Process for manufacturing an aluminum-chromium alloy part with superimposed successive solid metals layer

Abstract

The invention relates to a process for manufacturing a part, comprising the formation of successive solid metal layers (201 . . . 20n) that are stacked on one another, each layer describing a pattern defined from a numerical model (M)), each layer being formed by depositing a metal (25), referred to as filling metal, the filling metal being subjected to an input of energy so as to melt and form said layer by solidifying, in which process the filling metal is provided in the form of a powder (25), the exposure of which to an energy beam (32) results in melting followed by solidification such that a solid layer (201 . . . 20n) is formed, the process being characterized in that the filling metal (25) is an aluminum alloy comprising at least the following alloying elements: 2 to 10% by weight of Cr; 0 to 5% by weight, preferably 0.5 to 5% by weight, of Zr. 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 having remarkable mechanical properties, while obtaining a process that has an advantageous output.

Claims

1. A method for manufacturing a part comprising 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 addition metal, the addition metal being subjected to a provision of energy so as to melt and to form, by solidifying, said layer, wherein the addition metal takes the form of a powder, the exposure of which to an energetic beam results in melting followed by solidification so as to form a solid layer, wherein the addition metal is an aluminum alloy comprising at least the following alloy elements: Cr, in accordance with a fraction by mass lying between 2% and 10%; Zr, in accordance with a fraction by mass lying between 0% and 5%, optionally between 0.5% and 5%.

2. The method according to claim 1, wherein the aluminum alloy comprises at least one of the following elements: Mn, according to a fraction by mass of between 0.06% and 6%, optionally no more than 3% and optionally no more than 2%; Ti, in accordance with a fraction by mass of between 0.01% and 5%, optionally at least 0.1%, optionally no more than 3%, optionally no more than 2% and optionally no more than 1%; V, in accordance with a fraction by mass of between 0.06% and 6%, optionally no more than 3%, optionally no more than 2% and optionally no more than 1%.

3. The method according to claim 1, wherein the aluminum alloy comprises at least one of the following elements: Ag, in accordance with a fraction by mass of between 0.06% and 1%; Li, in accordance with a fraction by mass of between 0.06% and 1%; Cu, in accordance with a fraction by mass of between 0.06% and 5%, the Cu content being less than the Cr content and optionally between 0.1% and 1%; Zn, in accordance with a fraction by mass of between 0.06% and 1%.

4. The method according to claim 1, wherein the aluminum alloy also comprises at least one of the following elements Sc, Hf, W, Nb, Ta, Y, Yb, Nd, Er, Co, Ni with a fraction by mass of at least 0.06% and no more than 5%, optionally no more than 3%, optionally no more than 2% and optionally no more than 1%, so as to form more dispersoids or fine intermetallic phases.

5. The method according to claim 1, wherein the aluminum alloy also comprises at least one of the following elements La, Ce or mischmetal, with a fraction by mass of at least 0.06% and no more than 6%, optionally no more than 3%, optionally no more than 2% and optionally no more than 1%.

6. The method according to claim 1, wherein the aluminum alloy also comprises at least one of the following elements W, Mo, In, Bi, Sr, Sn, Ba, Ca, Sb, P and B, with a fraction by mass of at least 0.01% and no more than 1% and optionally at least 0.06% and no more than 0.8%.

7. The method according to claim 1, wherein the aluminum alloy also comprises the element Mg in accordance with a fraction by mass of at least 0.06% and no more than 0.5%.

8. The method according to claim 1, wherein the aluminum alloy also comprises Fe and/or Si in accordance with a fraction by mass of at least 0.06% and no more than 1% each, and optionally at least 0.1% and no more than 2% each, and optionally at least 0.5% and no more than 1% each.

9. The method according to claim 1, comprising, following the formation of the layers, a heat treatment typically at a temperature of at least 100 C. and no more than 550 C., and/or a hot isostatic compression.

10. The method according to claim 9, wherein the hardness in an as-manufactured state is less than the hardness after heat treatment and/or hot isostatic compression, the difference in Knoop hardness being at least 10 HK.

