EP3941715A1

EP3941715A1 - Method for manufacturing an aluminium alloy part by additive manufacturing and aluminium alloy part obtained according to the method

Info

Publication number: EP3941715A1
Application number: EP20721629.2A
Authority: EP
Inventors: Mathieu OPPRECHT; Jean-Paul Garandet; Fernando LOMELLO; Guilhem Roux; Mathieu Soulier
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2019-05-13
Filing date: 2020-04-30
Publication date: 2022-01-26
Also published as: FR3096057A1; US20220212258A1; WO2020229197A1; JP2022532349A; FR3096057B1

Abstract

Disclosed is a method for manufacturing an aluminium alloy part by additive manufacturing comprising a step during which a layer of a mixture of powders is melted locally and then solidified, characterised in that the mixture of powders comprises: - first particles (10) comprising at least 80 wt% of aluminium and up to 20 wt% of one or more additional elements, and - second particles (20) of yttria, the volume percentage of second particles (20) in the mixture of powders preferably ranging from 0.5% to 5%.

Description

METHOD OF MANUFACTURING AN ALUMINUM ALLOY PART BY ADDITIVE MANUFACTURING AND ALUMINUM ALLOY PART

OBTAINED ACCORDING TO THIS PROCESS

DESCRIPTION

TECHNICAL AREA

The present invention relates to the general field of manufacturing aluminum alloy part by additive manufacturing.

The invention relates to a method of manufacturing aluminum alloy parts from a powder mixture containing aluminum-based particles and yttrin particles.

The invention also relates to an aluminum alloy part obtained with this process.

The invention is particularly advantageous since it makes it possible to remedy the problems of hot cracking of cracking aluminum alloys in additive manufacturing processes involving melting.

The invention finds applications in many industrial fields, and in particular in the automotive, aeronautics or even energy fields (for example, for the manufacture of heat exchangers).

STATE OF THE PRIOR ART

The different manufacturing processes of metal alloy parts by additive manufacturing (also called BD printing) have in common the use of the raw material in the form of powders and to shape the metal alloy via a step of melting these powders. .

The various additive manufacturing processes concerned include, in particular, powder bed fusion processes (or PBF for "Powder Bed Fusion" in English terminology) and processes for depositing material under concentrated energy (or DED for " Directed Energy Deposition ”in Anglo-Saxon terminology).

PBF processes consist in melting certain regions of a bed of powder, for example by means of a laser beam. DED processes consist of bringing the solid material, for example in the form of wire or powder, to melt it, for example by means of a laser beam, and to deposit the molten material.

With such processes, it is possible to industrially produce parts, of simple or complex shape, having satisfactory mechanical properties.

However, some aluminum alloys are subject to hot cracking problems resulting from columnar dendritic solidification, causing a microstructure sensitive to thermomechanical stresses during solidification, in particular for a solid fraction ranging from 0.9 to 0.98.

To remedy this drawback, various solutions have been considered.

For example, it is possible to change the chemical composition of the powder alloy. This is the case, for example, with the Scamalloy shade (APWORKS ©). It is a light alloy comprising aluminum and magnesium, modified with zirconium and scandium, developed specifically for additive manufacturing. During solidification, AhSc primary particles precipitate from the liquid and act as seeds for the growth of grains of the Al matrix. Scandium therefore allows a refinement of the microstructure and the development of equiaxed dendritic solidification. However, Scandium is a particularly expensive element, which significantly increases the costs of the raw material (by a factor of 4 compared to a standard aluminum powder).

Another solution consists in adding nanoparticles of a so-called germinating material, less expensive than scandium, to the aluminum powder to promote equiaxial solidification.

In document WO 2018/144323 A1, aluminum alloy powders are mixed with nanoparticles in Zr, Ta, Nb, Ti or even in one of their oxides, nitrides, hydrides, borides, carbides and aluminides to manufacture parts. made of aluminum alloy by additive manufacturing. Among the various embodiments described, parts are manufactured by selective laser melting (also denoted SLM) from, for example, a mixture comprising: B

- aluminum and tantalum nanoparticles 50 nm in diameter (1% by volume), or

- an aluminum alloy (AI7075 or AI6061) and zirconium nanoparticles of 500-1500nm in diameter (1% by volume).

