EP2552630B1 - Method for producing shaped bodies from aluminium alloys - Google Patents

Description

The technology of metal powder injection molding has gained a tremendous boost in recent years and is an established technology with a global annual turnover of about € 1 billion for the production of intricately shaped small parts. The possibility of combining the molding technology of plastic injection molding with the material diversity of powder technology has opened up interesting markets for many materials.

The manufacturing process consists essentially of the process steps described below. First, a feedstock is prepared in the form of a sprayable granulate of metal powder and a plastic component comprising at least two intensively mixed polymer components. This feedstock is then sprayed into molded parts in plastic injection molding machines. This so-called "green body" or "green body" usually contains about 40% by volume of plastic binder, which is removed in the subsequent step, the so-called debindering, for the most part. There remains only a residual component of the binder, the so-called. "Backbone", which ensures the residual strength of the unbent body. Debinding can be done in a variety of ways, e.g. thermally, by solvent, catalytically, etc., where it must be very well matched to the plastic binder used. The debinded body, the so-called "brown part" or "browning", is now subjected to a sintering process, in the first stage of which the "backbone" residual binder is normally thermally removed and the body is then sintered with appropriate shrinkage to form an approximately dense metallic component. The technology is currently used for high and low alloy steels, precious metals, hard metals, but also for ceramics.

Although several related patents exist, metal powder injection molding for aluminum materials has not been successfully introduced industrially since the mechanisms of sintering aluminum alloys are very different from those of the above-mentioned materials. The presence of non-reducible oxides on the surface of aluminum powders massively hinders sintering. For this reason, an oxygen-free atmosphere is generally described or suggested to be used in the specialist literature.

EP 329,475 A2 describes the processing of various metal powders, ceramics or alloys into moldings using a special organic binder mixture. Aluminum is mentioned as one of many possible starting materials, which should be sinterable with the binder system there. Suitable atmospheres for debinding include oxidizing, reducing and inert atmospheres - under low, normal or overpressure - and thus all conceivable options.

Katou et al., J. Jpn. Soc. Powder and Powder Metal. 42 (9), 1068-72 (1995 ) disclose the preparation of Ti-Al alloys in proportions of 45:55 to 55:45, while debinding in air or Ar vacuum. The goal was a debindering over 90%. The targeted sintering densities of more than 95% are achieved only partially - even when sintered in Ar vacuum, where the density was consistently higher than after debindering in air, which is attributed to oxidation, which was consistently pronounced when debinding in air as in Ar-vacuum. Carbides were also found in the sintered bodies, the presence of which is attributed to contamination with carbon from the furnace, but which is much more likely to result from incomplete debindering and hence the logical presence of organic carbon in the brown compact. Consequently, it is stated that debinding should be done in a vacuum and not in air.

In J. Jpn. Soc. Powder and Powder Metal. 51 (7), 2004-7 (2004 ), K. Katou et al. a few years later, the processing of pure aluminum to sintered bodies by means of MIM, wherein to investigate the influence of the atmosphere during debindering on the density of the sintered body was debindered both at 325 ° C in air and at 380 ° C under argon pressure, but in in all cases specifically only to "about 90%". After debindering in argon, the density of the resulting sintered bodies, depending on the grain size, was 86, 89 and 96% respectively, whereas in air debindering in two cases it was about 65% and in the third case, using the finest-grained starting powder. fell to 86%. The reasons given for this are oxidation of the aluminum or the amount of residual binder. Thus, the oxygen content of binder removal in Ar increased by 50%, while in air it increased by 2 to 3 times. The carbon content in the air-debindered sintered body was even 5 times that in Ar. Furthermore, it is found that the investigations of the thermal decomposition of the organic binder up to a temperature of 500 ° C would have shown that in inert gas, a decomposition rate of 99.5%, in the air atmosphere, however, only a decomposition rate of 96.5% can be achieved, and that the densities achieved with air-debindering are below 90% insufficient. By sintering close to the melting point of aluminum, it had also come to undesirable partial melting of the samples, which is referred to as a danger, which is why the sintering temperature should be lowered.

