KR20180121952A - A method of heat treating a component comprising at least one surface section comprising a metallic material and coated with a glaze coating or enamel coating - Google Patents

Abstract

The present invention relates to a method of heat treating at least one surface section (7) in or on a component (1) composed of a metal alloy with a glaze or enamel coating (9) (1) at a temperature equal to at least the minimum quench temperature in order to heat the component (1) to the same heating temperature as the component (1) and to form a high strength microstructure in the component (1) . According to the invention, the component (1) can be heat treated such that on the one hand the maximum strength of the component (1) is reached and on the other hand the chucking of the glaze or enamel coating (9) is reliably prevented. To this end, according to the invention, pre-cooling of the glaze or enamel coating (9) at least at the free surface (9 ') of the glaze or enamel coating (9) before quenching the component (1) The pre-cooling temperature corresponds to the temperature at which the glaze or enamel coating 9 starts to soften at a maximum and the cooling rate when the glaze or enamel coating 9 is pre-cooled is less than the cooling rate during quenching .

Description

A method of heat treating a component comprising at least one surface section comprising a metallic material and coated with a glaze coating or enamel coating

The invention relates to a component made of a metal alloy, in particular a light metal material, in which at least one surface section in or on the part is heat treated with a glaze or enamel coating.

Dr.-Ing. It is described in detail in an article by Wolfgang Kuehn and published in Oberflaechen Polysurfaces No 2/09, pages 6-9, entitled "Moeglichleiten und Grenzen der Emaillierung von Leichtmetallen" As such, the enamel coating is, above all, a glass layer suitable for coating the substrate with respect to melt temperature and thermal expansion coefficient. The enamel coating combines the properties of the glass surface with the process characteristics of the metal in the material. Unlike other coatings, a glass-metal laminate is formed during the stoving of each enamel coating, in which an intermediate layer, known as the intermetallic phase, is formed between the glass material and the metal substrate. These allow the coating to be particularly strongly bonded to the metal. To this end, modern enamels are made of a multi-component mixture, and these multi-component eutectic are used at low stubbing temperatures to achieve very good mechanical hardness and chemical resistance.

It is known from DE 10 2010 025 286 A1 that at least some sections of the inner surface of an exhaust duct made of a light metal cast for a combustion engine, for example a cylinder head, can be effectively protected from thermal overstress by coating a coating formed of a glass material It is known. The practical implementation of this proposal should endure the mechanical thermal stresses that occur during the operation of the coating on the one hand and the risk of the coating being chipped when machining sections of each component adjacent to the coated surface section It presents a special challenge in point.

When coating a glazed or enameled coating described in WO 2015/018795 A1 on a component made of light metal, the temperature at which the exposed component of the enamel coating on the surface during operation is exposed to the melting temperature of the light metal material and the coating itself It is clear that such coatings can still safely withstand thermal stress and mechanical stress and can reliably protect light metal substrates. Such enamel powders are therefore particularly suitable for coating surfaces exposed to hot exhaust gas streams during use. Such surfaces are generally present in the exhaust gas transport duct area of components such as combustion engines, cylinder heads, turbochargers, and the like. These types of components are typically fabricated in a casting process.

The contents of WO 2015/018795 A1 are incorporated herein by reference.

As described in detail in WO 2015/018795 A1, a suitably constructed slip or the like is applied to a surface section to be coated with a glaze or enamel coating. The entire component or at least each surface section area is then heated to the stubbing temperature. At this temperature, a glass mixture of coating melt and chemical bond is created between the coating and the base material of the component.

The mechanical properties of light metals, especially those made of aluminum alloys, can be precisely controlled by properly heat treating the castings. Thus, the component strength can be significantly increased by quenching after solution annealing, where the component reaches the ambient temperature at a low target temperature, for example, at a high rate during the process. It has proved to be particularly economical if the quenching temperature is stoved and heated and quenching from that temperature is carried out in one process.

