JP2013524006A - Method for producing molded product of aluminum alloy - Google Patents

Abstract

The present invention relates to a method for producing a molded article based on an aluminum alloy by metal injection molding, the method comprising: a) a metal contained in a desired alloy in the form of a metal powder and / or one or more metal alloy powders. Producing a feedstock by mixing with a binder, b) producing a green body by injection molding the feedstock, and c) at least partly from the green body by catalytic degreasing and / or solvent degreasing and / or thermal degreasing. A step of producing a brown body by removing the binder, and d) sintering the at least partially degreased brown body to obtain a desired molded product, characterized in step c) , Optionally after one or more degreasing steps, followed by thermal degreasing in an atmosphere containing at least 0.5% oxygen by volume (residual That) By removing the binder, the binder is completely removed, thereafter, thus obtained, it is to sinter fully defatted brown body.
[Selection] Figure 1

Description

  Metal injection molding technology has grown rapidly in recent years and has become a well-established technology for producing small complex parts, with annual worldwide sales of around 1 billion euros. The combination of molding technology applied to plastic injection molding and various materials used in powder engineering opens an interesting new market for many materials.

  The manufacturing method basically includes the following processing steps. Initially, a feedstock is produced in the form of injectable granules consisting of a metal powder and a plastic component comprising at least two fully mixed polymer components. The feedstock is then molded by a plastic injection molding machine to obtain a molded product. These so-called “green bodies” typically contain about 40% by volume of a plastic binder, with most of the binder being removed in a subsequent so-called degreasing (or “debinding”) step. The remaining binder components (so-called “backbone”) remain to ensure the residual strength of the product after degreasing. Degreasing can be accomplished in a variety of ways (eg, thermally, using a solvent, catalytically, etc.). The chosen process is carefully adapted to the plastic binder used for the granulate. After degreasing, the product (so-called “brown body”) is subjected to a sintering treatment, and in its first step, the remaining “backbone” binder is usually thermally removed, after which the product is sintered. And shrink to form an almost dense metal part. This technology is currently applied to high and low alloy steels, precious metals, hard metals as well as ceramics.

  Metal injection molding of aluminum materials is patented for this technology, but is not yet well established in the industry. This is due to the fact that the sintering mechanism of the aluminum alloy is completely different from that of the above materials. The non-reducing oxide on the surface of the aluminum powder is a major obstacle to sintering. For this reason, the publication only describes an oxygen-free atmosphere.

  The particular difficulty associated with the above treatment of aluminum is related to the relatively low melting point of aluminum (660 ° C.). The melting point of aluminum is even lower when alloying elements such as tin are added thereto. This results in the problem that the degreasing of the plastic component has to be carried out at a very low temperature and that the appropriate processing time frame is often too short to ensure complete removal of the plastic component. If the plastic component is not completely removed, an undesirable reaction between the organic residual component and the metal component can occur. That hinders the sintering process and thus impairs the mechanical properties obtainable by the method.

  Liu et al. In Powder Metallurgy 51, 78-83 (2008) describe a method of adding a block of tin (as alloying metal) and magnesium. Magnesium functions as a “sacrificial metal” (ie, as a trap for oxygen and moisture).

  Against this background, the object of the present invention is to develop a metal injection molding process for producing molded articles of aluminum material having good mechanical properties in a simple and reproducible manner.

DISCLOSURE OF THE INVENTION The present inventors have achieved this object by providing a method for producing a molded article based on an aluminum alloy by metal injection molding. This method includes the following steps.
a) producing a feedstock by mixing the metal contained in the desired alloy in the form of metal powder and / or one or more metal alloy powders with a binder;
b) producing a green body by injection molding the feedstock;
c) producing a brown body by at least partially removing the binder from the green body by catalytic degreasing and / or solvent degreasing and / or thermal degreasing;
d) Sintering the at least partially degreased brown body to obtain the desired molded product.
Here, the method of the present invention is that in step c), after one or more degreasing steps have been performed before, the thermal degreasing contains at least 0.5% by volume of oxygen in order to remove the (residual) binder. It is carried out in the atmosphere and is characterized in that the binder is completely removed and then the fully degreased brown body thus obtained is sintered.

