EP1041173A1 - Light metal cylinder block, method for making it and apparatus for carrying out the process - Google Patents

Abstract

A light metal cylinder block, having hard cylinder running surface layers of aluminum-silicon alloy containing finely disper round primary silicon particles, is new. A light metal cylinder block has cylinder running faces comprising a surface layer which has a hardness of NOTLESS 160 HV which consists of 10-14% Al-Si eutectic, 5-20% uniformly dispersed round primary silicon precipitate particles of 1-10 mu average diameter and balance pure Al phase. Independent claims are also included for the following: (i) production of the above light metal cylinder block by gravity, pressure or pressure die casting and then surface treatment with a laser beam parallel to a powder jet, the laser beam being pas with a width of ≥ 2 mm over the light metal matrix surface and the powder being heated to the melting temperature and inwardl diffused in 0.1-0.5 sec. at the laser beam incidence point; and (ii) equipment for carrying out the above process.

Description

The invention relates to a light metal cylinder block with at least a wear-resistant and tribologically optimized Cylinder tread, comprising a light metal matrix alloy and a hard metal-containing powder material that is used as a finely dispersed, Primary silicon excretions contain surface layer is present on the light metal matrix.

According to EP 0 837 152 A1 (Bayerische Motoren Werke AG) is a method for coating an existing aluminum alloy Known component of an internal combustion engine. In doing so, a Laser beam directed so that it is not directly on the surface of the component to be coated, but previously on one Powder jet hits. Because of the energy of the laser beam Powder is completely transferred from the solid to the liquid phase, so that it hits the component surface in shape fine droplets are deposited on it as layer material, which partially solidify amorphously due to the solidification conditions.

In the known method there is therefore no alloying of the Powder in the surface layer of the component, but it will a phase change of the coating material on the way to Surface performed, the aluminum-silicon powder in Laser beam is liquefied. When solidifying on the surface should release finely dispersed silicon, so-called primary silicon become.

Depending on the cooling rate, silicon crystals should be used be produced in the order of 1 to 5 microns. The one In practice, however, the rapid cooling required cannot be achieved because the energy of the laser beam is towards that coating component acts. The substrate surface is therefore very hot and can therefore heat the impacting Si melt not dissipate quickly enough so that no crystalline Phase and no primary crystals but amorphous phases.

According to the embodiment of the BMW patent, a on a worn layer thickness of 3 mm to achieve a smooth, flat surface of the layer material removed about 50% (Column 6, lines 10 to 15). This means a high loss of stock, to which is still an unused edge zone by a high Waviness of the droplet-like material applied as disadvantageous must be added.

From EP-A-0 221 276 it is also known an aluminum alloy by remelting their peripheral layers with laser energy train more wear resistant. Doing so will surface a layer of a binder, powdered silicon, copper and titanium carbide and then lasered in melted the surface. The additions to TIC are in the embodiments between 5 to 30% and cause a considerable increase in surface hardness.

From a tribological point of view, however, the extremely high Cooling rate during laser remelting is a high grain size, however, insufficient formation of the primary silicon achievable with this procedure. Hence the laser remelting for the production of cylinder liners from Reciprocating piston machines made of AlSi alloys with load-bearing plateaus made of primary silicon and reset, containing lubricants Areas unsuitable.

EP 0 411 322 A1 describes a process for producing more wear-resistant Surfaces on components made of an AlSi alloy described, which is based on the aforementioned EP 0 221 276, however, the layer prior to laser melting is a vaccine (Nucleating agent) added for primary silicon crystals becomes. The following substances are used as inoculants or nucleating agents called: silicon nitride, silicon carbide, titanium carbide, titanium nitride, Boron carbide and titanium boride.

In a preferred embodiment, the coating produced in the form of screen printing technology as a peel-off film applied the surface of the component in question. The fat the layer can preferably be 200 μm and the melting depth 400 up to 600 µm. It becomes a line-focused laser beam used in an inert atmosphere to melt down with a melting depth of 400 µm. The silicon content in the alloyed zone was 25% in the example a nickel content of 8% (hardness above 250 HV).

As already described, it is the latter method of remelting or melting, required Cooling while applying a layer on the matrix alloy to perform the desired finely dispersed excretions of the primary silicon. Because of the added Vaccines can cause reactions with the aluminum surface respectively. In addition, the coating measures for curved Surfaces are not always applicable.