In practice, however, it has been found that chipping or enamel coating can cause chipping or glazing on enamel coatings when quenching, e.g., quenching, at very rapid cooling rates after heating the glaze or enamel coating above the normal stubbing temperature of the glaze or enamel coating . Nevertheless, for components that are exposed to high mechanical stresses during use, such as, for example, the cylinder head of a combustion engine, quenching at such high cooling rates is often used. At the same time, these components are exemplary applications for components where the glaze or enamel coating is covered in the high thermal stressed areas.

For this background, it is desirable to use a metal material, in particular a light metal material, on one side to provide a glaze or enamel coating on at least one surface section in order to achieve the maximum strength of the component on the one hand and to safely prevent chipping or glazing of the enamel coating, There is a problem that suggests a way to heat treat the components on which the coating is provided.

The present invention solves this problem by the method indicated in claim 1.

Advantageous embodiments of the invention are set forth in the dependent claims, and the overall concept of the invention will be described in detail below.

Using the method according to the present invention, which consists of a metallic material, in particular a light metal material, for heat treating a component which is coated with a glaze or enamel coating which is consistent with the above-mentioned prior art in at least one surface section on the inside or above, And is heated to a heating temperature which is at least a minimum quenching temperature. The component is then quenched from at least the same temperature as the minimum quench temperature to create a high-strength microstructure within the component.

The heating temperature at which the component is heated before quenching is calculated so that the temperature of the component is at least equal to the minimum quench temperature when starting the quenching process, taking into account the temperature losses that may occur due to component transport or other intermediate operating steps.

According to the present invention, this method is used to pre-cool the glaze or enamel coating to a pre-cooling temperature which is at a temperature corresponding to the temperature at which the glaze or enamel coating starts to soften at least before quenching at least on the free- (pre-cooling).

Here, according to the present invention, the cooling rate at which the glaze or enamel coating is pre-cooled is lower than the cooling rate achieved during quenching.

Thus, through the pre-cooling provided by the present invention, the glaze or enamel coating is pre-cooled to a temperature below the component temperature, generally below the minimum quench temperature, and slowly enough to cure the glaze or enamel coating again before quenching do. Here, within the meaning of the present invention, the target temperature of pre-cooling is generally higher than the temperature at which the glass substrate is softened and the above-described chemical process occurs. As a result, the glaze or enamel coating is permanently and firmly bonded to the metallic material of the component. During pre-cooling, at least in the free-surface region of the coating, the coating is cooled to a temperature below this target temperature.

It has now been found that the process according to the invention is particularly suitable for heat treating components made of light metal materials, in particular aluminum-base materials.

The method according to the invention allows the components to be manufactured to withstand high stresses and ensures that the glaze or enamel coating of the component is completely retained during quenching. Components with a glaze or enamel coating in the component area can be quench-annealed without limiting the solution anneal, even if the temperature allows a considerably low temperature to ensure that the coating remains defect-free. Thus, the maximum mechanical properties that can be achieved in casting materials can be used to the greatest extent.

If the glaze or enamel coating is softened by heating at a temperature corresponding to at least the minimum quenching temperature and thus a conventional set of stubbing temperatures for staining the glaze or enamel coating, The coating is at least glued or enamel coated firmly bonded to the metallic substrate of the component and subsequently cured back to such an extent that it can withstand rapid temperature changes without chipping during quenching of the component as a whole.

Because the glaze or enamel coating is pre-cooled after heating the component to the heating temperature, the component can likewise be cooled to some degree during pre-cooling. Thus, in this case, the minimum quench temperature at which the component begins to quench may be set to a sufficiently high heating temperature such that the component temperature is lower than the originally reached heating temperature, or even after the temperature drop that occurs during component precooling, do.

The pre-cooling temperature at which the glaze or enamel coating is pre-cooled may generally be at least 30 캜, in particular at least 50 캜 lower than the minimum quenching temperature.

When the component is made of aluminum, the temperature at which the glass base of the glaze or enamel coating starts to soften is usually 480-650 ° C, in particular 510-540 ° C. Thus, chipping of the glaze or enamel coating from a component made of an aluminum material is particularly reliably prevented if the pre-cooling temperature is up to 480 ° C, in particular up to 470 ° C or 450 ° C. On the other hand, the typical minimum quench temperature for components made of Al material is at least 480 ° C, in particular at least 500 ° C, and indeed at least 520 ° C, in particular at least 530 ° C, proved to be particularly advantageous.

