excellent fluidity and freedom from hot shoxtness
that the hypereutectic A1-Si alloys possess. However,
the alloys of the invention do not suffer, as the
hypereutectic Al-Si alloys can do, from the segregation
Of large primary intermetallic particles.
During the machining of hypoeutectic Al-Si
alloys material generally builds up on the tool
tip which reduces the quality of the surface finish~
This does not occur with hypereutectic alloys
but tool wear is generally very highO Neither
-21~
build-up nor excessive tool wear occurs with
the alloys of the present invention.
Aluminium alloys generally have excellent
corrosion resistance. This has been shown to be
particularly so for the alloys of the invention
in both atmospheric conditions and also in engine
coolant circuit conditions. In the latter, corrosion
paths have been found to ~ollow closely the semi-
continuous silicon networks. However, when the
silicon particles are homogeneously dispersed~any
corrosion that occurs does so uniformly rather
than in a localized, damaging manner. For this
reason the continuous dispersion of modified
eutectic Si particles, which are present in the
alloys of the invention, reduces corrosion suscept-
ibility. Under simulated englne coolant conditions
(ASTM D2570) corrosion rates were generally less
than for those alloys (Australian alloys 601, 309,
313) presently used for cylinder heads and a~ter
650 hours of servi~e were of the order of 7xlO 3in/
year and 4xlO in/year for the as-cast and heat
treated (T6) alloys of the present invention,
respectively.
22
~.~7~
TABLE 4
_ _ .
Alloy Dimensional Change Cutting Speeds Corrosion Resistance
`i m/min (in./yr.)-ff^'
(Machinability)-^~
_
Temper As-Cast T5 T5 T6 T6
_ _
Alloy with- -3
in spec. of 0.09 0.02 400 400 4xlO
the present
invention
(Example l)
_ _ _
Hypereutectic
390 Alloy 0.08 0.01~100 <100
I Hypoeutectic 3
601 Alloy _0.15 _0.1 450 300 5xlO
1, , _
* Permanent dimensional change observed with samples after 1000 hours
I at 200C.
Cutting speeds in m/min which give approximately 20 minutes of
tool-life in lubricated, face-milling tests.
; Corrosion rates obtained after 650 hours of testing in a simulated
engine coolant test-rig (ASTM D2570 standard test).
- 23 -
i
5~
Examp e 3
A possible application for alloys with excellent
wear resistance is the production of automotive
cylinder heads with a reduced need for inserts in
the valve seat and valve guide regions. For this
application the alloy must resist both the wear
at the valve seats due to abrasîon, valve rotation
and continued cycles of compressive loads as well
as the wear at the valve guides due to a sliding
nature.
In order to assess the perfo~nance of various
alloys as valve seat materials, the alloys were
tested under conditions approximately those believed
to exist in actual practice. To this end a simulative
test-rig of the type shown in Fig. 7 was used.
It is believed that plastic deformation of
the valve seat area due to the com~ust;on pressure
(a cyclic compressive load~ ;s the main cause of
valve seat wear or recession. The stresses so
imposed are thought to range from 25-63MPa for the
popular engine designs in use in Australia. In
order to expedite comparative results these loads
were increased to 262.5MPa in the rig.
All tests were carried out at 185 C. The
fre~uency of loading in the ri~ was 3~hz (=engine
- speed of ~lOOr.p.m.~, which is in the range found
-24-
:, ..
in a four-stroke engine. All samples tested were
solution treated at 500-525C for 8 hours, quenched
in boiling water and then artificially aged a-t 180 C
for 4 hours.
The test results together with the chemical
compositions, growth rates and G/R ratios are given
in Table 5.
' Alloys 1 and 2 in the table were also tested
under dynamometer conditions; alloy 1 was found
clearly unsatisfactory; alloy 2 only mar~inally
satisfactory. Alloy 2 represents a conventional
automotive alloy which is regarded as amongst the
best of the commercial alloys for applications of
this type. In comparison with the performance
of this alloy in the simulative test rig, the
performance of the alloys of the invention (i.e.
alloys 7 and 8) was very superior.
Tests were also conducted at lower loads,
showing that a reduction in load of only 10%
increased life by 80%. Specifically, some 26
- further samples were tested to failure in the
simulative test rig at a temperature of 185C,
Fig. 8 shows the valve seat lives obtained as
a function of the applied stress.