A particular difficulty in the processing of aluminum in the manner described above is also the relatively low melting point of aluminum (660 ° C) produced by the addition of alloying elements, e.g. Tin, still lowered. The resulting problem is that the debinding of the plastic component must be completed at very low temperatures, which often makes the available process window too small to ensure complete removal. However, if this fails, undesirable reactions of residual organic constituents with the metallic components can occur, hindering sintering and thus impairing the mechanical properties that can be achieved.

For example, describe Liu et al. in Powder Metallurgy 51, 78-83 (2008 ) a method with the addition of tin as alloying metal as well as magnesium blocks, wherein the magnesium as a "sacrificial metal", ie as an oxygen and moisture scavenger used.

The object of the invention was, in this context, the development of a metal powder injection molding process, by the moldings of aluminum materials with good mechanical properties can be produced in a simpler and reproducible manner.

DISCLOSURE OF THE INVENTION

1. a) Herstellung eines Feedstocks durch Vermischen der in der gewünschten Legierung enthaltenen Metalle in Form von Metallpulvern und/oder einem oder mehreren Metalllegierungspulvern mit einem Binder;
2. b) Herstellung eines Grünlings durch Spritzgießen des Feedstocks;
3. c) Herstellung eines Bräunlings durch zumindest teilweises Entfernen des Binders aus dem Grünling durch katalytisches und/oder Lösungsmittel- und/oder thermisches Entbindern;
4. d) Sintern des zumindest teilweise entbinderten Bräunlings zum Erhalt des gewünschten Formkörpers;

wobei das erfindungsgemäße Verfahren dadurch gekennzeichnet ist, dass in Schritt c) der Binder vollständig entfernt wird, wobei, gegebenenfalls nach Durchführung eines oder mehrerer vorhergehender Entbinderungsstufen, eine thermische Entbinderung zur Entfernung des (Rest-)Binders erfolgt, die in einer zumindest 0,5 Vol.-% Sauerstoff enthaltenden Atmosphäre durchgeführt wird, wonach der so erhaltene, vollständig entbinderte Bräunling gesintert wird.This object has been achieved by the inventors by providing a process for the production of moldings based on aluminum alloys by metal injection molding, comprising the following steps:

1. a) production of a feedstock by mixing the metals contained in the desired alloy in the form of metal powders and / or one or more metal alloy powders with a binder;
2. b) production of a green compact by injection molding of the feedstock;
3. c) preparation of a browning by at least partial removal of the binder from the green compact by catalytic and / or solvent and / or thermal debinding;
4. d) sintering the at least partially debinded browning to obtain the desired shaped article;

wherein the inventive method is characterized in that in step c) the binder is completely removed, wherein, optionally after performing one or more preceding debinding steps, a thermal debinding takes place to remove the (residual) binder, which is in at least 0.5 Vol .-% oxygen-containing atmosphere is carried out, after which the resulting completely unbonded Braunling is sintered.

By this method, highly pure moldings of aluminum alloys are obtained, since there is no unwanted reactions of the plastic with the alloy metals due to the complete removal of the binder in step c). This complete removal of the binder succeeds - even at relatively low temperatures - due to the presence of oxygen in the atmosphere. Contrary to the prevailing theory that oxygen must be avoided at all costs, the inventors have found that a small proportion of at least 0.5% by volume does not appreciably promote the oxidation of the aluminum, but contributes to rapid and complete debindering. Depending on the composition of the powder mixture and the temperature conditions, for example, an oxygen content between 20 and 100 vol .-% is used, ie it can even be used pure O ₂ gas.

The aluminum alloy contains, besides aluminum, one or more other metals which are not specifically limited. Preferably, the alloying partners are selected from the group consisting of magnesium, copper, silicon and manganese, and are more preferably contained in a respective proportion of 0.5 to 25% by weight to obtain molded articles having desirable properties. Significantly lower melting metals, such as bismuth, tin, lead, indium, or even zinc, or alloys such as Wood's metal, sometimes called sintering aids for lowering serve the temperature of the onset of melting, are not required according to the present invention, but can still be added as alloying partners, if desired, to obtain sintered bodies of the corresponding alloys. In a particularly advantageous manner, the other metals are used as alloys with aluminum, ie as master alloy or so-called master alloy powder.

