PROCESS FOR MANUFACTURING AN ALUMINIUM ALLOY PART

Abstract

The invention relates to a process for manufacturing a part comprising a formation of successive solid metal layers (20.sub.1 . . . 20.sub.n), superposed on one another, each layer describing a pattern defined using a numerical model (M), each layer being formed by the deposition of a metal (25), referred to as solder, the solder being subjected to an input of energy so as to start to melt and to constitute, by solidifying, said layer, wherein the solder takes the form of a powder (25), the exposure of which to an energy beam (32) results in melting followed by solidification so as to form a solid layer (20.sub.1 . . . 20.sub.n), the process being characterized in that the solder (25) is an aluminium alloy comprising at least the following alloy elements: —Si; in a weight fraction of from 0 to 4%, preferably from 0.5% to 4%, more preferably from 1% to 4% and more preferably still from 1% to 3%; —Fe in a weight fraction of from 1% to 15%, preferably from 2% to 10%; —V in a fraction of from 0 to 5%, preferably from 0.5% to 5%, more preferentially from 1% to 5%, and more preferentially still from 1% to 3%; at least one element chosen from Ni, La and/or Co, in a weight fraction of from 0.5% to 15%, preferably from 1% to 10%, more preferably from 3% to 8% each for Ni and Co, in a weight fraction of from 1% to 10%, preferably from 3% to 8% for La, and in a weight fraction of less than or equal to 15%, preferably less than or equal to 12% in total. The invention also relates to a part obtained by this process. The alloy used in the additive manufacturing process according to the invention makes it possible to obtain parts with remarkable characteristics.

Claims

1. Method for manufacturing a part including a formation of successive solid metal layers, superimposed on each other, each layer describing a pattern defined from a digital model (M), each layer being formed by the deposition of a metal, referred to as solder, the solder being subjected to an input of energy so as to start to melt and to constitute, by solidifying, said layer, wherein the solder is in the form of a powder, the exposure of which to an energy beam (32) results in melting followed by solidification so as to form a solid layer, the method being wherein the solder is an aluminum alloy comprising at least the following alloy elements: Si, in a fraction by weight of 0 to 4%, optionally 0.5 to 4%, more optionally 1 to 4%, and even more optionally 1 to 3%; Fe, in a fraction by weight of 1% to 15%, optionally 2 to 10%; V, in a fraction by weight of 0 to 5%, optionally 0.5 to 5%, more optionally 1 to 5%, and even more optionally 1 to 3%; at least one element chosen from: Ni, La and/or Co, in a fraction by weight of 0.5 to 15%, optionally 1 to 10%, more optionally 3 to 8% each for Ni and Co, in a fraction by weight of 1 to 10%, optionally 3 to 8%, for La, and in a fraction by weight of less than or equal to 15%, optionally less than or equal to 12% in total.

2. Method according to claim 1, wherein the aluminum alloy also comprises at least one element chosen from: Mn, Ti, W, Nb, Ta, Y, Yb, Nd, Er, Cr, Zr, Hf, Ce, Sc and/or mischmetal, in a fraction by weight of less than or equal to 5%, optionally less than or equal to 3% each, and less than or equal to 15%, optionally less than or equal to 12%, even more optionally less than or equal to 5% in total.

3. Method according to claim 1, wherein the aluminum alloy also comprises at least one element chosen from: Sr, Ba, Sb, Bi, Ca, P, B, In and/or Sn, in a fraction by weight of less than or equal to 1%, optionally less than or equal to 0.1%, even more optionally less than or equal to 700 ppm each, and less than or equal to 2%, optionally less than or equal to 1% in total.

4. Method according to claim 1, wherein the aluminum alloy also comprises at least one element chosen from: Ag in a fraction by weight of 0.06 to 1° A, Li in a fraction by weight of 0.06 to 1%, Cu in a fraction by weight of 0.06 to 5%, optionally 0.1 to 2%, Zn in a fraction by weight of 0.06 to 1% and/or Mg in a fraction by weight of 0.06 to 1%.

5. Method according to claim 1, wherein the aluminum alloy also comprises at least one compound for refining the grains, optionally AlTiC or AlTiB2, in a quantity of less than or equal to 50 kg/tonne, optionally less than or equal to 20 kg/tonne, optionally less than or equal to 12 kg/tonne each, and less than or equal to 50 kg/tonne, optionally less than or equal to 20 kg/tonne in total.

