EP0899354B1 - Hyper-eutectic al-si alloy coating respectively an al-si composite - Google Patents

Description

The invention relates to a coating of an aluminum / silicon composite material for producing wear-resistant, low-friction layers and to processes for producing the coating, both of which are used in industry.

In the automotive industry, most of the still prevalent gray cast crankcases of reciprocating engines - their share was still dominant in Germany in 1994 at 96%, Europe at 82% - displaced by those made of light metals to reduce the gross vehicle weight and thus the fuel to improve utilization. For the production of crankcases made of light metal, for economic and technical reasons, the die casting of low alloyed aluminum such as AlSi10 will first qualify. Such alloys, in contrast to established in the engine but considerably more expensive atmospheric casting of hypereutectic aluminum-silicon alloys such as Alusil (Al-Sil7) unsatisfactory friction and wear behavior in contact with aluminum piston and piston rings and are therefore unsuitable as a friction partner.

Therefore, for future engines on the pouring tribologically suitable sockets of gray cast iron or hypereutectic aluminum-silicon can not be waived. For the preparation of these sockets z. B. to DE 44 38 550 A1 blanks produced in the known Ospray process and subsequently mechanically compacted. The semi-finished bush is first inserted into the mold before pouring and then covered with liquid aluminum. The typical wind force of such cans is 2 to 3 mm. Subsequently, the inside of the liner is coarse and fine twisted, honed and exposed. The alloys used include copper, so that in particular intermetallic phases such as How Al ₂ Cu are formed, which are required for the short-chipping processing of the layer surface. The use of these copper-containing alloys proves to be particularly problematic in connection with certain fuels.

Although the blocks spray-compacted according to DE 43 28 619 C2 and EP 0 411 577 B1 are indeed produced with copper-free aluminum / silicon alloys, they have hitherto not been used as cylinder liners, because the surface of the cylinder liners can not be machined with a short chip and are thus produced an economically unacceptable alternative dar.

Moreover, this bushing solution is associated with constructive, manufacturing and not least economic disadvantages such as limited adhesion of the AlSi10 melt on the bush surface, elaborate handling and high price. For this, the socket wall thickness affects the minimum cylinder spacing. The web width should be as low as possible, especially for future engines of small design, because it also determines the minimum external dimensions of the engine.

Thermal spraying offers further possibilities of applying wear-resistant coatings to the cylinder wall of the crankcases. The basic principle of thermal spraying is that a fusible or teilschmelzbarer material is melted in a high-speed hot gas jet into small spray droplets and accelerated in the direction of the surface to be coated (DIN 32530). Upon impact, the spray droplets solidify on the relatively cold metal surface and form a layer layer by layer. The advantage of this coating technology compared to electro-deposition, chemical or physical vapor deposition is the high application rate, which makes it possible to economically coat a cylinder bore in a few minutes. The methods of thermal spraying differ according to the mode of production and the properties of the high-speed hot gas jet.

High-speed flame spraying (HVOF) produces an acetylene-oxygen flame in which the spray particles are accelerated to supersonic speed and deformed on impact with the surface to be coated. The HVOF process has already been used for coating cylinder bores with an aluminum-bronze alloy (US Pat. No. 5,080,056) or an iron-aluminum composite (EP 0 607 779 A1), but produces excess heat, which is often only possible through additional, expensive cooling of the crankcase can be removed (US 5,271,967). In plasma spraying, gases such as argon, helium, nitrogen and / or hydrogen are transferred by an electric arc in a plasma state in which the powdery (EP 0 585 203 A1 and US 4,661,682) or wire-shaped (US Pat. No. 5,442,153) sprayed material is introduced laterally to be moderately accelerated and smelted compared to the HVOF. Here, the spray particles are heated to a higher temperature than the HVOF, so that they are in a molten state upon impact with the substrate, which provides for an intimate, cohesive connection of the layer to the substrate. Powder plasma spraying has already been used to coat cylinder bores with an iron-based layer (US 3,991,240). The wire plasma spraying was used to coat cylinder bores with an AISI 1045 steel (DE 195 08 687). However, the efforts to replace the cylinder liners made of gray cast iron by those of hypereutectic aluminum / silicon indicate that an iron-based cylinder surface can not meet the technical and tribological requirements of modern reciprocating engines.

