KR100696312B1 - Sinterable metal powder mixture for the production of sintered components - Google Patents

Abstract

The present invention relates to sinterable powder compositions, sintered components produced therefrom, and methods for prepared such components. Sinterable powder compositions are composed of an aluminum-based powder, and a first metal powder comprising molybdenum and/or tungsten. The aluminum based powder is composed of aluminum and magnesium, silicon, copper, zinc, titanium, tin, manganese, nickel, or combinations thereof. In another embodiment, the sinterable powder composition includes a second metal powder comprising copper, tin, zinc, lithium, magnesium, or combination thereof. The sinterable powder compositions may be used for the production of sintered components, including composite components, having not only sufficient strength values but also with high hardness.

Description

Sinterable Metal Powder Mixture for Manufacturing Sintered Parts {SINTERABLE METAL POWDER MIXTURE FOR THE PRODUCTION OF SINTERED COMPONENTS}

FIELD OF THE INVENTION The present invention relates to sinterable powder mixtures based on Al powders for producing sintered parts, in particular sintered parts for automobile manufacturing, sintered parts made therefrom, and methods of manufacturing such types of parts.

Aluminum is the preferred material, particularly in the aircraft industry and in the automotive industry, based on its special properties. Parts made of aluminum or aluminum containing materials are significantly lighter than conventional parts made of, for example, cast iron. By such a weight reduction, an increase in efficiency, a reduction in fuel consumption, and an improvement in exhaust gas level can be obtained, for example in an automobile.

There is an increasing demand for the application of aluminum to the automotive sector in the process of weight reduction of the preferred vehicle. For this reason, for example, in engine manufacture and transmission manufacture, steel (or cast iron parts), which have been used in parts until now, is replaced by aluminum parts or parts manufactured using aluminum. When combining steel or cast iron parts with aluminum parts, problems arise due to the different physical behavior of the material, so it is desirable to replace “classic” steel parts or cast iron parts with parts made from aluminum as much as possible. Do. This is because the problem caused by the difference in the materials used in the coefficient of thermal expansion, thermal conductivity, elasticity, and the like is thereby avoided. By using matched parts made from aluminum, very high efficiencies are also achieved.

In particular, since many engine parts, coupling parts, and transmission parts are manufactured by powder metallurgy, much attention has been paid to producing a powder mixture and providing a method for producing aluminum parts by powder metallurgy. . A disadvantage in producing parts by powder metallurgy using aluminum is that in particular aluminum and its alloys are covered with highly stable metal oxides upon air contact. As a result, above all, the specific surface area is increased. The oxide skin on the aluminum containing material used prevents the diffusion of particles of the powder material used for sintering. In addition, parts made of aluminum-containing materials exhibit reduced strength values, in particular low hardness, compared to parts made of steel or cast iron. In addition, the oxide skin on the aluminum containing material interferes with the mutual cold bonding of the particles in the usual press forming process.

Accordingly, there is a need for a sinterable powder mixture, which is a material that can be processed well by powder metallurgy, and that enables parts with good strength and high hardness to be produced by powder metallurgy. There is also a need for powder metallurgical processing of aluminum-containing sinterable powder mixtures of that type.

It is therefore an object of the present invention to provide a powder mixture which does not exhibit the above mentioned disadvantages, a part made from the powder mixture, and a corresponding method.

Such an object comprises, according to the invention, from 60 to 98.5% by weight, preferably from 75 to 92% by weight, based on the total amount of the powder mixture, containing Al-based powders of metals and / or alloys thereof, wherein the Al-based powders are Al And, if necessary, the following metals in terms of weight percentage based on the total amount of Al-based powder: 0.2 to 30% by weight Mg, 0.2 to 40% by weight Si, 0.2 to 15% by weight Cu, 0.2 to 15% by weight Zn, 0.2-15 wt% Ti, 0.2-10 wt% Sn, 0.2-5 wt% Mn, 0.2-10 wt% Ni, and / or less than 1 wt% As, Sb, Co, Be At least 0.8 to 40% by weight, preferably 8 to 15% by weight of the metal powder, consisting of Mo and / or W, containing at least one of Pb and / or B and based on the total amount of the powder mixture Sintered parts selected from metals and / or alloys thereof, in particular automotive parts Achieved by a sinterable powder mixture for the preparation.