6. Method according to claim 1, including, following the formation of the layers: solution heat treatment followed by quenching and aging, or heat treatment optionally at a temperature of at least 100° C. and no more than 400° C., and/or hot isostatic compression.

7. Metal part obtained by a method of claim 1.

8. Powder comprising, and optionally consisting of, an aluminum alloy comprising: Si, in a fraction by weight of 0 to 4%, optionally 0.5 to 4%, more optionally 1 to 4%, and optionally 1 to 3%; Fe, in a fraction by weight of 1% to 15%, optionally 2 to 10%; V, in a fraction by weight of 0 to 5%, optionally 0.5 to 5%, more optionally 1 to 5%, optionally 1 to 3%; at least one element chosen from: Ni, La and/or Co, in a fraction by weight of 0.5 to 15%, optionally 1 to 10%, more optionally 3 to 8% each for Ni and Co, in a fraction by weight of 1 to 10%, optionally 3 to 8% for La, and in a fraction by weight of less than or equal to 15%, optionally less than or equal to 12% in total.

Description

FIGURES

[0057] FIG. 1 is a diagram illustrating an additive manufacturing method of the SLM or EBM type.

[0058] FIG. 2 shows a micrograph of a cross section of an Al10Si0.3 Mg sample after surface sweep with a laser, cut and polished with two Knoop indentations in the re-melted layer.

DETAILED DESCRIPTION OF THE INVENTION

[0059] In the description, unless indicated otherwise:

[0060] the designation of the aluminium alloys is in accordance with The Aluminium Association;

[0061] the proportions of chemical elements are designated as % and represent fractions by weight.

[0062] FIG. 1 describes in general terms an embodiment wherein the additive manufacturing method according to the invention is implemented. According to this method, the solder 25 is in the form of an alloy powder according to the invention. An energy source, for example a laser source or a source of electrons 31, emits an energy beam, for example a laser beam or a beam of electrons 32. The energy source is coupled to the solder by an optical or electromagnetic-lens system 33, the movement of the beam thus being able to be determined according to a digital model M. The energy beam 32 follows a movement on the longitudinal plane XY, describing a pattern dependent on the digital model M. The powder 25 is deposited on a support 10. The interaction of the energy beam 32 with the powder 25 causes a selective melting of the latter, followed by solidification, resulting in the formation of a layer 20.sub.1 . . . 20.sub.n. When a layer has been formed, it is covered with powder 25 of the solder and another layer is formed, superimposed on the layer previously produced. The thickness of the powder forming a layer may for example be from 10 to 100 μm. This additive manufacturing method is typically known by the term selective laser melting (SLM) when the energy beam is a laser beam, the method being in this case advantageously executed at atmospheric pressure, and by the term electron beam melting (EBM) when the energy beam is a beam of electrons, the method in this case advantageously being executed at reduced pressure, typically less than 0.01 bar and preferably less than 0.1 mbar.

[0063] In another embodiment, the layer is obtained by selective laser sintering (SLS) or direct metal laser sintering (DMLS), the layer of alloy powder according to the invention being sintered selectively according to the digital model chosen with the thermal energy supplied by a laser beam.

[0064] In yet another embodiment that is not described by FIG. 1, the powder is sprayed and melted simultaneously by a beam, generally a laser beam. This method is known by the term laser melting deposition.

[0065] Other methods may be used, in particular those known by the names direct energy deposition (DED), direct metal deposition (DMD), direct laser deposition (DLD), laser deposition technology (LDT), laser metal deposition (LMD), laser engineering net shaping (LENS), laser cladding technology (LCT), or laser freeform manufacturing technology (LFMT).

[0066] In one embodiment, the method according to the invention is used for producing a hybrid part comprising a portion 10 obtained by extrusion and/or moulding and/or forging, optionally followed by machining, and an attached portion 20 obtained by additive manufacturing. This embodiment may also be suitable for repairing parts obtained by conventional methods.

[0067] It is also possible, in one embodiment of the invention, to use the method according to the invention for repairing parts obtained by additive manufacturing.

[0068] At the end of the formation of the successive layers, an untreated part or an as-manufactured part is obtained.