In the document by Martin et al. "3D printing of high-strength aluminum alloys", Nature 549 (2017), pages 365-369, aluminum alloy powders of series 7075 (bimodal distribution at 15pm and 45pm) and 6061 (dso of 45pm) have been mixed with 1% by volume of Zirconium nanoparticles stabilized with hydrogen (Zrhh) to remedy the problem of hot cracking of aluminum alloys obtained by SLM. The nanoparticles are “electrostatically” assembled on the base powder to obtain a uniform distribution. No information is given on the particle size of the nanoparticles used.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method of manufacturing parts made of aluminum alloys which do not exhibit cracks, the method having to be simple to implement and inexpensive.

For this, the present invention provides a method of manufacturing an aluminum alloy part by additive manufacturing comprising at least one step during which a layer of a mixture of powders is melted and then solidified,

the mixture of powders comprising:

- first particles comprising at least 80% by mass of aluminum and up to 20% by mass of one or more additional elements, and

- second particles in yttrin (Y2O3), the volume percentage of second particles in the mixture of powders ranging, preferably, from 0.5% to 5%.

The invention differs fundamentally from the prior art by the addition of particles of yttrium oxide (Y2O3) to the aluminum-based powder. The addition of such particles makes it possible to promote an equiaxial solidification structure and thus eliminate cracking in the final part. Against all expectations, yttrium oxide gives rise to germinating AUY particles by reaction with aluminum according to the following reactions: Indeed, even if Yttrium oxide appears to be more thermodynamically stable than alumina regardless of temperature (see Ellingham diagram shown in Figure 1 and obtained from data extracted from Chu et al. "Sintering of aluminum nitride by using alumina crucible and MoSh heating element at temperatures of 1650 ° C and 1700 ° C ", Ceramics International 35 (2009), 3455-3461), it has been observed that, during the additive manufacturing process, one forms the germinating phase AI ₃ Y by decomposition of yttrin.

Alternatively or concomitantly, the release of the metal Y can take place by dissolving the oxide precursor (or the second particles) in the metal bath.

It did not appear obvious that this AI3Y phase (2 ^nd reaction) has time to germinate since the lifetimes of the molten metal baths formed during the process are relatively short (from a hundred microseconds to a millisecond). At first glance, this in-situ reaction is neither thermodynamically nor kinetically favored by the thermal conditions imposed by the process.

Advantageously, yttrin is a stable oxide, easy to handle and / or to store, with respect to metallic elements known to be highly reducing.

Advantageously, the second particles have a larger dimension ranging from 5nm to 2pm, preferably from 10nm to 400nm, and even more preferably from 30nm to 50nm.

Advantageously, the volume percentage of second particles in the mixture of powders ranges from 1% to 3%. Advantageously, the first particles have a larger dimension ranging from 10 pm to 100 pm, for example from 10 to 45 pm, and preferably from 20 to 65 pm.

Advantageously, the additional elements are chosen from Cu, Si, Zn, Mg, Fe, Ti, Mn, Zr, Va, Ni, Pb, Bi and Cr.

Advantageously, the aluminum alloy is alloy 7075, alloy 6061, alloy 2219 or alloy 2024.

According to a first advantageous variant embodiment, the manufacturing process is a selective laser melting process.

According to a second advantageous variant embodiment, the manufacturing process is a selective melting process by electron beam.

The process has many advantages:

- be simple to implement, since it suffices to mix the powders. This is a dry process step, quick to perform and easy to set up, regardless of the amount of powders;

- be inexpensive, and therefore interesting from an industrial point of view. By way of illustration, the material cost of an aluminum alloy 6061 is about 60 € / kg and the material cost of a mixture of powders comprising the aluminum alloy 6061 and yttrin (2% by volume) is about 66 € / kg;

- be able to store / easily handle the yttrin powder, since it is an oxide: there is no need to use an inert atmosphere;

- be able to use powders whose particles are small since such yttrium particles are not pyrophoric (unlike yttrium particles of the same dimensions), which makes the process safer;

- be able to easily modify the volume ratio between the powders when the powder is mixed;

- be easily adaptable for any additive manufacturing process and for any aluminum alloy subject to the problem of hot cracking; - be able to use the parameters conventionally used in additive manufacturing processes.

The invention also relates to an aluminum alloy part, obtained according to the method described above, the part comprising yttrin. The part is devoid of any cracking / fissure.

