DE102007018123A1 - Method for producing a structural component from an aluminum-based alloy - Google Patents

Abstract

The present invention relates to a rapid prototyping method for producing a structural component from an aluminum-based alloy, wherein a starting material is melted pointwise by a heat source and allowed to solidify immediately thereafter, using as starting material an aluminum scandium alloy with a scandium (Sc). Proportion of at least 0.4 wt .-% is used.

Description

The The invention relates to a method for producing a structural component from an aluminum-based alloy by means of rapid prototyping, wherein a source material from a heat source locally melted and immediately afterwards solidifies again quickly, in layers to build a component with the desired final contour.

According to the invention, an aluminum-scandium alloy is used as the starting material for the production of so-called "rapid prototyping (RP)" components, which are to be understood as meaning components which, without "detours", ie without further thermo-mechanical process steps, directly and with The desired final contour can be produced and can be loaded in such a way that they can take on the mechanical-technological functions of "normally" produced components.This direct component generation is known in the art under a multiplicity of names or designations - "direct metal sintering" (DMS). "Powder metal sintering", "laser assisted metal sintering", "fusing" or "near net shaping", "solid free form fabrication (SF ³ )" etc. - which is generally referred to below as "rapid prototyping" In recent years, the term "rapid manufacturing" is often used to produce larger quantities. In the following, however, only the term "rapid prototyping" is to be used, but this is not meant to be limiting, for example to a small number of items.

All over, where very fast or under high time pressure unique or highly resilient Components for a (new) construction are needed such direct product generation methods of very large Interest. In addition to new constructions are also repairs, often very old components, for which no manufacturing and Device means exist for the above-described RP methods extremely important, otherwise fast and inexpensive Repairs of such components or components not possible would.

The The aforementioned RP method has in common that the component or RP material by a heat source, usually controlled by a CNC program (For example, a laser or an electron beam) locally melted and solidifies immediately afterwards. This is how incremental, the CNC program following, the 3-dimensional component geometry more or less point for point or step by step in layers or in layers. By the melting and solidification the RP component has globally considered a cast structure, which however, by the high local cooling rate is much finer-grained, than the cast structure, which one in completely in one pass cast components would find.

Since the mid-90s of the last century, intensive work has been done on the method of "directly building up" metallic structures through the local melting and solidification of a starting material, such as AEROMET (Minnesota, USA) using CO ₂ lasers and the Addition of Titanium Alloy Powder Computer-aided Manufactured component for aircraft construction This principle procedure was followed by many other companies, whereby individual elements of the process were changed.

Of Furthermore, it is known that in plastic injection molding the Alloy steel injection molds, just starting in the difficult Prototype phase, often also directly from steel powders (with Help of a laser beam) can be built up (sintered) to fast to be able to carry out the first tests. Here you are Meanwhile, a large number of companies or users on the Market, which use as systems engineering partly own constructions or buy commercially available systems.

The Application of direct laser sintering (DLS) to heavily loaded components Al alloys are still in their infancy. On the one hand the process technology is difficult (as from welding Al alloys are undesirably prone to pore formation. as well as to the solidification hot cracking, thereby alloy selection and process windows are limited), on the other hand, the strength properties insufficient to substitute a heavily loaded standard component (eg, eaten whole).

So For example, Al engine components (in standard engines, but also in motorsport), manufactured over an established Process chain (casting, forging and machining or as pure cast components), strength profiles of 250 MPa <Rm <350 MPa, 150 MPa <Rpo, 2 <300 MPa and 3% <A5 <10%. To fulfillment Such requirements are material technically several steps, starting with the casting, a annealing at a temperature greater than 450 ° C, followed by quenching in water, which is known to cause delay problems, and a subsequent heat aging necessary.

In engine construction, but also for other components, AlSi7-12Mgxyz alloys have been used for many years. If these materials were used in the form of powder or wire for direct component generation (this sometimes happens), the achievable strengths with Rm <250 MPa and Rpo, 2 <150 MPa and an elongation <10% would be so low that a direc The use in the desired product does not seem sensible. A subsequent thermal aging in a temperature range of 100 ° C to 250 ° C would improve the strength properties only slightly.

Only the previously mentioned complete production chain (annealing annealing, Quenching, etc.) would significantly improve the strength.

Other Al material systems, sometimes for the production of cast components used, such as AlZnMgxyz or AlCuxyz alloys, are also only partially suitable for the direct generation of components, because their strength properties are unsatisfactory from a structural point of view. They are also sensitive to corrosion and generally have a large Tendency to form solidification cracks.