EP 0 622 476 A1 describes a metal substrate with a laser-induced one MMC coating known. The MMC layer has one Layer thickness between 200 microns and 3 mm and contains homogeneous distributed SIC particles, preferably up to 40 percent by weight SiC as homogeneously distributed SIC particles in the MMC layer are included. The powder mixture is included for production. SiC powder and pre-alloyed AlSi powder in one laser beam heated, the for the preparation of a homogeneous Alloy from the powder mixture required heat content the powder impinging on the substrate is brought about. Products with hard metal materials such as SiC have a very high Hardness that is unfavorable for the wear behavior of the piston rings are. In addition, the processing is very complex because the top layer of the ceramic particles has to be removed, to achieve a functional, splinter-free tread.

The object of the present invention is therefore a light alloy cylinder block with at least one wear-resistant tribological to develop resilient tread in which the Surface layer made of 5 to 20% finely dispersed primary silicon there is a small marginal zone width in the transition to the matrix alloy and that in the transition zone free of defects and is oxide inclusions. The one used to manufacture the light alloy cylinder block Process should get by with fewer process steps, whereby chemical post-processing is completely dispensed with should.

The object is achieved by those specified in the claims Features resolved. The following are several exemplary embodiments indicated, which are preferred use cases of laser alloying according to the invention.

First, a device for coating the interior of a Light metal engine block made of aluminum or a magnesium alloy described, with a probe in the cylinder of a Engine blocks are sunk and at the same time pure silicon powder can be supplied. The probe has a powder feed and a laser beam device.

By means of a rotary drive arranged on the probe, a Powder application nozzle and an energy beam on the interior or steered the tread of the light metal engine block.

This device is intended for the alloying of hard material particles in the form of silicon over a spiral over the tread rotating laser beam with parallel supplied silicon particles respectively. So that the laser energy is spread over a wide range The laser beam has a track distributed on the matrix surface a linear focus with a track width of preferably 2 to 4 mm. Compared to one by point laser generated surface does not form a wavy at the focus Profile, but a flat band with finely dispersed primary silicon particles out. The band is called the Alloy Zone, being just a narrow transition zone (the peripheral zone) between on an alloyed zone and the matrix metal (see FIG. 1).

Since the powder just before it hits the metal matrix alloy has a grain structure and only in contact with the metal matrix alloy in the area of the laser beam melted within a contact time of 0.1 to 0.5 sec and is alloyed, can be in the linear focus achieve a low marginal zone share of approx. 10%. The laser track is lowered spirally in the cylinder bore, if necessary an overlap can be dispensed with, so that the useful parts practically collide. Thus arises a smooth, completely homogeneous surface layer that only still by finishing to remove a slight Ripple must be finished.

As an example of the processing according to the invention during manufacture a light alloy cylinder block with at least one wear-resistant, tribologically optimized cylinder running surface The following processing steps are assumed:

First, an alloy zone containing primary silicon with an average layer thickness of 300 to 750 µm in the matrix alloy generated. The exact values of the layer thickness depend of various influencing factors, such as process parameters, accuracy the device positioning and dimensional tolerance of the casting from. It is therefore in the following for all thicknesses of an "average" layer thickness spoken, the tolerance range can be kept very close since the device on Component can be centered.

The initial layer thickness of 300 to 750 microns is then in one further processing step to the desired final layer thickness by fine machining with a removal of up to 150 µm, such as e.g. by honing etc. According to the invention The final layer thickness achieved in the process is in the range from 150 to 650 µm. It is a pure diffusion layer, that defined by a special one in claims 1 and 2 Structure is marked.

With the control of the powder supply, the feed of the laser beam and the supplied laser energy allow the excretion variables adjust the hard phases. For excrement sizes less than 10 µm reduces the depth of destruction in the mechanical finishing of the hard phases, so that the previously required processing allowances for the removal of the destroyed Hard phases can be significantly reduced. (The depth of destruction is contained in the top layer, hard phases not firmly integrated.)

The surface is created by alloying with the laser beam hardened, with hardness values of the surface layer of at least 160 HV can be reached. As a result of the good hardening, honing the laser surfaces directly. Additional required so far mechanical or chemical processing steps for exemption the hard phases are also no longer required. This is the previously required drilling of the cylinder coatings no longer necessary because of the surface ripple depending on the overlap of the strip-shaped alloy zone negligible because it is very low.

Fig. 1

Prinzipbild einer erfindungsgemäß ausgebildeten Beschichtungseinrichtung im Teilquerschnitt;

Fig. 2

Prinzipbild einer erfindungsgemäß erzeugten Oberflächenschicht;

Fig. 3

Vergleichsbeispiel mit einer anderen Oberflächenstruktur;

Fig. 4

Querschnitt an einem Gußteil im Bereich der laserlegierten Zone.

