Aluminium alloy

Description

[0001] The present invention relates to an aluminium-silicon alloy. The alloy has use in the manufacture of pistons, in particular for use in internal combustion engines.

[0002] A satisfactory piston material must meet many differing requirements. In use, pistons are exposed to both static and dynamic stresses, while operating in bulk temperatures from sub-zero to up to 400°C. These stresses will also differ in different regions of the piston, for example a combustion bowl in a piston will be subject to different thermal and mechanical stresses than piston pin bosses. The piston must also have low thermal expansion, and possess good bearing characteristics with marginal lubrication over the noted range of temperatures. Also, the piston material must lend itself to being formed into a piston, for example by casting with subsequent working.

[0003] Known casting alloys for piston manufacture include those disclosed in US 3765877. Among the alloys disclosed therein is an aluminium based alloy including silicon from 7 to 20 percent, copper from 3.5 to 6 percent, up to 2.5 percent nickel, from 0.1 to 0.6 percent magnesium, and from 0.1 to 1.0 percent silver with the balance being aluminium and unavoidable impurities.

[0004] The present invention has an advantage improved boss strength and also improved high temperature strength in the region of the piston crown.

[0005] The alloy of the present invention is selected from a group of aluminium alloys with each alloy component element being present in weight percent as follows:

Si = 10.5 - 13.5

Cu = 2.0 - 4.0

Ni = 0.5 - 2.0

Mg = 0.8 - 1.5

Ag = 0.2-0.6

Co = 0.2 - 0.6

P at least 20 ppm,

optionally up to 0.1 wt% Zn

optionally up to 0.1 wt% Pb

optionally up to 0.1 wt% Sn

optionally up to 0.2 wt% Ti

optionally up to 0.2 wt% Zr

optionally up to 0.2 wt% V

optionally up to 0.35 wt% Fe

optionally up to 0.15 wt% Mn

optionally up to 0.03 wt% Cr

optionally up to 10 ppm each of Ca, Na, Sr and Li

and balance Al and unavoidable impurities.

[0006] The Nickel content in this alloy is believed to lead to the formation of thermally stable intermetallics. This in turn leads to high temperature strength for the alloy. More than 2 wt% Nickel leads to the formation of large Ni rich intermetallics, particularly for the low cooling rates associated with large piston castings, which are seriously detrimental to the high temperature fatigue strength of the alloy.

[0007] The Colbalt content is chosen to allow the formation of a large number of small intermetallics. This is believed to improve the mechanical properties of the alloy at 350°C. In addition, the presence of the Cobalt in the Aluminium alloy at a level in excess of 0.2 wt% is believed to reduce the diffusivity of the Copper in Aluminium, thereby slowing the overaging mechanism of the alloy. This has particular importance when considering the operation of a piston pin boss operating at around 200°C. However, the presence of the Cobalt is believed also to lead to an increase in fatigue strength of the alloy at 350°C. This is of particular importance when considering the operation of a combustion bowl of a piston which is typically subject to such temperatures.

[0008] The Silver is believed to give improved boss strength to a piston manufactured from this alloy. In particular, up to 0.6 wt% Silver increases the fatigue strength of the alloy at 200°C. The thermal conductivity of the alloy at 350°C is raised without adversely affecting the expansion coefficient. The addition of Silver in this range does not appear to cause castability problems.

[0009] The Titanium, Zirconium and Vanadium, where present are each believed to act as grain refining additions in the alloy.

[0010] Preferably, the Copper content is at least 2.5 wt%, and may be less than 3.5 wt%.

[0011] An alloy according to the invention may have the component elements in weight percent comprise:

Si = 10.5-11.5

Cu = 2.75 - 3.25

Ni = 0.8 - 1.2

Mg = 0.9 - 1.2

Ag = 0.45 - 0.55

Co = 0.25 - 0.35

Ti = 0.14 - 0.19

Pb = up to 0.1

Sn = up to 0.1, the total amount of Pb & Sn not exceeding 0.1

P between 50 - 100 ppm

and balance Al and unavoidable impurities

[0012] The present invention will now be described, by way of example only, with reference to the following illustrative examples.