According to the present invention, it is preferred to use binders which are known to be removable at low temperatures, more preferably polyacetal-based binders, for example polyoxymethylene (POM) binders, for example those described by BASF in US Pat EP 413,231 . WO 94/25205 and especially EP 446,708 disclosed and sold under the brand name Catamold ^® . In order to promote rapid and complete removability at low temperatures and in the presence of oxygen, a high polyacetal content is desirable in the binder, and therefore, the binder is preferably 50 to 95%, more preferably 80 to 90%, of polyacetal. Alternatively, binder systems can be used which are based on wax polymer-based and in which the main component wax by previous Lösungsentbinderung, ie prior to the inventive implementation of the thermal debinding in the presence of oxygen, is removed.

Debinding in step c) of the process of the invention may involve a single step of thermal debinding in the presence of oxygen, in which the entire binder is removed. Alternatively, one or more preceding debinding steps may be performed to remove the bulk of the binder, followed by the thermal debinding step of the present invention to remove the residual binder in the presence of oxygen. Thus, a previous debinding step may also be a thermal debindering - in the absence or also in the presence of oxygen. That is, as debindering can also be a multi-stage thermal debindering at different process parameters, such as different temperature or atmosphere, eg without and with oxygen or with air and pure oxygen, etc.

In preferred embodiments of the invention, first a catalytic debinding and / or a Lösungsentbinderung performed in step c) before the thermal debinding to remove the residual binder in the presence of oxygen. In this case, the bulk of the binder is already removed from the composition, so that in the subsequent thermal debinding preferably only the "backbone" component needs to be removed.

The catalytic debinding is carried out preferably in the presence of at least one acid selected from nitric acid, oxalic acid, formic acid and acetic acid, since these acids accelerate the complete removal of the preferred polyacetal binder by acidolysis, without leading to undesirable side reactions with the alloying partners. In the case of solution debonding, on the other hand, the bulk of the binder is obtained by extraction with a suitable solvent or solvent mixture, e.g. Acetone, n-heptane, water etc., removed. Particularly preferred according to the present invention is a catalytic debindering with sublimed oxalic acid.

As already mentioned, the thermal debinding to remove the residual binder in step c) is carried out at a relatively low temperature in order to suppress oxidation reactions, especially of the aluminum in the powder mixture. By a relatively low temperature herein is meant a temperature well below the melting point of aluminum, preferably below 500 ° C, more preferably between 100 and 420 ° C. In particular, an empirically optimized temperature profile for the respective powder mixture is set, which preferably provides a heating rate of not more than 5 K / min, more preferably not more than 1 to 2 K / min. As a result, the mixture to be debindered is heated in a gentle, uniform manner.

The sintering step d) of the process of the present invention is not specifically limited except for the requirement that the binder must be completely removed beforehand. Preferably, however, is sintered to form a liquid phase, as will be explained in more detail below.

The hitherto known technology of powder metallurgical molding of aluminum alloys by means of compression molding is based on the theoretical approach that the surface of the aluminum particles coated with an aluminum oxide layer is mechanically damaged by the pressing process in the matrix, whereby a metallurgical reaction is made possible in the first place. In the case of a (completely) bindered brown body from powder injection molding, however, it is de facto a metal powder spill, with the oxide skins of the metals not being exposed to any mechanical stress and therefore not subject to this known mechanism. That is, there are no direct metal-to-metal contacts between the powder particles. Nevertheless, it is possible in the process according to the invention, by suitable choice of the sintering conditions to achieve the required shrinkage, by means of which manifests the compression of the sintered body, and thus to obtain largely dense components.