The surface structure achievable according to the invention on an engine block running surface is explained in more detail below with the aid of a comparative example. Show it:

Fig. 1

Block diagram of a coating device designed according to the invention in partial cross section;

Fig. 2

Block diagram of a surface layer produced according to the invention;

Fig. 3

Comparative example with a different surface structure;

Fig. 4

Cross-section on a casting in the area of the laser-alloyed zone.

According to Figure 1, the coating device designed according to the invention from a powder feeder 1 at its end 1a has a nozzle 1b directed towards the tread 5.

The energy is supplied via a laser beam device 2, a focusing system 3 and a deflecting mirror 4, the ensures that the laser beam 6 only on the tread surface 7 hits with the powder.

According to the known optical laws, the laser beam 6 linear, preferably focused as X, I or 8 and then for example by tilting the mirror on the tread surface 7 shown. Due to the shape of the illustration, the Energy input can be controlled so that the excretion structure can be influenced at its edges.

By rotating the mirror 4, the laser beam 6 travels over the Tread surface 7 so that there is a strip-like band results. If at the same time a feed movement in the direction the cylinder axis 8 takes place, results from superposition a spiral coating of the tread surface of the two movements 7. The rotating and the translational Movement in the direction of the cylinder axis 8 should be one on the other be tuned so that the turns of the spiral are tight abut each other so that there is a closed alloy zone results.

FIG. 2 shows the alloy zone 10, which is produced according to the invention with a line focus, and consists of a zone 11 which is rich in excretions and two zones 12, 13 which are arranged on the side and have little precipitation. Figure 2 shows the state of the alloy zone immediately after the laser coating, it being evident that the proportion of the low-precipitation zone L _AL , based on the usable length L _{NL of} the precipitation-rich zone, is relatively small. The corresponding areas in FIG. 3 are designated L _AK , which belong to the edge zones 15, 16, 17.

In FIG. 3, three alloy zones produced with a conventional circular focus are shown as a comparative example, the coating width approximately matching in the method with line focus and in the method with circular focus. It can be seen that the usable length L _{NK of} the structure rich in excretions in the method with circular focus is considerably less than the usable length in the line focus L _NL . Furthermore, the usable depth of the hardened surface layer in the circular focus is considerably less than in the line focus, since in the circular focus a structure with little elimination extends into deeper zones of the cylinder block structure. This is illustrated in the cross section according to FIG. 3 by the wide edge zones 15, 16, 17.

Since the usable depth in the comparative example according to FIG. 3 is less than the same depth of penetration in the example according to the invention according to FIG. 2, the quality of the coating according to the comparative example is less favorable. Furthermore, the required removal ΔH _{WK is} significantly higher in the comparative example with the same machining depth as in the inventive example (ΔH _WL ), since the circular focus creates a wavy surface layer which has a lower usable material proportion M _K in the area of the tread than a corresponding tread section according to FIG. 2 ( L _NL ).

In the _{example of} the invention, the usable material _fraction is L _NL , while M _{K is formed} as the sum of the individual _values L _NK1 , L _NK2 , L _NK3 .

The light alloy cylinder block according to the invention therefore has a more wear-resistant cylinder tread, thanks to uniform Distribution of the fine primary Si precipitates optimized tribologically is and by linear focus and overlapping Coating can be produced with significantly reduced production costs is.

It is illustrated on the basis of the microstructure in FIG. 4. It is a micrograph with a magnification of 200: 1, in the right part of the picture A a cast alloy of the type AlSi9Cu3 and in the left part B a tribologically optimized surface layer with finely dispersed primary silicon precipitates is recognizable. The primary silicon content here Example 10%, the primary phase diameter 4.4 µm and the distance the Si primary phases 13 µm.

What is special about the resilience of the new material of importance is the connection of the alloy zone B to the matrix structure A. On micrograph 4 you can see that in the transition zone C there are no oxides or other defects. This is based on the fact that the alloy zone is quasi "in situ" the matrix structure was formed and thus a uniform one Material with different compositions in area A, B was created.

Reference list

1

Powder feed

1a

End of powder feed

1b

jet

2nd

Laser beam device

3rd

Focusing system

4th

Deflecting mirror

5

Tread

6

laser beam

7

Tread surface

8th

Cylinder axis

9

-

10th

Alloy zone

11

Eliminating zone

12.13

Elimination-poor zone

14

-

15, 16, 17

Marginal zones

M _K

Proportion of material

L _NK

Usable length of the elimination-rich structure

L _NL

Usable length of the elimination zone

L _AL

Proportion of the low-excretion zone

L _AK

Areas that belong to the marginal zones

WH _WK

Removal of comparative example

▵H _WL

Removal example of invention

A

Matrix structure

B

Alloy zone

C.