[0069] The metallic parts obtained by the method according to the invention are particularly advantageous since they have smooth surfaces and do not have any hot cracking. Moreover, they have a hardness in the as-manufactured state less than that of an 8009 reference, and at the same time hardness after heat treatment greater than that of an 8009 reference. Thus, unlike the alloys according to the prior art such as the 8009 alloy, the hardness of the alloys according to the present invention decreases less between the as-manufactured state and the state after heat treatment. The lower hardness in the as-manufactured state of the alloys according to the present invention compared with an 8009 alloy is considered to be advantageous for suitability for the SLM method, by causing a lower level of stresses during the SLM manufacturing and thus lower sensitivity to hot cracking. The higher hardness after heat treatment (for example one hour at 400° C.) of the alloys according to the present invention compared with an 8009 alloy provides better thermal stability. The heat treatment could be a hot isostatic compression (HIC) step following SLM manufacturing. Thus the alloys according to the present invention are soft in the as-manufactured state but have better hardness after heat treatment, and hence better mechanical properties for parts in service. The 10 g Knoop hardness in the as-manufactured state of the metal parts obtained according to the present invention is preferably 150 to 350 HK, more preferentially 200 to 340 HK. Preferably, the 10 g Knoop hardness of the metal parts obtained according to the present invention, after heat treatment of at least 100° C. and of no more than 550° C. and/or hot isostatic compression, is 150 to 300 HK, more preferentially 160 to 250 HK. The method for measuring the Knoop hardness is described in the following examples. The powder according to the present invention may have at least one of the following characteristics:

[0070] mean particle size of 10 to 100 μm, preferably 20 to 60 μm;

[0071] spherical shape. The sphericity of a powder may for example be determined using a morphogranulometer;

[0072] good castability. The castability of a powder can for example be determined according to ASTM B213;

[0073] low porosity, preferably 0 to 5%, more preferentially 0 to 2%, even more preferentially 0 to 1% by volume. The porosity can in particular be determined by scanning electron microscopy or by helium pycnometry (see ASTM B923);

[0074] absence or small quantity (less than 10%, preferably less than 5% by volume) of small particles (1 to 20% of the mean size of the powder), referred to as satellites, which stick to the larger particles.

[0075] The powder according to the present invention can be obtained by conventional atomisation methods using an alloy according to the invention in liquid or solid form or, alternatively, the powder can be obtained by mixing primary powders before exposure to the energy beam, the various compositions of the primary powders having a mean composition corresponding to the composition of the alloy according to the invention.

[0076] It is also possible to add non-meltable and insoluble particles, for example oxides or TiB.sub.2 particles or carbon particles, in the bath before atomisation of the powder and/or during deposition of the powder and/or when the primary powders are mixed. These particles can serve to refine the microstructure. They can also serve to harden the alloy if they are of nanometric size. These particles may be present in a fraction by volume of less than 30%, preferably less than 20%, more preferentially less than 10%.

[0077] The powder according to the invention can be obtained for example by gas jet atomisation, plasma atomisation, water jet atomisation, ultrasound atomisation, centrifugation atomisation, electrolysis and spheroidisation, or grinding and spheroidisation.

[0078] Preferably, the powder according to the present invention is obtained by gas jet atomisation. The gas jet atomisation method commences with the pouring of a molten metal through a nozzle. The molten metal is next hit by neutral gas jets, such as nitrogen or argon, and atomised into very small droplets, which cool and solidify while falling inside an atomisation tower. The powders are next collected in a can. The gas jet atomisation method has the advantage of producing a powder having a spherical shape, unlike water jet atomisation, which produces a powder having an irregular shape. Another advantage of gas jet atomisation is good powder density, in particular because of the spherical shape and the particle size distribution. Yet another advantage of this method is good reproducibility of the particle size distribution.

[0079] After manufacture thereof, the powder according to the present invention can be stoved, in particular in order to reduce the moisture thereof. The powder may also be packaged and stored between manufacture and use thereof.

[0080] The powder according to the present invention can in particular be used in the following applications:

[0081] selective laser sintering (SLS);

[0082] direct metal laser sintering (DMLS);

[0083] selective heat sintering (SHS);

[0084] selective laser melting (SLM);

[0085] electron beam melting (EBM);

[0086] laser melting deposition;

[0087] direct energy deposition (DED);

[0088] direct metal deposition (DMD);

[0089] direct laser deposition (DLD);

[0090] laser deposition technology (LDT);

[0091] laser engineering net shaping (LENS;)

[0092] laser cladding technology (LCT);

[0093] laser freeform manufacturing technology (LFMT);

[0094] laser metal deposition (LMD);

[0095] cold spray consolidation (CSC);

[0096] additive friction stir (AFS);

[0097] field assisted sintering technology (FAST) or spark plasma sintering; or

[0098] inertia rotary friction welding (IRFW).