11. The method for manufacturing a part comprising a formation of successive solid metal layers, superimposed on each other, in order to form an untreated part, each layer describing a pattern defined from a digital model, each layer being formed by the deposition of a metal, referred to as addition metal, the addition metal being subjected to a provision of energy so as to melt and to form, by solidifying, said layer, wherein the addition metal takes the form of a powder, the exposure of which to an energetic beam results in melting followed by solidification so as to form a solid layer, the addition metal being an aluminum alloy of claim 1 having an Mg content of less than 0.5% by weight, wherein the untreated part optionally has a Knoop hardness of between 100 HK and 200 HK and the untreated part is next heat treated and/or subjected to hot isostatic compression at a temperature above 350 C. so as to increase Knoop hardness by at least 20 HK.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The figure is a diagram illustrating an additive manufacturing method of the selective laser melting (SLM) or EBM type.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(2) In the description, unless indicated to the contrary:

(3) the designation of the aluminum alloys is in accordance with the naming established by The Aluminum Association;

(4) the proportions of chemical elements are designated as % and represent fractions by mass;

(5) the hardnesses are evaluated by the Knoop method for a load of 0.01 kg (10 g), the term Knoop hardness 0.01 or Knoop hardness being used indifferently.

(6) The figure describes in general terms an embodiment wherein the additive manufacturing method according to the invention is used. According to this method, the addition material 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 addition material by an optical system or electromagnetic lenses 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 along the longitudinal plane XY, describing a pattern dependent on the digital model. 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 addition metal and another layer is formed, superimposed on the layer previously produced. The thickness of the powder forming a layer may for example be between 10 and 100 m. This additive manufacturing mode is typically known by the term selective laser melting (SLM) when the energy beam is a laser beam, the method advantageously being executed at atmospheric pressure, and by the name electron beam melting (EBM) when the energy beam is a beam of electrons, the method advantageously being executed under reduced pressure, typically less than 0.01 bar and preferably less than 0.1 mbar.

(7) Preferably, in particular in the case where selective laser melting is used, use is made of a heated plate in order to improve processability and to prevent cracking. The plate can preferably be heated to a temperature of 50 to 300 C., more preferentially 100 to 250 C.

(8) 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 in accordance with the digital model with thermal energy supplied by a laser beam.

(9) In yet another embodiment, not described by the figure, the powder is sprayed and melted by a beam, generally laser, simultaneously. This method is known by the term laser melting deposition.

(10) Methods known in particular 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), and laser freeform manufacturing technology (LFMT).

(11) In one embodiment the method according to the invention is used for producing a hybrid part comprising a part obtained by conventional rolling and/or spinning and/or molding and/or forging optionally followed by machining and an attached part obtained by additive manufacturing. This embodiment may also be suitable for repairing parts obtained by the conventional methods.

(12) In one embodiment of the invention it is also possible to use the method according to the invention for repairing parts obtained by additive manufacture.

(13) At the end of formation of the successive layers, an untreated part or a part in the as-manufactured state is obtained.

(14) The metal parts obtained by the method according to the invention are particularly advantageous since they have smooth surfaces, do not have a hot cracking, have a hardness that is not too high in the as-manufactured state but which can increase significantly through heat treatment. Advantageously, the hardness in the as-manufactured state is lower than the hardness after heat treatment and/or hot isostatic compression, the Knoop hardness difference being at least 10 HK, preferably at least 20 HK, preferably at least 30 HK and preferentially at least 40 HK. Thus, unlike the alloys of the prior art, such as the 8009 alloy, the Knoop hardness in the as-manufactured state is preferably less than 300 HK and advantageously less than 200 HK, and preferably less than 150 HK. Advantageously the Knoop hardness in the as-manufactured state is at least 50 HK, advantageously at least 80 HK, and preferably at least 90 HK. In one embodiment of the invention the Knoop hardness in the as-manufactured state is between 100 HK and 200 HK. Preferably, the metal parts according to the invention are characterized, after heat treatment of at least 100 C. and no more than 550 C. and/or hot isostatic compression, by a 0.01 Knoop hardness of at least 100 HK and preferably at least 120 HK or even at least 140 HK and preferentially at least 150 HK and by the absence of hot cracking.

(15) The present inventor found that a method for manufacturing a part comprising formation of successive solid metal layers, superimposed on one another, in order to form an untreated part, each layer describing a pattern defined from a digital model, each layer being formed by the deposition of a metal, referred to as an addition metal, the addition metal being subjected to a provision of energy so as to melt and to form, by solidifying, said layer, wherein the addition metal takes the form of a powder, the exposure of which to an energetic beam results in melting followed by solidification so as to form a solid layer, the addition metal being an aluminum alloy as described above having an Mg content of less than 0.5% by weight, the method being characterized in that the untreated part preferably has a Knoop hardness of between 100 HK and 200 HK and in that it is next heat treated and/or subjected to hot isostatic compression at a temperature above 350 C. so as to increase the Knoop hardness thereof by at least 20 HK is particularly advantageous.

(16) The invention will be described in more detail in the following example.

(17) 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 description.

EXAMPLE

Example 1

(18) In this example the properties of various alloys were evaluated in a selective laser melting (SLM) machine.