Samples designated ~ and ~ represent the invention
with the material of the latter being in the "as
, -25-
,
cast" and of the former in the fully heat treated
condition (T6 temper).
The chemical compositions were within the
following limits by weight:
Si 13 - 15 %
Fe 0.3 - 0.4%
Cu 2.0 - 2.2%
Mg 0.4 - 0.6%
Zr 0.04 - 0.06%
Ni 2.0 - 2.5%
Mn 0.4 - 0.5%
Sr 0.03 - 0.05%
Ti 0.05 - 0.07~
Growth rates were between 300-700~ms and G/R
ratios were between 1000-2000Cs/cm~.
Samples designated o represent a conventional
automotive alloy 390 as referred to in Example l
Table 3.
This is regarded as among the best of the
commercial alloys for applications of this type.
It will be seen that the performance of the alloys
of the invention exceeds that of the conventional alloy.
--26--
~7~ 7
In order to assess the performance of various alloys
as valve guide materials, accelerated sliding wear
tests were conducted.
These were carried out with a pin-on disc arrangement
in which an aluminium pin was rubbed, under an applied
stress of 3.6kPa, against a EN25 steel disc. The sliding
speed was 3msec 1 and the tests were conducted dry.
The actual mechanisms of plastic deformation leading
to wear in this accelerated sliding wear situation were
very similar to the mechanisms causing wear under the
cyclic compressive situation. It was found, therefore,
that the same excellent wear resistance obtained in
the cyclic compressive testing for alloys of the invention
was xepeated in the sliding tests (Table 6). The
performance of these alloys was clearly superior when
compared with other alloys having reasonable sliding
wear resistance.
With such superior performance in both the simulated
valve seat and valve guide tests the alloys of the
invention might well reduce the need for inserts in
aluminium cylinder heads.
-
- ~ --~ - ---
o o`
v ~ _ ~ ~ o ~ ~.~ u .A ~ V ~.J ,C ~ V
~ Cl. C 1~. C 3 .~ ~ . V, V Q. C v C c ~: C -8 c _ ~ 0
~ v ~o U ~ ~, o ~ .J ~ 3 ~ v v ~ u ~ ~ ~ o ~ ~ ~ c ~ ~ û '~'
o Y 0 ~ ~ ~7 _ c ~ 0 c ~ v 8 ~ ~ ~ tJ
yo oo c o ~ ~ ~ a C ~ 8 0. ~ o v~ v ~ ~ ~ 0 ~ 0 0 0
__ ~ D. ~ C~ -- V ~ O. ~ L ~ ~ ~ ~ .a ~ vl ~. D. .. .
~o¢~0
O tgD O g O rg~ O O
~ _~ ~ V r~ ~ ~ u~ r~ ~D ~ .r
~ ~ O ~ ~ O O _
~ X ~O ~ 3~ ~ ~` ~ O
~ _ . _
~ ~ O O O O O O O O
O ~ ~ g o g v~ g ~n u~
~ 0~ ~ ~ r~ r~ ~r ~ _
¢ _ _ ._ _.
~nl ~1", " g g o g o g g g
¢l ~ ~ u~ u~ ~ .~
_
C~ U~ U~ ,~ CO ~ .o
O O O O ~, ~ O O O O
1~ O O D O _ O __ O O O
:i: O ~ O O - ~ ---V,
:1: _ __ 7 O ~11 rl u o
O ~ ~ l O O O O O O
~5 ~ ~ UOl -- _ O ~ CO ~ ' U~
:~: O O O O O O O .__
B o o ~o ID
- - - - ~ - -- - -
~ ~ ~0 ~ ~O ~ ~ ~ ~D
~ o l o o o o- o o ~
u~ _ _~ _~ ~r
~ _l ~i r~ . _ ~ I_--.
¢ - - -
~- - 28 -
L r7 5i 6 ~ 7
TABLF._
Alloy No* Temper As-Cast Average Sliding Average Sliding
Microstructure Distance Prior Distance at
to any Wearwhich the Alloy
being Detected Pin has Re
(cmxlO5) cessed O.lmm
(cmxlO5)
1 T5"'-
,~,~-Dendrites 7.1 7.4
T6 8.0 12.7
2 T5***Primary 1.2 7.3
T6Intermet.allics 5.4 12.5
7 As-CastFully 7.4 11.4
_ T6 Eutectic 9.6 17.6
* Alloy N refers to the same Alloy Ns in Table 5.