According to the present invention, pre-cooling of the glaze or enamel coating to the pre-cooling temperature can be performed by passing the fluid flow across the glaze or enamel coating. For this purpose, it is particularly suitable to adjust the temperature of the gas flow appropriately. To this end, compressed air has proven to be a particularly advantageous cooling gas, since in the operating environment in which the method according to the invention is applied, compressed air can be used easily and the compressed air flow can be easily adjusted to provide the necessary cooling to be. It is clear, however, that nitrogen or other similar gases may also be used as examples of protective gases that may be utilized or indicated to prevent reactions between the metal substrate and the gas flow. Each gas flow may be concentrated by a nozzle arrangement that faces the glaze or enamel coating so that the gas flow is concentrated and cooled over each surface section covered by the glaze or enamel coating.

Physically, the layer thickness and thermo-physical data cause the propagation speed of the temperature wave by the cooling medium, and the propagation of the temperature wave is determined by what is known as the thermal conductivity or thermal diffusivity of the glaze or enamel coating. Assuming that the thermal wave does not reach the cast surface by pre-cooling, the metal substrate of the component is not affected. If the layer thickness of the glaze or enamel coating of the type included herein is generally the layer thickness actually used, the cooling time for this is generally at most 60 seconds, in particular at most 40 seconds. Cooling below the minimum quench temperature required for a typical layer thickness can be reliably assured by limiting the pre-cooling duration to a maximum of 20 seconds, especially 5-20 seconds.

Typical layer thicknesses of glaze or enamel coatings are up to 5 mm, especially up to 2 mm.

The specific duration of the pre-cooling of the glaze or enamel coating required in all cases can be determined in a customary manner by those skilled in the art by experimentally measuring the specimen of the component to be heat treated. For this, on the one hand, the temperature drop of the glaze or enamel coating occurring during pre-cooling and, on the other hand, the temperature profile in the interface region between the glaze or enamel coating and the metallic material of the component bearing the coating, Or determined by theoretical means. Ideally, the duration of the pre-cooling is set such that the temperature of the light metal material of the component whose surface section is coated with a glaze or enamel coating is at least equal to the minimum quench temperature.

Here, for the purposes of the present invention, it is sufficient that only the free surface of the glaze or enamel coating is cooled to the pre-cooling temperature so that the temperature of the glaze or enamel coating area in contact with the metal substrate is at a temperature above the minimum quench temperature Is basically assumed. By restricting pre-cooling over the layer of glaze or enamel coating near the free surface according to the free surface of the coating simply, chipping of the glaze or enamel coating in subsequent quenching is prevented. At the same time, since the surface of the coating has already been cooled, the thus formed components and layer-based units are subjected to compressive stress, thereby increasing the resistance of the coating.

The pre-cooling rate during practical use is in the range of less than 5 K / sec. When the cooling rate is at least 0.5 K / sec, the pre-cooling during the pre-cooling of the glaze or enamel coating is rapid, It is not over cooled.

The heat treatment conducted according to the present invention can be usually carried out by quenching after solution annealing. When the component is a casting made of a light metal material, especially an Al material, the annealing time is generally 0.5-5 hours.

The component can then be quenched at a cooling rate of at least 5K / sec, especially at least 7K / sec or at least 10K / sec. In practice, a cooling rate of up to 50 K / s has proved to be reliable, and in all cases, the specific cooling rate achieved for a component where the wall thickness variation is significant and the material locally segregated over the component volume may be wide .

The actual quenching of the component can be carried out in a conventional manner after precooling the glaze or enamel coating according to the invention. Water is particularly suitable as quenching medium here. However, other quenching media such as spray mist, polymer, oil or gas may be used if desired.

The cooling rate achieved in all cases can be set in a manner similar to that known by the quench medium temperature. As an example, if water is used as the quench medium, the water temperature can be the maximum boiling point to prevent an excessively high cooling rate in the component.

