EP1304396B1 - Coating process - Google Patents

Description

The invention relates to a method for coating one of Aluminum alloy existing components, in particular of the Valve seat portion of a cylinder head of an internal combustion engine.

To the highly loaded valve seat portion of a particular from a Aluminum alloy existing cylinder head in particular in terms To optimize strength, load capacity and abrasion and wear resistance, It is known to use correspondingly resilient valve seat rings. For example, DE 197 21 406 A1 describes a valve seat, which in a cylinder head made of aluminum or an aluminum alloy inserted and / or associated with them.

However, it has been found that the connection between valve seat and cylinder head, in particular due to large temperature fluctuations over a wide range and the associated Thermal expansion and the high load is very critical, so you has gone over, instead of valve seat rings a direct Coating the seat surface to the cylinder head.

In this context, reference is made to EP 843 022 A1, which to a method for forming a valve seat by means of thermal Spray coating refers.

As before, in particular, the heat transfer between the cylinder head and valve seat with respect to the high temperature operating stability very critical. In addition, there is a very high tendency of the valve seat materials used for cracking. Especially heavy weigh these disadvantages High-performance engines as well as vehicles that have the lubricating effect of the liquid fuel is missing - such as in gas / hydrogen vehicles- because here are special, extreme loads in terms of temperature and wear prevail.

The object of the invention is to provide a method for applying a To provide coating material, thereby avoiding the mentioned disadvantages a valve seat area with a special hardness without Tendency for cracking is provided. The generated coating should good wear resistance at high temperatures, high hardness and strength, have good thermal conductivity and lubricity.

The object is achieved according to the features of claim 1, wherein using an alloy powder, the 10-70 wt .-%, in particular 20-50 wt .-% silicon (Si) and 5-50 wt .-%, in particular 10 -40% by weight of titanium (Ti), balance aluminum (Al) and optionally up to 25% by weight, in particular 1-15% by weight of nickel (Ni) and / or up to 20% by weight, in particular 1-10 wt .-% copper (Cu), and optionally boron nitride (BN), graphite, B ₂ O ₃ and / or Co / Cr ₂ O _{2 by} weight with together up to 20%, in particular 5-10%, and optionally SiC and / or B ₄ C by weight up to 30%, in particular 5-20% contains, by means of a high energy beam, in particular a laser beam, the alloy powder at least partially converted from the solid to the molten phase and in a molten bath on the Part surface is on / introduced, whereupon in the following solidification process in the matrix matrix a high-melting intermetallic Al-Ti phase is formed with embedded Si particles.

Advantageous developments of the method according to the invention are Subject matter of the subclaims 2 to 4.

As particularly favorable, it has been found, if the Alloy powder by means of a suitable nozzle comprising a Powder conveyor, which cooperates with the laser beam, on the Component surface is applied by the powder in the laser beam or at least partially melted at least in its vicinity. Conveniently, the component is cooled during the coating and the coating takes place under a protective gas atmosphere.

Fig. 1

ein Schliffbild eines Gefüges mit hohem Si-Anteil unter Verwendung eines herkömmlichen Legierungspulvers,

Fig. 2

ein Schliffbild eines Gefüges mit hohem Si-Anteil unter Verwendung des erfindungsgemäßen Verfahrens,

Fig. 3

schematisch und beispielhaft die Aufbringung des Legierungspulvers auf den Ventilsitzbereich eines Zylinderkopfes.

Hereinafter, a particularly preferred embodiment of the invention will be described with reference to figures. Show

Fig. 1

a micrograph of a high Si-content microstructure using a conventional alloy powder,

Fig. 2

a microsection of a structure with a high Si content using the method according to the invention,

Fig. 3

schematically and exemplarily the application of the alloy powder on the valve seat portion of a cylinder head.