The method produces a high purity molded product of aluminum alloy. This is because the binder is completely removed in step c), so that no undesirable reaction between the alloyed metal and the plastic material occurs. Due to the oxygen present in the atmosphere, complete removal of the binder is achieved even at relatively low temperatures. Contrary to the current teaching that the presence of oxygen should be completely prevented, we have found that a small amount of oxygen (at least 0.5% by volume) does not significantly increase the oxidation of aluminum and is faster, more complete It was found that it contributes to degreasing. Depending on the composition of the powder mixture and the temperature conditions, for example, an oxygen content of 20 to 100% by volume is applied. This means that it is even possible to use pure O ₂ gas.

  Aluminum alloys include one or more other metals in addition to aluminum, which are not subject to any particular limitations. The alloy partner is preferably selected from the group consisting of magnesium, copper, silicon and manganese and may be included in particular in a proportion of 0.5 to 25% by weight in order to obtain a shaped product with the desired properties. preferable. Metals such as bismuth, tin, lead, indium, or zinc, or alloys such as wood metal, which have a markedly low melting point and can sometimes function as sintering aids that lower the temperature at which melting begins, It is not necessary in the present invention. However, if necessary, it may be added as an alloying partner in order to obtain a sintered body of each alloy. In particular, it is advantageous to use other metals in the form of alloys with aluminum (ie as so-called master alloy powders).

  According to the invention, it is preferred to use binders that are known to be removable at low temperatures, in particular binders based on polyacetal, such as poly (oxymethylene) (POM) binders, which are For example, BASF is disclosed in EP413231, WO94 / 25205 and in particular EP446708 and is marketed under the trademark Catamold®. The binder contains a high percentage of polyacetal and preferably contains 50-95%, more preferably 80-90% polyacetal, which facilitates rapid and complete removal in the presence of oxygen at low temperatures. desirable. Alternatively, a binder system based on wax and polymer may be used, and the wax as the main component is removed by solvent degreasing prior to it (ie, thermal degreasing is performed in the presence of oxygen according to the present invention). Before it is called).

  Degreasing in step c) of the inventive method may comprise one thermal degreasing step in the presence of oxygen from which the binder is completely removed. Alternatively, one or more preceding degreasing steps may be performed to remove most of the binder, followed by the thermal degreasing step of the present invention to remove the remaining binder in the presence of oxygen. Good. The preceding degreasing step may also be a thermal degreasing step (in the absence of oxygen or likewise in the presence of oxygen). It performs a multi-step thermal degreasing process using various processing parameters for degreasing (eg, at different temperatures or in different atmospheres (eg, presence of oxygen, air or pure oxygen, etc.)). It also means that it is possible.

  In a preferred embodiment of the invention, catalyst degreasing and / or solvent degreasing is performed in step c) prior to thermal degreasing to remove the remaining binder in the presence of oxygen. In these previous degreasing steps, most of the binder is already removed from its composition, so that only the “backbone” component remains and is removed by subsequent thermal degreasing.

  The catalytic degreasing is preferably carried out in the presence of at least one acid selected from nitric acid, oxalic acid, formic acid and acetic acid, and these acids cause acid decomposition without leading to undesirable side reactions with the alloy components. Accelerates complete removal of the desired polyacetal binder. In the case of solvent degreasing, most of the binder is removed by extraction with a suitable solvent or mixed solvent (eg, acetone, n-heptane, water, etc.). It is particularly preferred to apply catalytic degreasing using sublimated oxalic acid according to the invention.

  As described above, the thermal degreasing treatment for removing the residual binder in step c) is carried out at a relatively low temperature in order to avoid the oxidation reaction of aluminum contained in the powder mixture. In this specification, the relatively low temperature is a temperature that is significantly lower than the melting point of aluminum, preferably 500 ° C. or less, and more preferably 100 to 420 ° C. It is particularly preferred to set an optimized temperature profile for each powder mixture, and it is particularly desirable to have a heating rate of 5 K / min or less, more preferably 1-2 K / min or less. In this way, the mixture to be defatted is gradually and uniformly heated.

  The sintering step d) of the method of the present invention is not particularly limited, except that the binder must be completely removed beforehand. However, as described in more detail below, it is desirable to perform the sintering step with the liquid phase formed.