As described above, the method according to the present invention is particularly suitable for heat treating components for a combustion engine, in which at least one duct is provided and at least one surface section is coated with a glaze or enamel coating.

In order to prevent over-cooling of the component sections in contact with the area covered by the glaze or enamel coating during pre-cooling, the component sections in which the glaze or enamel coating is not coated with screens, insulating materials and the like, have.

After quenching, the components heat-treated in accordance with the present invention may be subjected to other heat treatments, such as aging in a conventional manner, to further optimize the properties of the component in the field to which the component is applied.

1 schematically shows an example of a type of part which is heat treated in accordance with the invention in the form of a cylinder head 1 for a combustion engine in a section which is arranged in a manner transverse to the longitudinal extension of the cylinder head 1 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings showing an exemplary embodiment.

A cylinder head 1 cast with an aluminum casting material such as an AlSi11- or AlSi10Cu0.5Mg alloy typically used for this purpose has a flat contact surface 2. The flat contact surface is provided with a cylinder head gasket, not shown here, if necessary, during operation, and the cylinder head gasket is seated on the engine block of each combustion engine, also not shown. Here, the combustion engine has combustion chambers arranged in a row and pistons moving up and down, which are not shown here.

The contact surface 2 has a number of spherical recesses 3 corresponding to the number of cylinders of the combustion engine and forms the upper edge of the combustion chamber of the combustion engine in the stroke direction of the piston of the combustion engine.

The inlet duct 5 entering from the longitudinal side portion 4'of the cylinder head 1 is opened towards each of the recesses 3 and during operation each fuel-air mixture flows through the inlet duct 5 Is introduced into the combustion chamber. At the same time, an exhaust duct 6 leading from each recess 3 to the longitudinally opposite side portion 4 "of the cylinder head 1 is connected, and the exhaust gas generated in the combustion process through the exhaust duct 6 And is discharged from the combustion chamber of the combustion engine.

The inner surface 7 of the exhaust duct 6 surrounding the exhaust duct 6 is in contact with the exhaust duct 6 at a high temperature that flows into the exhaust duct 6 at a high speed when the suction port is opened in the area around the suction port 8, It receives high temperature and large mechanical stress from the exhaust gas.

In order to protect the inner surface 7 from these stresses, the inner surface 7 is covered with an enamel coating 9 covering the inner surface 7 over the entire length of the exhaust duct 6 with an average thickness of 400 μm.

The cylinder head 1 is arranged in a line in the longitudinal direction of the cylinder head 1 and has a large number of exhaust ducts corresponding to the number of valves associated with the combustion chamber covered with the enamel coating 9 6).

The preparation of the enamel coating (9) and its composition are described in the above-mentioned WO 2015/018795 A1, the contents of which are already incorporated into the present application.

In order to stove the enamel coating 9 so that the enamel coating 9 is firmly adhered to the Al substrate of the component, first the cylinder head 1 is heated to the stubbing temperature 520 캜.

For the heat treatment according to the present invention, the cylinder head 1 is solution-annealed at a heating temperature of 535 DEG C for 1.5 hours.

At the end of the annealing, the cylinder head 1 is taken out in an annealing furnace not shown in this specification within 10 seconds, and then placed in the holding device 10.

The holding device 10 is part of a pre-cooling device which also includes a nozzle device 11. The nozzle arrangement 11 is provided with nozzles 12 which are directed into the discharge port 13 of each exhaust duct 6 which is constituted on one longitudinal side 4 " , The surface of the longitudinal side portion 4 "surrounding the discharge port 13 is thermally isolated from the surroundings by the screen 14 comprising the heat-resistant material.

The nozzle device 11 is connected to a central compressed air supply 15 through which the compressed air at ambient temperature reaches the nozzle device 11. The compressed air flow D is directly directed to the free surface 9 of the enamel coating 9 through the nozzle 12 associated with each exhaust duct 6 of the cylinder head for pre- '). Within 30-40 seconds the enamel coating 9 is precooled in this manner to a pre-cooling temperature of less than 470 ° C.

