EP0640759B1 - Partially reinforced aluminium cast construction part and method of manufacturing same - Google Patents

Abstract

The invention relates to a partially reinforced aluminium cast component comprising an aluminium casting and a spray-compacted aluminium reinforcing part at least partially enclosed, by being cast in, by the base material of the casting. The method for manufacturing such a component comprises the formation of a reinforcing element from spray-compacted material, the insertion of this element into the casting mould, the surrounding of the reinforcing element with an aluminium casting alloy and the solidification of the melt. A component of this kind is distinguished by the fact that a complete, strong material bond is present in the joints between the aluminium casting and the reinforcing part.

Description

The invention relates to a partially reinforced Al cast component, consisting of an Al cast part and a reinforcing part, at least partially encased by the base material thereof, and the method for producing such reinforced Al cast components.

Due to their low specific weight, simple shape and easy processability, cast aluminum components are used in many different ways. Complicated workpieces, such as. B. inexpensive manufacture of pistons for internal combustion engines, cylinder heads or engine blocks. Such components, in particular certain areas of these components, are subject to high thermal and / or mechanical loads when subjected to operating stress. In order to withstand these loads, when using conventional aluminum casting materials, unfavorable constructions with large wall thicknesses are often required or difficult-to-cast aluminum alloys have to be used. Such alloys are e.g. B. hypereutectic AlSi cast alloys, which are used to increase the necessary wear resistance and thermal conductivity of cylinder liners. However, these alloys can only be cast with great effort and in small series. The wear resistance of the tread is achieved by means of special etching and coating processes, which are also justifiable on a small scale with regard to their environmental impact and the disposal of the chemicals that are produced.

On the other hand, since aluminum casting materials in other areas of the above-mentioned components meet the requirements there, various methods are known for reinforcing aluminum casting components in the highly stressed areas of these components with materials which have the desired mechanical and physical properties. It is known, among other things, to reinforce aluminum casting materials with fibers or particles. This will achieved a high wear resistance in particular. On the other hand, the thermal load capacity is hardly affected, since the matrix of such materials represents the conventional cast aluminum alloy. Only special casting processes that require slow cycle times and high pressures are suitable for the production of such reinforced materials.

Another disadvantage of such a method is the complex finishing, which is only possible with diamond tools, and if fibers are cut during machining, these can separate from the matrix over time and lead to damage to the components that come into contact with the fibers .

It is also already known to combine powder-metallurgical aluminum materials with aluminum casting materials. This is u. a. possible with the help of the friction welding process. Both the powder metallurgical reinforcement material and the cast material can each be produced according to optimal parameters. When these materials are joined by friction welding, there is only a brief temperature load, so that the material properties of the reinforcing material are hardly reduced. Friction welding is, however, limited to simple component geometries, since only axial and no radial welding is possible. In addition, there is the risk that the friction welding creates stresses in the component, which make additional heat treatment necessary for relaxation. Another disadvantage of this method is the number of method steps. Friction welding itself is an additional step, and in order to achieve reproducible results, both the reinforcing part and the cast workpiece must be machined before welding.

DE-PS 31 00 755 describes a component which has an insert made of dispersion-hardened sintered aluminum, which is introduced into the component by pouring, pressing or welding. Pouring as a manufacturing process of reinforced Al castings is inexpensive, since no additional process step, such as. B. in friction welding, is necessary to produce the composite. A disadvantage of the component proposed in DE-PS 31 00 755 is that no perfect connection is achieved in the joining zone. Due to the high gas content of the powder-metallurgically manufactured materials, they are not very suitable for pouring. When contacting a powder metallurgical component, which either consists of an Al sintered material (powder metallurgical molding process) or a PM material (powder metallurgical semi-finished process), which, for. B. was produced by atomizing aluminum melt, cold isostatic pressing and subsequent hot extrusion to full density, with the melt of the conventional cast aluminum alloy, there is immediate outgassing with strong pore formation in the joining zone and in the powder metallurgical component. This pore formation prevents a good material composite.

It is therefore the object of the present invention to create a component made of partially reinforced aluminum casting which can be produced in a simple and inexpensive manner and which has a complete material composite between aluminum casting and reinforcing part.

This object is achieved in that a component is made available, consisting of an aluminum casting and a reinforcing part, at least partially encapsulated by its base material, which consists of a spray-compacted aluminum material. Spray compacting and the further process steps of extrusion or forging can be used to produce aluminum profiles or aluminum forgings that are far superior in their properties to conventional cast aluminum alloys. These Al materials have significantly lower gas contents than the Al sintered materials or PM-Al materials, which are even lower than the gas contents of conventional cast aluminum or wrought aluminum alloys. In addition, this process can be used to produce materials that are similar in mechanical and physical properties to the Al-PM materials produced by spraying. In comparison to conventionally cast Al materials, the spray compacting method makes it possible to increase the Si content in the Al material to over 35% by weight Si without any problems. This makes it possible to set the coefficient of thermal expansion to any value between 23 · 10 ^-6 K ^-1 and 13 · 10 ^-6 K ^-1 . Since the contents of other alloy elements such as Fe, Ni, Cu, Mg can be set within wide limits for technically meaningful and usable alloys, it is very easy to set materials precisely for a given application. The low gas contents enable these materials to be poured in without the formation of pores, which enables technically sensible and inexpensive composite components.