By adding a first group of metals and / or alloys thereof consisting of Mo and / or W, parts which exhibit very high hardness by such a powder mixture can be produced by powder metallurgy. The hardness value of the parts made from powders selected from the metals of the first group and / or alloys thereof is from 5 to 35%, preferably 10 compared to the hardness values of those without addition of such metals from the first group and / or alloys thereof. To 25%. In particular, by adding the first group of metals and / or alloys thereof to the Al-based powder, among other things, mutual cold bonding of the particles generated during the press molding process, in particular by recompression, is improved. This ultimately improves the diffusion of the individual particles during the individual sintering process, resulting in parts with high strength values and high hardness.

Further, the sinterable powder mixture preferably contains a second group of metals and / or alloys thereof consisting of Cu, Sn, Zn, Li and / or Mg. The addition of such a second group of metals and / or their alloys is presumed to cause the alloy and / or intermetallic phase to be formed by the Al based powder, especially during the press molding process, in particular during recompression. As a result, formation of an oxide skin on the surface of the Al-based powder to be used is prevented. In addition, the second group of alloys and / or their alloys are at least partially transitioned to at least a partial liquid state at the sintering temperature during the inherent sintering process, so that in particular the metals of the first group and / or their alloys are Al Improved bonding to the system powder.

The ratio of the amount of metal of the first group and / or its alloys to the amount of metal of the second group and / or its alloys in the powder mixture is preferably in the range of 1: 8 to 15: 1 by weight fraction. . More preferably, the ratio is in the range of 2: 1 to 6: 1 by weight fraction. In such a mixing ratio, it is realized that the first group of metals and / or alloys thereof are maximally bonded to the Al-based powder. Thereby, a part having a high hardness can be obtained by such a powder mixture.

In another preferred configuration of the present invention, the Al-based powder is 0.2 to 15% by weight of Mg, 0.2 to 16% by weight of Si, 0.2 to 10% by weight of Cu, and / or in addition to Al, based on the total amount of Al-based powder. It contains 0.2 to 15% by weight of Zn. It is also preferable to contain a second group of metals and / or alloys thereof consisting of Cu, Zn, and / or Sn.

The sinterable powder mixture preferably contains a lubricant in an amount of 0.2 to 5% by weight, based on the total amount of the powder mixture. In that case, self-lubricating agents such as MoS ₂ , WS ₂ , BN, MnS and other carbon modifiers such as graphite and / or coke, polarized graphite and the like are provided as lubricants. Preference is given to adding 1-3% by weight of lubricant to the sinterable powder mixture. By using such lubricants, self-lubricating properties can be imparted to parts made of sinterable powder mixtures.

The sinterable powder mixture may also contain a binder and / or a gamma agent. Such binders and / or gamma agents are preferably selected from the group comprising polyvinylacetates, waxes, in particular amide waxes such as ethylenebisstearoylamide, shellac, polyalkyleneoxides and / or polyglycols. The polyalkylene oxides and / or polyglycols are used as polymers and / or copolymers having an average molecular weight of 100 to 500,000 g / mol, preferably 1,000 to 3,500 g / mol, more preferably 3,000 to 6,500 g / mol. It is preferable. Such formulations are preferably administered in amounts ranging from about 0.01 to 12% by weight, preferably from 0.5 to 5% by weight, more preferably from 0.6 to 1.8% by weight, based on the total amount of the powder mixture. The binder and / or gamma agent facilitate the removal of parts made from the sinterable powder mixture from the pressure forming mold.

The powder mixture can be prepared by mixing the individual components in hot air (hot mixing) as well as at room temperature (cold mixing) by a conventional apparatus such as a rocking mixer, in which case hot mixing is preferred.

