SK5151Y1 - Fluid-tight sintered metall parts and production method - Google Patents

Description

Technical field

The technical solution relates to liquid-tight sintered metal parts characterized by high resistance to load essentially made of mixtures of non-ferrous metal powders.

BACKGROUND OF THE INVENTION

A mixture of non-ferrous metals is also understood to mean a mixture containing a small amount of iron - up to 8% by weight, small amounts of iron which may be present as alloying additives are acceptable.

Sintered parts having a high durability in connection with the present invention are sintered parts having a higher hardness than (without pressure) substantially solid state sintered parts without additional compression aids having the same chemical composition.

In the context of this application, a liquid-tight member is meant to have an impermeable surface that does not allow any liquid, such as liquids or gases, to penetrate at an elevated pressure (0.1 to 100 bar), also called hermetic.

In particular, processes and technical terms in the field of sintering (sintering processes) known to those skilled in the art are used and explained in the text.

In general, sintering refers to the processing of starting materials in the form of powders, which, in combination with physical properties, by a metallurgical melting process, cannot be economically produced. After compression, the moldings in the sintering furnace are heat treated by a controlled and controlled process. This processing of the powder compact takes place at a temperature ranging from a half of the melting point to the melting point. Sintering is particularly temperature dependent. Shrinkage and porosity depend on temperature and pressure.

As a standard, sintering is performed in a sintering furnace under a protective atmosphere at a pressure equal to ambient pressure.

Sintering products are characterized by: • high use of raw material • high degree of geometric reproducibility in mass production • possibility to combine various alloyed parts, even those that do not produce any homogeneous melts.

There are different variations of sintering:

Liquid phase sintering

The particles of high melting point material are sintered together during sintering by a phase formed from another material, which causes strong shrinkage.

Solid state sintering

Prevention of the formation of a liquid phase is anticipated, as opposed to sintering in the liquid phase, as this leads to less delay in the production of the final assembly parts. Basically, there is only diffusion at the grain boundaries. Only in solid phase sintering does recrystallization (formation of new grains) occur. At the recrystallization temperature, a new texture is formed in the furnace. It is known that this is dependent on temperature and pressure as described above.

There is a smooth transition between liquid and solid phase sintering.

Pressure assisted sintering

During sintering under increased pressure, contacts between adjacent grains are easier to form between which better diffusion occurs.

Hot isostatic pressing

In hot isostatic pressing (HIP), the stampings are individually sintered individually in a pressure chamber, which is only acceptable for series production in exceptional cases.

Continuous isostatic pressing

Continuous isostatic pressing is described in EP-A-14121113. It exerts pressure on the extruded pin during solid phase sintering.

Standard sintering

Standard sintering is carried out under pressure in a furnace under shielding gas, especially for materials that readily react at elevated temperatures with the gas replaced by the shielding gas. For example, it will be an oxygen-free gas to prevent the formation of oxides, or it will be a dry gas to prevent the formation of

EN 5151 B6 hydroxides. In standard sintering, a powder, granulate, semolina or the like will be used for sintering together with compression aids, typically the compression molding will be non-axial to the final mold, and the molding thus produced will be sintered at temperatures of 1/2 to 4/5 of the melting temperature. and optionally the freezing point of the metal powder, optionally under a protective atmosphere.

Processing forms following pressing:

Calibration:

Calibration is to be understood in relation to sintered parts, the three-dimensional compression of the part, with its small densification, which compensates for deformations occurring during sintering. The geometry changes only slightly. A correction of the curvature resulting from sintering is achieved. This is followed by no basic shape adjustment, but very simple pressing. After a slight change in shape by a few percent, there is no new forming.

Free draft is a two-dimensional forming and is characterized by the smoothing of the surface of sintered parts.

Chamfering - chamfering of edges

By this we mean in the context of sintered parts the removal of sharp edges on the product without changing its dimensions.

Preparation of sintering powders

Cold pressing

The powder, with or without the compression aid, will be consolidated without heat supply.

Hot pressing

The powder will be hot sintered without sintering, with higher thermal properties of the auxiliary die used than cold pressing being desired.

Auxiliary pressing means

It may be a means for separating or lubricating, or also a means for improving adhesion which will increase the strength of the compact and also reduce the pressing force required to compact the powders.

By this we mean both separating aids that assist in ejecting moldings from the molds, as well as lubricating means that improve the sliding properties of the individual powder particles with each other, such as waxes, graphite, or silicone oil. Preference is given to auxiliaries which, during sintering, are separated or chemically transformed, for example, burnt.