[0099] The invention will be described in more detail in the following example.

[0100] The invention is not limited to the embodiments described in the above description or in the following examples, and may vary widely in the context of the invention as defined by the claims accompanying the present invention.

EXAMPLES

[0101] Various alloys according to the present invention, referred to as Innov1, Innov2 and Innov3, and an 8009 alloy of the prior art were cast in a copper mould using an Indutherm VC 650V machine for obtaining ingots 130 mm high, 95 mm wide and 5 mm thick. The composition of the alloys obtained by ICP is given as a percentage weight fraction in the following table 1.

TABLE-US-00001 TABLE 1 Alloys Si Fe V Ni Co La Ba Sb Sn Refer- 1.8 8.65 1.3 — — — — — — ence (8009) Innov1 1.95 3.92 1.22 5.16 — — — — — Innov2 1.91 3.88 1.14 — 4.83 — — — — Innov3 1.82 6.45 1.1 — — 4.78 0.025 0.054 0.050

[0102] The refining compound ATSB was added to the alloys Innov1 and Innov2, in a quantity of 10 kg/tonne.

Example 1

SLM on Discs

[0103] The alloys as described in table 1 above were tested by a fast prototyping method.

[0104] Samples were machined for sweeping the surface with a laser, in the form of discs with a thickness of 5 mm and a diameter of 27 mm, from the ingots obtained above. The discs were placed in an SLM machine and sweeps of the surface were carried out with a laser, following the same sweep strategy and method conditions representative of those used for the SLM method. It was in fact found that it was possible in this way to evaluate the suitability of the alloys for the SLM method and in particular the surface quality, sensitivity to hot cracking, hardness in the untreated state and hardness after heat treatment.

[0105] Under the laser beam, the metal melts in a bath 10 to 350 μm thick. After the passage of the laser, the metal cools quickly as in the SLM method. After the laser sweep, a fine surface layer 10 to 350 μm thick was melted and then solidified. The properties of the metal in this layer are close to the properties of the metal at the core of a part manufactured by SLM, since the sweep parameters are judiciously chosen. The laser sweep of the surface of the various samples was carried out by means of a PM100 selective laser melting machine made by Phenix Systems. The laser source had a power of 200 W, the manufacturing temperature was 200° C., the vector difference was 50 μm and the diameter of the beam was 60 to 80 μm. Two different sweep speeds were tested for each sample: 600 mm/s and 900 mm/s.

[0106] 1) Sensitivity to Hot Cracking

[0107] It is known that some alloys cannot be used in SLM since the samples crack during the SLM construction. It has been shown that this cracking may also be obtained by the sweeping of the surface with a laser. Thus this method (sweeping of the surface with a laser) makes it possible to simulate an SLM method and to eliminate alloys that would crack during an SLM method.

[0108] The discs obtained above were cut in the plane perpendicular to the direction of the laser passes and were next polished. The sensitivity to hot cracks (during the sweeping of the surface with a laser) was evaluated by metallographic observations (×200) on cross sections of the treated zones. The results are summarised in table 2 below. The mark 1 corresponds to the absence of microcracks, the mark 2 to the presence of microcracks of less than 50 μm, and the mark 3 to the presence of microcracks of more than 50 μm.

TABLE-US-00002 TABLE 2 Alloy Mark Reference (8009) 3 Innov1 1 Innov2 2 Innov3 1

[0109] Thus, according to table 2 above, only the alloys according to the present invention make it possible to obtain good resistance to hot cracking. Moreover, a smooth surface with few or no defects was observed.

[0110] 2) Measurement of Knoop Hardness

[0111] Hardness is an important property for alloys. This is because, if the hardness in the layer re-melted by sweeping the surface with a laser is high, a part manufactured with the same alloy will potentially have a high breaking point.

[0112] In order to evaluate the hardness of the re-melted layer, the discs obtained above were cut in the plane perpendicular to the direction of the laser passes and were next polished. After polishing, hardness measurements were carried out in the re-melted layer. The hardness measurement was carried out with a Durascan apparatus from Struers. The Knoop 10 g hardness method with the long diagonal of the indentation placed parallel to the plane of the re-melted layer was chosen in order to keep sufficient distance between the indentation and the edge of the sample. Fifteen indentations were positioned halfway through the thickness of the re-melted layer. FIG. 2 shows an example of the hardness measurement. Reference 1 corresponds to the re-melted layer and reference 2 corresponds to a Knoop-hardness indentation.

