HOT CHAMBER CASTABLE ZINC ALLOY

ALLIAGE DE ZINC COULABLE EN CHAMBRE CHAUDE

English Abstract

The alloy contains, in % by weight:
a) either 15-20 Al and 8-10 Cu, or 25-30 Al and
15-20 Cu; and
b) 0.01-2 Si, 0-0.1 Mg, 0-0.5 Ti, 0-0.5 Cr,
0-1 Mn, 0-0.5 Nb and 0-0.1 of a rare-earth
metal or metal mixture, the remainder being
zinc.
This alloy has a good creep resistance and an
excellent tensile strength when it contains 15-20 Al
and 8-10 Cu and an excellent creep resistance and a
good tensile strength when it contains 25-30 Al and
15-20 Cu.

French Abstract

L'alliage contient, en % en poids: (a) soit 15-20 Al et 8-10 Cu, soit 25-30 Al et 15-20 Cu; et (b) 0,01-2 Si, 0-0,1 Mg, 0-0,5 Ti, 0-0,5 Cr, 0-1 Mn, 0-0,5 Nb et 0-0,1 d'un métal ou d'un mélange de métaux des terres rares, le reste étant du zinc. Cet alliage présente une bonne résistance au fluage et une excellente résistance à la traction, lorsqu'il contient 15-20 Al et 8-10 Cu, et une excellente résistance au fluage et une bonne résistance à la traction, lorsqu'il contient 25-30 Al et 15-20 Cu.

Claims

-6-
CLAIMS
1. ~Zinc-based alloy containing Al and Cu, which
can be cast under pressure in a hot-chamber machine,
characterized in that it contains, in % by weight,
15-20 Al, 8-10 Cu, 0.01-2 Si, 0-0.1 Mg, 0-0.5 Ti,
0-0.5 Cr, 0-1 Mn, 0-0.5 Nb and 0-0.1 of a rare-earth
metal or metal mixture, the remainder being zinc and
the impurities unavoidably present in zinc and the
abovementioned alloying elements.
2. ~Zinc-based alloy containing Al and Cu, which
can be cast under pressure in a hot-chamber machine,
characterized in that it contains, in % by weight,
25-30 Al, 15-20 Cu, 0.01-2 Si, 0-0.1 Mg, 0-0.5 Ti,
0-0.5 Cr, 0-1 Mn, 0-0.5 Nb and 0-0.1 of a rare-earth
metal or metal mixture, the remainder being zinc and
the impurities unavoidably present in zinc and the
abovementioned alloying elements.
3. ~Alloy according to Claim 1, characterized in
that it contains 15-18 Al.
4. ~Alloy according to Claim 2, characterized in
that it contains 25.5-28.5 Al and 15-18 Cu.
5. ~Alloy according to any one of Claims 1-4,
characterized in that it contains 0.1-1 Si.
6. ~Alloy according to any one of Claims 1-6,
characterized in that Zn, Al and Cu have a purity of
.cndot. 99.99 %, .cndot. 99.95 % and .cndot. 99.99 % respectively.
7. ~Process for the manufacture of articles made of
a zinc-based alloy containing Al and Cu by casting
under pressure in a hot-chamber machine, characterized
in that the alloy is the alloy according to Claims 1-6
and in that the casting is performed at a temperature
equal to or lower than 460°C.
8. ~Process for the manufacture of articles made of
a zinc-based alloy containing Al and Cu by casting
under pressure in a cold-chamber machine or by gravity
casting, characterized in that the alloy is the alloy
according to Claims 1-6.
9. ~Use of the alloy according to Claims 1-6 as
antifriction material.