The object of the invention is to develop a thermally sprayed, wear-resistant layer, in particular for engine construction in terms of wear resistance and lubricating oil consumption, while the risk of wear for the counter-component is reduced.

The object is achieved with a coating having the features of claim 1 and with respect to the method with a method having the method steps of claim 4. Through the use of special essentially copper-free aluminum / silicon spray powders for the application of the coating according to the invention by means of atmospheric, thermal spraying, a heterogeneous layer structure of aluminum mixed crystal, embedded silicon particles or silicon primary precipitates is formed during the layered layer formation of the coating. which may also be present side by side, intermetallic phases such as Mg ₂ Si and extremely finely divided oxides, the formation and distribution of the oxides being solely due to the non-equilibrium properties of atmospheric thermal spray processes. The matrix may further comprise a hypereutectic aluminum / silicon alloy. Surprisingly, in spite of the absence of copper, the layer surface of a coating according to the invention can be processed in an economically short-chipping manner, which can presumably be attributed to the oxides which are finely distributed on the layer surface and preferably also within the coating. In addition, the coating has improved wear resistance.
For producing the short-chipping and substantially copper-free aluminum / silicon layers by means of atmospheric thermal spraying is due to the good melting of the spray particles, the formation of finely divided oxides, their good adhesion to the substrate and the moderate heat transfer into the component atmospheric plasma spraying prefers. In addition, this method offers the possibility to perform custom coatings, so that can be dispensed with the surface finishing of the layer on the pre-turning.
For economic and technical reasons, a coating is expedient which ensures good, in particular short-chipping, workability of its surface. For this wear-resistant, short-span machinable coating can be used to coat crankcases, is in addition to the reduction of combustion residues by reducing lubricating oil consumption interest to use this for all different fuels worldwide, so the coating, especially when used for the cylinder surfaces of internal combustion engines is copper-free ,

Furthermore, it is also advantageous that with the inventive (wear-resistant aluminum-silicon) coating after a diecasting process, for example, a cylinder surface can be coated in a die-cast engine block made of light metal such as aluminum or magnesium by means of a thermal spraying process, which on the previous usual but Complex liner solution can be dispensed with. Also, the thickness of the actual, tribological running layer on the tribologically non-executable, but good to be cast and machined crankcase can be significantly reduced. It is, for example, with 0.1 to 0.2 mm less than 1/10 of the usual sleeve wall thickness today and therefore offers the opportunity to build much more compact engines.

Expediently, plasma spraying is used to produce the coating. With this non-equilibrium method, it is also possible to form microstructures which otherwise can not be represented metallurgically. Because of the high energy density and the large Parametervielzahl the method z. B. almost defined oxides are formed in the layer structure, on the one hand carry a short-chipping processing of the layer surface and on the other hand, a significant contribution to the wear resistance of the layers. By using agglomerated spray powders, it is also possible to add any desired foreign materials to the layer, including those which are distinct from the aluminum alloy different melting points such as hard metal or ceramic particles but also dry lubricants.

Conveniently, the coating according to the invention can be integrated without changing the manufacturing equipment installed today in the series, which eliminates the costly production and handling of the cylinder liners and considerable amounts of material can be saved. With the method according to the invention, the coating can be carried out at high application rates in particularly short cycle times, wherein the coating is very accurately applied to the cylinder wall of the crankcase and a fine surface quality is set. These measures eliminates the need for elaborate reworking steps such as, for example, pre-turning, and possibly even even fine turning, thereby significantly reducing the manufacturing costs.

Fig. 1

ein Schliffaufnahme der sphärischen Spritzpartikel aus der Legierung A und

Fig. 2

Rasterelektronenmikroskopaufnahme einer plasmagespritzten Schicht

Further useful embodiments of the invention are the dependent claims. Moreover, the invention is explained with reference to (alloy) examples and with reference to embodiments shown in the figures closer. It shows

Fig. 1

a cross-section of the spherical spray particles of the alloy A and

Fig. 2

Scanning electron micrograph of a plasma-sprayed layer

In order to produce the coatings shown in the figures, spray powders of copper-free aluminum / silicon alloys or aluminum / silicon composites were developed. In addition to the optimization of the composition, emphasis was placed on the shape of the individual spray powder particles, the powder particle distribution and the flow behavior of the spray powders in the spray powders.