  A known technique for producing aluminum alloy moldings by powder metallurgy compression molding is that the surface of the alumina-coated aluminum particles in the matrix is mechanically scratched by the compression treatment, and the scratches enable a metallurgical reaction. Based on theoretical assumptions. However, the (completely) defatted brown body obtained by injection molding is in effect a packed layer of metal powder, and the metal oxide film is not subjected to any mechanical load, so this known It does not depend on the mechanism. This means that there is no direct metal-metal contact between the powder particles. Nevertheless, by properly selecting the sintering conditions, the method of the present invention has succeeded in achieving the required reduction in which the compaction of the sintered body becomes apparent and, thus, to the maximum extent possible. It has succeeded in obtaining compressed molded parts.

  Therefore, according to the present invention, an embodiment is preferred in which in step d) the fully defatted brown body is sintered while forming a liquid phase. Without wishing to be bound by any theory, we have the liquid phase (partially intermediate, but mainly stationary, i.e. in a thermodynamic equilibrium with the solid Al phase. Is) between the metals in the powder mixture through fine crevices, fine pores or similar “openings” in the oxide film of the metal powder particles and by creep under the oxide film. It is believed that contact is established and thus promotes the formation of a high compression sintered body from a completely defatted brown body. It is particularly preferred that the sintering in step d) is performed at a temperature between the solidus and liquidus temperatures of each aluminum alloy, so that at any point during the sintering process the alloyed metal Some (which can be controlled by selecting an appropriate temperature profile) are in the liquid state, effectively preventing loss of dimensional stabilization.

  The composition of each atmosphere in the individual steps of the method of the present invention is not subject to any particular limitation except that oxygen is present due to the thermal degreasing of step c), and the skilled person The optimum atmosphere for each powder mixture can be selected, and vacuum is also an option. However, the sintering step d) can be carried out in an extremely dry, nitrogen-containing atmosphere (ie pure nitrogen), at normal or reduced pressure (“partial pressure sintering”), or with nitrogen and pure inert gas (helium). Argon), preferably in an air-fuel mixture having a dew point below -40 ° C. This is because the presence of nitrogen significantly promotes the wettability of the powder particles with the resulting metal melt.

  After the sintering step, optionally, additional processing may be performed that is suitable for the finished molded part to maintain the desired shape. For example, it is possible to apply the known hot isostatic pressing (HIP) method to achieve the desired final density of the molded article. In this method, residual holes still present after the sintering step are sealed under the influence of external gas pressure and high temperature.

Brief Description of Drawings
FIG. 1 is a photograph of a green body (top) and a sintered body (bottom) obtained therefrom in Example 9. FIG. 2 is a photograph of a green body (left) and a sintered body (right) obtained therefrom in Example 10.

  The invention will now be described in more detail with reference to specific, non-limiting exemplary embodiments.

EXAMPLES All of the feedstocks produced in the following examples were homogenized in a laboratory compound heated to 190 ° C. Tensile test bars or hollow cylinders were each formed from these feedstocks by injection molding according to ISO 2740, applying the method of the invention as described below. A hydraulic injection molding machine with a PIM device (Battenfeld HM 600/130) was used for the production of green bodies.

  In the first step, the feedstock was first filled into the funnel of the injection molding machine. The injection molding process for producing the green body included the following steps. Using a heated injection cylinder with a rotating screw inside, the pretreatment charge material is plasticized and charged in one dose according to preset parameters (eg rotation speed, loading capacity, back pressure, etc.) . Thereafter, the pre-charged amount was injected into the appropriately preheated equipment. Depending on the feedstock and binder used therein, the plasticization temperature in the injection cylinder ranged between 120-220 ° C, and the temperature in the equipment was between 25-140 ° C. After a sufficiently long cooling time, the injection molding equipment was opened and the green body was discharged and removed from the equipment using a handling device.

Example 1 Tensile Test Bar: Solvent Degreasing / Heat Degreasing A commercially available metal powder mixture (Alumix® 231 (Ecka)) (14% by weight silicon, 2.5% copper in addition to aluminum) %, Containing 0.6 wt% magnesium) with a solvent binder consisting of wax / thermoplastic material to obtain a feedstock.

