Aluminum materials for additive manufacturing techniques and products manufactured using same

Abstract

The present invention relates to metallurgy, in particular aluminum-based alloys for the production of additive manufacturing powders, including selective laser melting. The aluminum powder alloy comprises the following components in percentage by weight: 0.3 to 1.5 percent of iron, 0.35 to 2.6 percent of cerium, 0.15 to 0.4 percent of titanium, 0.3 to 1.5 percent of iron, 0.35 to 2.6 percent of cerium and 0.15 to 0.4 percent of titanium; 0.2-2.0 of at least one element (total or individual) from Group A, including manganese, lanthanum and yttrium; 0.6-1.5 of at least one element (total or individual) from group B, including zirconium, vanadium, chromium, hafnium and scandium; optionally: from 3 to 60 ppm of hydrogen and from 1.5 to 4.5 ppm of magnesium; and aluminum and unavoidable impurities, including up to 0.2 silicon, up to 0.05 copper, and up to 0.05 zinc.

Description

Technical Field

[0001] The present invention relates to metallurgy, and more particularly to aluminum-based alloys for producing powders, which can be used to manufacture parts using traditional powder metallurgy techniques and additive manufacturing techniques including selective laser melting. Background Art

[0002] Aluminum materials are divided into two categories: one is alloys that can be hardened, and the other is alloys that cannot be hardened by solution treatment, quenching, and subsequent artificial or natural aging. Due to the precipitation of a large number of nanoscale hardening particles during the heat treatment process, age-hardening alloys have better mechanical properties. However, quenching of precision parts manufactured using powder metallurgy and additive manufacturing techniques may cause deformation and defects. Alloys that do not require quenching are needed. Generally, 3D printing and powder metallurgy can produce rapidly solidified alloys, in which the concentrations of various elements contained are much higher than the equilibrium concentration, so they have high strength but poor ductility. Some applications require highly plastic materials. Selective laser melting and similar 3D metal printing techniques essentially deposit metal layers on the substrate of the same metal. The challenge lies in how to obtain high ductility and high strength of aluminum alloys simultaneously.

[0003] There is currently known a rapidly solidified aluminum alloy containing chromium (US Patent US5049211, publication date: September 17, 1991). The alloy contains 1 to 7 wt% of chromium and at most 6 wt% of X, where X is selected from one of the refractory metals niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). Due to the high content of transition metals and low ductility, the impact strength is extremely low.

[0004] Patent EP2112241 (publication date: September 21, 2011) describes an alloy strengthened by L12. The alloy composition is as follows: nickel 4 - 25%; cerium: 2 - 25%; at least one of the following elements: scandium (0.1 - 4%); erbium (0.1 - 20%); thulium (0.1 - 15%); ytterbium (0.1 - 25%); lutetium (0.1 - 25%), and at least one of the following elements: gadolinium (2 - 30%); yttrium (2 - 30%); zirconium (0.5 - 5%); titanium (0.5 - 10%); hafnium (0.5 - 10%); niobium (0.5 - 5%); and iron (0.5 - 15%). This alloy is manufactured using rapid solidification technology and has very high strength. However, due to over-alloying, it is difficult to manufacture the final product using selective laser melting or any other technology except traditional powder metallurgy techniques. Another disadvantage is that this alloy contains a large amount of rare and expensive elements.

[0005] An aluminum alloy known for use in additive manufacturing techniques (patent number: EP3406372, publication date: January 1, 2020) consists of the following components (mass percentage):

[0006]

[0007]

[0008] This alloy has high heat resistance and high strength in some models. However, a large amount of eutectic forming elements will reduce ductility, thus shortening the fatigue life. In addition, due to the presence of a large number of alloying elements, the corrosion resistance of this alloy is likely to be lower compared to corrosion-resistant aluminum alloys.