Advantageously, the part is a heat exchanger.

Other characteristics and advantages of the invention will emerge from the additional description which follows.

It goes without saying that this additional description is given only by way of illustration of the subject of the invention and should in no case be interpreted as a limitation of this subject.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments given purely as an indication and in no way limiting, with reference to the appended drawings in which:

FIG. 1 previously described is an Ellingham diagram representing the stabilities of aluminum oxide (Al ₂ 0 ₃ ) and of yttrium oxide (Y ₂ 0 ₃ ),

FIG. 2 schematically represents a mixture of powders according to a particular embodiment of the process of the invention.

The different parts shown in the figures are not necessarily on a uniform scale, to make the figures more readable.

The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with one another.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The process for manufacturing an aluminum alloy part by additive manufacturing comprises the following successive steps: a) provide a mixture of powders comprising, and preferably consisting of:

a first powder comprising first particles 10 made of a first material comprising at least 80% by weight of aluminum and up to 20% by weight of one or more additional elements,

a second powder comprising second particles 20 made of a second material, the second material being yttrium oxide,

b) forming a layer of the mixture of powders,

c) locally melting the layer of the mixture of powders, preferably by scanning a laser beam or by scanning an electron beam, so as to form a plurality of molten zones,

d) cooling the plurality of molten areas in step c) so as to form a plurality of solidified zones, this plurality of solidified zones constituting the first elements of the parts to be constructed.

Advantageously, steps b), c) and d) can be repeated at least once so as to form at least one other solidified zone on the first solidified zone. The process is repeated until the final shape of the part is obtained. The first powder mixture layer is formed on a substrate.

The addition of yttrin particles 20 to the first aluminum-based particles 10 of interest makes it possible to obtain an equiaxial solidification structure and a final piece of aluminum alloy without cracking.

Preferably, the first particles 10 are functionalized by the second particles 20 (FIG. 2).

Preferably, the second particles 20 consist of yttrin.

The second yttrium oxide powder preferably represents from 0.5% to 5% by volume of the mixture of powders, preferably from 1% to 3%.

According to an advantageous embodiment, the first particles 10 have a larger dimension ranging from 10 pm to 100 pm and the second particles 20 have a larger dimension ranging from 5 nm to 2 pm and, preferably, from 10 nm to 400 nm. The first particles 10 and the second particles 20 are elements which may be of spherical, ovoid or elongated shape. Preferably, the particles are substantially spherical and their largest dimension is their diameter.

The first powder is formed of first particles 10 of a first material. The first material comprises at least 80% by mass of aluminum.

The first particles 10 can comprise up to 20% of one or more additional elements (also called alloying elements). These elements are preferably chosen from zinc, magnesium, copper, silicon, iron, manganese, titanium, vanadium, bismuth, lead, nickel, zirconium and chromium. Preferably, the additional element or one of the additional elements is magnesium.

Preferably, the alloy is an aluminum alloy 7075, an alloy 2024, an alloy 2219 or an aluminum alloy 6061.

The mixture of powders provided in step a) is produced upstream of the additive manufacturing process.

In a preferred embodiment of the invention, the first powder and the second powder are mixed with the dynamic mixer BD, for example with a Turbula ^® mixer. Alternatively, it could be a mechanosynthesis process.

During step c), a sufficiently energetic beam is used to melt at least the first particles 10.

The deposited layer can be locally melted or completely melted.

The melting step makes it possible to create melted patterns in the layer of the mixture of powders. One or more zones of molten particles can be made to form the desired pattern. The particles 10 forming the pattern melt completely so as to lead, during solidification (step d), to one or more zones solidified in an aluminum alloy.

Advantageously, steps b), c) and d) can be repeated at least once so as to form at least one other solidified zone on the first solidified zone. The process is repeated until the final shape of the part is obtained. The non-solidified powders are then removed and the final part is detached from the substrate.

The part obtained, according to one of these processes, can be subjected to an annealing step (heat treatment) to reduce internal stresses and improve mechanical properties.

According to a first variant embodiment, it is a powder bed laser melting (SLM) process. By way of illustration and without limitation, the parameters of the manufacturing process by laser fusion on a powder bed are:

- between 50 and 500W for laser power;

- between 100 and 2000 mm / s for the laser speed;

- between 25 and 120 pm for the distance between two vector spaces (“hatch” in English terminology);

- between 15 and 60pm for the layer thickness.