Consequently the disadvantage of the previously known RP methods is that the achievable strength of the created structural components in As a rule, it is not sufficient for the resulting structural components to be able to use it immediately. Rather, the structural components usually have a solution annealing - ever according to alloy composition (temperatures higher than 450 ° C) - a subsequent quenching and a subsequent heat aging are subjected to microstructure to achieve that have the required strength properties. Especially when quenching occurs but then the problem of delay (and unevenly distributed residual stresses) through which the process, the aim of which is therein, is immediate To obtain contoured components is questioned.

The It is therefore an object of the present invention to provide a method for the production of conformal structural components made of aluminum-based alloy specify with the strength properties are achievable, the a direct intended use of the Allow generated structural part.

According to the invention solves this problem by providing, in an RP process, wherein a starting material is melted and immediately thereafter quickly solidifies again to a component with the desired Build up final contour layer by layer, as starting material an aluminum scandium alloy whose scandium (Sc) content is at least 0.4% by weight lies. Preferably, the scandium (Sc) content is between 0.41 Wt .-% and 2.0 wt%, more preferably between 0.8 wt .-% and 1.4% by weight.

at a preferred embodiment of the invention Method, the starting material, so the aluminum scandium alloy, in addition the element magnesium in the range of 2.0 wt .-% to 10% by weight. The magnesium (Mg) alloy is more preferably intermediate 3.0 wt .-% and 6.0 wt .-% and between 4.0 wt .-% and 5.0 wt .-%.

It has been shown that produced according to the invention Structural components made of aluminum scandium starting materials or Aluminum magnesium scandium starting materials of the above specified composition excellent material properties comprising directly using the generated structural component allow. The inherently high cooling rates of RP process make it possible to achieve high strengths, high yield strengths, excellent corrosion behavior and a very good weldability to achieve. RP structural components produced according to the invention typically have a tensile strength (Rm) of greater than 300 MPa and a yield strength (Rpo.2) of more than 200 MPa and an elongation at break (A5) of over 10%.

Although aluminum material systems with scandium and magnesium are known from the prior art (cf. US Pat. No. 3,619,181 . DE 100 248 594 A1 . US 625831881 ), however, the aluminum material systems disclosed there with scandium or magnesium are used only for standard metal sheets. An indication of the use of such material systems in connection with the direct component generation by means of rapid prototyping methods, such as direct metal sintering, is not found. In contrast, in the prior art (see EP 0 918 095 A1 or US 6,139,653 ) only discloses using aluminum scandium material systems or aluminum-magnesium-scandium material systems for precision casting or even rolling processes. The decisive advantage that results from the use according to the invention of such known material systems results from the combination of these material systems with the RP method and makes possible in this way the direct metal sintering of heavy-duty structural components made of aluminum alloy. It also uses the fact that the melting of the starting material is followed by solidification with subsequent rapid cooling to temperatures <350 ° C, since the released heat of fusion easily in the component holder (on which the structural component is built) or in the growing structural component can drain itself.

The attractiveness of the method according to the invention can be increased by the fact that according to a further embodiment of the invention, the starting material is accompanied by such additional alloying elements which behave complementarily or substitutively to scandium, in particular Zr, Ti, Ta, Hf, Y, Er. The metallurgist knows all these elements as so-called dispersoid-forming elements (usually in the stoichiometric form Al ₃ X), which are used for microstructure, thermo-mechanical microstructural stabilization and strength enhancement. Typically, the proportion of these di-isoide-forming elements per element at a maximum of 2.0 wt .-% and a total of at most 3.0 wt .-%. Particularly preferably, the proportion of scandium-complementary or substituted elements in total is not more than 0.8 wt .-%.

For the material system aluminum-magnesium-scandium are suitable as other alloy components, depending on the desired mechanical technological properties, the elements Zn, Mn, Ag, Li, Cu, Si, Fe wherein the proportion of these additional alloying elements may be from 0.05% to 2.0% by weight per element.

the preparation, have the aluminum scandium alloys or aluminum-magnesium-scandium alloys used It is known that impurities of other elements, their content individually not more than 0.5% by weight and in total not more than 1.0% by weight is.

moreover can the source material before or during of the RP process further admixtures of metallic or not metallic (eg ceramic) materials (eg as a powder) added become.

in the Normally, in the method according to the invention the starting material is provided in the form of powder or wire. The combination of the material system AlMgSc with direct metal sintering shows but also very good results of the structural component produced, if the starting material before melting, resulting in another Forming the invention is proposed as a sintered, cast or extruded molding.