Such composite components are produced by positioning the reinforcing component, for example an extruded section, a forging or a component produced using a machining process, from a spray-compacted Al alloy at the point in the casting mold where reinforcement is to take place in the finished casting workpiece. Depending on the mass of the reinforcement component in relation to the mass of the cast workpiece, it is necessary, in order to achieve a good connection by partial melting, that the reinforcement component is preheated. With the choice of the preheating temperature, the degree of melting can be adjusted so that the reinforcing component is also complete is melted and this results in complete mixing with the casting material in the area of the reinforcement, as a result of which the latter is partially alloyed on. Furthermore, it is helpful for a particularly good connection if the melt flows around the reinforcement component in parallel and at a sufficiently high speed, as a result of which the oxide layer which is always present on aluminum is washed off and there is direct contact of the Al melt with the oxide-free Al surface is coming. This washing process can be achieved either by skillful choice of the sprue points, by stirring, by generating eddy currents with the aid of induction coils, or similar means which produce a flow of the melt parallel to the surface of the reinforcing component during or directly after the casting.

The invention is explained below using exemplary embodiments:

Fig. 1-

ein Schliffbild einer Fügezone zwischen sprühkompaktiertem Al-Werkstoff (AlSi20Fe5Ni2) und Al-Guß (AlSi18CuMgNi)

Fig. 2 -

ein Schliffbild einer Fügezone zwischen PM-Al-Werkstoff (AlSi20Fe5Ni2) und Al-Guß (AlSi18CuMgNi)

Fig. 3 -

ein Schliffbild einer Fügezone zwischen PM-AL-Werkstoff (AlSi35Fe2Ni1) und Al-Guß (AlSi9Cu3)

Fig. 4 a,b -

schematische Darstellung von Kolbenoberteilen

Fig. 5 -

schematische Darstellung des Kolbenbodens

Show it:

Fig. 1-

a micrograph of a joining zone between spray-compacted Al material (AlSi20Fe5Ni2) and Al casting (AlSi18CuMgNi)

Fig. 2 -

a micrograph of a joining zone between PM-Al material (AlSi20Fe5Ni2) and Al casting (AlSi18CuMgNi)

Fig. 3 -

a micrograph of a joining zone between PM-AL material (AlSi35Fe2Ni1) and Al casting (AlSi9Cu3)

4 a, b -

schematic representation of upper piston parts

Fig. 5 -

schematic representation of the piston crown

Example 1: Comparison of the composite according to the invention with a composite made of PM-Al material and cast aluminum.

Extruded round bar sections ¢ 85 mm x 55 mm made of the alloy AlSi20Fe5Ni2 were cast in a steel mold. For comparison purposes, on the one hand a spray-compacted alloy and on the other hand a PM alloy became the same Composition used. A piston alloy AlSi18CuMgNi was used as the casting material. The extrusion sections were placed in the open mold and preheated to 450 ° C. The melt temperature was 720 ° C. The melt was poured into the mold open on top of the extrusion sections and the washing-off process was supported by stirring after the pouring. When using the spray-compacted alloy (Fig. 1), a perfect connection without pores in the joining zone could be achieved. In the case of the PM alloy (FIG. 2), large pores formed in the connection zone and in the PM material due to the outgassing and "efflorescence" on the outside. On tensile samples from the spray-compacted variant, in which the joining zone was in the middle of the measuring length, values were determined after the heat treatment as the cast alloy achieved in this state. The break always occurred in the casting material, clearly next to the joining zone.

Further tests were carried out with rings (outer diameter = 48 mm, inner diameter = 37 mm, height = 7 mm) made of the spray-compacted alloy AlSi35Fe2Ni1. These rings were placed over a mandrel in a steel mold open at the top and cast with the cylinder head alloy G-AlSi9Cu3. The melt temperature was 720 ° C. The rings were either placed cold in a preheated mold directly before casting, or heated together with the mold. In addition, in some experiments, the melt was stirred immediately after the casting. Pore-free connections could be made with all experiments. The insertion of cold rings in a die preheated to 400 ° C. with subsequent casting proved to be particularly favorable. By stirring directly after the casting, a perfect connection with an extremely fine structure on the ring side could be achieved (FIG. 3). But pore-free joining zones could also be achieved with other test conditions. Heating the rings to 500 ° C with subsequent casting also leads to a very good connection, whereby the Si primary precipitates, in contrast to the conditions mentioned above, become coarser (from 3-7 µm to 10 - 20 µm) .