Embodiments according to the invention are therefore preferred in which the completely debinded browning material is sintered in step d) to form a liquid phase. This liquid phase, which in the view of the inventors - without wishing to be bound to a particular theory - to a part intermediary, but predominantly stationary, ie in thermodynamic equilibrium with the solid Al phase, is present over microcracks, pores or the like "Openings" in the oxide skins of the metal powder particles and infiltration of the oxide skins forth the required contact between the metals in the powder mixture ago and thus supports the formation of a high-density sintered body from the completely unbonded Bräunling. Particularly preferably, the sintering in step d) is carried out at a temperature between the solidus and the liquidus temperature of the respective aluminum alloy, so that at any time during the sintering process only a controllable by the choice of a corresponding temperature profile proportion of the alloy metals in liquid Phase exists, which effectively prevents loss of dimensional and dimensional stability.

The composition of the particular atmosphere in the individual steps of the process according to the invention is not particularly limited except for the presence of the oxygen in the thermal debinding in step c), and the person skilled in the art can select in each individual step the most suitable atmosphere for the respective powder mixture , whereby also vacuum is possible. However, the sintering step d) is preferably carried out in an extremely dry nitrogen-containing atmosphere, i. in pure nitrogen, under normal pressure or reduced pressure ("partial pressure sintering"), or in a mixture of nitrogen and pure inert gas (helium, argon), preferably with a dew point <-40 ° C, since the presence of nitrogen with the wettability of the powder the resulting molten metal significantly supported.

If appropriate, sintering may be followed by a suitable after-treatment, by means of which the finished molded parts are obtained in the desired shape. For example, the known method of hot isostatic pressing (HIP) can be used to bring the moldings to the desired final density. In this case, residual pores remaining after sintering are pressed by the simultaneous action of external gas pressure and temperature, and the pore walls are welded together.

BRIEF DESCRIPTION OF THE DRAWINGS

• Fig. 1 is a photograph of the green compact (top) and the resulting sintered body (bottom) of Example 9.
• Fig. 2 is a photograph of the green compact (left) and the resulting sintered body (right) of Example 10.

The invention will be described below with reference to non-limiting specific embodiments.

EXAMPLES

All feedstocks prepared in the examples below were homogenized in a heated kneader at 190 ° C. From these feedstocks, tensile test bars or hollow cylinders were molded by means of injection molding in accordance with ISO 2740, the method according to the invention being used as follows. To produce the green parts, a hydraulic injection molding machine (Battenfeld HM 600/130) with PIM equipment was used.

In a first step, the feedstock was first filled into a funnel of the injection molding machine. The powder injection molding for the production of the green parts was carried out in the following steps: The prepared feed material was plasticized and pre-dosed by means of a heated injection cylinder in which a screw rotates according to preset setting parameters (such as, for example, rotational speed, metering volume, dynamic pressure, etc.). Subsequently, the pre-dosed quantity was injected into a suitably tempered tool. Depending on the feedstock or binder used, the plasticizing temperature in the injection cylinder was between 120 and 220 ° C, while in the tool between 25 and 140 ° C prevailed. After sufficient cooling time, the injection mold was opened and the green part ejected from the tool and removed with a handling.

Example 1 - Tension rods: Solution debonding / thermal debinding

A commercially available metal powder mixture (Alumix ^® 231 of Ecka) consisting of aluminum, with 14 wt .-% of silicon, 2.5 wt .-% copper and 0.6 wt .-% magnesium, was with a group consisting of wax / thermoplastic Solvent binder carefully mixed into a feedstock. Feedstock component Proportion (% by weight) Alumix 231 powder * 74.8 Solvent binder: wax content 14.8 Solvent binder: thermoplastic content 8.2 stearic acid 2.2 100.0 * Commercially available metal powder mixture of aluminum with 14% by weight of silicon, 2.5% by weight of copper and 0.6% by weight of magnesium (from Ecka)

Debinding and sintering of the tension rods

This feedstock was first debinded by solvent extraction in a 60 L oven with acetone at a temperature of 45 ° C over 12 h.

