MXPA00011598A - Light metal cylinder block, method for producing the same and device for carrying out said method - Google Patents

Abstract

The invention relates to a light metal cylinder block that comprises at least one wear resisting and tribologically optimized cylinder face and that consists of a light metal matrix alloy with a finely dispersed surface layer containing primary silicon deposits. Said surface layer consists of globular grains with grain diameters between 1 and 10&mgr;m and contains 10 to 14%AlSi eutectics, 5 to 20%primary silicon, remainder pure Al phase. According to the inventive method for producing the light metal cylinder block, a laser beam is guided across the light metal matrix surface in a strip width vertically to the direction of feed of at least 2 mm. Hard material powder is heated up to a melting temperature at the point of incidence of the laser beam on the light metal matrix surface and is diffused. The inventive device for coating the face of hollow cylinders consists of a powder supply means, a laser beam device and a focussing system with a deviation mirror. The powder supply means and the laser beam device are guided in parallel to each other in the radial and in the axial direction of the hollow cylinder. The focussing system is provided with a linear beam gate. The powder supply means is provided with a dosing unit which is used to adjust the volume flow of the powder depending on advance speed of the laser beam.

Description

BLOCK OF LIGHT METAL CYLINDERS, METHOD FOR MANUFACTURING AND APPARATUS FOR CARRYING OUT THE PROCESS Description of the invention The invention relates to a block of light metal cylinders with at least one wear surface of the cylinder that is wear resistant and tribologically optimized comprising a light metal matrix alloy and a hard metal containing powder which exists on the light metal matrix as a finely dispersed surface layer containing primary silicon depositions. According to EP 0 837 152 Al (Bayerische Motoren erke AG) a method is known for coating a component of an internal combustion machine constituted by an aluminum alloy. In this, a laser beam is guided in such a way that it does not hit directly on the surface of the component to be coated, but previously it impinges on a jet of dust. Through the energy of the laser beam, the powder is completely transformed from the solid phase to the liquid phase, so that when it hits the surface of the component, it is deposited on it as a layer of material in the form of fine droplets that, under the conditions of solidification partly solidify in amorphous form.