** Aged 4hrs. at 180C.
*** . Aged 6hrs. at 200C.
.
-- 2 9 -
.
Example 4
Alloys of different compositions but conforming to the specifications
of the invention were also tested in -the sirnulative test rig (compressive
loading) under the same temperature and frequency conditions as for Example 3
and at a load of 262.5 MPa. The test results are given in Table 7.
An alloy composition within the preferred composition range provided
the best wear resistance while compositions outside this preferred composition
range but within the specification of the invention gave lesser wear resistance
but levels which were still significantly superior to other alloys.
The microstructure of an alloy within the broad specifications
of the invention is shown in Figure 9. This alloy conforms to the preferred
composition of the invention in al] aspects except for the high Fe content
(0.55 wt.%). The microstructure of this alloy is a result of specific solidification
conditions (G equal to 600~msl and G/R equal to 1300C s/cmZ) and heat treatmentconditions (solution treated 8 hours at 500C, aged 16 hours at 160C). ~aturally
with the different solidification and heat treatment conditions as allowed
within the specification of the invention, slightly different microstructures for
this alloy can be obtained.
- 30 -
~75~
., . .
aJ, o ~ ~ a~ ~ o
d P~ ~ I ~:4 ~ u~ ~ ,
E ~ '4 ~ I E ~ ?~
d 5~ ~ s~ d
~ o C o ~ o O ~ O ~ o (J
(~ O ~ ~ 0 ~7 ~
O ~) 0 ( ) ~ 0 I~J ~ 0 rl rl
rl ~) E 0 ~ 0 ,~ 5 C:
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.
U~ o o o
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0 ~j ,V~ 0 U~
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0 1 1 ~:: " ~ . o~
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r~ Llrl 0 C~ ~ q) X ~
rl O O O
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oo o o o
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r~ C~ ,
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o o o
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d n o o ~
o Z C~ C`i C~l
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o o~ C~ U~ ~:
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- 31 -
~75~
Example 5
Another possible application for alloys having
excellent wear characteristics is in many types of
compressor uni-ts where the aluminium is in rubbing
contact with soft types of seals and rotors and both
mating surfaces need to remain as smooth as possible.
Testing has been carried out to assess the performance
of various aluminium alloys in this application.
Examp]es of the surface roughness of aluminium alloys
after prolonged periods of testing in this application
are shown in Figs. 10 and 11. The results shown are for
three alloys:
(a) a hypoeutectic alloy CP 601 (Table 4) of
good strength and hardness with a composition of:
7.0Si, 0.2Fe, 0.35Mg, 0.02Sr, and 0.03Ti (Figs. lO~a)
and ll(a).
(b) the high strength, hypereutectic Al-Si alloy,
390, (see Example 1) commonly used for wear resistant
applications (Figs. lO(b) and ll(b) ).
(c) an alloy of the present invention having a
composition the same as that given in Example 1 and
whose wear surface structure approximated to that
achieved with a growth rate of approximately 400~ms 1 and
a G/R ratio of approximately 2500Cs/cm (Figs. lO(c) and ll(c) ).
I-t is very evident, that with prolonged testing,
the aluminium matrix in the hypoeutectic alloy (containing
- 32 -
7~ ~ ~t~
~-dendrites) was deformed and small amounts ultimately
removed from the surface. This wear "debris" then
acted as an abrasive medium to produce further wear
of the two contacting surfaces. With the hypereutectic
alloy, the large primary intermetallics in this structure
directly abraded the softer material. Microcracks
also initiate~ in and near the large intermetallics
which resulted in'detachment of metal. The fully eutectic
alloys of the present invention, however, were very
resistant to any form of delamination and did not
damage the softer, contacting surface - in fact a
polishing action was obtained.
~3~-
~75~7
Example 6
The Si particles in the alloys of the invention can be modified
by elements other than strontium and in -this example sodium is shown to be
a suitable modifier. In Figure 12, a microstructure is shown which was obtainedby solidifying at a growth rate of 700~ms l and a G/R ratio of 1300C~s/cm2
and the composition of which was:
Si14.0 wt%
Cu2.2 wt%
Ni2.1 wt%
Mg0.45 wt%
Fe0.30 wt%
Mn0.45 wt%
Zr0.05 wt%
Na- 0.01 wt%
Ti0.05 wt%
A~Remainder, apart from impurities
- - 34 -