To compact the base member when sintered in the furnace, it is often followed by solution annealing, which by recrystallization improves the structures formed by sintering. This is followed by conventional processing of sintered parts, such as grinding, turning, and coating of sintered parts.

In general, sintered parts made of metal powder mixtures, in particular in the case of non-homogeneous melting powder mixtures, can exhibit porosity or mixed areas due to different diffusion rates according to known processes. These damage the structure of the sintered parts and their mechanical and technological properties to such an extent that a leaky, porous surface layer is formed or the entire part is defective. The properties of the sintered powder component thus produced are deteriorated as a result of these unpredictable damaged areas. There are also large differences between the individual sintered parts produced, which is manifested in increased tendency to fracture of material along non-homogeneous regions, also in increased surface roughness and reduced surface hardness. This is particularly the case when sintered parts are used in heavy-duty operation, for example as gears, pump wheels, etc. The disadvantages of the prior art process result in higher costs due to the high degree of confusion.

On the other hand, it is the object of the invention to manufacture sintered parts having a high surface hardness, withstand high mechanical loads and are liquid-tight.

The essence of the technical solution

The drawbacks described in the prior art are solved by means of a liquid-tight sintered part which can withstand high loads and is produced in the underlay:

• a mixture of non-ferrous metal powders; • an intermediate molding manufactured substantially without compression aids;

• by pressure sintering the molding in a shielding gas at a temperature of up to 70% of the melting temperature of the metal, • preferably up to 60% of the melting temperature of the metal, • optionally subjected to a solution annealing, • optionally calibrating and further processing.

SK 5151 B6

Further advantageous solutions result from the dependent claims.

Preferably, the sintered metal parts produced according to the invention have a density of from 95% to 97% of the theoretical density of the metal powder mixture.

As a starting mixture for sintering, metal powder material, alloy particles, tungsten carbide, particles used to improve wear resistance, fibers and compression aids are used.

For the purposes of this application, a molding without a molding aid means a molding without molding aid, or a molding containing less than 5% by weight of molding aid, and also molding which, on the basis of the known knowledge of removing molding aid, it contains less than 1% by weight, preferably up to 0.5% by weight, preferably up to 0.01% by weight. compression aid.

Preferably, for the purposes of the invention, sintered metal parts will be made predominantly from the group of light metals, in particular Al, Mg, Be, Ti. The other components may be other metals or elements such as Cu, Si, Zn, O, C, Fe, etc.

Preferably, the separation of the compression aid will be accomplished by sintering in a sintering furnace in the presence of an inert gas such as noble gases, H ₂ , N ₂ , CO ₂ , or a mixture thereof to prevent formation of oxides or hydroxides during sintering.

Since the molding according to the invention contains only a small amount or is completely squeezed without pressure wax residues, surprisingly good liquid-tight parts can be produced (while avoiding the formation of a liquid phase during sintering). It was not expected that such conventional non-pressurized standard sintered moldings, substantially free of compression aid, at such a low solid phase sintering temperature (resulting in energy cost savings) would provide high-tight products with a very stable shape.

It appears that this sintering process provides sintered parts with a persistent hardness, highly loadable, which due to the high density and the relatively spherical grain shape of the sintered parts which are continuously isostatically extruded on the extrusion press, according to the method described in EP-A1 - 1412113 made as liquid-tight, harder, having less ductility, which is required for heavily loaded components.

Advantageously, according to the invention, a powder compact produced by a known powder compacting method will be used as the starting material for separating the compression aid.

According to another embodiment, this continuous sintered product, controlled by cooling, can be achieved by controlled cooling, for example by cooling by spraying with water by turbidity, to achieve a fine crystalline structure. This may be followed by a defined heat treatment, for example in the case of aluminum-alloyed alloys, solution annealing. The cooled component may be machined. As a post-treatment a surface improvement can be made or a calibration can be performed. The sintered part may be subjected to a heat treatment to improve its structure.

Also, components made of non-homogeneously melting metal mixtures produced by this technical solution exhibit high hardness and limited ductility with limited ductility, as compared to those which have been continuously isostatically pressed, and similarly density can be achieved.

For use with intruded parts as components, their mechanical and technological values such as elasticity, tensile strength and elongation can be very well influenced.

For example, a component made by non-pressurized sintering of an aluminum alloy with 13 wt. Silicon has an elongation to fracture of 10% of the elongation of a component made of the same alloy which has been continuously isostatically sintered.

