EP0771365B1 - Hot chamber castable zinc alloy - Google Patents

Abstract

Alloy containing, in percentage 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, 0-1Mn, 0-0.5 Nb and 0-0.1 of a metal or a mixture of rare earth metals, the remainder being zinc. The alloy has excellent creep and tensile strength, when it contains 15-20 Al and 8-10 Cu weight percent, and excellent creep and tensile strength when it contains 25-30 Al and 15-20 Cu.

Description

The present invention relates to a zinc-based alloy containing Al and Cu, flowable under pressure in a chamber machine hot.

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, called "ACuZinc 5" consists of 5.0-6.0% Cu, 2.8-3.3% Al and 0.025-0.05% of Mg, remains Zn (all percentages given in this patent applications are% by weight). The creep resistance of this alloy, although appreciably superior to that of alloys Zamak or ZA sunk for a long time in a hot chamber, is still relatively small.

The object of the present invention is to provide an alloy such as defined above, which has better creep resistance than the aforementioned known alloy.

soit

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 et 0-0,1 d'un métal ou d'un mélange de métaux des terres rares, cette composition étant appelée ci-après variante I,

soit

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 et 0-0,1 d'un métal ou d'un mélange de métaux des terres rares, cette composition étant appelée ci-après variante II,

le reste étant du zinc et les impuretés inévitablement présentes dans le zinc et les éléments d'alliage précités.
En effet, il a été trouvé d'une part que les deux variantes présentent à l'état liquide, à des températures ne dépassant pas 460°c, une si faible agressivité vis-à-vis des aciers qu'elles sont coulables en chambre chaude et d'autre part que la variante I présente à l'état coulé une bonne résistance au fluage et une excellente résistance à la traction, tandis que la variante II présente à l'état coulé une excellente résistance au fluage et une bonne résistance à la traction. Les teneurs en Al et Cu, mentionnées ci-dessus, doivent être respectées ; autrement, le point de fusion de l'alliage monte au-dessus de 450° C, ce qui a pour conséquence que l'alliage n'est plus coulable en chambre chaude, car son agressivité vis-à-vis de l'équipement de coulée devient trop grande au-dessus de 460°C. Si la teneur en silicium est inférieure à 0,01 %, la résistance à la traction et la résistance au fluage se détériorent. Une teneur en silicium de plus de 2 % rend l'alliage, à l'état fondu, trop pâteux et trop agressif.To this end, according to the invention, the alloy contains, in% by weight:

is

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 metal or a mixture of rare earth metals, this composition being hereinafter called variant I,

is

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 metal or a mixture of rare earth metals, this composition being hereinafter called variant II,

the remainder being zinc and the impurities inevitably present in the aforementioned zinc and the alloying elements.
Indeed, it has been found on the one hand that the two variants have in the liquid state, at temperatures not exceeding 460 ° C., such low aggressiveness with respect to steels that they are pourable in the chamber hot and on the other hand that variant I has in the cast state a good creep resistance and an excellent tensile strength, while variant II has in the cast state an excellent creep resistance and a good resistance to traction. The contents of Al and Cu, mentioned above, must be respected; otherwise, the melting point of the alloy rises above 450 ° C, which has the consequence that the alloy is no longer pourable in a hot chamber, because its aggressiveness towards the equipment of flow becomes too large above 460 ° C. If the silicon content is less than 0.01%, the tensile strength and creep resistance deteriorate. A silicon content of more than 2% makes the alloy, in the molten state, too pasty and too aggressive.

(a) 17-19 Al, 4,5-5,5 Cu, 0,9-1,3 Si, 0,8-1,2 Mg, reste Zn (CS-A-135802)

(b) 28,6 Al, 3,1 Cu, 1 Si 0,1 ca, 0,2 Ni, reste Zn (GB-A-769483)

(c) 20-40 Al, 0-5 Cu, 0-1 Si, 0-0,1 Mg, 0,25-2 d'au moins un métal des métaux des terres rares, reste Zn (US-A-4789522)

(d) 55 Al, 8 Cu, 6,5 Si, 4,5 Be, 0,12 Ni, 0,6 Ca, reste Zn (US-A-2870008) Parmi ces alliages connus, les alliages (a) et (c) sont les plus proches de l'alliage selon l'invention. L'alliage (a) a une teneur trop faible en Cu et une teneur trop élevée en Mg pour qu'il puisse être coulé en chambre chaude. L'alliage (c) présente également une teneur trop faible en Cu ; par ailleurs, il est extrêmement difficile de préparer un alliage contenant 0,25-2 % de métaux des terres rares, ne fût-ce qu'à l'état oxydé, à cause de la grande affinité de ces métaux pour l'oxygène.

It should be noted 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, residue Zn (CS-A-135802)

(b) 28.6 Al, 3.1 Cu, 1 Si 0.1 ca, 0.2 Ni, residue Zn (GB-A-769483)

(c) 20-40 Al, 0-5 Cu, 0-1 Si, 0-0.1 Mg, 0.25-2 of at least one metal of the rare earth metals, residue Zn (US-A-4789522 )

(d) 55 Al, 8 Cu, 6.5 Si, 4.5 Be, 0.12 Ni, 0.6 Ca, Zn residue (US-A-2870008) Among these known alloys, the alloys (a) and ( c) are the closest to the alloy according to the invention. The alloy (a) has too low a Cu content and a too high Mg content for it to be poured in a hot chamber. Alloy (c) also has too low a Cu content; moreover, it is extremely difficult to prepare an alloy containing 0.25-2% of rare earth metals, even in the oxidized state, because of the great affinity of these metals for oxygen.