Description

CA 02185013 2005-10-04
Hot chamber castable zinc alloy
The present invention rel.~3tc.~~ t.o a zinc-based
alloy containing Al and Cu, which can be cast under
S pressure in a hot-chamber machine.
Such an alloy is described in the document
"SAE technical paper series 930788. ACuZinc . improved
zinc alloys for die casting application, M.D. Hanna and
M_S. Rashid. International Congress and Exposition
Detroit, Michigan, March 1-5, 1993." This known alloy,
rM
called "ACuZinc 5" consists of 5.0-6.0 °~ of Cu, 2.8
3.3 g of A1 and 0.025-0.05 ~ of Mg, remainder Zn (all
the percentages given in the present patent application
are ~ by weight). The creep resistance of this alloy,
TM
~5 while substantially superior to that of the Zamak or ZA
alloys which for a long time have been cast in a hot
chamber, is still relatively low.
The aim of the present invention is to
provide an alloy as defined above which has a better
creep resistance than the abovementioned known alloy.
To this end, according to the invention, the
alloy contains, in ~ by weight:
either 15-20 A1, 8-10 Cu, 0.01-2 Si, 0-0.1 Mg,
0-0.5 Ti, 0-0.5 Cr, 0-1 Mn, 0-0.5 Nb and 0-0.1 of
a rare-earth metal or metal mixture, this
composition being called hereinafter variant I,
or 25-30 Al, 15-20 Cu, 0.01-2 Si, 0-0.1 Mg, 0-0.5 Ti,
0-0.5 Cr, 0-1 Mn, 0-0_5 Nb and 0-0.1 of a rare
earth metal or metal mixture, this composition
3o being called hereinafter variant II,
the remainder being zinc and the impurities unavoidably
present in zinc and the abovementioned alloying
elements.
It has been found, in fact, on the one hand
3S that the two variants in the liquid state, at
temperatures not exceeding 460°C, exhibit such a low
aggressivity towards steels that they can be cast in a
hot chamber and, on the other hand, that:., in the cast
state, variant I exhibits a good creep resistance and
4u an excellent tensile strength, whereas, in the cast

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state, variant II exhibits an excellent creep
resistance and a good tensile strength. The A1 and Cu
contents referred to above must be adhered to;
otherwise the melting point of the alloy rises above
450°C and the result of this is that the alloy is no
longer castable in a hot chamber because its
corrosivity towards the casting equipment becomes too
great above 460°C. If the silicon content is lower than
0.01 o the tensile strength and the creep resistance
worsen. A silicon content of more than 2 ~ makes the
alloy too pasty and too corrosive in the molten state.
It is appropriate to report here that the
following alloys have already been described:
(a) 17-19 Al, 4.5-5.5 Cu, 0.9-1.3 Si, 0.8-1.2 Mg,
IS remainder Zn (CS-A-135802)
(b) 28.6 A1, 3.1 Cu, 1 Si, 0.1 Ca, 0.2 Ni, remainder
Zn (GB-A-769483)
(c) 20-40 A1, 0-5 Cu, 0-1 Si, 0-0.1 Mg, 0.25-2 of at
least one rare-earth metal, remainder Zn
(US-A-4789522)
(d) 55 A1, 8 Cu, 6.5 Si, 4.5 Be, 0.12 Ni, 0.6 Ca,
remainder Zn (US-A-287008)
Among these known alloys the alloys (a) and (c) are
those most closely related to the alloy according to
the invention. Alloy (a) has too low a Cu content and
too high an Mg content to be capable of being cast in a
hot chamber. Alloy (c) also has too low a Cu content;
furthermore, it is extremely difficult to prepare an
alloy containing 0.25-2 ~ of rare-earth metals, even if
only in the oxidized state, because of the high
affinity of these metals for oxygen.
Variant I advantageously contains 15-18 0
and, preferably, 15-17 ~ Al.
The preferred A1 and Cu contents of variant II are
25.5-28.5 ~ and 15-18 ~ respectively.
The preferred Si content of both variants is 0.1-1 ~.
Both variants may contain
- up to 0.1 ~ Mg to improve, if need be, the
intercrystalline corrosion resistance;