Example 2: Application of the composite according to the invention to pistons for internal combustion engines.

Pistons for internal combustion engines are an example of an application for partial reinforcement with the aid of casting. Upper piston parts are shown in FIGS. 4a and 4b. Figure 5 shows the schematic representation of the piston crown.

Pistons 1 are today mostly made of Si-containing eutectic or hypereutectic cast alloys. Particularly in the case of pistons for direct injection diesel engines that are subjected to high loads, the bowl rim zone 4 is exposed to high temperatures and mechanical loads. In the areas of the piston skirt 5, aluminum cast materials 2 meet the requirements there. By pouring spray-compacted aluminum alloys (e.g. AlSi20Fe5Ni2) into the stressed areas, the bowl rim zone 4 or the entire combustion chamber bowl 7 can be inexpensively strengthened 3, which makes it possible to design the piston 1 with which more effective combustion can be achieved. Further reinforcement options on piston 1 are e.g. the area of the ring groove 6, where some iron-based materials are already poured in to minimize wear due to the movement of the piston rings.

A further reinforcement according to the invention can be provided in the area of the top land (see Figure 5). The use of spray-compacted high-performance aluminum at these points results in considerable improvements due to the perfect combination of the casting alloy 2 with the reinforcements 3. It is thereby possible to minimize the distance between the uppermost piston ring and the piston crown 9, which leads to reduced pollutant values.

Example 3: Application of the composite according to the invention to cylinder heads of internal combustion engines.

Another example is the reinforcement of cylinder heads of internal combustion engines to the combustion chamber side. Due to the resulting high temperatures and the formation of a temperature gradient, tensions occur in the cylinder head, which usually lead to cracks in the area of the webs between the valves. If a reinforcement is carried out in these areas with a material that on the one hand withstands the thermal and mechanical loads better, and on the other hand has a different coefficient of thermal expansion than the cast alloy of the cylinder head, which has to be used because of the complexity and the mold filling capacity, the tension can induced by the temperature gradient, do not reach critical values for crack formation.

Example 4: Application of the composite according to the invention in cylinder liners of internal combustion engines

Another example is the cylinder liner of internal combustion engines. In order to be able to mass-produce aluminum engine blocks in a large series at low cost, the use of easily castable aluminum alloys is imperative. However, due to their insufficient wear resistance, these alloys require reinforcement of the piston running surface. This is achieved today by casting a cast iron cylinder liner. The disadvantage here is poor thermal conductivity and a very different thermal expansion. There is also no complete material bond between the bushing and the block (casting gap), which also influences the thermal conductivity and mechanical strength. The use of hypereutectic AlSi cast alloys enables the desired wear resistance and thermal conductivity without the use of liners, but such alloys can only be cast with great effort and in small series (as described above).

When using bushings made of spray-compacted material, it is possible on the one hand to use easily castable alloys for the engine block and on the other hand to obtain a wear-resistant running surface without special etching processes. Due to the complete material composite and the good thermal conductivity of the liner material, the overall thermal conductivity is considerably better than when using gray cast iron bushings.

REFERENCE SIGN LIST

1

component according to the invention

2nd

Al cast

3rd

Reinforcement part

4th

Trough edge reinforcement

5

Piston shirt

6

Ring bearer

7

Combustion chamber trough

8th

Cooling channel

9

Piston crown

Claims (8)

1. Construction part (1), comprising an aluminium casting (2) and a reinforcing member (3), which is surrounded by the base material of said casting at least partially by integral casting, said reinforcing member being formed from a spray-compacted aluminium material and forming a full, solid composite material with the aluminium casting (2) in the joint zones.
2. Method of producing a partially reinforced aluminium cast construction part (1) according to claim 1, characterised by the following method steps:

   - providing a reinforcing member (3), which is formed from spray-compacted material and defines at least one portion of the finished construction part (1);

   - inserting the reinforcing member (3), in a compact, solid form, into the intended space in the casting mould, which forms the construction part (1);

   - filling the remaining space of the casting mould with the molten mass of the conventional cast aluminium material; and

   - subsequently solidifying the molten mass.
3. Method according to claim 2, characterised in that the reinforcing member (3), formed from spray-compacted material, is configured as an extruded profile portion.
4. Method according to claim 2, characterised in that the reinforcing member (3), formed from spray-compacted material, is configured as a forged piece.
5. Method according to claims 2 - 4, characterised in that the reinforcing member (3), inserted into the casting mould, is preheated.
6. Method according to claim 5, characterised in that the preheating temperature is so selected that the reinforcing member (3) is completely fused.
7. Method according to claims 2 - 6, characterised in that the molten mass of cast aluminium is poured into the casting mould parallel to the surface of the reinforcing member (3) and at such a great speed that it washes away the oxide layer existing on the aluminium of the reinforcing member (3).
8. Method according to claim 7, characterised in that the washing operation is achieved by the selection of the sprue locations and/or by agitation and/or by the production of eddy currents by means of induction coils.

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