EXAMPLE 1

[0013] The use of a specific alloy composition in manufacture of forged pistons has proven to be particularly advantageous. The metal alloy compositions of a first alloy according to the present invention with the component elements being indicated in weight percent are:

Si = 10.5 - 13.5

Cu = 2.0 - 4.0

Ni = 0.5 - 2.0

Mg = 0.8 - 1.5

Ag = 0.2 - 0.6

Co = 0.2 - 0.6

P at least 20 ppm,

and balance Al and unavoidable impurities.

EXAMPLE 2

[0014] A second alloy according to the invention has a similar composition to the first alloy save that the nickel is present from 0.5 to 1.5 wt%.

EXAMPLE 3

[0015] A third alloy according to the present invention has a similar composition to the first and second alloys, but may additionally comprise at least one of the following component elements:

up to 0.1 wt% zinc

up to 0.1 wt% lead

up to 0.1 wt% tin

EXAMPLE 4

[0016] A fourth alloy according to the present invention has a similar composition to that of Example 3, but may additionally comprise at least one of the following component elements:

up to 0.1 wt% titanium

up to 0.1 wt% zirconium

up to 0.1 wt% vanadium

EXAMPLE 5

[0017] A fifth alloy according to the present invention with the component elements being indicated in weight percent are:

Si = 10.5 - 11,5

Cu = 2.75 - 3.25

Ni = 0.8 - 1.2

Mg = 0.9 - 1.2

Ag = 0.45 - 0.55

Co = 0.25 - 0.35

Ti = 0.14 - 0.19

Pb = up to 0.1

Sn = up to 0.1, the total amount of Pb & Sn not exceeding 0.1

between 50 - 100 ppm P

and balance Al and unavoidable impurities

EXAMPLE 6

[0018] A sixth alloy according to the present invention has a similar composition to the fifth alloy according to the present invention, but may additionally comprise at least one of the following component elements:

up to 0.35 wt% iron

up to 0.15 wt% manganese

up to 0.1 wt% zinc

up to 0.03 wt% chrome

[0019] The alloys of the present invention, in addition to their use in the manufacture of forged pistons, may be used in the manufacture of gravity die cast pistons.

Claims

1. An aluminium alloy for internal combustion engine pistons in which the component element are indicated in weight percent comprising:

Si = 10.5-13.5

Cu = 2.0 - 4.0

Ni = 0.5 - 2.0

Mg = 0.8 - 1.5

Ag = 0.2 - 0.6

Co = 0.2 - 0.6

P at least 20 ppm,

optionally up to 0.1 wt% Zn

optionally up to 0.1 wt% Pb

optionally up to 0.1 wt% Sn

optionally up to 0.2 wt% Ti

optionally up to 0.2 wt% Zr

optionally up to 0.2 wt% V

optionally up to 0.35 wt% Fe

optionally up to 0.15 wt% Mn

optionally up to 0.03 wt% Cr

optionally up to 10 ppm each of Ca, Na, Sr and Li

and balance Al and unavoidable impurities.

2. An alloy according to claim 1, characterised in that the element Nickel is present in the range 0.5 to 1.5 wt%.

3. An alloy according to either on of claims 1 and 2, characterised in that the component elements in weight percent comprise:

Si = 10.5 - 11.5

Cu = 2.75 - 3.25

Ni = 0.8-1.2

Mg = 0.9 - 1.2

Ag = 0.45 - 0.55

Co = 0.25 - 0.35

Ti = 0.14 - 0.19

Pb = up to 0.1

Sn = up to 0.1, the total amount of Pb & Sn not exceeding 0.1

P between 50 - 100 ppm

and balance Al and unavoidable impurities

4. A piston manufactured from an alloy according to any previous claim.

5. A piston according to claim 4, characterised in that the piston is manufactured by forging.

6. A piston according to claim 4, characterised in that the piston is manufactured by gravity die casting.

Ansprüche

1. Aluminiumlegierung für Verbrennungsmotorkolben, wobei die Elementkomponenten in Gew.-% angegeben sind, umfassend:

Si = 10,5 - 13,5

Cu = 2,0 - 4,0

Ni = 0,5 - 2,0

Mg = 0,8 - 1,5

Ag = 0,2 - 0,6

Co = 0,2 - 0,6

P in mindestens 20 ppm

gegebenenfalls bis zu 0,1 Gew.-% Zn

gegebenenfalls bis zu 0,1 Gew.-% Pb

gegebenenfalls bis zu 0,1 Gew.-% Sn

gegebenenfalls bis zu 0,2 Gew.-% Ti

gegebenenfalls bis zu 0,2 Gew.-% Zr

gegebenenfalls bis zu 0,2 Gew.-% V

gegebenenfalls bis zu 0,35 Gew.-% Fe

gegebenenfalls bis zu 0,15 Gew.-% Mn

gegebenenfalls bis zu 0,03 Gew.-% Cr

gegebenenfalls bis zu 10 ppm von jedem Element von Ca, Na, Sr und Li

und als Rest Al und unvermeidbare Verunreinigungen.

2. Legierung nach Anspruch 1, dadurch gekennzeichnet, daß das Element Nikkel in einem Bereich von 0,5 bis 1,5 Gew.-% vorhanden ist.

3. Legierung nach einem der Ansprüche 1 und 2, dadurch gekennzeichnet, daß die Elementkomponenten in Gew.-%:

Si = 10,5 - 11,5

Cu = 2,75 - 3,25

Ni = 0,8-1,2

Mg = 0,9-1,2

Ag = 0,45 - 0,55

Co = 0,25 - 0,35

Ti = 0,14 - 0,19

Pb = bis zu 0,1

Sn = bis zu 0,1, wobei der Gesamtanteil von Pb und Sn 0,1 nicht übersteigt,

P zwischen 50 - 100 ppm

und als Rest Al und unvermeidbare Verunreinigungen umfassen.

4. Kolben, hergestellt aus einer Legierung nach einem vorhergehenden Anspruch.

5. Kolben nach Anspruch 4, dadurch gekennzeichnet, daß der Kolben durch Schmieden hergestellt ist.

6. Kolben nach Anspruch 4, dadurch gekennzeichnet, daß der Kolben durch Dauerformguß hergestellt ist.

Revendications

1. Alliage d'aluminium pour des pistons de moteurs à combustion interne, dans lequel les éléments constitutifs sont indiqués en pourcentage en poids, comprenant :

Si = 10,5 - 13,5

Cu = 2,0 - 4,0

Ni = 0,5 - 2,0

Mg = 0,8 - 1,5

Ag = 0,2 - 0,6

Co = 0,2 - 0,6

P au moins 20 ppm

facultativement jusqu'à 0,1 % en poids de Zn

facultativement jusqu'à 0,1 % en poids de Pb

facultativement jusqu'à 0,1 % en poids de Sn

facultativement jusqu'à 0,2 % en poids de Ti

facultativement jusqu'à 0,2 % en poids de Zr

facultativement jusqu'à 0,2 % en poids de V

facultativement jusqu'à 0,35 % en poids de Fe

facultativement jusqu'à 0,15 % en poids de Mn

facultativement jusqu'à 0,03 % en poids de Cr

facultativement jusqu'à 10 ppm de chacun des éléments consistant en Ca, Na, Sr et Li

et le reste constitué de Al et des impuretés inévitables.

2. Alliage suivant la revendication 1, caractérisé en ce que l'élément consistant en nickel est présent en une quantité comprise dans l'intervalle de 0,5 à 1,5 % en poids.

3. Alliage suivant une des revendications 1 et 2, caractérisé en ce que les éléments constitutifs, en pourcentage en poids, sont les suivants :

Si = 10,5 - 11,5

Cu = 2,75 - 3,25

Ni = 0,8 - 1,2

Mg = 0,9 - 1,2

Ag = 0,45 - 0,55

Co = 0,25 - 0,35

Ti = 0,14 - 0,19

Pb = jusqu'à 0,1

Sn = jusqu'à 0,1, la quantité totale de Pb et Sn ne dépassant pas 0,1

P entre 50 et 100 ppm

et le reste consistant en Al et les impuretés inévitables.

4. Piston produit à partir d'un alliage suivant l'une quelconque des revendications précédentes.

5. Piston suivant la revendication 4, caractérisé en ce qu'il est produit par forgeage.

6. Piston suivant la revendication 4, caractérisé en ce qu'il est produit par coulée en coquille par gravité.