The invention also relates to a sintered part produced according to the method according to the invention. Sintered parts according to the invention of this type exhibit significantly higher strength values and hardness than sintered parts produced by conventional methods. The sintered part according to the invention preferably exhibits a tensile strength of at least 140 N / mm 2 measured according to DIN EN 10002-1. It is preferable that tensile strength exceeds 200 N / mm <2>, and it is more preferable that it exceeds 300 N / mm <2>. The sintered part according to the invention preferably exhibits an elastic modulus of at least 70 kN / mm 2, measured according to DIN EN 10002-1, more preferably greater than 80 kN / mm 2.

The sintered part according to the invention in another preferred configuration exhibits a hardness of at least 100 (HB 2.5 / 62.5 kg) measured according to DIN EN 24498-1. Preferably, the hardness is greater than 110, and more preferably greater than 125.

In another preferred configuration the sintered part is formed as a cog wheel, a pump wheel, in particular an oil pump wheel, connecting rods and / or rotor sets.

A sintered part in the sense of the present invention means a part made of a completely sinterable material, and on the other hand it also means a composite part, wherein the main body of such a composite part can be made of an aluminum-containing powder mixture, for example Other bodies joined to the body may be made of other materials, such as sintered or bulk steel or cast iron or mass aluminum castings. On the contrary, the composite part has a sintered layer made of an aluminum-containing powder mixture, for example only on its end face or on its side, while the main body may be made of, for example, sintered or massive steel or cast iron. In that case, the sintered part may be calibrated and / or age hardened in hot air.

Finally, the present invention relates to a method for producing not only sintered parts but also composite parts with the powder mixture according to the present invention.

A first step of placing the powder mixture in the first mold;

A second step of press molding the powder mixture into a green body;

A third step of at least partially recompressing the shaped body; And

A fourth step of sintering the recompressed compacts.

The process according to the invention has the advantage that it is possible to produce parts on the one hand which exhibit excellent strength values on the one hand and, on the other hand up to a particularly high density and hardness, by the high density already obtained in the third step before the inherent sintering process. In particular, by recompression carried out according to the method according to the invention, the age hardening by conventional reprocessing steps following the sintering step, for example by leaving it during calibration and / or hot air, can be significantly shortened, or in some cases usually Reheating or calibration may be omitted. As a result, the overall process is shortened, thereby improving productivity and thereby achieving economic benefits.

By the recompression of the third step of the process according to the invention, it is advantageously realized that the oxide skin on the surface of the material used is mechanically broken to obtain a better cold bond during the press molding process. This also improves the diffusion of the individual material particles in the inherent sintering process. Thereby, parts with high strength values and especially very high hardness can be obtained. The press molding process carried out in the second and third stages of the process according to the invention can be carried out at high temperatures (hot press molding), especially under the addition of the above-mentioned formulations, in particular polyglycols, but also at room temperature (cold press molding) and And vibration compression. Here, vibration compression means a method in which vibration is superimposed on the pressure forming process at least temporarily during the pressure forming process, and the vibration can be introduced via at least one pressure forming stamp. It is also possible to combine the above-mentioned pressure forming methods. Sinterable materials may be powders or metal mixtures, especially metal powders such as steel such as chromium / nickel steel, bronze, nickel-based alloys such as Hastelloy, Inconel, metal oxides, metal nitrides, metal silicides and the like and / or Ceramic powders and especially aluminum containing powders or aluminum containing powder mixtures, which may contain high melting point components such as, for example, platinum and the like. The powder used and its particle size are determined depending on the respective purpose of use. Iron-containing powders are preferably alloy 316 L, alloy 304 L, Inconel 600, Inconel 625, Monel, and Hastelloy B, Hastelloy X, and Hastelloy C. In addition, the sinterable material may be, in whole or in part, short fibers or fibers, preferably fibers such as metal fiber nonwovens having a diameter of about 0.1 to 250 μm and a millimeter size of several μm to 50 mm in length.