By way of example, two essentially copper-free aluminum / silicon alloy systems were selected as the wettable powder, an alloy A (see FIG. 1) for interaction, in particular with iron-coated pistons, and an alloy B (see FIG. 2) preferably being used for uncoated pistons.

Examples of possible alloys are given in the following examples, wherein the numbers indicate the content in percent by weight:

example 1 Alloy A:

• Silicon 23.0 to 40.0%, preferably about 25%
• Magnesium 0.8 to 2.0%, preferably about 1.2%
• Zircon maximum 0.6%
• Iron maximum 0.25%
• Manganese, nickel, copper and zinc maximum 0.01% each
• Rest aluminum.

Example 2

• Silizium 23,0 bis 40,0%, vorzugsweise etwa 25%
• Nickel 1,0 bis 5,0%, vorzugsweise etwa 4%
• Eisen 1,0 bis 1,4%, vorzugsweise etwa 1,2%
• Magnesium 0,8 bis 2,0%, vorzugsweise etwa 1,2%
• Zirkon maximal 0,6%
• Mangan, Nickel, Kupfer und Zink maximal jeweils 0,01%
• Rest Aluminium.

The alloy B differs from the alloy A only by the slightly higher content of iron and nickel:

• Silicon 23.0 to 40.0%, preferably about 25%
• Nickel 1.0 to 5.0%, preferably about 4%
• Iron 1.0 to 1.4%, preferably about 1.2%
• Magnesium 0.8 to 2.0%, preferably about 1.2%
• Zircon maximum 0.6%
• Manganese, nickel, copper and zinc maximum 0.01% each
• Rest aluminum.

Example 3 Alloy C:

• Silicon 0 to 11.8%, preferably about 9%
• Magnesium 0.8 to 2.0%, preferably about 1.2%
• Zircon maximum 0.6%
• Iron maximum 0.25%
• Manganese, nickel, copper and zinc maximum 0.01% each
• Rest aluminum.

Example 4 Alloy D:

• Silicon 0 to 11.8%, preferably about 9%
• Nickel 1.0 to 5.0%, preferably about 4%
• Iron 1.0 to 1.4%, preferably about 1.2%
• Magnesium 0.8 to 2.0%, preferably about 1.2%
• Zircon maximum 0.6%
• Manganese, nickel and zinc maximum 0.01% each
• Rest aluminum.

Example 5 Alloy E:

• Silicon 11.8 to 40%, preferably about 17%
• Magnesium 0.8 to 2.0%, preferably about 1.2%
• Zircon maximum 0.6%
• Iron maximum 0.25%
• Manganese, nickel, copper and zinc maximum 0.01% each
• Rest aluminum.

Example 6 Alloy F:

• Silicon 11.8 to 40%, preferably about 17%
• Nickel 1.0 to 5.0%, preferably about 4%
• Iron 1.0 to 1.4%, preferably about 1.2%
• Magnesium 0.8 to 2.0%, preferably about 1.2%
• Zircon maximum 0.6%
• Manganese, nickel, copper and zinc maximum 0.01% each
• Rest aluminum.

FIG. 1 shows a cross-section of the spherical spray particles made from the alloy A, from which the aluminum mixed-crystal structure and the Si primary vacancies can be clearly seen. The cut was etched to attack the aluminum mixed crystal and thus to clarify the microstructure. In addition to the silicon primary precipitations, the microstructure consists of primary aluminum mixed-crystal dendrites in which the dendrite arms are enveloped by eutectic silicon. The size of the dendrite arms varies greatly, so that they can be resolved only conditionally. The variations in the fineness of the present structure comes, on the one hand, from the fluctuations in temperature and speed of individual melt droplets and, on the other hand, from the different nucleation during the solidification of different melt droplets. Such a fine structure characterizes thermally sprayed layers with respect to microstructures, which are obtained via powder-metallic routes, and is responsible for the good wear resistance of these layers.