• jusque 0,1 % Mg pour améliorer, si nécessaire, la résistance à la corrosion intercristalline ;
• jusque 0,5 % Ti, jusque 0,5 % Cr et jusque 1 % Mn pour améliorer, si nécessaire, la ductilité ;
• jusque 0,5 % Nb pour améliorer, si nécessaire, la résistance à la corrosion externe, c'est-à-dire pour retarder la formation de sels blancs) ; et
• jusque 0,1 % d'un métal ou d'un mélange de métaux des terres rares pour diminuer, si nécessaire, la tension superficielle de l'alliage à l'état fondu.

Variant I advantageously contains 15-18% and preferably 15-17% Al.
The preferred Al and Cu contents of variant II are 25.5-28.5% and 15-18% respectively.
The preferential Si content of the two variants is 0.1-1%.
Both variants may contain

• up to 0.1% Mg to improve, if necessary, the resistance to intercrystalline corrosion;
• up to 0.5% Ti, up to 0.5% Cr and up to 1% Mn to improve, if necessary, the ductility;
• up to 0.5% Nb to improve, if necessary, the resistance to external corrosion, i.e. to delay the formation of white salts); and
• up to 0.1% of a metal or a mixture of rare earth metals to reduce, if necessary, 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 fragile in the solid state. The alloy also becomes pasty, when the limits given above for Ti, Cr and Mn are outdated. Nb contents of more than 0.5% and Nb contents rare earth metals of more than 0.1% are difficult to achieve because of the great affinity of these elements for oxygen.

It is desirable that the Zn, Al and Cu, used to manufacture the alloy, have a purity of ≥ 99.99%, ≥ 99.95% and ≥ 99.99% respectively, because it has been found that the presence in the alloy of impurities adversely affects its fluidity and mechanical properties. We preferably uses zinc with a purity of ≥ 99.995% and aluminum with a purity of ≥ 99.97%.

It is obvious that, when the alloy contains a metal having a very high affinity for oxygen, such as for example Y, at least one part 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 tests comparison, the results of which are given in the attached diagram.

• Zamak 5 :    4% Al, 1% Cu, 0,04% Mg, reste Zn ;
• ACuZinc 5 :    3% Al, 5,5% Cu, 0,04% Mg, reste Zn ;
• X27 :    17% Al, 9,5% Cu, 0,5% Si, reste Zn ;
• X28 :    27% Al, 16,5% Cu, 0,1% Si, reste Zn.

Two known alloys, Zamak 5 and ACuZinc 5, were tested, and two alloys according to the invention, a first according to variant I, which will be designated below by "X27" and a second according to variant II, which will be designated below. -after by "X28"
Composition of these alloys:

• Zamak 5: 4% Al, 1% Cu, 0.04% Mg, residue Zn;
• ACuZinc 5: 3% Al, 5.5% Cu, 0.04% Mg, residue Zn;
• X27: 17% Al, 9.5% Cu, 0.5% Si, remains Zn;
• X28: 27% Al, 16.5% Cu, 0.1% Si, remains Zn.

• temps de cycle : 12 secondes
• température du bain : 420-460°C
• pression exercée sur le métal : 50 MPa
• vitesse du piston : 1,2 m/s
• diamètre de buse : 9,5 mm
• température du moule : 180-250°C

Test pieces of these alloys were poured into 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
• mold temperature: 180-250 ° C

The shape and dimensions of these test pieces are those prescribed by the Technical Committee of European Zinc Producers for specimens to be used in the tensile test of sheets and sheets 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, giving the elongation (in%) measured as a function of time (in hours), are represented at attached diagram.

It can be seen that the alloys according to the invention, and in particular the alloy according to variant II, resist creep much better than known alloys.

The excellent tensile strength and very high hardness of variant I and the good tensile strength and suitable hardness of variant II of the alloy according to the invention are illustrated by the data given in the table below. below. Alloy Tensile strength (Mpa) Vickers hardness (5 Kgf) Zamak 5 286 105 ACuZinc 5 270 - X27 435 181 X28 276 140

The tensile tests were carried out at room temperature with a pulling speed of 1 cm / min on test pieces of thickness of 3 mm, manufactured as described above.

The present invention also relates to a manufacturing process articles of a zinc-based alloy containing Al 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 carried out at a temperature equal to or lower than 460 ° C.

As the alloy of the invention is pourable in a hot room, it is necessarily pourable in a cold room and by gravity.
The present invention therefore also relates to a process for manufacturing articles of a zinc-based alloy containing Al and Cu by pressure casting in a cold room machine or by gravity casting, this process being characterized in that the alloy is the alloy of the invention.
The present invention also relates to the use of the alloy according to the invention as an anti-friction material.

Claims (9)

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, in % by weight, 15-18, and preferably, 15-17 Al.
4. Alloy according to Claim 2, characterized in that it contains, in % by weight, 25.5-28.5 Al and 15-18 Cu.
5. Alloy according to any one of Claims 1-4, characterized in that it contains, in % by weight, 0.1-1 Si.
6. Alloy according to any one of Claims 1-5, characterized in that Zn, Al and Cu, used for the manufacture of the alloy, have a purity of > 99.99 %, ≥ 99.95 % and ≥ 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.

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