|Title of Invention||
"A METHOD OF PRODUCING AN ALUMINIUM CYLINDER BLOCK HAVING AT LEAST ONE WEAR-RESISTANT AND TRIBOLOGICALLY OPTIMIZED CYLINDER RUNNING FACE AND DEVICE FOR CARRYING OUT THE METHOD"
|Abstract||This invention relates to an aluminium cylinder block comprising a cylinder running face, which is coated with silicon. The invention also relates to a method by which the silicon is applied to the running face comprising melting powdered metal silicon, which is fried at eh face in a powdered metal beam, under heat of a laser which is fired at the running face at the point of impact of the powdered beam. Furthermore, the invention relates to a device with which the cylinder block may be manufactured.|
The invention relates to an aluminium cylinder block
having at least one wear-resistant and tribologically
optimised cylinder running face, method, for producing same
and device for carrying out the method,
According to EP 0 837 152 Al (Bayerische Motoren Werke AG), there is known a method of coating a component of an internal combustion engine, which component consists of an aluminium alloy. A laser beam is directed in such a way that it does not directly reach the surface of the component to be coated, but first hits a powder beam. As a result of the energy of the powder beam, the powder is transformed completely from the solid phase into the liquid phase, so that the powder, when hitting the component surface, is separated in the form of fine droplets as a coating material on the component surface, which fine droplets, as a result of the solidification conditions solidify so as to be partially amorphous.
Therefore, in the case of the prior art method, the powder is not alloyed into the surface layer of the component, but there takes place a phase transformation of the coating material on its way to the surface, with the aluminium silicon powder being liquefied in the laser beam. When the powder solidifies on the surface, the object is to release a finely dispersed silicon, a so-called primary silicon.
Depending on the cooling speed, the purpose is to produce silicon crystals whose size ranges between 1 to 5 µm. However, rapid cooling, as required, cannot be achieved in practice because of the energy of the laser beam acting on the component to be coated. In consequence, the substrate surface heats up very quickly and therefore cannot discharge quickly enough the heat of the arriving Si melt, so that instead of a crystalline phase and primary crystals, there occurs an amorphous phase.
In accordance with the embodiment of the BMW patent, in the case of an applied layer thickness of 3 mm, approximately 50% are removed to achieve a smooth, planar surface of the coating material (column 6, lines 10 to 15). This means high removal losses and an unused boundary zone as a result of the pronounced waviness of the material applied drop-wise, which constitutes an additional disadvantage.
Furthermore, it is known from Ep-A-0 221 276 to render an aluminium alloy more wear-resistant by remelting its surface layer by laser energy. A layer consisting of a bonding agent, silicon in powder form, copper and titanium carbide is applied to the surface and subsequently melted into the surface by laser. According
to the embodiments listed, TIC is added in amounts ranging between 5 and 30% and achieves a considerable increase in the surface hardness.
However, from a tribological point of view, the extremely high cooling speed during laser remelting achieves a high degree of core fineness, but a sufficient amount of primary silicon cannot be produced with this method. Therefore, laser remelting is not suitable for producing cylinder running faces of reciprocating piston engines consisting of AlSi alloys with supporting plateaus of primary silicon and set-back regions containing lubricants.
EP 0 411 322 describes a method for producing wear-resistant surfaces of components made of an AlSi alloy, which method is based on the previously mentioned EP 0 211 276, but prior to carrying out the laser remelting process, the layer is provided with an inoculation agent (germ forming agent) for primary silicon crystals. The following substances are mentioned as inoculation agents or germ forming agents: silicon carbide, titanium carbide, titannitride, boron carbide and titanium boride.
In a preferred embodiment, the coating is produced by silk-screen technology in the form of a peel-off coating and applied to the surface of the component concerned. The coating thickness can preferably amount to 200 µm and the melting-in depth can amount to 400 to 600 µm. Use is made of a linearly focussed laser beam in an inert atmosphere to be able to achieve a melting-in depth of 400 µm. In the example given, the silicon content in the alloyed zone amounted to 25% with a nickel content of 8% (hardness in excess of 250 HV).
As already mentioned above, it is necessary, in the case of the latter processes of remelting and melting-in, to carry out a cooling process while applying a coating on to the matrix alloy in order to achieve the required finely dispersed segregations of primary silicon. Because of the addition of inoculation agents, reactions can take place on the aluminium surface. In addition, the coating measures cannot always be applied to curved surfaces.