Accordingly, in the known process, an interleaving of the powder with the surface layer of the component is not carried out but a phase transformation of the coating material in the path to the surface is carried out, in which the powder Aluminum-silicon fluidizes in the laser beam. When solidifying on the surface, finely dispersed silicon known as primary silicon must be released. Depending on the cooling rate, they must produce silicon crystals of the order of magnitude from 1 to 5 μm. However, in practice, the rapid cooling required for this can not be achieved, since the energy of the laser beam acts on the component to be. coated. As a result, the surface of the substrate becomes very hot and therefore can not discharge the heat of the incident Si melt quickly enough, so that a crystalline phase and primary crystals are not produced, but amorphous phases are produced. According to the exemplary embodiment of the BMW patent, in the case of a deposition of 3 mm thickness of the layer approximately 50% of the coating material is removed to obtain a smooth, flat surface (column 6 rows 10 to 15). ). This represents a high erosion loss to which a useless marginal zone must still be added as a disadvantage due to a high undulation of the deposited material in the form of droplets. It is also known from EP-A-0 221 276 to make an aluminum alloy more resistant to wear by recasting its edge layers with laser energy. In this, a layer of a binder, silicon in the form of powder, copper and titanium carbide is applied to the surface and then interfused on the surface with the laser. The TIC additions are between 5 to 30% in the embodiments and have the effect of a considerable increase in the hardness of the surface. Although, under tribological aspects with this process, a great fineness of grain can be obtained due to the extremely high cooling rate when remelting by laser, it is not possible, however, to achieve sufficient primary silicon formation. Due to this, laser remelting for the manufacture of sliding surfaces of cylinders of AISi alloy lifting piston machines with supporting areas of primary silicon and retracted areas containing lubricants is inadequate. In EP 0 411 322 A1, a method for producing wear-resistant surfaces in components of an AISi alloy is described, starting from the previously mentioned EP 0 221 276, in which, however, prior to laser interfusion, an inoculation agent (bacteria former) is added to the layer for primary silicon crystals. The following substances are named as inoculating agents or bacteria-forming agents: silicon nitride, silicon carbide, titanium carbide, titanium nitride, boron carbide and titanium boride. In a preferred embodiment, the coating is produced in the form of the screen printing technique as a release sheet and is applied to the surface of the respective component. The thickness of the layer may preferably be 200 μm and the depth of the interfusion 400 to 600 μm. A laser beam focused in a linear manner in an inert atmosphere is used to perform the interfusion with a fusion depth of 400 μm. The proportion of silicon in the alloy zone was 25% in the example, with a nickel content of 8% (hardness above 250 HV). As already described previously, in the processes of remelting and interfusion mentioned to the latter it is necessary to carry out a cooling during the deposition of a layer on the matrix alloy to obtain the finely dispersed depositions of the primary silicon that are desired. Due to the added inoculation agents, reactions with the aluminum surface can take place. In addition, the coating measures are not always possible to apply in the case of curved surfaces. A metal substrate with laser-induced MMC coating is known from EP 0 622 476 A1. The MMC layer has a layer thickness between 200 μm and 3 mm, and contains homogeneously distributed ICS particles, with the MMC layer preferably containing up to 40 weight percent SiC as homogeneously distributed ICS particles. For processing, the mixture of powder containing SiC powder and AISi powder of previous alloy is heated in a laser beam, being that the thermal content required for the production of a homogeneous alloy of the powder mixture is generated by the powder that hits the substrate. The products with hard metal substances such as SiC have a very high hardness which is inconvenient for the wear behavior of the piston rings. Furthermore, the processing is very complex in that it is necessary to lower the upper layer of ceramic particles in order to obtain a sliding surface free of fragments capable of functioning. Accordingly, the task of the present invention is to develop a cylinder