DE102006032110A1 - Process for coating an aluminum-silicon cast article - Google Patents

Abstract

In order to develop a method for applying at least one adherent layer to at least one object made of aluminum-silicon casting in such a way that the formation of cracks due to the application of the layer in the article to be coated is prevented, it is proposed that the layer be applied by means of cold gas spraying , The present invention further relates to an engine block of an aluminum-silicon alloy, in particular of aluminum-silicon casting, for example with an aluminum content of 83 weight percent (wt .-%) and with a silicon content of 17 wt .-% (so-called AlSi17), with at least one adherent layer applied by means of cold gas spraying and an internal combustion engine with at least one such engine block.

Description

Technical area

The The present invention relates to a method of applying at least a firmly adhering layer on at least one object Aluminum-silicon casting.

State of the art

Items out Aluminum-silicon casting are used in many industrial sectors Manufacture coated with a firmly adhering layer, these Layer, for example, as wear protection, as corrosion protection, for surface finishing, to improve the electrical and thermal conductivity or for electrical and thermal insulation.

in this connection the layer is thermally applied to the object to be coated injected. Known method to layers or coatings Different types by means of thermal spraying on materials made of aluminum-silicon casting are, for example, plasma spraying, Arc spraying or flame spraying, such as high-speed flame spraying.

adversely however, in these thermal spraying processes, during coating a heat input takes place in the object to be coated. This thermal load leads Cast articles for the formation of notches and cracks, in a further step must be closed again. Finest cracks show up over time and lead to Breakage as well as premature wear with the result of repairs incurred or shorten the life of the components.

Especially pronounced These problems are shown in engine blocks made of aluminum-silicon casting, because engine blocks are exposed to very high mechanical and thermal loads during operation. However, such problems also occur in other aluminum-silicon castings on, such as with radiator parts or in chassis components and also in heat exchangers.

Another disadvantage of the coating by means of thermal spraying method is the fact that the surface of the object to be coated pretreated before applying the layer, for example by blasting, such as by blasting or by irradiation, roughened with corundum, in order to ensure sufficient adhesion applied layer on the object to reach. Various methods for preparing the surface intended for coating with a thermally sprayed layer are known, for example, from the document DE 103 14 249 B3 known from the prior art.

traditionally, is used as a coating for engine blocks For example, an aluminum-silicon alloy by means of arc spraying applied with wire: the layer thus applied is already applied and fulfilled the required technical characteristics. In this coating process arises However, a high proportion of fine dust, a so-called overspray. This one does not adhere to the component. Usually the Overspray collected by a suction system and separated.

• – eine ungleichmäßige Verteilung sowie
• – ein hoher Oxidgehalt der aufgetragenen Schicht.

Other disadvantages of arc spraying with air

• - an uneven distribution as well
• A high oxide content of the applied layer.

In younger Time a method was developed, the so-called cold gas spraying, in which the spray particles in a "cold" carrier gas be accelerated to high speeds. The coating is caused by the impact of the particles on the workpiece with high kinetic energy formed. Upon impact, the particles form not in the "cold" carrier gas melt, a dense and adherent layer, being plastic Deformation and resulting local heat release for cohesion and Adhere the sprayed layer to the workpiece. An oxidation and / or Phase transformations of the coating material can thus be largely avoid.

The Spray particles are added as a powder, the used Powder usually a particle size of 1 Micrometer to 100 microns. It is also possible, however, powder with significantly larger particles to use. The high kinetic energy of the spray particles in the relaxation of the carrier gas. After injection of the spray particles into the gas jet, the Gas in a nozzle relaxed, with gas and spray particles at speeds above the speed of sound are accelerated.

Such a method and apparatus for cold gas spraying are in the document EP 0 484 533 B1 from the prior art as well as in the publication "Plant engineering and process control in cold gas spraying equipment Engineering and Process Control for Cold Spraying" by P. Richter, W. Krömmer and P. Heinrich in the conference volume ITSC 2002 (International Thermal Spray Conference and Exposure, DVS Special Session in Essen 2002, Reprint 47 / 02, eds. Linde AG, Linde Gas Division) described in detail.

When Nozzle becomes In the case of cold gas spraying, as a rule, a de Laval nozzle or Laval nozzle is used. The carrier gas is expanded together with the spray particles in the Laval nozzle. While the pressure in the Laval nozzle drops the carrier gas velocity increases to values up to 3,000 meters per second and the particle velocity to values up to 1,400 meters per second.

Laval nozzles exist from a convergent and a divergent adjoining in the current direction Section. As a carrier gas Nitrogen is usually used, but also argon, helium and mixtures from these three gases are used.

From Advantage is a warming the carrier gas before the relaxation and thus heating of the spray particles, wherein a melting of the spray particles is excluded. The final speed the spray particles coming from the nozzle, from the material of the spray particles, from the temperature of the spray particles and the carrier gas type depends is in almost all cases at least 500 meters per second; usually, however, more than 650 meters per second and often even more than 800 meters per second reached.

Illustration of the present invention: Task, solution, Advantages; best way to execute of the present invention

outgoing from the disadvantages and shortcomings set out above as well as in appreciation of the prior art is the present invention the task is based on a method of the type mentioned above to further educate that the emergence of on the application of the layer attributable Cracks in the object to be coated is prevented.

These The object is achieved by a method with the specified in claim 1 Characteristics solved. advantageous Embodiments and expedient developments The present invention is characterized in the subclaims.

Of the The present invention is thus the essential property of Cold gas spraying on the basis that during coating no significant heat in the Object is introduced. So there the object to be coated when applying the layer is not exposed to thermal stress, the basic material of the object remains unaffected, and that Arising from local heat supply attributable Defects or cracks are prevented.

in the Contrary to known thermal coating methods, such as Arc spraying, provides the coating method of the invention Furthermore, the advantage that the surface of the article for coating does not have to be pretreated. For example, deleted in particular in the light metal sector, the operation of surface pretreatment by blasting, resulting in a cost reduction as well as a simplification of the coating process leads.