Fig. 1 shows a micrograph of one using an aluminum-silicon powder coated component of an aluminum alloy. According to the state of Technique, this type of coating is used in particular the Wear resistance of an aluminum component by alloying or application of alloying elements in the area of the surface increase. Has been used in the present case, an aluminum-silicon powder which is applied / applied in the molten state is, with a very high Si addition, the cooling formed with Fig. 1 structure. Clearly visible in the Aluminum base structure 10 embedded rod / lamellar silicon crystals 12a, 12b, 12c. The aim is a high concentration of these silicon crystals as well as their firm anchoring in the basic aluminum structure 10. In the present high silicon concentration of about 60 wt. %, the silicon particles form rod / lamellar with a size of up to several 100 microns. This due to a very adverse material behavior. The coated in this way The area is very brittle and tends to crack. A desired high Si content is the disadvantageous education large, rod / lamellar Silicon crystals contrary.

A micrograph of a means of the method according to the invention Fig. 2 shows the structure produced Alloy powder contains in the present embodiment in addition to the Base element aluminum a very high silicon content of about 62 wt .-% and about 20 wt .-% titanium. For the preparation of the alloy powder is a Processed metal alloy with the appropriate composition into powder, if necessary, it may also be advantageous to alloy powder different Mix the composition, leaving an alloy powder with the desired Composition arises.

Under the influence of the alloying element titanium (Ti), 20 Al-Ti phases are formed in the basic matrix. Particularly preferred is the formation of refractory Al-Ti phases, such as Al ₃ Ti, whose melting point is about 1340 ° C. Silicon particles 22 are embedded in this very robust base matrix 20, with the alloying element titanium furthermore effecting grain refinement when it is deposited from the melt. The micrograph shown in Fig. 2 shows this base matrix 20 with embedded silicon particles 22, the silicon particles 22 despite the high silicon content of about 60 wt.% Very finely dispersed in a size of only about 20 .mu.m, in particular from 1 to 5 microns. The Si content can be greatly increased without the Si primary crystals forming from the melt becoming too large and bar / lamellar.

Depending on the proportion of titanium (Ti) and / or silicon (Si) can be within wide limits the Macrohärte - for example, to over 550 HV at AlSi50Ti30 - steer, where Nevertheless, an increased tendency to cracking is avoided. Possibly advantageous addition of small amounts of pitch (Ni) in the range 1 to 15 wt. % and / or copper (Cu) in the range 1 to 10% by weight.

As very beneficial, it has also been found, the alloy powder a High-temperature lubricant such as boron nitride (BN) contribute, whereby the use in high-performance engines and gas / hydrogen engines is favored. In this case, the coating powder with a very fine Bornitrit-dust so prepared that the alloy powder grains are completely enveloped by BN. It may be expedient according to another embodiment, a second powder tower or a second powder nozzle for simultaneous transport of the base alloy powder and the BN and both only briefly to mix before / during application.

During the solidification of the melt after coating, small islands of boron nitrite, which act as lubricating pockets, are formed in the layer, which islands are exposed again and again during operational wear. Over the life of the coated surface so a permanent lubricating effect is achieved. A proportion of 5 to 10 wt .-% is usually sufficient, with possibly up to 20 wt .-% BN can be added. In the same way other high-temperature lubricants - such as graphite, B ₂ O ₃ and / or Co / Cr ₂ O ₃ - can be added to the powder material.

Further wear resistance of the microstructure matrix can furthermore be achieved by adding hard material particles. For example, SiC and / or B ₄ C can be incorporated as a wear-resistant carrier by weight in amounts of up to 30%, in particular 5 to 20%. In conjunction with a fuel such as gas or hydrogen or in high-performance engines, B ₄ C also assumes the role of a solid lubricant due to its oxidation to B ₂ O ₃ .

The coating takes place - as shown in FIG. 3 - by means of a coating lance 32, which includes a supply 37 for the alloy powder and a light guide 33 for coupling a laser beam comprises. As a laser is a diode laser or a solid state laser such as Nd: YAG laser with a power of about 3kW used. The alloy powder is fed through the feed 37 of a nozzle 38 supplied, from which a powder jet 36 emerges; the from the light guide 33rd emerging laser beam is transmitted by means of a plurality of optical elements schematically and exemplarily with 34a, 34b indicated - focused. The Coating lance 32 is rotatable relative to the component 30 and / or displaceable, so that a targeted regional coating of the component 30 is possible; if necessary the focus of the laser beam 35 and / or the nozzle 38 adjustable ,.