of light metal cylinders with at least one wear-resistant sliding surface, subject to tribological stress, in which the surface layer is constituted by 5 to 20 % of finely dispersed primary silicon which, in the transition to the matrix alloy, has a short width of the marginal zone and which in the transition zone is free of defective points and oxide inclusions. The method applied for the manufacture of the light metal cylinder block must require fewer stages of operation, and chemical reprocessing must be completely dispensed with. The task is solved by the characteristics indicated in the patent claims. In the following, various exemplary embodiments will be set forth, since these are preferred embodiments of the laser alloy according to the invention. First, an apparatus for coating the interior space of a lightweight aluminum engine block or a Magnesium alloy in which a probe is inserted into the cylinder of a motor block and simultaneously pure silicon powder can be fed in. The probe comprises a powder feed device and a laser beam device.

By means of a rotary drive mechanism arranged in the probe, a dust ejector nozzle and an energy beam are guided over the inner space or the sliding surface of the light metal motor block. With this apparatus, the interplay of particles of hard material in the form of silicon must be carried out by means of a laser beam with silicon particles supplied in parallel that spirally rotate on the sliding surface. In order that the laser energy is distributed on the surface of the matrix on a wide track, the laser beam has a focus of linear shape with a track width of preferably 2 to 4 mm. Compared to a surface produced by a laser in the form of a point, in the case of the focus, a wave-shaped profile is not formed, but a flat strip with particles of primary silicon that are firmly dispersed. The strip is designated the overlying zone, since it only comprises a narrow transition zone (the marginal zone) between the superposed zone and the metal of the matrix (see figure 1). Since the powder at the time prior to impacting on the alloy of the metal matrix has a granular structure and only melts and is interalled on contact with the alloy of the metal matrix in the laser beam area within a time of contact from 0.1 to 0.5 sec., in the case of the focus in a linear way it is possible to obtain a reduced proportion of marginal zone of approximately 10%. The laser track is lowered spirally into the cylinder, where necessary, if necessary, an overlap can be dispensed with, so that the useful portions practically abut one another. In this way, a smooth, totally homogeneous surface layer is produced, which is only necessary to be processed by a fine finish to eliminate a slight undulation. As an example of the processing according to the invention in the manufacture of a block of light metal cylinders with at least one wear-resistant tribologically optimized cylinder sliding surface, the following steps of the process are carried out: First, an overlaying zone containing primary silicon with a mean layer thickness of 300 to 750 μm in the matrix alloy. The exact values of the thickness of the layer depend on various magnitudes that influence, such as process parameters, accuracy of the placement of the device and dimensional tolerance of the casting. Accordingly, hereinafter, we refer to a "medium" layer thickness in the case of all thickness indications, the tolerance zone being kept very narrow by virtue of the fact that the device can be centered on the component. The thickness of the starting layer of 300 to 750 μm is then reduced in another step of the operation to the final layer thickness desired by a fine finish with a subtraction of up to 150 μm, as for example by fine grinding. The final layer thickness obtained according to the process according to the invention is in the range of 150 to 650 μm. In this case, it is a pure diffusion layer characterized by a particular structure defined in claims 1 and 2. With the control of the powder feed, the advance of the laser beam and the laser energy supplied, the magnitudes of the laser can be adjusted. deposition of hard phases. In deposition quantities less than 10 μm, the destruction depth is reduced in the final mechanical processing of the hard phases, so that it is possible to significantly reduce the additional operations required so far for the elimination of the destroyed hard phases. destruction is determined by the hard phases not firmly bound, contained in the upper layer.) Through the interplay with the laser beam the surface hardens, reaching hardness values of the surface layer of at least 160 HV .