EP 0 622 476 Al proposes a metal substrate with a laser-induced MMC coating. The MMC coating comprises a coating thickness between 200 µm and 3 mm and contains homogeneously distributed SIC particles; in a preferred embodiment, up to 40% by weight of SiC is contained in the MMC coating in the form of homogeneously distributed SIC particles. For production purposes, the powder mixture containing SiC powder and pre-alloyed AlSi powder is heated in a laser beam, with the heat content required for producing a homogeneous alloy from the powder mixture being provided by the powder applied to the substrate. Products containing hard metal materials such as SiC comprise a very high hardness which is disadvantageous for the wear behaviour of the piston rings. Furthermore, machining is very complicated and expensive because the top layer of the ceramic particles has to be removed in order to achieve a functionable, splinter-free running face.
It is therefore the object of the present invention to develop a light metal cylinder block having at least one wear-resistant and tribologically loadable running face, wherein the surface layer consists of 5 to 20% of finely dispersed primary silicon which, in the region of transition to the matrix alloy, comprises a narrow
boundary zone width and which is free from defects and oxide inclusions in the transition zone.
The method used for producing the light metal cylinder blocks should have fewer process stages, and a subsequent chemical treatment is to be eliminated completely.
The objective is achieved by the characteristics given in the claims. Below, several embodiments will be referred to; they represent preferred applications of the laser alloying method in accordance with the invention.
First, there will be described a device for coating the interior of a light metal engine block made of aluminium or a magnesium alloy, wherein a probe in lowered into the cylinder of the engine block with pure silicon powder being introduced at the same time. The probe comprises powder supply means and a laser beam device.
A rotary drive arranged at the probe directs a powder ejection nozzle and an energy beam on to the interior, i.e. the running face of the light metal cylinder block.
The purpose of this device is to alloy hard material particles in the form of silicon by means of a laser beam rotating spiral-like across the running face into silicon particles supplied in parallel. To ensure that the laser energy is distributed over a wide track on to the matrix surface, the laser beam comprises a linear focus with a track width of preferably 2 to 4 mm. As compared to a surface produced by a spot beam, a focus does not result in a wavy profile, but in a flat band with finely dispersed primary silicon particles. The band is referred to as alloyed-on zone and there is only a narrow transition
zone (of the boundary zone) between the alloyed-on zone and the matrix metal (see Figure 1).
The powder comprises a grain structure shortly before hitting the metal matrix alloy and is melted and alloyed-in only when coming into contact with the metal matrix alloy in the region of the laser beam within a contact time of 0.1 to 0.5 seconds, so it is possible, by means of the linear focus, to achieve a small boundary zone percentage of approx. 10%. The laser track is lowered spiral-like in the cylinder bore, and overlapping can be eliminated, if necessary, so that the effective parts practically about one another. There is thus produced a smooth, completely homogeneous surface layer which only needs to be finished by precision machining to eliminate a slight waviness.
As an example of the inventive machining operation applied when producing light metal cylinder blocks with at least one wear-resistant, tribologically optimised cylinder running face, the following machining stages take place:
First, an alloyed-on zone containing primary silicon with a mean layer thickness of 300 to 7 50 µm is produced in the matrix alloy. The exact values of the layer thickness depend on different influencing factors such as process parameters, positioning accuracy of the device and dimensional tolerances of the casting. Therefore, when thicknesses are given below, reference is always made to a "mean" layer thickness, and the tolerance range can be kept very narrow because the device can be centred at the component.
In a further machining stage, the starting layer thickness of 300 to 750 µm is then reduced by precision machining, such as honing, to the required end layer thickness by removing up to 150 µm. The end layer thickness achieved by the inventive method ranges between 150 and 650 µm. The layer is a pure diffusion layer characterised by a structure, especially as defined in claims 1 and 2.
The segregation values of the hard phases can be set by controlling the powder supply, the laser beam feed and the laser energy supplied. In the case of precipitation values smaller than 10 µm, the destruction depth while finish-machining the hard phases is reduced, so that the previously required machining allowances for removing the destroyed hard phases can be reduced considerably. (The destruction depth is determined by the hard phases which are contained in the top layer and which are not firmly bonded in.)
By using the laser beam for alloying-in purposes, the surface is hardened, with surface layer hardness values of at least 160 HV being achieved. Because of the good hardening results, the laser-treated surfaces can be honed directly. Furthermore, previously required additional mechanical and chemical treatment stages for exposing the hard phases are no longer necessary. This also means that it is no longer necessary to bore out the cylinder coatings because, depending on the degree of overlap of the strip-like alloyed-on zone, the surface waviness is negligibly small.
