EP3277854B1 - Aluminium casting alloy, a process for the manufacture of an engine component, engine component and the use of an aluminium casting alloy for the manufacture of an engine component - Google Patents

Description

TECHNICAL AREA

The present invention relates to an aluminum casting alloy, a method for manufacturing an engine component, in particular a piston for an internal combustion engine, in which an aluminum casting alloy is gravity-poured by casting, an engine component at least partially made of an aluminum casting alloy, and the use an aluminum casting alloy for producing such an engine component.

STATE OF THE ART

In recent years there has been an increasing demand for particularly economical and thus ecological means of transport, which have to meet high consumption and emission requirements. In addition, there has always been a need to make engines as powerful and low-consumption. A key factor in the development of high-performance and low-emission internal combustion engines are pistons, which can be used at ever higher combustion temperatures and combustion pressures, which is essentially made possible by more efficient piston materials.

Basically, a piston for a combustion engine must have a high heat resistance and at the same time to be as light and firm as possible. It is of particular importance how the microstructural distribution, morphology, composition and thermal stability of highly heat-resistant phases are formed. An optimization in this regard usually takes into account a minimum content of pores and oxide inclusions.

The material sought must be optimized for both isothermal fatigue strength (HCF) and thermo-mechanical fatigue strength (TMF). In order to design the TMF as well as possible, the goal is always to achieve the finest possible microstructure of the material. A fine microstructure reduces the risk of microplasticity or microcracks on relatively large primary phases (especially primary silicon precipitates) and hence the risk of crack initiation and propagation.

Under TMF stress, microplasticities or microcracks occur on relatively large primary phases, particularly primary silicon precipitates, due to different coefficients of expansion of the individual constituents of the alloy, namely the matrix and the primary phases, which can significantly reduce the life of the piston material. To increase the life is known to keep the primary phases as small as possible.

In particular, high-alloy near-eutectic or hypereutectic aluminum-silicon alloys feature favorable mechanical properties at high operating temperatures. In this case, with regard to the primary silicon and the resulting intermetallic phases, the phase size must be limited.

The DE 10 2011 083 969 A1 discloses in this context a method for producing an engine component, in particular a piston for an internal combustion engine, at an aluminum alloy is poured by gravity die casting process. In this case, the aluminum alloy has the following alloying elements: silicon: 6 wt .-% to 10 wt .-%, nickel: 1.2 wt .-% to 2 wt .-%, copper: 8 wt .-% to 10 wt. -%, magnesium: 0.5 wt .-% to 1.5 wt .-%, iron: 0.1 wt .-% to 0.7 wt .-%, manganese: 0.1 wt .-% to 0 , 4 wt .-%, zirconium: 0.2 wt .-% to 0.4 wt .-%, vanadium: 0.1 wt .-% to 0.3 wt .-%, titanium: 0.1 wt. -% to 0.5 wt .-%. However, high concentrations of the costly element copper are needed to make the high temperature alloy.

Similarly, conventional aluminum casting alloys for thermally heavy duty engine components typically require between 5 and 7 weight percent for the sum of the alloying elements copper and nickel and 11 to 13 weight percent silicon. The high silicon content increases the risk of large and numerous primary silicon precipitations.

PRESENTATION OF THE INVENTION

An object of the present invention is to provide a high-temperature cast aluminum alloy which can be produced inexpensively.

The solution to this problem is achieved by the alloy according to claim 1. Preferred embodiments of the invention will become apparent from the relevant subclaims.

An aluminum casting alloy consisting of the alloying elements Silicon: 9.0% by weight to <10.5% by weight, Nickel: From 0.8% to <1.9% by weight, Copper: 1.8% by weight to <3.6% by weight, Magnesium: From 0.5% to 1.8% by weight, Iron: 0.9% by weight to <1.4% by weight, Zirconium and / or vanadium: in each case 0.05 to <= 0.3 or 0.2% by weight, Manganese: up to <= 0.4% by weight, Titanium: up to <= 0.15% by weight, Phosphorus: up to <= 0.05% by weight, and the balance aluminum and unavoidable impurities has particularly favorable properties in terms of thermal stability. Of the elements zirconium and vanadium, at least one is present, with a concentration of up to 0.3% by weight in the case of zirconium and 0.2% by weight in the case of vanadium, being in the above list and in claim 1 by "zirconium to <= 0.3 wt .-%, vanadium to <= 0.2 wt .-%" can be replaced.