[0113] The hardness was measured on the Knoop scale with a 10 g load after laser treatment (in the as-manufactured state) and after supplementary heat treatment at 400° C. for four hours, making it possible in particular to evaluate the suitability of the alloy for hardening during a heat treatment and the effect of any HIC treatment on the mechanical properties.

[0114] The 10 g Knoop hardness values in the untreated state and after 4 hours at 400° C. are given in table 3 below (HK).

TABLE-US-00003 TABLE 3 10 g Knoop hardness in 10 g Knoop hardness Alloy the untreated state after 4 hours at 400° C. Reference (8009) 359 155 Innov1 261 179 Innov2 272 193 Innov3 331 188

[0115] The alloys according to the present invention (Innov1, Innov2 and Innov3) showed a 10 g Knoop hardness in the untreated state lower than that of the 8009 alloy but, after four hours at 400° C., greater than that of the reference 8009 alloy. Without being bound by the theory, it is supposed that the higher hardness after four hours at 400° C. is very probably associated with slower coagulation kinetics of the dispersoids (better thermal stability).

Example 2

SLM on Powder

[0116] Ingots cast from the compositions described in table 1 above were atomised by the UTBM (Université de Technologie de Belfort Montbéliard) in order to obtain a powder by gas jet atomisation (the method described above). Granulometric analysis of the powders obtained was carried out by laser diffraction using a Malvern Mastersizer 2000 granulometer in accordance with ISO 13320. The curve describing the change in the volume fraction as a function of the diameter of the particles forming the powder generally describes a distribution that can be assimilated to a Gaussian distribution. The 10%, 50% (median) and 90% fractiles of the distribution obtained are generally referred to as D.sub.10, D.sub.50 and D.sub.90 respectively.

[0117] The D.sub.10, D.sub.50 and D.sub.90 characteristics of the powders obtained are given in table 4 below.

TABLE-US-00004 TABLE 4 Alloy D.sub.10 (μm) D.sub.50 (μm) D.sub.90 (μm) Reference (8009) 33.5 52.3 81.2 Innov1 42.3 58.1 81.2 Innov2 39.5 60.7 93.6 Innov3 58.6 88.3 132

[0118] Thus it is possible to manufacture powders from the alloys according to the invention.

[0119] In this example, parts were produced by the SLM method previously described. The tests were carried out on a 400 W Renishaw AM 400 machine from UTBM. For each of the alloys Innov1, Innov2 and Innov3, several cubes with sides of 7 mm were manufactured while varying the method parameters (see table 5 below). The porosity of the cubes thus obtained was determined (by polishing and then image analysis) and is given in table 5 below.

TABLE-US-00005 TABLE 5 Energy Velocity Volume velocity Alloy (J/mm.sup.3) (mm/s) (mm.sup.3/s) Porosity Innov1 96 891 3.2 2.3 127 714 2.4 0.2 102 833 2.8 0.2 97 776 2.6 0.9 129 776 2.6 0.1 114 825 2.5 0.7 95 825 3.0 1.4 118 825 2.7 0.6 95 952 3.1 0.8 124 776 2.3 0.1 104 776 2.8 0.2 92 891 2.9 1.8 Innov2 116 891 2.23 3.0 96 891 2.67 3.2 127 714 1.96 0.8 102 833 2.29 1.2 129 776 2.13 2.0 114 825 2.06 3.2 95 825 2.47 3.3 89 825 2.27 3.2 118 825 2.27 1.1 124 776 1.94 0.8 104 776 2.33 0.9 92 891 2.45 1.8 Innov3 87 891 2.23 2.7 116 891 2.23 3.0 127 714 1.96 1.0 102 833 2.29 1.2 129 776 2.13 0.7 95 825 2.47 3.5 118 825 2.27 0.8 124 776 1.94 1.2 104 776 2.33 2.5

[0120] Thus it is possible to obtain parts having acceptable porosities with the method according to the present invention. The porosity could be improved by optimisation of the method, or even with a post-manufacture treatment of the HIC (hot isostatic compression) type.

[0121] Furthermore, none of the samples tested exhibited any cracking during SLM manufacturing.