AT509613A1 - METHOD FOR PRODUCING MOLDINGS FROM ALUMINUM ALLOYS - Google Patents

Description

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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 " usually contains about 40 vol .-% plastic binder, which is removed in the subsequent step, the so-called debinding, 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 unbound body, the so-called " brown part " or " tanning ", 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 a nearly 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 of aluminum alloys are very different from those of the above-mentioned materials. Namely, the presence of non-reducible oxides on the surface of aluminum powder severely inhibits sintering. For this reason, the literature also consistently describes an oxygen-free atmosphere. -1 - «· · · ·« «« * * «* ····« t * · * * * * ♦ · · · »♦» · · j ··· ··· # · # # · «··

·· ** · * · ·· I

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, Liu et al. in Powder Metallurgy 51, 78-83 (2008) discloses a method of adding tin as alloying metal as well as magnesium blocks, wherein the magnesium is referred to as " sacrificial metal ", i. as an oxygen and moisture scavenger.

Against this background, the object of the invention was the development of a metal powder injection molding process, by means of which the molded body made of aluminum materials with good mechanical properties can be produced in a simpler and reproducible manner.

DISCLOSURE OF THE INVENTION

This aim 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: a) production of a feedstock by mixing the metals contained in the desired alloy in the form of metal powders and / or one or a plurality of metal alloy powders with a binder; b) production of a green compact by injection molding of the feedstock; 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; -2-

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. For example, depending on the composition of the powder mixture and the temperature conditions, an oxygen content of between 20 and 100% by volume is used, i. even pure 02 gas can be used.

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, e.g. Bismuth, tin, lead, indium, or even zinc, or alloys such as Wood's metal, sometimes serving as sintering aids to lower the onset of melting temperature, are not required in the present invention, but may be added as alloying partners to sintered bodies if desired the corresponding alloys.

In a particularly advantageous manner, the other metals as alloys with aluminum, i. as master alloy or so-called Masteralloy powder used. m

In the present invention it is preferred to use binders which are known to be removable at low temperatures, more preferably polyacetal-based binders, e.g. Polyoxymethylene (POM) binders, for example those as disclosed by BASF in EP 413,231 ^ WO 94/25205 ^ and especially EP 446.70 ^ and are also sold under the trade 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 based on wax-polymer-based and in which the main component wax by prior Lösungsentbinderung, i. E. before carrying out the thermal debinding in the presence of oxygen according to the invention 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, e.g. without and with oxygen or with air and pure oxygen etc. -4- ♦ ········································································································. ·· ♦ · · · ta · * · * · a · # »

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 majority of the binder is already removed from the composition *, so that in the subsequent thermal debindering 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. -5- • · ···· + m ········ ··· ψ

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. However, a (completely) de-bonded brown body from powder injection molding is, in fact, 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 inventors' view, without wishing to be bound by any particular theory, is to some extent intermediate but predominantly stationary, i. in thermodynamic equilibrium with the solid Al phase, poses microcracks, pores, or similar " openings " in the oxide skins of the metal powder particles and infiltration of the oxide skins, the required contact between the metals in the powder mixture and thus supports the formation of a high-density sintered body from the completely unbound 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 all times during the sintering process, only one of the alloying metals in the liquid phase which can be controlled by the selection of a corresponding temperature profile is present , which effectively prevents a loss of dimensional and dimensional stability.

The composition of the respective atmosphere in the individual steps of the method according to the invention, apart from the presence of the oxygen at -6- ··· # ··· * · »· i · · · · I · * t · · · · · · · m The thermal debinding in step c) is not particularly limited and the person skilled in the art can choose in each individual step the most suitable atmosphere for the respective powder mixture, vacuum also being 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 noble gas (helium, argon), preferably with a dew point < -40 eC, since the presence of nitrogen significantly supports the wettability of the putr particles with the resulting molten metal.

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 (above) and the sintered body (bottom) obtained therefrom of Example 9.

Fig. 2 is a photograph of the green compact (left) and the sintered body (right) thereof obtained in 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, -7- * ♦ * «« «· + + · · · · * *

The method according to the invention was 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 hopper of the injection molding machine. Powder injection molding to produce the green parts was carried out in the following steps: The processed feedstock was heated by a heated injection cylinder in which a worm rotates according to preset setting parameters (such as, for example, rotational speed , Dosing volume, back pressure, etc.) plasticized and pre-dosed. 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. -8- * «9 ··» 9 ··· · f * * * · * 9 φ 9 * »· · ·« · ··· «t * * · · · *« * ♦ «·» ·· · * · * ·· 999 9 ·· «· · · 9 9 9 ·

Example 1 - Zuastäba: Lösunasentbinderuna / thermal Entbinderuna

A commercially available metal powder mixture (Alumix® 231 from Ecka) consisting of aluminum with 14 wt.% Silicon, 2.5 wt.% Copper and 0.6 wt.% Magnesium was coated with a wax / thermoplastic Solvent binder is 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 silicon, 2.5% by weight copper and 0.6% by weight magnesium (from Ecka)

Debinding and sintering of the toasts

This feedstock was first debinded by solvent extraction in a 60 L oven with acetone at a temperature of 45 ° C within 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 with a Heating rate of 3 K / min was removed 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).