For example, to produce a composite part having a sintered layer of sinterable material on the end face of a body made of steel or cast iron, the sinterable material may be formed on the main body by, for example, a conventional method in the first step of the process according to the invention. Attach to. However, for example, there may also be measures to spray (Wet Powder Spraying (WPS)) the material in powder form. To do so, it is necessary to make a suspension of the sinterable material. It is preferred to contain stabilizers and / or dispersants, especially solvents such as water, methanol, ethanol, isopropanol, terpenes, C ₂ -C ₅ alkenes, toluol, trichloroethylene, diethyl ether, C ₁ -C ₆ It is preferably selected from the group comprising aldehydes, and / or ketones, in which case a solvent which can be vaporized at a temperature below 100 ° C. is preferred, the amount of solvent used is based on the total amount of the sinterable powder mixture used. It is preferably in the range of about 40 to 70% by weight, preferably in the range of about 50 to 65% by weight.

The recompression (which may also be referred to as intermediate compression) performed in the third step may be performed by a known method conventionally used for pressure molding a molded body. That is, for example, the molded article press-molded in the second step can be put back into a conventional mold, and can be recompressed at least partially by a suitable press-molded stamp in the mold. The recompression tool is preferably formed in whole or in part in a conical shape so as to enable very high compression at a predetermined predetermined point.

In a preferred embodiment of the process according to the invention, the molded body is dewaxed in a further step before the third step. Such dewaxing is carried out in particular under a mixture of nitrogen, hydrogen, air, and / or their gases with an intentional air supply. Dewaxing can also be done with an endothermic gas or an exothermic gas, but can also be done in a vacuum. It is preferable that dewaxing can be done by interfering microwaves and / or ultrasonic waves, or only by temperature-inducing microwaves. Finally, dewaxing may be done with a solvent or supercritical carbon dioxide, such as alcohol, with or without the action of temperature, microwave, or ultrasonic waves or a combination of such methods. By the method according to the invention for recompressing in the third step, a density of about 2 to 40%, preferably 5 to 30%, more preferably 15 to 25% higher than the density before recompression is obtained. .

In a second step of the process according to the invention a starting density in the range of 2.1 to 2.5 g / cm 3, preferably 2.2 to 2.4 g / cm 3 and more preferably 2.25 to 2.38 g / cm 3 measured according to DIN ISO 2738 It is preferable to press-form the molded object which has a.

In another embodiment of the method according to the invention, it is preferred to spray the mold into which the dewaxed shaped body is put, optionally with a gamma agent or to deposit the molded body before placing the molded body. It is also very preferred to carry out the sintering process in the fourth step under nitrogen having a dew point of less than -40 ° C, preferably less than -50 ° C. In that case, it is preferable to perform sintering under pure nitrogen. In addition, when the density and / or composition of the molded body is appropriate, the sintering may be performed under air, hydrogen, a mixture of nitrogen and hydrogen with or without an intentional air supply, endothermic gas, exothermic gas, or in vacuum. In that case, sintering can be performed by an interference microwave or a temperature induction microwave.

It is preferred that the sintering step is followed immediately by the necessary heat treatment, in particular homogenization annealing. In that case, the heat treatment may be performed depending on the chemical composition of the obtained part. Alternatively or additionally to the heat treatment, the sintered part may be quenched, starting from the sintering temperature or homogenizing annealing temperature, preferably in water or by gas quenching.

It is common to perform further surface compression before and after sintering. It is possible to introduce compressive internal stresses in the surface area by sand blasting, shot peening, rolling and the like. Calibration may be carried out before or after homogenization annealing. In that case, the calibration is carried out using a pressure of 900 N / mm 2 at room temperature or at a high temperature up to the forging temperature. In some cases, in particular, calibration may be performed on a solid line, in which case the sintering heat can be drawn directly from the part.

The calibration tool and / or forging tool used for calibration can be formed in whole or in part in a conical shape, so that very high compression can be realized in a predetermined constant area. In that case, the temperature of the calibration tool and / or forging tool may vary depending on the part to be machined and, in some cases, may be maintained in an isothermal range. Surface compression or the introduction of compressive internal stresses on the surface is possible even before or after heat treatment or calibration.