Due to the good hardening it is possible to carry out fine grinding directly on the laser surfaces. Neither are the additional mechanical or chemical operation steps, hitherto necessary to release access to the hard phases, required anymore. Accordingly, the previously required boring of the cylinder liners is no longer required because the waviness of the surface according to the overlap of the stripe-shaped overlap zone is insignificant as small. The surface structure that can be obtained according to the invention on a sliding surface of a motor block based on a comparative example is explained in more detail below. They show: fig. 1 concept of the principle of a coating apparatus configured according to the invention in partial cross-section; fig. 2 concept of the principle of a surface layer produced according to the invention; fig. 3- Comparative example with another surface structure; fig. 4 cross section of a casting in the area of the laser alloy area. According to Figure 1, the coating apparatus configured according to the invention is constituted by a powder feeding device 1 which at its end has a nozzle lb directed towards the sliding surface 5. The power supply is effected through a laser beam device 2, a focusing system 3 and a reflecting mirror 4 having the function that the laser beam 6 only impacts the surface 7 of the sliding surface together with the dust. According to the known laws of optics, the laser beam 6 is focused in a linear fashion, preferably as X, I or 8, and is then reproduced on the surface 7 of the sliding surface, for example by tilting the mirror. The amount of energy applied can be controlled by the shape of the reproduction, so that the structure of the deposition can be influenced in its relief at the edges. By rotating the mirror 4, the laser beam 6 moves along the surface 7 of the sliding surface so that a strip in the form of a ribbon is obtained. If at the same time an advancing movement is made in the direction of the cylinder axis 8, by superimposing both movements a spiral-shaped coating of the surface 7 of the sliding surface is obtained. The rotational and translational movement in the direction of the cylinder axis 8 must therefore be adjusted in such a way that the turns of the spiral are closely adjacent to each other, so that a compact area of overhang is obtained. Figure 2 shows the zone 10 of overheating that occurs with a linear focus according to the invention, which is constituted by a carr 11 rich in deposition and two deposition zones 12, 13 arranged laterally. Figure 2 shows the condition of the overlying area immediately after laser coating, it being recognized that the proportion of the LAL area deficient in deposition with respect to the useful length LNL of the deposition rich zone is relatively small. The corresponding areas are denoted by LAK in FIG. 3, which belong to the marginal areas 15, 16, 17. In FIG. 3, three overlaying areas produced with a conventional circular focus are shown as a comparative example, in which the width of the Coating of the process with linear focus coincides approximately with that of the process with circular focus. It can be seen that the useful length LNK of the deposition-rich structure is substantially smaller in the process with circular focus than the useful length LN of the process with linear focus. In addition, the useful depth of the hardened surface layer is substantially with the circular focus than with the linear focus, since with the circular focus the structure deficient in deposition extends to deeper areas of the structure of the cylinder block. This is illustrated in the cross section according to Figure 3 by the wide marginal zones 15, 16, 17. By virtue of the fact that at the same depth of penetration the useful depth in the exemplary embodiment according to FIG. 3 is smaller than in the example according to the invention according to FIG. 2, the quality of the coating according to the example comparative is worse. Additionally, the recess? HWK required in the comparative example at the same processing depth as in the example of the invention is substantially greater (? HW), because the circular focus produces a wavy surface than in the area of the surface of sliding has a smaller proportion of useful material M than a corespiring sliding surface segment according to figure 2 (LNL). The proportion of useful material in the example of the invention is L-UL, while M? it is formed as the sum of the individual values tiK, LN 2, LNK3 • Accordingly, the block of light metal cylinders according to the invention has a more wear resistant sliding surface, which is optimized tribologically by uniform distribution of the fine Si primary deposits, and that through the linear approach and overlapping can occur with a significantly reduced manufacturing expense. This is illustrated based on the image of the structure of figure 4. It is an image of a 200: 1 amplification imager, where a cast alloy of the type AlSi9Cu3 can be seen in the right part of the image. and in the left part B of the image a tribologically optimized surface layer with finely dispersed depositions of primary silicon. The proportion of primary silicon in the present example is 10%, the diameter of the primary phase is 4.4 μm, and the distance between the primary phases of Si of 13 μm. For the capacity of resistance to the effort of the new material, the linkage of the zone B of over alloy to the structure A of the matrix is of special importance. In the micrograph 4 it can be seen that in the transition zone C there are no oxides and other defective points. This is due to the fact that the overreaching zone was formed almost "in situ" from the structure of the matrix, which produced a unitary material with different compositions in area A, B.List of reference symbols 1 Powder feed device End of powder feed device lb Nozzle 2 Laser beam device 3 Focusing system 4 Reflector mirror 5 Sliding surface Laser beam 7 Surface of sliding surface 8 Cylinder shaft 9 10 Overreaching zone 11 Deposition rich zone 12, 13 Deposition deficient zone 14 15,16,17 Marginal areas M? Proportion of material LNK Useful length of the structure rich in deposition LNL Useful length of the zone rich in deposition LAL Proportion of the area deficient in deposition LftK Areas that belong to marginal areas HLWK Recess in the comparative example HLWL Recess in the example of the invention A Structure of the matrix B Overhang area C Transition zone