Length shrinkage results: 11.6%

Shrinkage of the bar diameter: 12.25%

Sintered density: 2.36 g / cm 3 -9- 99 ♦ · ··· 9 1 · · · · 9 · · · * # 9 9 · 9 × 9 × 9 ♦ * * * · · · ·· »· 99 * · «· · · ♦ · * 9 # 9 ·« «« · ♦ * *

Example 2 - Zuastäbe: thermal Entbinderuna in one step

Proportion (wt.% 1 67.1 4.3 25.8 2.8 100.0

Feedstock component

aluminum powder

Masteralloy powder * POM binder

Lucryl G55 ** * Aluminum and magnesium master alloy in the ratio 50:50 ** Commercially available polymethylmethacrylate (PMMA, from BASF)

Debinding and sintering of the toasts

Here, a complete thermal debinding was carried out in a 40-liter oven with 200 l / h of pure oxygen according to the following debindering profile:

- Heating up to 130 X with a heating rate of 2 K / min - 4h holding time at 130 X - Heating up to 200 X with a heating rate of 2 K / min

- 5 h hold time at 200 ° C

- Heating to 420 X with a heating rate of 2 K / min -4h hold time at 420 X

Weight loss after thermal debinding was 24.2%.

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

Length shrinkage results: 12.27%

Shrinkage of the rod diameter: 14.52% Sintered density: 2.46 g / cm 3 -10- ···· * · * · · · · · · · »·········································································. · * · · · «·· *» »· ··» < «« · * ··· «·»

··· ♦ · «· # · I

Example 3 - Supplies: two-fold thermal debinding

Proportion (% by weight) 70.1 2.2 24.0 3.7 100.0

Feedstock component

aluminum powder

Magnesium powder POM binder

Surfactant * * Ethoxylated Ci3-Ct5-oxo-alcohol with 7 EO units

Debinding and sintering of the toasts

First, a first thermal debinding was carried out in a 50-liter 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.

Length shrinkage results: 9.5%

Shrinkage of the bar diameter: 11.4% Sintered density: 2.13 g / cm 3 -11 - ·········································································································· φ φ · φφφ * »φ ···« ι · φ φ «· φ» · 4 ΦΦ Μ ΦΦ Φ Φφ t

Example 4 - Toast bars: katalvtische / thermal Debbinderuna

Feedstock component proportion (wt .-% 1

Aluminum powder 70.1 *

Magnesium powder 2.2 POM binder 24.0

Surfactant * 3.7 100.0 * Ethoxylated Ci3-Ci5-Oxoalkohol with 7 EO units Debinding and sintering of Zuastäbe

First, a catalytic debinding in a 50-liter furnace with 2% by volume of HNO3 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 had probably been formed by reaction of Mg with HNO3.

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.

Length shrinkage results: 10.7%

Shrinkage of the bar diameter: 14.65%

Sintered density: 2.36 g / cm 3 -12- ·························································································. • * • · • ·· · »·· * t *» *

Example 5 - Toast bars: katalvtische / thermal Debbinderuna

Proportion (% by weight) 70.1 2.2 24.0 3.7 100.0

Feedstock component

aluminum powder

Magnesium powder POM binder

Surfactant * * Ethoxylated C13-Ci5-oxo-alcohol with 7 EO units debinding and sintering of the Zuastäbe

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 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 -13- 99 9 99 99 ·········································································································································································································· ·· 99 ··· «« · ·

Example 6 - Tensile Bars: Catalan / 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 silicon, 2.5% by weight copper and 0.6% by weight magnesium (from Ecka) ** ethoxylated C 13 -C 15 Oxoalcohol with 7 EO units

Debinding and sintering of the toasts

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.

Length shrinkage results: 11.2%

Shrinkage of the bar diameter: 13.2%

Sintered density: 2.45 g / cm 3 -14- »· ·» t · * * * t 4 • · * ·· · • · * ·· ♦ · »· ··» * ·· ·

Example 7 - Zuastäbe: katalvtjsche / thermal Entbinderuna

Feedstock component Aluminum powder Masteralloy powder * POM binder surfactant **

Proportion f% by weight) 68.0 4.3 24.0 -3 J 100.0 * Pre-alloy of aluminum and magnesium in the ratio 50:50 ** Ethoxylated Ci3-Ci5-oxo-alcohol with 7 EO units

Debinding and sintering of the sugar bars First, a catalytic debinding was carried out analogously 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 -15- • ft • ft • * ················· Ft ft ft ft ft ft ft ft ft ft