2 shows a scanning electron micrograph of a plasma-sprayed layer, which was produced with the spray powder of alloy A. The layer made with the spray powder of Alloy A was honed and exposed mechanically. In the production of layers, narrow dimensional tolerances were observed, so that it was possible to dispense with rough and fine turning. In addition to the homogeneous distribution of the primary silicon effluents, intermetallic phases and pores are also recognizable, which hold back small amounts of oil during operation and which determine the formation of a thin film of oil on the surface of the cylinder surface.

In order to increase the proportion of coarse Si particles in the layer, aluminum / silicon composite powders have been developed. The agglomerated composite powders consist of fine silicon particles and fine, metallic particles of an aluminum-silicon alloy, which are bonded to each other by means of inorganic or organic binders, wherein the proportion of silicon particles 5 to 50% and the proportion of alloy particles is 50 to 95%. The silicon particles have a mean particle size of 0.1 to 10.0 microns, preferably about 5 microns. The metallic particles have an average particle size of 0.1 to 50.0 microns, preferably about 5 microns and consist of either alternatively employable hypoeutectic alloys C or D, or from both alternatively employable hypereutectic alloys E or F. By the use of hypereutectic alloy particles is the proportion of aluminum mixed crystal in the layer structure is maintained while the formation of the aluminum mixed crystal in the layer structure is suppressed by the use of hypoeutectic aluminum / silicon particles.

The coating according to the invention, for example, a cylinder running surface of a cylinder bore assumes that the casting of the Leichmetallblocks done in the usual way in die-casting, but without the inserted into the mold cylinder liners. The interior of the cylinder bore of the crankcase is then coarsely pre-turned in one operation to ensure the required shape and position tolerances. Subsequently, the aluminum-silicon layer is applied. The coating operation may be carried out either in the form of inserting and axially moving into the bore a suitable commercially available internal burner rotating about the center axis of the cylinder bore or a non-rotating burner in the cylinder bore of the rotating crankcase and along the central axis of the cylinder bore is guided to spray the layer on the cylinder wall at almost röch angle. The latter is procedurally simpler and safer, because the supply of the necessary media such as electrical energy, cooling water, primary and secondary gas and spray powder by a rotating unit is problematic.

Claims (12)

1. Coating of an aluminium/silicon composite material,
   characterised in that
   the heterogeneous layer structure of the coating consists of an aluminium solid solution with embedded silicon particles or primary silicon precipitates or both embedded silicon particles and also primary silicon precipitates, and with intermetallic phases such as Mg₂Si and oxides, the mean size of the embedded silicon particles or primary silicon precipitates being smaller than 10 µm, the mean size of the oxides being smaller than 5 µm and the coating being essentially free from copper, i.e. the copper content being smaller than 1% by weight (wt.-%), preferably smaller than 0.1 wt.-% and particularly preferably smaller than 0.01 wt.-%.
2. Coating according to Claim 1,
   characterised in that
   it contains either embedded silicon particles or both embedded silicon particles and primary silicon precipitates.
3. Coating according to Claim 1,
   characterised in that
   it further comprises a hypereutectic aluminium/silicon alloy and primary silicon precipitates are present.
4. Process for the production of a coating according to any of Claims 1 to 3,
   characterised in that
   the coating is produced by a thermal, in particular atmospheric plasma spraying method, and by virtue of setting appropriate spraying parameters, oxides are formed.
5. Process according to Claim 4,
   characterised in that
   for an alloy A, an initial spraying material of the following composition is used, the numerical data expressing content in percent by weight:

   silicon 23.0 to 40.0%, preferably about 25%

   magnesium 0.8 to 2.0%, preferably about 1.2%

   zirconium maximum 0.6%

   iron maximum 0.25%

   manganese, nickel, copper and zinc maximum 0.01% each

   remainder aluminium.
6. Process according to Claim 4,
   characterised in that
   for an alloy B, an initial spraying material of the following composition is used, the numerical data expressing content in percent by weight:

   silicon 23.0 to 40.0%, preferably about 25%

   nickel 1.0 to 5.0%, preferably about 4%

   iron 1.0 to 1.4%, preferably about 1.2%

   magnesium 0.8 to 2.0%, preferably about 1.2%

   manganese, copper and zinc maximum 0.01% each

   remainder aluminium
7. Process according to Claim 4,
   characterised in that
   as the initial spraying material an agglomerated composite powder is used, which consists of fine silicon particles and fine metallic particles held together by inorganic or organic binders, the proportion of silicon particles being 5 to 50% and the proportion of alloy particles being 50 to 95%, the silicon particles having a mean grain size of 0.1 to 10.0 µm, preferably around 5 µm, the metallic particles having a mean grain size of 0.1 to 50.0 µm, preferably around 5 µm, and for an alloy C, the following composition is used, the numerical data expressing content in percent by weight:

   silicon 0 to 11.8%, preferably about 9%

   magnesium 0.8 to 2.0%, preferably about 1.2%

   zirconium maximum 0.6%

   iron maximum 0.25%

   manganese, nickel, copper and zinc maximum 0.01% each

   remainder aluminium.
8. Process according to Claim 4,
   characterised in that
   as the initial spraying material an agglomerated composite powder is used, which consists of fine silicon particles and fine metallic particles held together by inorganic or organic binders, the proportion of silicon particles being 5 to 50% and the proportion of alloy particles being 50 to 95%, the silicon particles having a mean grain size of 0.1 to 10 µm, preferably around 5 µm, the metallic particles having a mean grain size of 0.1 to 50.0 µm, preferably around 5 µm, and for an alloy D, the following composition is used, the numerical data expressing content in percent by weight:

   silicon 0 to 11.8%, preferably about 9%

   nickel 1.0 to 5.0%, preferably about 4%

   iron 1.0 to 1.4%, preferably about 1.2%

   magnesium 0.8 to 2.0%, preferably about 1.2%

   zirconium maximum 0.6%

   manganese, copper and zinc maximum 0.01% each

   remainder aluminium.
9. Process according to Claim 4,
   characterised in that
   as the initial spraying material an agglomerated composite powder is used, which consists of fine silicon particles and fine metallic particles held together by inorganic or organic binders, the proportion of silicon particles being 5 to 50% and the proportion of alloy particles being 50 to 95%, the silicon particles having a mean grain size of 0.1 to 10 µm, preferably around 5 µm, the metallic particles having a mean grain size of 0.1 to 50.0 µm, preferably around 5 µm, and for an alloy E, the following composition is used, the numerical data expressing content in percent by weight:

   silicon 0 to 11.8%. preferably about 9%

   magnesium 0.8 to 2.0%, preferably about 1.2%

   zirconium maximum 0.6%

   iron maximum 0.25%

   manganese, nickel, copper and zinc maximum 0.01% each

   remainder aluminium.
10. Process according to Claim 4,
    characterised in that
    as the initial spraying material an agglomerated composite powder is used, which consists of fine silicon particles and fine metallic particles held together by inorganic or organic binders, the proportion of silicon particles being 5 to 50% and the proportion of alloy particles being 50 to 95%, the silicon particles having a mean grain size of 0.1 to 10.0 µm. preferably around 5 µm, the metallic particles having a mean grain size of 0.1 to 50.0 µm. preferably around 5 µm, and for an alloy F, the following composition is used, the numerical data expressing content in percent by weight:

    silicon 0 to 11.8%, preferably about 9%

    nickel 1.0 to 5.0%, preferably about 4%

    iron 1.0 to 1.4%, preferably about 1.2%

    magnesium 0.8 to 2.0%, preferably about 1.2%

    zirconium maximum 0.6%

    manganese, copper and zinc maximum 0.01% each

    remainder aluminium.
11. Use of a coating according to at least one of Claims 1, 2 or 3 to coat a cylinder working surface of reciprocating piston engines, preferably with crankcases made of grey cast iron or an alloy based on iron, aluminium or magnesium.
12. Use of a process according to at least one of Claims 4 to 10 to produce a coating for a cylinder working surface of reciprocating piston engines, preferably with crankcases made of grey cast iron or an alloy based on iron, aluminium or magnesium.