Claims (3)

1. CLAIMS 1. Lightweight metal cylinder block with at least one tribologically optimized wear-resistant cylinder sliding surface, consisting of a light metal matrix alloy with a surface layer containing deposition of finely dispersed primary silicon, characterized because the primary silicon consists of uniformly distributed rounded grains, with an average grain diameter between 1 and 10 μm, and the surface layer contains 10 to 14% of eutectic AIS, 5 to 20% of primary silicon, rest phase Pure, being that the minimum hardness of the surface is 160 HV 2. Block of cylinders of light metal according to claim 1, characterized in that the primary phases of Si are distributed in the layer of the surface at a distance of 1 - 5 diameters of primary phase 3. Block of cylinders of light metal according to one of the preceding claims, characterized in that the primary silicon is available ne in the alloy of the matrix in an area of overhang in the form of a strip with a strip width of at least 2 mm and an average thickness of the layer of 150 - 650 μm, with the stripes extending spirally on the sliding surface of the cylinder. 3. Light metal component according to one of the preceding claims, characterized in that the width of the strip is from 2 to 4 mm. The light metal component according to one of the preceding claims, characterized in that in the case of several adjacent overlying areas an overlap of the strips is provided, the width of the overlap being 5 to 10%. 6. Block of light metal cylinders with at least one tribologically optimized wear-resistant cylinder sliding surface, consisting of a light metal matrix alloy with a surface layer containing deposition of finely dispersed primary silicon, which exists as a pure diffusion layer formed by an overlying zone rich in deposition and marginal areas deficient in deposition, characterized in that the depositions are formed by primary silicon grains of uniformly distributed rounded shape, with an average grain diameter between 1 and 10 μm, and the over alloy zone consists of 10 to 14% of eutectic AISi, 5 to 20% of primary silicon, rest of the pure aluminum phase and has a minimum hardness of 160 HV. 7. Method for the manufacture of a cylinder of light metal cylinders with at least one wear-resistant and tribologically optimized cylinder sliding surface comprising a light metal matrix alloy and a powder material with a hard substance content It exists in the light metal matrix as a surface layer containing depositions of finely dispersed primary silicon, by gravity, vacuum or pressure casting processes with subsequent surface finishing by laser beam and applied powder streams parallel to each other, characterized in that the laser beam is guided with a strip width transverse to the direction of advance of at least 2 mm on the light metal matrix surface, and because the powder is only heated to its melting temperature and interdiffs at the point of incidence of the laser beam on the surface of the light metal matrix in a contact interval of 0.1 to 0.5 seconds. The method according to claim 7, characterized in that the alloy of the light metal matrix is completely melted at least at a depth of 350 μm at the point of incidence and is transformed to the plasma state at the surface of the matrix alloy of light metal. 9. Method according to one of the preceding claims, characterized in that during the diffusion the molten powder forms a zone of over-alloying having a layer thickness of 500-1000 μm. 10. Method according to one of the preceding claims, characterized in that in the time interval immediately prior to the incidence on the matrix alloy, the powder has a granular structure and only melts and forms the interlacing upon contact with the alloy of the light metal matrix in the area of the laser beam within a contact interval of 0.1 to 0.5 seconds. Method according to one of the preceding claims, characterized in that the speeds of advancement of the laser beam and the powder jet are controlled in such a way that a) a diffusion is carried out in the alloy of the metal matrix with penetration depths of 350 to 850 μm, b) by means of a slow controlled cooling of the overreaching zone, primary phases of rounded shape are formed smaller than 10 μm, separated by 1 to 5 diameters of primary phases, c) a deposition of the hard phases is obtained with a layer hardness of HV 110 to 160. Method according to claim 11, characterized in that the advance speed is 0.8 to 4.0 m per minute with an area of incidence of the laser beam approach of 1 to 10 mm2 and a power of laser from 3 to 4 kW. 13. Method according to one of the preceding claims, characterized in that the laser beam spirals with a linear focus along the internal sliding surface of a hollow cylinder and by the addition of a powder Si is formed with a zone of over alloy in the form of a strip containing primary silicon. Method according to one of the preceding claims, characterized in that the average finishing depth of the overlapping zone is 750 μm. Method according to one of the preceding claims, characterized in that access to the hard phases of the overlying zone is generated by a mechanical operation, the recess in the upper layer being-less than 30% of the total thickness. Method according to one of the preceding claims, characterized in that the overreaching zone is subjected to fine grinding without an intermediate operation. 17. Apparatus for carrying out a process for coating the sliding surface of hollow cylinders constituted by a powder feeding device, a laser beam device and a focusing system with a reflecting mirror, characterized in that the device for feeding powder and the laser device are guided parallel to one another in the radial and axial direction of the hollow cylinder, because the focusing system has a linearly-shaped beam output with a beam width of 2.0 to 2.5 mm, and because in the device powder feed is provided a dosing device through which you can adjust the flow volume of the powder as a function of the speed of advance of the laser beam. . 18. Apparatus according to claim 17, characterized in that the focusing system has a focus in the form of X, I or 8, which in the upper and lower marginal zones allows a greater energy output compared to the central focus area. SUMMARY \ A cylinder block of light metal with at least one wear-resistant and tribologically optimized cylinder sliding surface consists of a light metal matrix alloy with a surface layer containing depositions of finely dispersed primary silicon. This is formed by rounded grains with grain diameters between 1 and 10 μm. The surface layer contains 10 to 14% of AISi eutectic, 5 to 20% of primary silicon, rest of pure Al phase. When manufacturing a block of light metal cylinders, a laser beam with a strip width transverse to the direction of advance of at least 2 mm, and the powder containing hard substance is guided along the surface of the light metal matrix. it is heated to the melting temperature and interdiffs on the surface of the light metal matrix at the point of incidence of the laser beam. An apparatus for coating sliding surfaces of hollow cylinders is constituted by a powder feeding device, a laser beam device and a reflector mirror focusing system. The powder feed device and the laser device are guided parallel to one another in the radial and axial direction of the hollow cylinder. The focusing system has a beam output linearly. The powder feed device is provided with a dosing device through which the flow volume of the powder can be adjusted as a function of the speed of advance of the laser beam.