Below, the surface structure achievable in accordance with the invention on an engine block running face will
be described in greater detail with reference to a comparative example.
Figure 1, in the form of a partial cross-section, illustrates the principle of a coating device designed in accordance with the invention.
Figure 2 illustrates the principle of a surface layer produced in accordance with the invention.
Figure 3 shows a comparative example having a different surface structure.
Figure 4 is a cross-section of a casting in the region of the laser-alloyed zone.
In accordance with Figure 1, the coating device designed in accordance with the invention consists of powder supply means 1 which, at their end 1a, comprise a nozzle 1b directed towards the running face 5.
The energy is supplied by a laser beam device 2, a focussing system 3 and a deflecting mirror 4 which ensure that the laser beam does not meet the powder close before it hits the running face surface 7.
According to the known laws of optics, the laser beam 6 is focussed so as to be linear, preferably X-, I- or 8-shaped and then copied on the running face surface 7, for example by tilting the mirror. The amount of energy introduced can be controlled by the form of the copy, so that the precipitation structure can be influenced at the boundaries.
By turning the mirror 4, the laser beam 6 moves across the running face surface 7, so that a strip-like band is obtained. If, at the same time, the laser beam 6 is moved forward towards the cylinder axis 8, the overlapping of the two movements results in a spiral-like coating on the running face surface 7. The rotating movement and the translatory movement towards the cylinder axis 8 should be adjusted to one another in such a way, that the windings of the spiral are close together, thus achieving a closed alloyed-on zone.
Figure 2 shows the alloyed-on zone 10 produced with a linear focus in accordance with the invention and consisting of a zone 11 high in precipitations and laterally arranged zones 12, 13 low in precipitations. Figure 2 shows the condition of the alloyed-on zone directly after laser treatment, and it can be seen that the percentage of the zone LAL low in precipitations is relatively low, relative to the effective length LNL of the zone which is high in precipitations. The respective regions in Figure 3 have been given the reference symbol LAK and are associated with the interface zones 15, 16, 17.
For comparative purposes, Figure 3 shows three alloyed-on zones produced with a conventional circular focus. The coating width produced by a linear focus is approximately identical to that produced by a circular focus. It can be seen that in the case of the method using a circular focus, the effective length LNK of the structure high in precipitations is considerably shorter than the effective length LNL achieved by a linear focus. Furthermore, in the case of a circular focus, the effective depth of the hardened surface layer is very much shorter than in the
case of the linear focus, because in the case of the circular focus, a structure low in precipitations extends down to the deeper zones of the cylinder block structure. This is illustrated in the cross-section according to Figure 3 by the wide interface zones 15, 16, 17.
As, with the same depth of penetration, the effective depth in the comparative example according to Figure 3 is shorter than in the inventive example according to Figure 2, the coating quality in the comparative example is lower. Furthermore, with the machining depth being the same in the comparative example and in the example according to the invention, the amount of material ?HWK having to be removed in the comparative example is considerably higher (?HWL) because the circular focus produces a wavy surface layer which, in the region of the running face, comprises a smaller effective material percentage MK than a corresponding running face portion according to Figure 2 (LNL).
The effective material percentage amounts to LNL in the example according to the invention, whereas MK is formed as the sum of the individual values LNK1, LNK2, LNK3.
The inventive light metal cylinder block therefore comprises a wear-resistant cylinder running face which is tribologically optimised as a result of the uniform distribution of the fine Si primary precipitations and which, due to linear focussing and overlapping treatments, can be produced at reduced production costs.
This is illustrated by the structure shown in Figure 4 which is a micro-section shown in a 200: 1 enlargement, with the righthand half A of Figure 4 showing a cast
alloy of type AlSi9Cu3 and the lefthand half B of the Figure showing a tribologically optimised surface layer with finely dispersed primary silicon precipitations. In the present example, the primary Si percentage amounts of 10%, the primary phase diameter to 4.4 µm and the distance between the Si primary phases to 13 µm.
As far as the load bearing capacity of the new material is concerned, particular significance has to be attached to the bonding of the alloyed-on zone B with the matrix structure A. It can be seen at the micro-section 4 that the transition zone C does not contain any oxides or other defects. This is due to the fact that the alloyed-on zone was produced practically "in situ" from the matrix structure, thus achieving a uniform material with different compositions in regions A and B.