[0009] Patent Application No.: US2021129270 (Publication Date: May 6, 2021) provides an aluminum-based material for additive manufacturing technology, with the following composition (wt.%):

[0010]

[0011] Cerium and nickel in the alloy are sufficient to form at least one of the following intermetallic compounds: Al23Ni6Ce4, Al7Ni2Ce, Al20Mn2Ce, or Al3Ni.

[0012] This alloy is designed to work in high-temperature environments. It does not require hardening heat treatment, but due to the high content of alloying elements, its ductility is low.

[0013] Another known aluminum alloy for additive manufacturing (U.S. Patent No.: US2022168811, Publication Date: June 2, 2022) contains the following elements (mass percentage):

[0014] Titanium 0.1 - 15.0

[0015] Scandium 0.1 - 3.0

[0016] Zirconium 0.1 - 3.0

[0017] The rest is aluminum and unavoidable impurities.

[0018] For transition metals, the alloy is prone to precipitation hardening. Some embodiments of the present invention are material compositions with low manufacturability. According to the phase diagram, the alloy is in a region composed entirely of intermetallic compounds and has little ductility. This will lead to cracking.

[0019] Patent CN110791686 (Publication Date: February 14, 2020) discloses an aluminum powder, which is the prototype of the present invention. This patent proposes an aluminum powder alloy for additive technology, with its composition being Al-XY, where X is one of the following elements: Fe; Co; Ni; and Y is one of the following elements: Sc, Ti, and Zr. The atomic content of element X is 0.1-10%, and the atomic content of element Y is 0.1-5%. The rest is aluminum. This material does not require quenching. Due to the large difference in the content of alloying elements, the ductility of some components is extremely poor, and a high content of element X will greatly reduce the corrosion resistance. Summary of the Invention

[0020] The object and technical effect of the present invention are to prepare an aluminum alloy that can be used as a powder for manufacturing parts by additive technology. This alloy has a high strength (not less than 320 MPa) without quenching and artificial aging treatment. The material should also have good 3D printing formability and high corrosion resistance to meet the usage requirements in various corrosion environments.

[0021] To achieve this technical effect, a powder aluminum alloy is proposed. The alloy includes iron and cerium; at least one element from Group A, including manganese, lanthanum, and yttrium; at least one element from Group B, including zirconium, vanadium, chromium, hafnium, and scandium; optionally: hydrogen and magnesium; aluminum and inevitable impurities, including silicon, copper, and zinc; the content of each of the above elements (by weight percentage) is as follows:

[0022] Iron 0.3–1.5,

[0023] Cerium 0.35–2.6,

[0024] Titanium 0.15–0.4;

[0025] At least one element from Group A, where Group A includes:

[0026] Manganese, lanthanum, and yttrium 0.2-2.0 (total or individual);

[0027] At least one element from Group B, where Group B includes:

[0028] Vanadium, chromium, hafnium, and scandium 0.6-1.5 (total or individual);

[0029] Optionally:

[0030] Hydrogen 3-60 ppm

[0031] Magnesium 1.5-4.5; and

[0032] Aluminum and inevitable impurities, including:

[0033] Silicon, copper, and zinc,

[0034] The contents of silicon, copper and zinc are as follows:

[0035] Silicon at most 0.2

[0036] Copper at most 0.05

[0037] Zinc at most 0.05,

[0038] The structure contains an aluminum solid solution, eutectics and nanoscale dispersed phases of not more than 10% of the AlB-type phase, and the dispersed phases are formed by Group B elements.

[0039] "Overall or individual" refers to the content (quantity) of one or more elements (overall) within a given range.

[0040] The preferred contents (by weight percentage) are as follows: iron: 0.3 - 1.0; cerium: 0.35 - 1.0; titanium: 0.15 - 0.25; at least one Group A element: 0.5 - 2.0; at least one Group B element: 0.6 - 0.8; magnesium: 2.0 - 4.0 (by weight percentage). Description of the Drawings

[0041] Figure 1 - Cubic samples manufactured by selective laser melting technology. A typical cube by 3D printing. A: Composition Y; B: Composition No. 3.