Finally, it is also possible to finally apply a coating on the sintered part. Preference is given here to methods of hard coating and / or anodizing the components, such as thermal spraying methods such as plasma spraying, flame spraying or physical and / or chemical methods such as PVD, CVD and the like. However, it is also possible to attach the coating by pure chemical methods such as, for example, by gamma lacquers or nanocomposite materials which may contain Teflon. Such coatings modify the surface of the part to suit its purpose in terms of hardness, roughness and coefficient of friction.

Hereinafter, such and further advantages of the present invention will be described based on examples.

Example 1:

ECKA Granulate GmbH & Co. The composition is made from KG company Al4Cu1Mg0.5Si (formerly known as aluminum alloy name AC2014, the base material powder is based on the total amount of powder 4% by weight of Cu, 1% by weight of Mg, 0.5% by weight of Si and Al-based powder, containing 94.5% by weight of Al), 1.5% by weight of amide as a binder named Mikrowachs C, manufactured by Hoechst, as the company name ECKA Alumix 123 (92.5% by weight of Al). The wax was mixed with molybdenum powder or tungsten powder according to the table below. Here, mixing was performed for 5 minutes in a rocking mixer by adding molybdenum powder or tungsten powder to the Al-based powder previously contained at room temperature.

The Al-based powder showed a particle size distribution of 45 to 200 μm, with an average particle diameter (D ₅₀ ) of 75 to 95 μm. The mixed molybdenum powder or tungsten powder is produced by HC Starck GmbH & Co. It was obtained from KG and showed an average particle diameter (D ₅₀ ) of 25 μm with a particle size distribution in the range of about 5 to 50 μm.

The powder mixture was then placed in a mold and pressure molded into a shaped body in the form of a pump wheel for about 0.2 to 0.5 seconds at room temperature under a pressure of about 175 N / mm 2 (calculated for a wheel end face of 20 cm 2). The density of the molded body was about 2.35 to 2.38 g / cm 3. The molded product thus produced is then dewaxed at about 430 ° C. for about 30 minutes and then sintering temperature of 610 ° C. under pure nitrogen atmosphere with a dew point of −50 ° C. in a conveyor furnace set at a speed of 3.4 m / h. Sintering was carried out over 30 minutes. In that case, the molded body was present in an Al ₂ O ₃ pattern. Next, homogenization annealing was performed over 1.5 hours at the temperature of 515 degreeC. After that, the sintered pump wheel was quenched by quenching for 10 seconds with water having a temperature of about 40 ° C.

It was then calibrated to a theoretical density of 97-98% using a pressure of about 810 N / mm 2 at 200 ° C.

The sintered pump wheels were then age hardened over 16 hours in hot air at 160 ° C. after calibration. The tensile strength (R _m ), modulus of elasticity and elongation were then determined in accordance with DIN EN 10002-1 on standardized specimens. In addition, hardness was determined according to DIN EN 24498-1 (Brinell hardness) by a hard steel ball having a diameter of 2.5 cm and a load of 62.5 kg. The obtained values are shown in Table 1 below.

Example 2:

The test mentioned in Example 1 above was repeated except that the copper powders commercially available from Eckart Granules under the trade name Ecka Kupfer CH-S were added and mixed together. Such additive mixing was first performed in the form of mixing molybdenum powder or tungsten powder with copper powder for 5 minutes at room temperature in a rocking mixer, and then mixing it with Al-based powder over 5 minutes in a rocking mixer. The copper powder showed an average particle diameter (D ₅₀ ) of 25 μm and a particle size distribution in the range of 5 to about 50 μm. Copper powder was prepared by electrolysis, and individual particles were present in the form of dendritic crystals.

Various mixtures were prepared, which were sintered with a pump wheel as described in Example 1 with or without recompression. For recompression, the molded body was press-molded and then dewaxed at a temperature of about 430 ° C. for 30 minutes under a nitrogen atmosphere, followed by a second mold identical to the first mold sprayed with a gamma agent GLEITMO 300 from Fuchs Lubritech GmbH, Weilerbach, Germany. Recompression at room temperature under pressure of 760 N / mm 2 at room temperature for about 0.2 to 0.5 seconds so that the density of the recompressed molded body is about 2.8 to 2.9 g / cm 3, thus being about the density of the non-recompressed pump wheel molded body. 19 to 23% above, ie about 95% of theoretical density.