The alloy powder emerging from the nozzle 38 is sprayed in the direction of the component to be coated, wherein it is at least partially melted by the heat of the laser beam. The powder jet 36 is thereby guided in the vicinity of the laser beam 35 or through it. The powder jet emerges from the nozzle 38 in such a way that, when hitting the component surface 31a of the component 30 to be coated, the required area is exposed to the required amount of alloy powder. The focus 35a of the laser beam 35 is adjusted so that it lies exactly on the component surface; if the heating is too strong here, it may also be advantageous to guide the coating lance 32 in such a way that the component surface comes to lie above or below the focus 35a. The energy density in the focal spot of the laser beam is approximately 10 ⁴ W / cm ² .

There is a combined application / introduction of the alloy powder in the Coating area - the valve seat area. In the present case an alloying takes place in the 1/10 mm range connected with an application of a few millimeters, approx. 2-3 mm, thick layer; that shown and described with FIG Wear protection layer is firmly anchored in the base material in this way.

During the coating process, the component - the cylinder head - expediently cooled. This is a compromise between a fast Heat dissipation to prevent over-melting of the Base material, between an ideal gradient for the formation of the desired structure and between a slow cooling and low Temperature differences found to avoid cracks.

To avoid the formation of unwanted oxides, the entire Coating process under a protective gas atmosphere such as under argon or nitrogen. The powder material is sprayed with inert gas, the Inert gas in the feed 37 carried or in a separate line to Area of the nozzle 38 is passed.

Alternatively to the described application of the alloy powder, the Alloy powder also, for example in the form of a paste on the zu coating area are applied. The coating lance then comprises only the laser device and optionally a protective gas supply device which makes it structurally very simplified.

The provided for coating cylinder head blank is total with a made certain allowance, so that may subsequently be in the coating occurring heat distortion in the finishing can be compensated. The Pre-processing of the valve seat areas to be coated is done with a certain undersize, since there is applied a layer. During the Coating the valve seat portion 31a, 31b, 31c, 31d moves the Coating lance 32 with a linear speed of up to 3 m / min and is thereby turned accordingly. There are several adjacent caterpillars - ever wide one to two - with a degree of overlap of approx. 30-50% applied. Finally, the coated area is finished by machining.

Claims (4)

1. A method of coating an aluminium-alloy component, especially the valve seat region (31a, 31b, 31c, 31d) of a cylinder head (30) of an internal combustion engine, using an alloy powder which contains

   10-70 wt.%, especially 20-50 wt.% of silicon (Si) and 5-50 wt.%, especially 10-40 wt.% titanium (Ti), remainder aluminium (Al), and if required

   up to 25 wt.%, especially 1-15 wt.% nickel (Ni) and/or up to 20 wt.%, especially 1-10 wt.% copper (Cu) and if required

   boron nitrite (BN), graphite, B₂O₃ and/or Co/Cr₂O₂ in proportions by weight totalling up to 20%, especially 5-10% and optionally

   SiC and/or B₄C in proportions by weight totalling up to 30%, especially 5-20%, the alloy powder being applied by a high-energy beam, especially a laser beam (35), wherein the powder (36) is at least partly converted from the solid to the molten phase and is deposited or incorporated in a molten pool on the surface of the component, so that during the subsequent solidification process a high-melting intermetallic Al-Ti phase (20) with incorporated Si particles (22) forms in the primary structural matrix.
2. A method according to claim 1, characterised in that the alloy powder is applied to the component surface by a suitable powder-conveying device comprising a nozzle (38) and co-operating with the laser beam (35), in that the powder is at least partly melted in or at least near the laser beam (35).
3. A method according to claim 1 or 2, characterised in that the component (30) is cooled during the coating process.
4. A method according to claim 1 or 2, characterised in that coating is effected in an inert atmosphere.

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