[0042] Figure 2 - SEM images of the powder after atomization (spraying) and sieving (SEM stands for scanning electron microscope).

[0043] Figure 3 - Structures of Samples of Compositions 1, 2, 3, A, B. Microstructures of Alloy No. 1 (A), Alloy No. 5 (B) and Alloy No. 6 (C). Detailed Description of the Invention

[0044] It is necessary to add iron within the specified range to form a eutectic structure, thereby reducing the tendency to generate hot brittleness and hot cracks during rapid solidification. When the iron content is lower than this range, a solid-solution-like structure will be formed at a high solidification rate. Since iron enhances the pitting corrosion sensitivity of aluminum, an excessive iron content will reduce its corrosion resistance. Although according to the equilibrium phase diagram, the eutectic point in the aluminum-iron system is in the 1.8 weight percentage concentration region, the recommended range is sufficient to form a eutectic.

[0045] The addition of cerium also contributes to the formation of eutectic structures. Compared with iron, the influence of cerium on corrosion resistance is also much smaller. In addition, cerium can form a separate eutectic phase with aluminum, and can also partially form ternary phases with aluminum, iron and other elements, including migratory phases. The content of cerium is limited to maintain high ductility, while ductility decreases when a large amount of eutectic phases are formed. Cerium dioxide can be used as a substitute for cerium. Rare earth elements and iron in non-metals are also alloying elements, which generally do not significantly change the properties of 3D printed products.

[0046] A specified amount of titanium forms a fine-grained structure in the printed part. The formation of Al3Ti nano-dispersed intermetallic compounds refines the part structure, thus further reducing the sensitivity to hot cracks. Excessive titanium content will form a large number of undesirable intermetallic compounds. In addition, titanium significantly increases the melting point of the alloy, thus requiring overheating treatment and increasing energy consumption.

[0047] Group A elements (Mn (manganese), La (lanthanum), Y (yttrium)) are eutectic-forming additives (they undergo eutectic transformation in the "aluminum corner" region of the phase diagram). These elements can improve the processability of 3D printing and contribute to further precipitation strengthening. This is because the solubility of these elements in aluminum is variable at different temperatures. At high solidification rates, these elements tend to form abnormally supersaturated solid solutions. They precipitate from the solid solution to form binary nano-scale phases, resulting in hardening. Since the solubility of these elements is limited even during non-equilibrium solidification, it is necessary to limit their maximum total content to maintain high ductility and avoid the generation of cold cracks. To maintain high ductility, the content of Group A elements is preferably not more than the eutectic point shown in the equilibrium phase diagram, because the high solidification rate during powder atomization and printing may shift this point.

[0048] As shown in the binary equilibrium phase diagram, most of the Group B elements (Zr (zirconium), V (vanadium), Cr (chromium), Hf (hafnium), Sc (scandium)) are of the peritectic reaction type (except scandium). Their solubilities in aluminum are different, and they form supersaturated solid solutions. When quenched at high speed in the liquid state, the maximum solubility often increases significantly. This is the case for gas atomization and 3D printing. Therefore, during the subsequent annealing process, nano-scale dispersed precipitates are formed. These precipitates have an obvious hardening effect, but the ductility does not decrease significantly. It is very important to limit the maximum content of the additive so that it does not exceed the limit of abnormal solubility, because the intermetallic compounds formed during solidification will have an adverse effect on ductility and fatigue life. Experiments show that it is recommended to limit the maximum content of each element to 2 - 3 times the maximum solubility shown in its equilibrium phase diagram. The alloy should contain both Group A elements and Group B elements, because this can make various dispersoids evenly distributed in the regions near the crystal grains and grain boundaries.

[0049] Oxygen in the powder is the result of atomization. This brings many positive effects. Another effect is the reduction of flammability, which is due to the formation of a protective oxide film on the surface of each particle during the oxidation reaction when the droplets solidify. For the horizontal atomization process, a small amount of added oxygen helps to improve the sphericity of the powder, which is due to the increase in surface tension. Nevertheless, the oxygen content in the powder should be limited to avoid the formation of large oxide inclusions. During the printing process, when the powder is remelted, they may become the concentration of nuclear gas.