Then, the cylinder head 1 is removed from the holding device 10, and immersed in a water bath at a temperature of 95 캜 for 5 seconds. In this manner, the cylinder head 1 is quenched to an ambient temperature.

It can be artificially aged at 200 ° C for 1 - 200 hours after quenching process. In the examples described herein, the aging period was chosen to be 5 hours.

The hardening scale obtained by the heat treatment is the yield strength of the material of which the cylinder head 1 is made.

After artificial aging, the cylinder head (1) cast with an AlSi10Cu0.5Mg alloy according to the quenching medium used has the following yield strength when quenched at a quenching temperature of 535 deg.

1 Cylinder head (component)
2 The contact surface of the cylinder head 1
3 The recess of the cylinder head (1)
4 ", 4 "cylinder head 1,
5 inlet duct
6 exhaust duct
7 The inner surface of the exhaust duct 6
8 Suction port of exhaust duct (6)
9 Enamel coating
9 'The face of the enamel coating 9
10 Holding device
11 nozzle device
12 nozzles
13 outlet port
14 screens
15 Compressed air supply
D compressed air flow

Claims (14)

A method of heat treating a component (1) wherein at least one surface section (7) inside or above a component (1) composed of a metal alloy is coated with a glaze or enamel coating (9)
- heating the component (1) to a heating temperature at least equal to the minimum quenching temperature,
- to heat the component (1) starting at least at the same temperature as the minimum quench temperature, so as to form a high strength microstructure in the component (1)
Cooling the glaze or enamel coating (9) at least on the free side (9 ') of the glaze or enamel coating (9) before quenching the component (1), said pre- Corresponds to the temperature at which the glaze or enamel coating 9 begins to soften,
Characterized in that the cooling rate when the glaze or enamel coating (9) is pre-cooled is less than the cooling rate during quenching. The method according to claim 1,
Characterized in that the glaze or enamel coating (9) is pre-cooled to a pre-cooling temperature by passage of a fluid across the glaze or enamel coating (9). 3. The method of claim 2,
Wherein the fluid is a compressed air flow. ≪ RTI ID = 0.0 > 8. < / RTI > The method according to claim 2 or 3,
Characterized in that the fluid is directed towards the glaze or enamel coating (9) by means of a nozzle arrangement (11). 10. A method according to any one of the preceding claims,
Characterized in that the precooling holding time is set such that the temperature of the metal material of the component (1) on the surface section (7) on which the glaze or enamel coating (9) is coated is at least equal to the minimum quenching temperature. A method of heat treating a component coated with a coating. 10. A method according to any one of the preceding claims,
Characterized in that the cooling rate when the glaze or enamel coating (9) is pre-cooled is less than 5 K / sec. 10. A method according to any one of the preceding claims,
Characterized in that the cooling rate when the glaze or enamel coating (9) is pre-cooled is less than at least 0.5 K / sec. 10. A method according to any one of the preceding claims,
Characterized in that the cooling rate when quenching the component (1) after pre-cooling the glaze or enamel coating (9) is at least 5 K / sec. 10. A method according to any one of the preceding claims,
Characterized in that the cooling rate when quenching the component (1) after pre-cooling the glaze or enamel coating (9) is at most 50 K / sec. 10. A method according to any one of the preceding claims,
Wherein the pre-cooling temperature is at least 30 占 폚 lower than the minimum quenching temperature. 11. The method of claim 10,
Wherein the pre-cooling temperature is at least 50 DEG C lower than the minimum quench temperature. 10. A method according to any one of the preceding claims,
Wherein the pre-cooling temperature is at most 480 ° C. 10. A method according to any one of the preceding claims,
Wherein the metallic material of the component (1) is a light metal material, especially an aluminum-based material. 10. A method according to any one of the preceding claims,
Characterized in that the component 1 is a component 1 for a combustion engine in which at least one duct 6 is provided and in which at least one surface section 7 is coated with a glaze or enamel coating 9 Wherein the glaze or enamel coating is coated.

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