Of the Use of the cold gas spraying process thus leads to the surface of the to be coated object, for example, the surface of the to be coated engine block, no thermal stress and therefore it does not lead to a melting of spray particles and substrate comes; this makes possible the abandonment of a pretreatment of the surface; rather, it becomes a homogeneous one and stable coating of the workpiece formed by the cold gas spray particles Impact with high kinetic energy on the surface of the workpiece.

advantageously, the cold gas spraying takes place by means of cold spray particles an aluminum alloy, for example of an aluminum-silicon alloy, such as an aluminum-silicon alloy with an aluminum content of 88 weight percent (wt.%) and having a silicon content of 12% by weight (= so-called AlSi12).

There is also the casting of an aluminum-silicon alloy, be through the inventive method metallurgical problems almost completely locked out. This is due to the fact that after coating only equal or at least similar materials border each other and the adjacent materials have similar or identical electronegativities.

One Another advantage of the present invention is therefore that for the Cold gas spray particles the same or a very similar material can be selected can, from which the cast object consists. By the cold gas spraying Consequently, a connection arises from the same or similar Materials, thereby avoiding metallurgical problems.

With the method according to the invention is it thus possible an aluminum-silicon cast object, For example, an aluminum-silicon cast engine block, to simple Way to coat. The covered object and / or The coated engine block can then be considered qualitatively flawless Component be used.

In the method according to the invention, the cold gas spray particles form a homogeneous layer upon impact with the article due to their high kinetic energy. The applied Layer is thus as good as non-porous and very dense. It is advantageous to use cold gas spray particles having a size of from about 1 micron to about 300 microns, preferably to about 100 microns, most preferably to about 50 microns. With spray particles of this size, a particularly homogeneous layer is produced, which can be applied very precisely.

One Another advantage of the present invention is the low oxide content the layer applied by cold gas spraying; the oxide content only corresponds to that of the starting powder of the spray particles. By the use of cold gas spraying it is possible, oxide-free Layers with very good adhesion to the base material or to the object too produce.

Also is in the inventive method in Compared to conventional thermal coating process of overspray significantly reduced.

In Advantageous design AlSi17 castings are coated. The aluminum-silicon casting of the article thus advantageously has an aluminum content of 83 weight percent (wt%) and a silicon content of 17 wt% on.

With Motor blocks are particularly advantageously coated with the method according to the invention. With the method according to the invention is it thus possible engine blocks Made of aluminum-silicon casting in a very simple way with at least to coat a layer produced by cold gas spraying, wherein the layer may be at least one intermediate layer. With the method according to the invention is it also possible Other components made of aluminum-silicon casting in an advantageous manner to coat, such as radiator parts and suspension components, about axle carrier, and also heat exchangers.

The The present invention further relates to an engine block an aluminum-silicon alloy, in particular of aluminum-silicon casting, for example with a Aluminum content of 83 weight percent (wt .-%) and with a silicon content of 17 wt .-% (so-called AlSi17), with at least one means Cold gas spraying, in particular by means of the method according to the above set forth type, applied adherent layer, for example with at least one by means of cold gas spraying, in particular by means of the method according to the above set forth type, applied adherent interlayer.

There the adhesive mechanism of the layer one on plastic deformation based stapling is eliminated thermal stress of the engine block. Because engine blocks are exposed to very high loads, the coatings must be very be resilient. The applied by cold gas spraying layer has this property in an excellent way. Continue to find no thermal stress even in the coated engine block while the defect attributable to the coating or tensions.

Consist Layer and engine block of the same or at least one similar material, so are the use during the total operating time of the engine block no metallurgical Problems. Consequently, it is advantageous if the layer made of an aluminum-silicon alloy. A layer of aluminum or another aluminum alloy is also possible.

The The present invention finally relates to an internal combustion engine with at least one engine block according to the above Art.

Claims (10)

Method for applying at least one adherent layer to at least one object made of aluminum-silicon casting, characterized in that the layer is applied by means of cold gas spraying. Method according to claim 1, characterized in that the layer as at least one intermediate layer is applied. Method according to claim 1 or 2, characterized in that the cold gas spraying by means of cold gas spray particles from an aluminum alloy, in particular from an aluminum-silicon alloy, for example, AlSi12 with an aluminum content of 88 weight percent (Wt .-%) and with a silicon content of 12 wt .-%, takes place. Process according to at least one of the claims 1 to 3, characterized in that the cold gas spraying means Cold gas spray particles of a size of about 1 micron to about 300 microns, in particular a size of up to to 100 microns, for example a size of up to 50 microns, he follows. Process according to at least one of the claims 1 to 4, characterized in that the surface of the article before the Applying the layer untreated, especially unirradiated, is. Process according to at least one of the claims 1 to 5, characterized in that the object at least an engine block is. Engine block made of an aluminum-silicon alloy, in particular of aluminum-silicon casting, for Example with an aluminum content of 83% by weight (wt .-%) and with a silicon content of 17% by weight (so-called AlSi17), with at least one adherent by means of cold gas spraying Layer. Engine block according to claim 7, characterized in that the layer at least one intermediate layer is. Engine block according to claim 7 or 8, characterized in that the layer of an aluminum alloy, in particular from an aluminum-silicon alloy, for example from AlSi12 with an aluminum content of 88 weight percent (wt.%) and a Silicon content of 12 wt .-%, is. Internal combustion engine, characterized by at least an engine block according to at least one of the claims 7 to 9.