The Bräunling thus obtained contained a residual binder content of about 14.5 wt .-%, which then by thermal debinding according to the invention by means of a temperature profile of 150 ° C to 320 ° C for 1 h and then from 320 to 420 ° C for 1.5 h was removed at a heating rate of 3 K / min under a pure oxygen-containing atmosphere. The thus completely unbonded Bräunling was then sintered at 560 ° C within 1 h in pure nitrogen (dew point: -50 ° C).

Results

• Length shrinkage: 11.6%
• Shrinkage of the bar diameter: 12.25%
• Sintered density: 2.36 g / cm ³

Example 2 - Tension rods: thermal debindering in one step

Feedstock component Proportion (% by weight) aluminum powder 67.1 Master Alloy Powder * 4.3 POM Binder 25.8 Lucryl G55 ** 2.8 100.0 * Master alloy of aluminum and magnesium in the ratio 50:50
** Commercially available polymethylmethacrylate (PMMA, from BASF)

Debinding and sintering of the tension rods

• Aufheizen auf 130 °C mit einer Heizrate von 2 K/min
• 4 h Haltezeit bei 130 °C
• Aufheizen auf 200 °C mit einer Heizrate von 2 K/min
• 5 h Haltezeit bei 200 °C
• Aufheizen auf 420 °C mit einer Heizrate von 2 K/min
• 4 h Haltezeit bei 420 °C

Der Gewichtsverlust nach der thermischen Entbinderung betrug 24,2 %.Here a complete thermal debindering was carried out in a 40 l oven with 200 l / h of pure oxygen according to the following debindering profile:

• Heating to 130 ° C with a heating rate of 2 K / min
• 4 h hold time at 130 ° C
• Heating to 200 ° C with a heating rate of 2 K / min
• 5 h hold time at 200 ° C
• Heating to 420 ° C with a heating rate of 2 K / min
• 4 h hold time at 420 ° C

Weight loss after thermal debinding was 24.2%.

Subsequently, the sintering was carried out at a furnace setting temperature of 665 ° C, which corresponds to a temperature within the furnace of about 630 ° C, during 1 h in pure nitrogen.

Results

• Length shrinkage: 12.27%
• Shrinkage of the bar diameter: 14.52%
• Sintered density: 2.46 g / cm ³

Example 3 - Tension rods: double thermal debinding

Feedstock component Proportion (% by weight) aluminum powder 70.1 magnesium powder 2.2 POM Binder 24.0 surfactant * 3.7 100.0 * Ethoxylated C ₁₃ -C ₁₅ oxo alcohol with 7 EO units

Debinding and sintering of the tension rods

First, a first thermal debinding was carried out in a 50 l oven in 500 l / h of air at 180 ° C for 14 h. Weight loss: 27.0%.

This was followed by a second thermal debindering to 420 ° C under pure oxygen within 1 h, which in turn was sintered under nitrogen at a Ofeneinstelltemperatur of 665 ° C for 1 h.

Results

• Length shrinkage: 9.5%
• Shrinkage of the bar diameter: 11.4%
• Sintered density: 2.13 g / cm ³

Example 4 - Tensile Bars: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) aluminum powder 70.1 magnesium powder 2.2 POM Binder 24.0 surfactant * 3.7 100.0 * Ethoxylated C ₁₃ -C ₁₅ oxo alcohol with 7 EO units

Debinding and sintering of the tension rods

First, a catalytic debinding in a 50-liter oven with 2% by volume of HNO ₃ in 500 l / h of nitrogen (technically pure) at 140 ° C for 10 h. Weight loss: 22.1%. There were pearl-like outgrowths on the surface, which were probably formed by reaction of Mg with HNO ₃ .

Subsequently, as in Example 3, a thermal debindering to 420 ° C under pure oxygen within 1 h, after which it was again sintered at a Ofeneinstelltemperatur of 665 ° C for 1 h under nitrogen.