The resulting shaped bodies were then sintered as described above, and calibrated to a theoretical density of 97 to 98% under pressure of 810 N / mm 2, but at room temperature, and age-cured. The mixing ratio of molybdenum powder or tungsten powder to copper powder was 5: 1 by weight fraction. Such mixing ratios and identified physical property values can be cited from Table 2.

As can be seen from Table 2, recompression has a positive effect on the physical properties. In particular, the hardness of the manufactured pump wheel can be further raised.

By means of the invention, it is possible to produce sintered parts, in particular based on Al powders, which exhibit not only excellent strength values but also high hardness. This makes it possible to use such parts at points of intense stress, in particular engines or transmissions. In addition, by omitting the calibration and age hardening of the sintered parts, the parts can be manufactured even better and faster.

Claims (15)

60 to 92% by weight of Al based powder, a first group consisting of 6.4 to 15% by weight of Mo or W and 1.6 to 25% by weight of Cu, Sn, Zn, Li or Mg based on the total amount of the powder mixture A second group of metals or alloys thereof, wherein the Al-based powder is a balance by weight based on the total amount of Al and Al-based powder, the next metal, 0.2-30% by weight Mg, 0.2-40% by weight Si, 0.2-15 wt% Cu, 0.2-15 wt% Zn, 0.2-15 wt% Ti, 0.2-10 wt% Sn, 0.5-5 wt% Mn, 0.2-10 wt% Ni And less than 1% by weight of at least one of As, Sb, Co, Be, Pb or B. A sinterable powder mixture for producing a sintered part. delete The method according to claim 1, wherein the ratio of the amount of the first group of metals or their alloys to the amount of the second group of metals or alloys thereof in the powder mixture is in the range of 1: 4 to 9: 1 by weight fraction. Sinterable powder mixture characterized in that. According to claim 1, Al-based powder is 0.2 to 15% by weight of Mg, 0.2 to 16% by weight of Si, 0.2 to 10% by weight of Cu or 0.2 to 15% by weight in addition to Al based on the total amount of Al-based powder Sinterable powder mixture, characterized in that containing Zn. The sinterable powder mixture of claim 1, wherein the second group of metals or alloys thereof contains Cu, Zn or Sn. The sinterable powder mixture of claim 1 wherein the powder mixture contains from 0.2 to 5% by weight of a lubricant based on the total amount of the powder mixture. A sintered part, which is made of the sinterable powder according to any one of claims 1 to 6. 8. The sintered part according to claim 7, wherein the sintered part exhibits a tensile strength of at least 140 N / mm 2 measured according to DIN EN 10002-1. 8. The sintered part according to claim 7, wherein the sintered part exhibits an elastic modulus of at least 70 kN / mm2 measured according to DIN EN 10002-1. The sintered part according to claim 7, wherein the sintered part exhibits a hardness of at least 100 (HB 2.5 / 62.5 kg) measured according to DIN EN 24498-1. A first step of placing the powder mixture in the first mold; A second step of press molding the powder mixture into shaped bodies; A third step of at least partially recompressing the shaped body; And A method for producing a sintered part and a composite part with a powder mixture according to any one of claims 1 to 6, characterized in that it comprises a fourth step of sintering the recompressed molded body. The method for producing a sintered part and composite part according to claim 11, wherein the molded body is dewaxed before the third step. The method for producing a sintered part and composite part according to claim 11, wherein the density of the molded product obtained by the recompression performed in the third step is made about 2 to 40% larger than the density before recompression. The method of manufacturing a sintered part and composite part according to claim 11, wherein a gamma agent is sprayed on the second mold before the molded body is put into the second mold in the third step. 12. The method of claim 11 wherein the sintering process is performed under nitrogen having a dew point of less than -40 ° C.