To the Melting of the starting material is a variety of possibilities given. Usually this is done by a laser steel, an electron beam or an arc. But it can too a chemical, exothermic reaction can be used, or the starting material is heated capacitively, conductively or inductively. Also any Combination of these different heat sources is possible.

In terms of The achievable material properties takes place in a preferred Embodiment of the invention Procedure, the cooling of the molten starting material with a cooling rate in the temperature interval Tliquidus - T350 ° C, which is greater than 100 K / sec. Although such cooling rates inherent in the RP process can be used to achieve higher cooling rates an additional Cooling can be used. The big advantage of this high cooling rate is based on the Al (Mg) Sc material system in the possibility of certain amounts of scandium in the supersaturated solid solution to keep constrained. Owns the used RP process significantly higher cooling rates, then is even an increase in the required scandium content to about 0.8% by weight possible.

moreover it is advantageous if the solidification and cooling of the molten starting material under inert gas or in a vacuum takes place, as inert gas preferably such or mixtures Such gases are used, which in the prior art for Welding of aluminum materials are known.

Although not normally required, a heat treatment downstream of the RP process can still improve the material properties of the structural component produced and, in particular, increase the strength and toughness. Subsequent heat treatment may typically be carried out at temperatures between 100 ° C and 400 ° C for a period of 10 minutes to 100 hours (e.g., 250 ° C-400 ° C / 10 minutes-100 hours or 300 ° C-350 ° C / 1 h-10 h). Particularly preferred is the subsequent heat treatment in the temperature range of 250 ° C to 400 ° C, for a duration that causes the formation of coherent Al ₃ Sc phases. That is, the subsequent heat treatment, an additional, significant solidification of Al (Mg) Sc material (in the RP component) by a so-called precipitation hardening on the formation of coherent Al ₃ Sc phases possible. The strengths that can be achieved are then still sufficient for the tensile strength and the yield strength above 400 MPa, for a direct application, sufficient elongation (A5> 5%). As a result, the already good strength of the directly generated structural component can be significantly increased by the subsequent heat treatment, without the toughness and the corrosion behavior being degraded in a way that endangers the application. Of course, the heat treatment can also be carried out in several stages and / or steps.

Of Furthermore, the structural component after the subsequent Heat treatment of a rapid cooling (eg Quenching in water) to room temperature followed by Hot storage in the temperature range 100 ° C-250 ° C be subjected to a period of 10 minutes to 100 hours.

Example:

• a) Zugfestigkeit im direkt generierten Werkstoff zustand (Mittelwert aus 2 Messungen): Rm = 346 MPa Rpo,2 = 257 MPa A5 = 12%
• b) Zugfestigkeit im direkt generierten Werkstoffzustand mit anschließender Wärmebehandlung 300°C/5 Std. (Mittelwert aus 2 Messungen): Rm = 450 MPa Rpo,2 = 400 MPa A5 = 5%

To demonstrate the method according to the invention and the advantages of an RP structural component produced therewith, the following experiment was carried out guided:
By means of a focused Nd-YAG laser beam (laser power: 3000 watts, focusing: 150 mm, focus diameter: 300 μm) was a AlMg4.6Sc1,4-wire (diameter 1.0 mm, delivery volume 7 m / min, process speed 2m / min) melted so as to directly generate a block-shaped component. As a substrate, and thus at the same time as a heat sink, a 20 mm thick and 100 × 300 mm block of AlMg5,2MnZnZr alloy was used. Onto this substrate, the AlMgSc device was line-shaped until it had a size of 150 × 50 × 5 mm. An additional cooling was not used. Finally, the AlMgSc component was removed from the substrate and its properties evaluated metallurgically. The RP component was subjected to tensile tests based on EN 10 002 taken. The following characteristic values were determined:

• a) Tensile strength in the directly generated material state (average of 2 measurements): Rm = 346 MPa Rpo, 2 = 257 MPa A5 = 12%
• b) Tensile strength in directly generated material condition followed by heat treatment 300 ° C / 5 hours (average of 2 measurements): Rm = 450 MPa Rpo, 2 = 400 MPa A5 = 5%

These Characteristics are therefore particularly surprising since the metallographic Assessment of the RP component structure showed that the cross-sectional areas the tensile specimens by a pore content of 5-10% massive were weakened. For a non-porous cross section So to expect an even higher tensile strength.