(19) 8009 or AS7G06 alloy discs or ones made from an alloy according to the invention, with a thickness of 5 mm and a diameter of 27 mm, were prepared from small ingots. The discs were placed in a selective laser melting (SLM) machine and the surface was swept with a laser with the same sweeping strategy and method conditions representative of those used for the selective laser melting (SLM) method. The present inventor in fact found that it was possible in this way to evaluate the suitability of the alloys for the selective laser melting (SLM) method and in particular the surface quality and the sensitivity to hot cracking.

(20) The composition of the alloys used is given in table 1 below.

(21) TABLE-US-00001 TABLE 1 Alloy Si Fe Mn V Cr Zr Mg Ti Invention 0.05 0.16 1.0 4.9 1.5 8009 1.8 8.7 0.23 1.3 AS7G06* 7.0 0.6 0.2 *nominal values

(22) In the following tests, the laser source had a power of 200 W, the width of a laser passage being 100 m, with an overlap between two successive passages, the manufacturing temperature was 200 C. The sweep speed was 900 mm/s. A Phenix Systems PM100 selective laser melting (SLM) machine was used.

(23) The surface quality was evaluated qualitatively according to the following scale, the mark 1 being the most favorable. 1: very smooth surface without surface defects 2: smooth surface without surface defects 3: rough surface without surface defects 4: very rough surface with surface defects.

(24) Sensitivity to hot cracks was assessed on cross sections of the treated zones in accordance with the following scale, the mark 1 being the most favorable. 1: absence of microcracks 2: presence of microcracks of less than 50 m 3: presence of microcracks of more than 50 m.

(25) Hardness was measured according to the Knoop scale with a load of 10 g after laser treatment and after additional heat treatment at 400 C., making it possible in particular to assess the suitability of the alloy for hardening during heat treatment and the effect of any HIP treatment on the mechanical properties.

(26) The results obtained are presented in table 2 below.

(27) TABLE-US-00002 TABLE 2 Knoop Knoop hardness hardness (0.01) after Hot- (0.01) after additional Surface cracking laser treatment for 4 Alloy assessment assessment treatment hours at 400 C. Invention 1 1 118 HK 162 HK 8009 4 3 360 HK 155 HK AS7G06 1 1 132 HK 72 HK

(28) The alloy according to the invention is particularly advantageous since it makes it possible to obtain a smooth surface, without hot cracking and with high hardness after treatment at 400 C.

Example 2

(29) An alloy according to the present invention having the composition as presented in table 3 below, in percentages by weight, was prepared.

(30) TABLE-US-00003 TABLE 3 Alloy Mn Cr Zr Invention 1.0 5 2

(31) 5 kg of alloy powder was atomized successfully using a VIGA (vacuum inert gas atomization) atomizer. The powder was used successfully in a selective laser melting machine of the FormUp 350 model for producing tensile test blanks. The tests were carried out with the following parameters: layer thickness: 60 m, laser power: 370 W-390 W, heating of plate: 200 C., vector difference: 0.11-0.13, laser speed: 1000-1400 mm/s. The blanks were cylindrical with a height of 45 mm and a diameter of 11 mm for the tensile tests in the manufacturing direction (Z direction), and 124545 mm.sup.3 parallelepipedal blocks for the tests in the XY direction (perpendicular to the manufacturing direction). After manufacture by selective laser melting (SLM), the blanks were subjected to a relaxation heat treatment of 2 hours at 300 C. Some blanks were tested in the pre-relaxation state and other blanks were subjected to an additional treatment for 1 hour or 4 hours at 400 C. (hardening annealing).

(32) Cylindrical test pieces were machined from the blanks described above. Tensile tests were carried out at ambient temperature in accordance with NF EN ISO 6892-1 (2009-10) and ASTM E8-E8M-13a (2013).

(33) TABLE-US-00004 TABLE 4 Direction Heat treatment Rp0.2 (MPa) Rm (MPa) A % Z Untreated state 301 to 333 356 to 380 2.6 to 6.7 Z 1 h at 400 C. 377 to 396 425 to 438 2.9 to 3.3 XY Untreated state 332 to 365 380 to 403 6.7 to 11.2 XY 1 h at 400 C. 392 to 428 434 to 463 2.6 to 6.7 XY 4 h at 400 C. 409 to 437 452 to 474 3.1 to 5.1

(34) The heat treatment leads to a significant increase in the mechanical strength compared with the untreated state, associated with a reduction in elongation. The alloy according to the present invention therefore makes it possible to dispense with a conventional heat treatment of the solution heat treatment/quenching type.