Degreasing and sintering of tensile test bars First, the feedstock was degreased by solvent extraction with acetone in a 60 liter oven at 45 ° C. for 12 hours.
The brown body thus obtained contains about 14.5% by weight of residual binder, and this residual binder is then subjected to thermal degreasing according to the present invention in an atmosphere containing pure oxygen to 150-320%. A temperature profile in the range of 1 hour at 0C and then 1.5 hours at 320-420C was applied and removed. The brown body thus completely defatted was then sintered in pure nitrogen (dew point: −50 ° C.) at 560 ° C. within 1 hour.
Result length shrinkage: 11.6%
Rod diameter shrinkage: 12.25%
Sintering density: 2.36 g / cm ³

Example 2 Tensile Test Bar: One Thermal Degreasing

Degreasing and sintering of tensile test bars Complete thermal degreasing was performed in a 40 l oven in the presence of 200 l / h of pure oxygen according to the following degreasing profile.
Heating up to 130 ° C at a heating rate of -2K / min-Maintaining the temperature at 130 ° C for 4 hours-Heating at 200 ° C at a heating rate of 2K / min-Maintaining the temperature at 200 ° C for 5 hours-At a heating rate of 2K / min Heat to 420 ° C.-Maintain temperature at 420 ° C. for 4 hours Weight lost during thermal degreasing period was 24.2%.
The rod was then sintered in pure nitrogen for 1 hour. The oven temperature was set to 665 ° C and the temperature in the oven was about 630 ° C.
Result length shrinkage: 12.27%
Rod diameter shrinkage: 14.52%
Sintering density: 2.46 g / cm ³

Example 3 Tensile Test Bar: Twice Thermal Degreasing

Degreasing and sintering of tensile test bars Initially, a first thermal degreasing was performed in a 50 l oven in air (500 l / hr) at 180 ° C. for 14 hours. The weight loss was 27.0%.
Then, the second thermal degreasing was performed in pure nitrogen within 1 hour at a temperature up to 420 ° C., and then sintered again at an oven temperature set at 665 ° C. for 1 hour.
Result length shrinkage: 9.5%
Rod diameter shrinkage: 11.4%
Sintering density: 2.13 g / cm ³

Example 4 Tensile Test Bar: Catalyst / Heat Degreasing

Degreasing and sintering of tensile test bars First, catalytic degreasing was performed in a 50 l oven using 2 vol% HNO ₃ (industrial grade) in nitrogen (500 l / hr) at 140 ° C. for 10 hours. It was. The weight loss was 22.1%. Subsequently, beaded outgrowth was observed on the surface. It was thought that it was formed by the reaction of Mg with HNO ₃ .
Thereafter, thermal degreasing is performed in pure nitrogen within 1 hour at a temperature up to 420 ° C. as described in Example 3 and then again sintered at an oven temperature set at 665 ° C. for 1 hour. It was.
Result length shrinkage: 10.7%
Rod diameter shrinkage: 14.65%
Sintering density: 2.36 g / cm ³

Example 5 Tensile Test Bar: Catalyst / Heat Degreasing

Degreasing and sintering of tensile test bars First, catalytic degreasing according to Example 4 was carried out at 140 ° C. for 24 hours with 80 g of oxalic acid anhydride placed on a sublimation dish instead of HNO ₃ . The weight loss was 23.0%. When oxalic acid was used, no external growth appeared on the surface. Thereafter, thermal degreasing and sintering was also performed according to Example 4.
Resulting length shrinkage: 14.28%
Rod diameter shrinkage: 15.68%
Sintering density: 2.42 g / cm ³

Example 6 Tensile Test Bar: Catalyst / Heat Degreasing

Degreasing and sintering of tensile test bars Initially, catalytic degreasing was performed according to Example 5. The weight loss was 25.2%. Thereafter, thermal degreasing and sintering were performed according to Example 4. The oven temperature was set at 560 ° C.
Result length shrinkage: 11.2%
Rod diameter shrinkage: 13.2%
Sintering density: 2.45 g / cm ³

Example 7 Tensile Test Bar: Catalyst / Heat Degreasing

Degreasing and sintering of tensile test bars Initially, catalytic degreasing was performed according to Example 5. The weight loss was 23.2%. Thereafter, thermal degreasing and sintering were performed according to Example 4.
Result length shrinkage: 12.6%
Rod diameter shrinkage: 13.25%
Sintering density: 2.56 g / cm ³