According to another variant embodiment, it is an electron beam fusion process on a powder bed (EBM). By way of illustration and without limitation, the parameters of the manufacturing process by fusion by electron beam on a powder bed are:

- between 50 and 3000W for the electron beam;

- between 100 and 8000 mm / s for the speed of the beam;

- between 50 and 150 pm for the distance between two vector spaces;

- between 40 and 60pm for the layer thickness.

The machines used for additive manufacturing processes include, for example, a powder delivery system ("powder delivery system"), a device for spreading and homogenizing the surface of the powder ("Roller" or " Blade ”), a beam (for example an infrared laser beam at a wavelength of approximately 1060nm), a scanner to direct the beam, and a substrate (also called a plate) which can descend vertically (along a Z axis perpendicular to the bed of powder).

The assembly can be confined in a closed and inerted enclosure, to control the atmosphere, but also to prevent the dissemination of powders. Although this is in no way limiting, the invention particularly finds applications in the field of energy, and more particularly, heat exchangers, in the field of aeronautics, and in the field of the automobile.

Illustrative and nonlimiting examples of one embodiment:

In this example, a cube shaped part with dimensions 10mm * 10mm * 12mm is made by printing by SLM.

The part is obtained from a mixture of two powders: an aluminum alloy powder and an yttrin powder.

The particle size of the aluminum alloy powder (AI6061) is as follows: dio = 27.5 μm, dso = 41.5 μm and dgo = 62.7 μm.

Regarding the Y2C> 3 powder, its particle size ranges from 30nm to 50nm.

The mixture of the two powders is made in a glove box from: 1200mL of the aluminum alloy powder to be refined, 24mL of the yttrium oxide powder (mixture at 2% by volume), and 250mL of Zirconia balls of 3mm diameter, used to homogenize the mixture. The volume of the mixing pot is 6.5L.

The filling rate, defined as the ratio of the volume represented by the particles 10, the particles 20 and the zirconia beads to the volume of the mixing pot, is approximately 23%.

The mixture is passed to 3D dynamic mixer, for example in the Turbula ^® during lOh.

The mixture is then coarsely sieved (1mm) to recover the zirconia beads, then it is used to make a part by 3D printing.

By way of illustration, the SLM conditions making it possible to obtain the densest cubes are as follows: laser power: 190-270W; laser speed: 400-800mm / s, vector space: 100pm; layer thickness (powder bed): 20pm.

Claims

1. A method of manufacturing an aluminum alloy part by additive manufacturing comprising a step during which a layer of a mixture of powders is locally melted and then solidified, characterized in that the mixture of powders comprises:

- first particles (10) comprising at least 80% by weight of aluminum and up to 20% by weight of one or more additional elements, and

- second particles (20) in yttrin, the volume percentage of second particles in the mixture of powders preferably ranging from 0.5% to 5%.

2. Method according to any one of the preceding claims, characterized in that the second particles (20) have a larger dimension ranging from 5nm to 2pm, preferably from 10nm to 400nm, and even more preferably from 30nm to 50nm.

3. Method according to any one of the preceding claims, characterized in that the volume percentage of second particles 20) in the mixture of powders ranges from 1% to 3%.

4. Method according to any one of the preceding claims, characterized in that the first particles (10) have a larger dimension ranging from 10 pm to 100 pm, and preferably from 20 to 65 pm.

5. Method according to any one of the preceding claims, characterized in that the additional elements are chosen from Cu, Si, Zn, Mg, Fe, Ti, Mn, Zr, Va, Ni, Pb, Bi and Cr.

6. Method according to any one of the preceding claims, characterized in that the aluminum alloy is alloy 7075, alloy 2024, alloy 2219 or alloy 6061.

7. Method according to any one of claims 1 to 6, characterized in that the manufacturing process is a selective laser melting process.

8. Method according to any one of claims 1 to 6, characterized in that the manufacturing process is a selective melting process by electron beam.

9. Method according to any one of claims 1 to 8, characterized in that the powder mixture is produced with a dynamic mixer BD or by mechanosynthesis.

10. Part made of aluminum alloy obtained according to the method as defined in any one of claims 1 to 9, characterized in that it comprises yttrium.

11. Part according to the preceding claim, characterized in that the part is a heat exchanger.