Light metal cylinder block, method of producing same and device for carrying out the method
List of reference numbers
1 powder supply means
1a end of powder supply means
2 laser beam device
3 focussing system
4 deflecting mirror
5 running face
6 laser beam
7 running face surface
8 cylinder axis 9
10 alloyed-on zone
11 zone high in precipitations
12, 13 zone low in precipitations
15,16,17 boundary zones
MK percentage of material
LNK effective length of structure high in
precipitations LNL effective length of zone high in precipitations LAL percentage of zone low in precipitations LAK regions associated with the interface zones
?HWK material removed in comparative example ?HWL material removed in example according to the invention
A matrix structure B alloyed-on zone C transition zone
1. A method of producing an aluminium cylinder block having at least one
wear-resistant cylinder running face, which has a minimum hardness of
160 HV and is tribologically optimized,
- in which the aluminium block is cast from an aluminium matrix alloy in a gravity, low-pressure, or pressure diecasting method, and
- in which surface processing is subsequently performed in the form of laser and powder beams occurring parrailelly to one another forming a surface layer by alloying Si powder into the aluminium matrix in such a way that a finely dispersed alloyed-on zone containing primary silicon precipitates results,
- the laser beam being guided in a linearly focused way in a strip width of at least 2 mm, measured transversely to the advance direction, over the aluminium matrix and the Si powder not until in the incidence point of the laser beam being heated in a contact time of 0.1 to 0.5 seconds to tine melting temperature and at the same time being alloyed into the aluminium matrix, and
- the advance speed of the laser beam and powder beam being controlled in such a way that the primary silicon is present in the surface layer over an average layer thickness of 300 µm to 750 µm.
2. The method as claimed in Claim 1, wherein in the incidence point the
aluminium matrix alloy is completely melted to a depth of at least 350
µm and is converted into the plasma state at the aluminium matrix
3. The method as claimed in one of Claims 1 or 2, wherein on the instant shortly before the incidence on the metal matrix alloy, the silicon powder has a grain structure and the powder is melted and alloyed in not until upon contact with the metal matrix alloy in the region of the laser beam within a contact time of 0.1 to 0.5 seconds.
4. The method as claimed in one of Claims 1 to 3 wherein for a focused incidence area of the laser beam of 1mm2 and a laser light output of 3 to 4 KW, the advance speed of the laser beam and powder beam is 0.8 m to 4.0 m per minute.
5. The method as claimed in one of Claims 1 to 4, wherein the laser beam rotates with its focus in a spiral on the inner running face of a hollow cylinder and a strip-shaped alloyed-on zone containing primary silicon is formed at the same time by adding a Si powder.
6. The method as claimed in one of Claims 1 to 5, wherein the average processing depth in the alloyed-on zone is 750 µm.
7. The method as claimed in Claims 1 to 6, wherein the hard phases of the alloyed-on zone are exposed by mechanical processing, the abrasion of the uppermost layer being less than 30% of the total layer thickness.
8. The method as claimed in Claims 1 to 7, wherein the alloyed-on zone is honed directly without intermediate processing.
9. A device for performing the method of a running face coating of hollow
cylinders as claimed in any one of Claims 1 to 8, having a powder feed
device (1), having a laser beam device (2), and having a focusing
system (3), which has a deflection mirror (4), characterized in that
- the powder feed (1) and laser beam device (2) are guided parallel to one another in the radical and axial directions of the hollow cylinder,
- the focusing system (3) has a linear beam outlet having a beam width of 2.0 mm to 2.5 mm, and
- the powder feed is provided with a dosing device, via which the volume flow of the powder is adjustable as a function of the advance speed of the laser beam.
10. The device as claimed in Claim 9, wherein the focusing system (3) has
an X-shaped, I-shaped, or 8-shaped focus shape, which allows an
elevated energy emission at the upper and lower edge zones in
comparison to the middle focus region.
This invention relates to an aluminium cylinder block comprising a cylinder running face, which is coated with silicon. The invention also relates to a method by which the silicon is applied to the running face comprising melting powdered metal silicon, which is fried at eh face in a powdered metal beam, under heat of a laser which is fired at the running face at the point of impact of the powdered beam. Furthermore, the invention relates to a device with which the cylinder block may be manufactured.
|Indian Patent Application Number||IN/PCT/2000/00461/KOL|
|PG Journal Number||19/2007|
|Date of Filing||31-Oct-2000|
|Name of Patentee||VAW ALUMINIUM AG..,|
|Applicant Address||GEORG-VON-BOSSELAGER-STR.25 53117 BONN,|
|PCT International Classification Number||C23C 26/02,24/10|
|PCT International Application Number||PCT/EP00/02125|
|PCT International Filing date||2000-03-10|