Results

• Length shrinkage: 10.7%
• Shrinkage of the bar diameter: 14.65%
• Sintered density: 2.36 g / cm ³

Example 5 - Tensile Bars: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) aluminum powder 70.1 magnesium powder 2.2 POM Binder 24.0 surfactant * 3.7 100.0 * Ethoxylated C ₁₃ -C ₁₅ oxo alcohol with 7 EO units

Debinding and sintering of the tension rods

First, a catalytic debinding was carried out analogously to Example 4, but using 80 g of anhydrous oxalic acid on a Sublimierschale instead of HNO ₃ at 140 ° C for 24 h. Weight loss: 23.0%. Due to the use of oxalic acid, no outgrowths appeared on the surface. Subsequently, thermal debinding and sintering were also carried out analogously to Example 4.

Results

• Length shrinkage: 14.28%
• Shrinkage of the bar diameter: 15.68%
• Sintered density: 2.42 g / cm ³

Example 6 - Tensile Bars: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) Alumix 231 powder * 70.8 POM Binder * 25.6 surfactant ** 3.6 100.0 * Commercially available metal powder mixture of aluminum with 14% by weight of silicon, 2.5% by weight of copper and 0.6% by weight of magnesium (from Ecka)
** Ethoxylated C ₁₃ -C ₁₅ oxo alcohol with 7 EO units

Debinding and sintering of the tension rods

First, a catalytic debinding was carried out analogously to Example 5. Weight loss: 25.2%. Subsequently, thermal debinding and sintering were carried out analogously to Example 4, but at a Ofeneinstelltemperatur of 560 ° C.

Results

• Length shrinkage: 11.2%
• Shrinkage of the bar diameter: 13.2%
• Sintered density: 2.45 g / cm ³

Example 7 - Tensile Bars: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) aluminum powder 68.0 Master Alloy Powder * 4.3 POM Binder 24.0 surfactant ** 3.7 100.0 * Master alloy of aluminum and magnesium in the ratio 50:50
** Ethoxylated C ₁₃ -C ₁₅ oxo alcohol with 7 EO units

Debinding and sintering of the tension rods

First, a catalytic Entbinderung analogous to Example 5. Weight loss: 23.2%. Subsequently, thermal debinding and sintering were carried out analogously to Example 4.

Results

• Length shrinkage: 12.6%
• Shrinkage of the rod diameter: 13.25%
• Sintered density: 2.56 g / cm ³

Example 8 - Hollow Cylinder: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) aluminum powder 68.0 Master Alloy Powder * 4.3 POM Binder 24.0 surfactant ** 3.7 100.0 * Master alloy of aluminum and magnesium in the ratio 50:50
** Ethoxylated C ₁₃ -C ₁₅ oxo alcohol with 7 EO units

Debinding and sintering of the hollow cylinder

First, a catalytic debinding was carried out analogously to Example 5. Weight loss: 23.7%. Subsequently, thermal debinding and sintering were carried out analogously to Example 4.

Results

• Height shrinkage: 17.24%
• Shrinkage of the diameter: 14.48%
• Sintered density: 2.59 g / cm ³

Example 9 - Tensile Bars: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) aluminum powder 67.1 Master Alloy Powder * 4.3 POM Binder * 25.8 Lucryl G55 ** 2.8 100.0 * Master alloy of aluminum and magnesium in the ratio 50:50
** Commercially available polymethylmethacrylate (PMMA, from BASF)

Debinding and sintering of the tension rods

First, a catalytic debinding analogous to Example 5. Weight loss: 25.7%. Subsequently, thermal debinding and sintering were carried out analogously to Example 4.

Results

• Length shrinkage: 13.57%
• Shrinkage of the bar diameter: 19.55%
• Sintered density: 2.59 g / cm ³

Example 10 - Hollow Cylinder: Catalytic / Thermal Debinding

Feedstock component Proportion (% by weight) aluminum powder 67.1 Master Alloy Powder * 4.3 POM Binder 25.8 Lucryl G55 ** 2.8 100.0 * Master alloy of aluminum and magnesium in the ratio 50:50
** Commercially available polymethylmethacrylate (PMMA, from BASF)

Debinding and sintering of the hollow cylinder

First, a catalytic debinding analogous to Example 5. Weight loss: 25.6%. Subsequently, thermal debinding and sintering were carried out analogously to Example 4.