Since the formation of a melt phase is prevented, immiscible components such as hard phases can also be treated. These are also homogeneously distributed.

In principle, a mixture of metal powders or alloys thereof and other materials such as hard particles, fibers, abrasion-resistant materials such as boron carbide, boron nitride and non-metallic materials can be used as the powder material.

Thus, metal-matrix composites can be produced, wherein the second component can be fibrous or also in the form of particles.

Short or long fibers or small proportions of particles between 5-30% by volume can be used as fibers. Whiskers have a length substantially less than 100 times their diameter; long fibers, continuous filaments or continuous fibers are those whose length is greater than 100 times their diameter. The fibers serve to improve the strength of the sintered parts.

Particle reinforced materials have certain additions of SiC, boron carbide, Al ₂ O _3, etc.

Other, typically sintered alloys, such as Ti alloys, in particular Ti / Nb, Ti / Al and TiAlNb alloys, also Co-Ti-B, Mg with SiC, boron carbide, or AlPb alloys can also be processed due to the high homogeneity process , with a high heat storage capacity which cannot be produced by the smelting metallurgical process. Beryllium and magnesium particles, etc. can also be processed. typical compositions are, for example, aluminum with Si, Mg, Cu, Zn and optionally Fe with a content of 10-40 wt. % Si, 0-3% wt. Mg, 0-5% wt. Cu, Zn, and Fe 0-7 wt. as well as other light metal alloys with magnesium, calcium, beryllium, etc.

SK 5151 B6

For aluminum sintered parts, aluminum sintered materials are offered, among others:

AISi, AlSiCu, AlCuMg with: Cu 3.8 to 4.4 wt%, Mg 0.5 to 1.0 wt%, balance Al.

• AlMgSi with AISi 0.4 - 0.8% mass, Mg 0.5 -1.0% mass, • AlZnMgCu with Cu 0.05 - 0.6% mass, Mg 0.25 -1.6 % A, Zn 0.1 -1.5%. AISi 1.5 - 8.0%, with more than 7%. Are u.

The technical solution relates in particular to sintered light metal parts which are difficult to machine. In this way, it is also possible to produce parts from nadutectic alloys.

Fusing of fibers such as ceramic, carbon or hard fiber will give higher strength - increase tensile strength, increase the yield point, increase the modulus of elasticity, increase heat and creep resistance, reduce thermal expansion coefficients . As wear-enhancing or hard materials, typical particles are SiC, AlN, BN, TiB ₂ , boron carbide, SiO ₂ , WC, fibers such as carbon fibers, metal fibers, ceramic or glass fibers.

Suitable metal phases may be selected from aluminum, titanium, copper, beryllium, magnesium, calcium, nickel, lithium, chromium, molybdenum, tungsten, bronze, niobium, lead, zinc and cobalt.

It is possible to sinter at temperatures close to 70% of the melting point of the main constituent of the starting metal powder mixture, in a shielding gas, which may be one of the noble gases, nitrogen, carbon dioxide.

Other objects, features and advantages will be apparent from the following description and claims, together with the accompanying drawings. For a full understanding of the essence of the technical solution are attached drawings showing:

BRIEF DESCRIPTION OF THE DRAWINGS

For a full understanding of the nature of the invention, the drawings are enclosed: FIG. 1 is a microscopic image of an AlSiCuMg alloy cut made by a conventional sintering process, FIG. 2 is a photomicrograph of a cut of an alloy produced according to the invention from an AlSiCuMg alloy having a composition as in FIG. 1, FIG. 3 is a schematic representation of sintered articles having a denser coating and a reduced interior; FIG. 4 is a schematic representation of a method of manufacturing sintered products according to the invention.

EXAMPLES

Hereinafter, a preferred embodiment of shaped parts made of AlSiCuMg alloy - but this is in no way limited thereto - will be described - according to this method, other sinterable metal powders such as Ti, Ta, Mg, Be, Cs can be formed and processed. , Cu.

Example 1

Production of sintered parts from AlSiCuMg

The base molding, made of AlSiCuMg aluminum powder blend, without molding aid, having a disc shape of 10 cm diameter and 10 mm thickness, will be sintered for 30 minutes at 590 ° C, under argon atmosphere, followed by dissolution annealing for 30 minutes at temperature 400 ° C.