Example B - Cavities: Catalytic / Thermal Debinding

Proportion (% by weight 1 68.0 4.3 24.0 3.7 100.0

Feedstock component Aluminum powder M astera lloy-P u Ive r * POM-Binder surfactant ** * Aluminum and magnesium prealloy in the ratio 50:50 ** Ethoxylated Ci3-Ci5-oxo-alcohol with 7 EO units

Debinding and sintering of Hohlzvlinder

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%

Diameter shrinkage: 14.48% sintered density: 2.59 g / cm3 -16-

Example 9 - Tension rods: catalytic / thermal debinding

Proportion fGew .-% 1 67.1 4.3 25.8 _2JL 100.0

Feedstock component

aluminum powder

Masteralloy powder * POM binder *

Lucryl G55 ** * Aluminum and magnesium master alloy in the ratio 50:50 ** Commercially available polymethylmethacrylate (PMMA, from BASF)

Debbinderuna and sintering of Zuastäfae

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

Length shrinkage results: 13.57%

Shrinkage of the bar diameter: 19.55%

Sinter density: 2.59 g / cm3 -17- ** * ····················································································································································································································· · + · · «·« «. ···· * · 1 t 4 · ··· «« ················································································································································································································································· POM binder 25.8 Lucryt G55 ** 2.8 100.0 * Master alloy of aluminum and magnesium in the ratio 50:50 ** Commercially available polymethyl methacrylate (PMMA, from BASF)

Debinding and sintering of Hohlzvlinder

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 / cm3

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. -18-

Claims (19)

4 ft ft ft 4 ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft 1. A process for the production of aluminum alloy moldings by metal injection molding, comprising the steps of: a) preparing 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) production of a green compact by injection molding of the feedstock; 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; d) sintering the at least partially debinded browning to obtain the desired shaped article; v characterized in that in step c) the binder is completely removed, wherein, optionally after performing one or more preceding debinding steps, a thermal debinding to remove the (residual) binder takes place, which is at least 0.5 vol .-% Oxygen-containing atmosphere is carried out, after which the resulting completely unbonded Braunling is sintered. 2. The method according to claim 1, characterized in that the .Aluminium alloy in addition to aluminum one or more metals selected from magnesium, copper, silicon and manganese. 3. The method according to claim 1 or 2, characterized in that the aluminum alloy in addition to aluminum contains one or more metals in a respective proportion of 0.5 to 25 wt .-%. 4. The method according to any one of claims 1 to 3, characterized in that the or the metal (s) is used as a master alloy ("Master Alloy") powder. -20- «· · · · · · · · · · · · · · · · · · · · · · · · · · · · ········································································ • · · I · · ·· ·· «* * Process according to any one of the preceding claims, characterized in that as binder a polyacetal-based binder, e.g. Polyoxymethylene (POM) binder is used. m 6. The method according to claim 5, characterized in that the binder consists of 50 to 95% of polyacetal. 7. The method according to claim 6, characterized in that the binder consists of 80 to 90% of polyacetal. 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, in one or more steps, is performed, in which the entire binder is removed. 9. The method according to any one of claims 1 to 7, characterized in that in step c) a Lösungsentbinderung to remove the main amount of the binder, followed by the thermal debinding to remove the residual binder are performed. 10. The method according to any one of claims 1 to 7, characterized in that in step c) a catalytic debinding to remove the Hauptinsge of the binder, followed by the thermal debinding to remove the residual binder are performed. 11. The method according to claim 10, characterized in that the catalytic debinding in the presence of at least one acid selected from nitric acid, oxalic acid, formic acid and acetic acid, is performed. 12. The method according to claim 11, characterized in that as acid sublimed oxalic acid is used. -21 - • 9 • 9 9 • 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 999 9 9 9 99 9 999 9 9 9 9 99 9 9 9 9 9 99 # 9 13. The method according to any one of the preceding claims, characterized in that the 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 the thermal debindering to remove the residual binder at a certain temperature profile between 100 and 420 ° C cjurehgeführt. 15. The method according to claim 13 or 14, characterized in that during the thermal debinding to remove the residual binder, the heating rate is not more than 5 K / min. 16. The method according to claim 15, characterized in that the heating rate is not more than 1 to 2 K / min. 17. The method according to any one of the preceding claims, characterized in that the completely unbonded Bräunling is sintered in step d) to form a liquid phase. 18. The method according to claim 17, characterized in that the sintering takes place at a temperature between the solidus and the liquidus temperature of the respective aluminum alloy. 19. The method according to any one of the preceding claims, characterized in that after the thermal debinding to remove the residual binder, the heating rate to the sintering temperature 4 to 20 K / min. Vienna, on - l April 2010 TECHNICAL UNIVERSITY OF VIENNA and co-applicants by: HÄUPL & ELLMEYER KG -22-