Example 8-Hollow cylinder: catalyst / thermal degreasing

Degreasing and sintering of the hollow cylinder Initially, catalytic degreasing was performed according to Example 5. The weight loss was 23.7%. Thereafter, thermal degreasing and sintering were performed according to Example 4.
Resulting height shrinkage: 17.24%
Shrinkage of outer diameter: 14.48%
Sintering density: 2.59 g / cm ³

Example 9 Tensile Test Bar: Catalyst / Heat Degreasing

Degreasing and sintering of tensile test bars Initially, catalytic degreasing was performed according to Example 5. The weight loss was 25.7%. Thereafter, thermal degreasing and sintering were performed according to Example 4.
Result length shrinkage: 13.57%
Rod diameter shrinkage: 19.55%
Sintering density: 2.59 g / cm ³

Example 10-Hollow cylinder: catalyst / thermal degreasing

Degreasing and sintering of the hollow cylinder Initially, catalytic degreasing was performed according to Example 5. The weight loss was 25.6%. Thereafter, thermal degreasing and sintering were performed according to Example 4.
Resulting height shrinkage: 16.52%
Shrinkage of outer diameter: 14.48%
Sintering density: 2.56 g / cm ³

  Thus, the method of the present invention can provide a sintered body of an aluminum alloy by injection molding. This sintered body is used in various fields including fields such as transportation, construction, mechanical engineering, packaging industry, steel industry, electronics, and household appliances, for example, for heat dissipation as a heat sink for electronic equipment, or for air conditioning. Suitable for practical use as system components.

Claims (19)

A method for producing a molded article based on an aluminum alloy by metal injection molding,
a) producing a feedstock by mixing the metal contained in the desired alloy in the form of metal powder and / or one or more metal alloy powders with a binder;
b) producing a green body by injection molding the feedstock;
c) producing a brown body by at least partially removing the binder from the green body by catalytic degreasing and / or solvent degreasing and / or thermal degreasing;
d) comprising each step of sintering the at least partially degreased brown body to obtain a desired molded article,
The feature is that in step c), after optionally performing one or more degreasing steps, thermal degreasing (residual) in the atmosphere containing at least 0.5% by volume of oxygen is performed. A method of removing the binder completely by removing, and thereafter sintering the completely degreased brown body thus obtained.   The method of claim 1, wherein in addition to aluminum, the aluminum alloy comprises one or more metals selected from magnesium, copper, silicon and manganese.   3. A method according to claim 1 or 2, characterized in that, in addition to aluminum, the aluminum alloy contains one or more metals, each in a percentage of 0.5 to 25% by weight.   The method according to claim 1, wherein the metal is used as a master alloy powder.   The method according to claim 1, wherein a polyacetal-based binder, for example a polyoxymethylene (POM) binder, is used as the binder.   The method according to claim 5, wherein the binder contains 50 to 95% of polyacetal.   The method according to claim 5, wherein the binder contains 80 to 90% of polyacetal.   8. Step c) comprises only thermal degreasing in the presence of oxygen, said thermal degreasing being carried out in one or more steps and removing all the binder. The method described.   The step c) includes solvent degreasing to remove most of the binder, and then removes the remaining binder by the thermal degreasing. Method.   The step c) includes catalytic degreasing to remove most of the binder, and then removes the remaining binder by the thermal degreasing. Method.   The method according to claim 10, wherein the catalytic degreasing is performed in the presence of at least one acid selected from nitric acid, oxalic acid, formic acid and acetic acid.   The method according to claim 11, wherein sublimed oxalic acid is used as the acid.   A method according to any one of the preceding claims, characterized in that the thermal degreasing to remove any residual binder is performed at a temperature below 500 ° C.   14. The method of claim 13, wherein the thermal degreasing to remove any residual binder is performed by applying a specific temperature profile in the range between 100 <0> C and 420 <0> C.   15. A method according to claim 13 or 14, wherein the heating rate during the thermal degreasing process to remove the residual binder does not exceed 5 K / min.   The method according to claim 15, wherein the heating rate does not exceed 1-2 K / min.   A method according to any one of the preceding claims, characterized in that in step d) the fully defatted brown body is sintered while forming a liquid phase.   The method according to claim 17, wherein the sintering is performed at a temperature between a solidus temperature and a liquidus temperature of each aluminum alloy.   A method according to any one of the preceding claims, characterized in that the heating rate to reach the sintering temperature after the thermal degreasing step is in the range of 4-20 K / min.