Results

• Height shrinkage: 16.52%
• Shrinkage of the diameter: 14.48%
• Sintered density: 2.56 g / cm ³

Thus, by the method according to the invention sintered bodies of aluminum alloys can be provided by means of injection molding, which are suitable for practical use in many fields, e.g. in the transport sector, construction, mechanical engineering, packaging, iron and steel, electrical engineering, household appliances, etc., for example for heat dissipation in electronic devices ("heat sinks") or as components of air conditioning systems.

Claims (19)

1. A method for producing molded articles based on aluminum alloys by metal powder injection molding, comprising the following steps:

   a) producing a feedstock by mixing the metals contained in the desired alloy in the form of metal powders and/or one or more metal alloy powders with a binder;

   b) producing a green body by injection molding said feedstock;

   c) producing a brown body by removing the binder from the green body by catalytic and/or solvent and/or thermal debinding;

   d) sintering the at least partially debound brown body to obtain the desired molded article;

   characterized in that, in step (c), said binder is completely removed, wherein, optionally after having carried out one or more previous debinding steps, thermal debinding is carried out to remove the binder or residual binder, said thermal debinding being carried in an atmosphere containing at least 0.5 % by volume of oxygen, whereafter the thus obtained completely debound brown body is sintered.
2. The method according to claim 1, characterized in that, in addition to aluminum, the aluminum alloy contains one or more metals selected from magnesium, copper, silicon, and manganese.
3. The method according to claim 1 or 2, characterized in that, in addition to aluminum, the aluminum alloy contains one or more metals at a perecentage of 0.5 to 25 % by weight, respectively.
4. The method according to any one of claims 1 to 3, characterized in that the metal(s) is/are used as (a) master alloy powder(s).
5. The method according to any one of the preceding claims, characterized in that a polyacetal-based binder, e.g., polyoxymethylene (POM) binder, is used as said binder.
6. The method according to claim 5, characterized in that said binder consists of 50 to 95 % of polyacetal.
7. The method according to claim 6, characterized in that said binder consists of 80 to 90 % of poylacetal.
8. The method according to any one of claims 1 to 7, characterized in that, in step (c), only thermal debinding in the presence of oxygen is conducted in one or more steps in which the binder is completely removed.
9. The method according to any one of claims 1 to 7, characterized in that, in step (c), solvent debinding to remove the main part of the binder, followed by said thermal debinding to remove the residual binder are conducted.
10. The method according to any one of claims 1 to 7, characterized in that, in step (c), catalytic debinding to remove the main part of the binder, followed by said thermal debinding to remove the residual binder are conducted.
11. The method according to claim 10, characterized in that said catalytic debinding is carried out in the presence of at least one acid selected from nitric acid, oxalic acid, formic acid, and acetic acid.
12. The method according to claim 11, characterized in that sublimated oxalic acid is used as the acid.
13. The method according to any one of the preceding claims, characterized in that said thermal debinding to remove the residual binder is carried out at a temperature below 500 °C.
14. The method according to claim 13, characterized in that said thermal debinding to remove the residual binder is carried out applying a specific temperature profile ranging between 100 and 420 °C.
15. The method according to claim 13 or 14, characterized in that the heating rate during said thermal debinding process for removing the residual binder does not exceed 5 K/min.
16. The method according to claim 15, characterized in that the heating rate does not exceed 1 to 2 K/min.
17. The method according to any one of the preceding claims, characterized in that, in step d), the completely debound brown body is sintered while forming a liquid phase.
18. The method according to claim 17, characterized in that sintering is carried out at a temperature between the solidus and the liquidus temperatures of the respective aluminum alloy.
19. The method according to any one of the preceding claims, characterized in that the heating rate to reach the sintering temperature after said thermal debinding step for removing the residual binder ranges from 4 to 20 K/min.

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