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- up to 0.5 ~ Ti, up to 0.5 ~ Cr and up to 1 °s Mn
to improve, if need be, the ductility;
- up to 0.5 ~ Nb to improve, if need be, the
resistance to external corrosion, that is to
say to retard the formation of white salts; and
- up to 0.1 ~ of a rare-earth metal or metal
mixture to lower, if need be, the surface
tension of the alloy in the molten state.
An Mg content of more than 0.1 ~ makes the
alloy pasty in the molten state and brittle in the
solid state. The alloy also becomes pasty when the
l imits indicated above f or Ti , Cr and Mn are exceeded .
Nb contents of more than 0.5 ~ and rare-earth metal
contents of more than 0.1 ~ are difficult to implement
because of the high affinity of these elements for
oxygen.
It is desirable that the Zn, A1 and Cu which
are employed for manufacturing the alloy should have a
purity of _> 99.99 ~, >_ 99.95 ~ and >_ 99.99
respectively, because it has been found that the
presence of impurities in the alloy unfavourably
affects its fluidity and its mechanical properties.
Zinc of a purity of - 99.995 ~ and aluminium of a
purity of - 99.97 ~ are preferably employed.
It is obvious that, when the alloy contains a
metal which has a very high affinity for oxygen, such
as, for example, Y, at least a proportion of this metal
may be present in the oxidized state.
The good creep resistance of variant I and the
excellent creep resistance of variant II of the alloy
according to the invention are illustrated by the
description, below, of a series of comparative tests
the results of which are given in the diagram enclosed
herewith.
Two known alloys, Zamak 5 and ACuZinc 5, have
been tested, together with two alloys according to the
invention, a first according to variant I, which will
be denoted hereinafter by "X27" and a second according

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to variant II, which will be denoted hereinafter by
"X28".
Composition of these alloys:
- Zamak 5: 4 ~ A1, 1 ~ Cu, 0.04 ~ Mg, remainder
Zn;
- ACuZinc 5: 3 % A1, 5.5 ~ Cu, 0.04 ~ Mg,
remainder Zn;
- X27: 17 ~ Al, 9.5 ~ Cu, 0.5 ~ Si,
remainder Zn;
t0 - X28: 27 ~ Al, 16.5 ~ Cu, 0.1 ~ Si,
remainder Zn.
Test pieces of these alloys were cast in a hot-
chamber machine.
The general casting conditions were as follows:
- cycle time: 12 seconds
- bath temperature: 420-460°C
- pressure exerted on the metal: 50 MPa
- piston speed: 1.2 m/s
- nozzle diameter: 9.5 mm
- mould temperature: 180-250°C
The form and the dimensions of these test pieces are
those specified by the European Zinc Producers'
Technical Committee for the test pieces to be employed
in the tensile test on sheets and foils made of zinc
and zinc alloys.
The test pieces were subjected to the creep
test at 100°C under a load of 40 MPa. The creep curves,
which give the elongation (in ~) measured as a function
of time (in hours), are shown in the diagram enclosed
herewith.
It is seen that the alloys according to the
invention, and especially the alloy according to
variant II, resist creep much better than the known
alloys.
The excellent tensile strength and the very
high hardness of variant I and the good tensile
strength and the appropriate hardness of variant II of
the alloy according to the invention are illustrated by
the data listed in the table below.

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TahlP
Alloy Tensile strength Vickers hardness
(MPa) (5 kgf)
Zamak 5 286 105
ACuZinc 5 270 -
X27 435 181
X28 276 140
The tensile tests were performed at ambient
temperature with a pull speed of 1 cm/min on test
pieces of 3-mm thickness, manufactured as described
above.
The present invention also relates to a process
for the manufacture of articles made of a zinc-based
alloy containing A1 and Cu by casting under pressure in
a hot-chamber machine, this process being characterized
in that the alloy is the alloy of the invention and in
that the casting is performed at a temperature equal to
or lower than 460°C.
As the alloy of the invention can be cast in a
hot chamber, it is necessarily capable of being cast in
a cold chamber and under gravity.
The present invention therefore also relates to a
process for the manufacture of articles made of a zinc-
based alloy containing Al and Cu by casting under
pressure in a cold-chamber machine or by gravity
casting, this process being characterized in that the
alloy is the alloy of the invention.
The present invention additionally relates to the use
of the alloy according to the invention as an
antifriction material.

Representative Drawing