The concentration of the alloying element iron according to the invention leads to a high proportion of intermetallic phases. By fine-tuning with respect to the other alloying elements, in particular copper and nickel, however, the formation of large, plate-shaped intermetallic phases is avoided. The latter limit both the castability, as well as the strength and durability of a made of this material component. Instead, the formed intermetallic phases are finely distributed, heat-resistant and thermally stable and therefore act as strength enhancing precipitates. This results in favorable properties in terms of the isothermal fatigue strength and the thermo-mechanical fatigue strength.

Furthermore, the increased tolerance threshold for iron compared to conventional aluminum-silicon alloys, the flexibility in terms of usable raw materials: Thus, for the production of the alloy according to the invention low-cost scraps are used, which were previously not recyclable due to their iron content.

The relatively low contents of copper and nickel also advantageously reduce the overall costs of alloy production, because they are among the most expensive alloying elements, so that each (partial) substitution of the two elements brings significant cost savings.

Reducing the silicon concentration over conventional aluminum-silicon alloys also advantageously results in alloying with fewer and smaller primary silicon phases, such that susceptibility to crack initiation and propagation is greatly reduced, particularly under TMF stress.

Advantageously, the invented aluminum casting alloy is processed according to the invention in the gravity die casting process.

An engine component, in particular a piston for an internal combustion engine, preferably consists at least partially of one of the aluminum casting alloys according to the invention. Such an engine component according to the invention has a high heat resistance. In the case of a piston produced according to the invention, only a small amount of primary silicon is present in its thermally highly loaded bowl edge region, so that the alloy leads in particular to a very high heat resistance of a piston produced according to the invention.

A further aspect of the invention resides in the preferred use of the above-described aluminum casting alloy for the production of an engine component, in particular a piston of an internal combustion engine.

Claims (10)

1. Aluminium casting alloy, characterised in that the aluminium casting alloy consists of the following alloy elements:

   silicon: 9.0 wt% to < 10.5 wt%,

   nickel: 0.8 wt% to < 1.9 wt%,

   copper: 1.8 wt% to < 3.6 wt%,

   magnesium: 0.5 wt% to 1.8 wt%,

   iron: 0.9 wt% to < 1.4 wt%,

   zirconium and/or vanadium: in each case 0.05 to <= 0.3 or 0.2 wt%,

   manganese: up to <= 0.4 wt%,

   titanium: up to <= 0.15 wt%,

   phosphorus: up to <= 0.05 wt%,

   the rest consisting of aluminium and unavoidable impurities.
2. Aluminium casting alloy according to claim 1, characterised in that it contains 9.0 wt% to 9.5 wt% or 9.5 wt% to < 10.5 wt% silicon.
3. Aluminium casting alloy according to claim 1 or 2, characterised in that it contains 1.0 wt% to < 1.5 wt% nickel.
4. Aluminium casting alloy according to one of the claims 1 to 3, characterised in that it contains > 3.0 wt% to < 3.6 wt% copper.
5. Aluminium casting alloy according to one of the claims 1 to 4, characterised in that it contains > 0.5 wt% to < 0.9 wt% magnesium.
6. Aluminium casting alloy according to one of the claims 1 to 5, characterised in that it contains 0.9 wt% to 1.1 wt% iron.
7. Aluminium casting alloy according to one of the claims 1 to 6, characterised in that it contains 0.2 wt% to 0.4 wt% manganese.
8. Process for the manufacture of an engine component using the gravity die casting method, in particular a piston for an internal combustion engine, characterised in that an aluminium casting alloy according to one of the claims 1 to 7 is cast.
9. Engine component, in particular a piston for an internal combustion engine, characterised in that it consists at least in part of an aluminium casting alloy according to one of the claims 1 to 7.
10. Use of an aluminium casting alloy for the manufacture of an engine component, in particular a piston for an internal combustion engine, characterised in that an aluminium casting alloy according to one of the claims 1 to 7 is used.