These pressureless sintered parts are then heat treated for 6 hours. at a temperature of 250 ° C, the sintered parts are calibrated in a calibration press with a force of 150 KN after heat treatment to obtain a final shape with a very narrow dimensional tolerance. These parts can be used without further processing as finished parts. The product shown in FIG. 2, has a hard surface and a density of 2.67 g / cm ³ (96% of theoretical density).

Example 2

Comparative test

AlSiCuMg disc sintered parts, equal to the percentages as in Example 1, were sintered in a conventional manner from the powder mixture as a comparative product, a base molded with 3% wax was pressed, and this disc was then in a wax removal device for 20 minutes. at 400 ° C, followed by sintering for 30 min. at 590 ° C under argon sintered, and annealed again at 400 ° C for 35 min. In FIG. 1, the porous surface areas are clearly visible.

Example 3

Production of sintered wheel with hard surface and easy to machine inner material.

SK 5151 B6

From the AlSiCuMg powder mixture, a compact will be pressed, a roll having a diameter of 10 cm, having a height of 4 cm, substantially free of the compression aid. This compact will be sintered in a sintering furnace at 590 ° C, in dry nitrogen for 30 min. A sintered piece is formed which is not quite dense inside. Such sintered parts are used as pump wheels, water or oil, having an internally machinable interior in which holes can be drilled, and the higher density outer surface is abrasion resistant.

In FIG. 1 and 2, it is possible to compare the microstructures of sintered aluminum wheels of AlSiCuMg produced using the traditional method of manufacturing hot sintering and thermal sintering of a molded molded article according to the invention, manufactured without a compression aid. It appears that the part produced according to the invention is clearly denser.

Table 1

Material values for AlSiCuMg (Al base, Si 16%, Cu 2.8% Mg 0.8%) (at room temperature, unless otherwise stated)

Measured value Ear, sintered piece According to EP1412113 Liquid-tight part Density g / cm ³ 2.77 2.67 Hardness HB 95 145 Tensile strength N / mm ² 340

It is clear from Table 1 that the sintered bodies produced by the continuous isostatic pressing process are denser, more precisely also that less rejects are produced in this way. According to EP 1412113, continuously isostatically molded sintered parts are more flexible, which suggests the apparent elongation and low hardness required especially for mechanical parts such as rotors and stators in camshaft systems or oil pumps, bearing parts, pump wheels, etc.

The parts produced according to the invention are used as chain wheels (for steel chains), belt wheels that require a hard surface layer with low abrasion. It appears that, assuming the same composition, the surface hardness of the parts produced according to the invention is higher than the surface hardness of the parts produced by the second methods.

In FIG. 3 shows the results of various structures of sintered parts made according to the invention. There is a denser surface area and a lighter inner area. These parts can be manufactured in less sintering time than the time required for complete sintering of the entire part. In this way, the lighter core remains, which has a lower hardness, but is an area more easily machinable.

Of course, the invention is not strictly limited to the construction, and / or the examples given / described, but various variations are possible without weakening the scope of protection of the invention as will be apparent to those skilled in the art.

Industrial usability

The liquid-tight sintered parts are used as pump wheels, water or oil, with an easily machinable interior in which holes can be drilled, while the higher density outer surface is abrasion-resistant.

Claims (5)

A process for the manufacture of a liquid-tight sintered metal part, characterized in that the molded product made of a mixture of non-ferrous metals without compression aids is sintered without pressure in a sintering furnace under a shielding gas at a temperature of up to 70%. subsequently, the sintered article is subjected to dissolving annealing and further processing. 2. A process for producing a liquid-tight sintered metal part according to claim 1, wherein the temperature reaches 60% of the melting temperature and the density is in the range of 95% to 96% of the theoretical density of the sintered metal powder mixtures. Method for producing a liquid-tight sintered metal part according to claims 1 and 2, characterized in that the starting mixture of the sintering powder materials consists of metals and metal alloys, as well as a small amount of alloy, hard, abrasion and fiber resistance components. Production method according to claims 1, 2 or 3, characterized in that the shielding gas is of the noble gas group and the solvent annealing is followed by veneering and / or calibration. SK 5151 B6 Liquid-proof sintered metal parts produced according to the above claims, characterized in that at least one metal in the powder mixture from which the base molding is made is selected from the following metals Al, Ca, Ti, Cu, Mg, Be, Cr, Si , bronze, Nb, Pb, Co, Zn as well as small amounts of alloys, boride, carbide, nitride, silicate and fiber group 5 metal, carbon, ceramic and / or glass, wherein the base molding contains less than 5% molding aids.