The Strength values show that an RP component made of AlMgSc material quite directly usable as a highly loaded structural component or can be integrated into a highly loaded structure. Furthermore lie the determined characteristic values (in particular with heat aftertreatment) significantly above the strengths of previously directly generated Al components. There are even the strengths of classically produced cast components (eg investment casting with complete conventional process chain to achieve the best material parameters Rm = 300-400 MPa) clearly exceeded.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 3619181 [0017]
• - DE 100248594 A1 [0017]
• - US 625831881 [0017]
• - EP 0918095 A1 [0017]
• US 6139653 [0017]

Cited non-patent literature

• - EN 10 002 [0028]

Claims (26)

A method for producing a structural component of an aluminum-based alloy by means of rapid prototyping, wherein a starting material is locally melted by a heat source and solidifies immediately thereafter, characterized in that as starting material an aluminum-scandium alloy is used. Method according to claim 1, characterized in that that an aluminum-candandium alloy is used which has a Scandium (Sc) content of at least 0.4 wt .-% contains. Method according to claim 1, characterized in that that an aluminum-scandium alloy is used, the one Scandium (Sc) content of 0.41 wt .-% to 2.0 wt .-%. Method according to claim 1, characterized in that that an aluminum-scandium alloy is used, the one Scandium (Sc) content of 0.8 wt .-% to 1.4 wt .-%. Method according to one of claims 1-4, characterized in that an aluminum scandium alloy is used which has a magnesium (Mg) content of 2.0% by weight to 10.0% by weight is zulegiert. Method according to one of claims 1-4, characterized in that an aluminum scandium alloy is used which has a magnesium (Mg) content of 3.0% by weight to 6.0% by weight is zulegiert. Method according to one of claims 1-4, characterized in that an aluminum scandium alloy is used which has a magnesium (Mg) content of 4.0% by weight to 5.0% by weight is zulegiert. Method according to one of the claims claim 5-7, characterized in that an aluminum-magnesium scandium Alloy is used which has at least one more alloying element the group consisting of Zn, Cu, Mn, Si, Li, Ag and Fe, at a level of from 0.05% to 2.0% by weight per element. Method according to one of claims 1-8, characterized in that a starting material is used, additionally added to such alloying elements are complementary to scandium (Sc) or substitutive Behavior, in particular Zr, Ti, Ta, Hf, Y, Er, with their share individually in the starting material 2.0 wt .-% and in total 3.0 wt .-% does not exceed. Method according to claim 9, characterized in that that a starting material is used in which the proportion of to Scandium (Sc) compatible elements in total content of 0.8 wt .-% does not exceed. Method according to one of claims 1-9, characterized characterized in that the starting material before or during the rapid prototyping process more admixtures of metallic or non-metallic materials are added. Method according to one of claims 1-11, characterized characterized in that the starting material in powder or wire form is present. Method according to one of claims 1-11, characterized characterized in that the starting material is sintered, cast or extruded molding. Method according to one of claims 1-13, characterized characterized in that for melting the starting material a Laser steel, an electron beam or an arc is used. Method according to one of claims 1-13, characterized characterized in that for melting the starting material a chemical exothermic reaction is used. Method according to one of claims 1-13, characterized characterized in that the starting material is capacitive, conductive or inductively heated. Method according to one of claims 1-13, characterized characterized in that for heating the starting material any combination of methods according to Claims 14-16 is used. Method according to one of claims 1-17, characterized characterized in that the cooling of the molten Starting material in the temperature interval Tliquidus - T350 ° C with a cooling rate greater than 100 K / sec he follows. Method according to one of claims 1-18, characterized characterized in that the cooling rate of the molten Starting material through additional cooling is increased. Method according to one of claims 1-19, characterized characterized in that the solidification and cooling of the molten Starting material under inert gas or in vacuum takes place. Method according to one of claims 1-20, characterized in that the structural component produced from the starting material of a subjected to subsequent heat treatment at temperatures between 100 ° C and 400 ° C for a period of 10 min to 100 h. A method according to claim 21, characterized in that the subsequent heat treatment takes place in the temperature interval of 250 ° C-400 ° C, for a duration which causes the formation of coherent Al ₃ Sc phases. Method according to claim 21 or 22, characterized that the subsequent heat treatment in several Steps and / or steps is performed. A method according to claim 21, 22 or 23, characterized characterized in that the structural component after the subsequent Heat treatment of a rapid cooling to room temperature is subjected. Method according to Claim 24, characterized that after rapid cooling, another hot aging in the temperature range 100 ° C-250 ° C for a duration of 10 minutes to 100 hours. Method according to one of claims 1-25, characterized characterized in that on a block-shaped base substrate made of an aluminum-magnesium alloy a wire-shaped Starting material of the composition AlMg4,6Sc1,4 by means of a laser beam melted line by line and is cooled and so on AlMgSc structural component is generated.