Transition zone

Claims (18)

Light metal cylinder block with at least one wear-resistant and tribologically optimized cylinder running surface, consisting of a light metal matrix alloy with a finely dispersed surface layer containing primary silicon precipitates,
the primary silicon consists of uniformly distributed, round-shaped grains with an average grain diameter between 1 and 10 µm and the surface layer contains 10 to 14% AlSi eutectic, 5 to 20% primary silicon, the rest pure Al phase, the minimum hardness of the surface 160 HV is. Light metal cylinder block according to claim 1, characterized in that the Si primary phases are distributed at a distance of 1-5 primary phase diameters in the surface layer. Light metal cylinder block according to one of the preceding claims,
characterized, that the primary silicon is arranged in a strip-shaped alloy zone with a strip width of at least 2 mm and an average layer thickness of 150-650 µm in the matrix alloy, the strips running spirally over the cylinder running surface. Light metal component according to one of the preceding claims,
characterized, that the strip width is 2 to 4 mm. Light metal component according to one of the preceding claims,
characterized, that in the case of several alloy zones arranged next to one another, an overlap of the disputes is provided, the overlap width being 5 to 10%. Light metal cylinder block with at least one wear-resistant and tribologically optimized cylinder running surface, consisting of a light metal matrix alloy with a finely dispersed surface layer containing primary silicon precipitates, which as a pure diffusion layer consists of a precipitation-rich alloy zone (11) and low-precipitation marginal zones (12, 13),
the precipitates are formed from uniformly distributed, round-shaped grains of primary silicon with an average grain diameter between 1 and 10 µm and the alloy zone consists of 10 to 14% AlSi eutectic, 5 to 20% primary silicon, the rest pure aluminum phase and a minimum hardness of 160 HV has. Process for producing a light metal cylinder block with at least one wear-resistant and tribologically optimized cylinder running surface, comprising a light metal matrix alloy and a hard material-containing powder material, which is present as a finely dispersed surface layer containing primary silicon precipitates in the light metal matrix, by means of gravity, low pressure or die casting processes followed by surface processing parallel laser and powder beams,
the laser beam being guided across the light metal matrix surface in a width of width across the feed direction of at least 2 mm and in which the powder is heated to the melting temperature and diffused only at the point of impact of the laser beam on the light metal matrix surface in a contact time of 0.1 to 0.5 seconds. Method according to claim 7,
characterized, that the light metal matrix alloy is completely melted in the point of impact at a depth of at least 350 μm and is converted into the plasma state on the light metal matrix surface. Method according to one of the preceding claims,
characterized, that the melted powder forms an alloying zone during diffusion, which has a layer thickness of 500-1000 µm. Method according to one of the preceding claims,
characterized, that the powder has a grain structure just before it hits the metal matrix alloy and is only melted and alloyed in contact with the metal matrix alloy in the area of the laser beam within a contact time of 0.1 to 0.5 sec. Method according to one of the preceding claims,
characterized, that the feed speeds of the laser beam and powder jet are controlled such that a) there is a diffusion into the metal matrix alloy with penetration depths of 350 to 850 μm, b) by slowly controlled cooling of the alloy zone, rounded primary phases of less than 10 μm are formed, the spacing of which is 1 to 5 times the primary phase diameter, c) an elimination of hard phases is obtained, with a layer hardness of HV 110 to 160. A method according to claim 11,
characterized, that the feed rate is 0.8 to 4.0 m per minute with a focused impact surface of the laser beam of 1 to 10 mm ² and a laser light output of 3 to 4 kW. Method according to one of the preceding claims,
characterized, that the laser beam rotates spirally with a line-shaped focus on the inner running surface of a hollow cylinder and a strip-shaped alloy zone containing primary silicon is formed by adding Si powder. Method according to one of the preceding claims,
characterized, that the average machining depth in the alloying zone is 750 µm. Method according to one of the preceding claims,
characterized, that the hard phases of the alloy zone are exposed by mechanical processing, the removal of the top layer being less than 30% of the total layer thickness. Method according to one of the preceding claims,
characterized, that the alloying zone is honed directly without intermediate processing. Device for carrying out the method of coating the tread of hollow cylinders, comprising a powder feed (1), a laser beam device (2) and a focusing system (3) with a deflecting mirror (4),
characterized, that powder feed (1) and laser beam device (2) are guided parallel to one another in the radial and axial directions of the hollow cylinder, that the focusing system (3) has a linear beam exit with a beam width of 2.0 to 2.5 mm and that the powder feed is provided with a metering device, by means of which the volume flow of the powder can be set as a function of the feed speed of the laser beam. Device according to claim 17,
characterized, that the focusing system (3) has an X-, I- or 8-shaped focus shape, which enables an increased energy output at the upper and lower edge zones compared to the central focus area.

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