[0050] Hydrogen is a functional additive. On the one hand, hydrogen has a positive effect on solid solution strengthening, which is related to the extremely small size of hydrogen atoms and their good migration ability in the aluminum lattice. On the other hand, when the concentration exceeds a certain value determined by experiments, the gas porosity will increase sharply, and the performance of the printed parts will also decline.

[0051] It is very important to limit certain inevitable impurities. Even trace amounts can have an adverse effect on the manufacturability and / or performance of the material. Especially silicon, its reaction with aluminum and iron will increase the thermal crack. In this case, instead of forming a two-phase, a three-phase is formed. Silicon also has an adverse effect on the supersaturation of the aluminum solid solution with certain transition metals (such as scandium). A small amount of copper will increase the tendency of thermal crack. Therefore, its content should be limited. A higher copper content has less impact on the casting performance, but can further enhance the solid solution strengthening effect. However, the effect of copper on the overall corrosion resistance is extremely adverse. Therefore, it is not recommended to use this element as an additive. Zinc is an undesirable element because it is volatile. When the aluminum powder is heated and remelted, zinc will be partially lost, resulting in the entry of impurities, thus increasing the porosity of the printed parts. In addition, if a positive effect of zinc on strength is desired, a higher zinc content is required, which will further increase the specific gravity of zinc.

[0052] Adding magnesium element within the specified range can further improve the strength of the alloy (increase by about 30 - 100 MPa), while not reducing its corrosion resistance or significantly weakening the plasticity. This is because magnesium is embedded in the lattice of the aluminum matrix, increasing the strength of the solid solution. To avoid serious powder contamination during the printing process, it is recommended to limit the content of magnesium. Note that even without adding magnesium, this alloy can provide a unique combination of strength, relative elongation and corrosion resistance.

[0053] This alloy can be used to manufacture powders required for various three-dimensional metal printing technologies.

[0054] Some invention application examples are listed below.

[0055] Example 1

[0056] The production method of the alloy is as follows:

[0057] Grade A8 aluminum (purity 99.8%) is melted and heated to at least 800 °C. Then Fe80F20 and element A (as a double aluminum compound) are added.

[0058] The melt is heated to 850 °C and held for 45 minutes. Then titanium and metallic cerium are added. After removing slag, a flux (2 kg / ton) is placed on the surface of the melt.

[0059] The metal is heated to a temperature at least 20 °C higher than the equilibrium liquidus temperature and held for 30 minutes. The melt is stirred every 15 minutes.

[0060] The dross is removed from the surface of the melt and samples are taken for chemical composition analysis.

[0061] After rapid analysis, the chemical composition is adjusted to meet the specification requirements.

[0062] Then, the melt is atomized into spherical powder through a nozzle. The particle size of the powder is classified into 20 - 63 microns.

[0063] The atomizing gas is a nitrogen - oxygen mixture (oxygen content 3 Vol.%).

[0064] Table 1 lists the chemical composition of the obtained powder.

[0065] Table 1

[0066]

[0067]

[0068] X and Y are elements added to the prototype alloy.

[0069] These powders are made by selective laser melting using an EOS M290 printer (https: / / www.eos.info / en / additive - manufacturing / 3d - printing - metal / eos - metal - systems / eos - m - 290). The laser power is 270 W, with different hatch distances, and the printing speed is between 400 - 1,500 mm / s.

[0070] The microstructure is studied to evaluate the quality of the samples. The slices are prepared according to the standard method. The unetched surface is analyzed using an inverted metallurgical microscope. Cubes of 10x10x10 mm are printed for microstructure study. The criteria for selecting the best printing parameters are crack - free and minimum porosity.

[0071] Under the optimal printing parameters, a cylinder with a diameter of 12 mm and a height of 90 mm was printed on the XY plane. After printing was completed, the part was taken out for heat treatment (annealing). According to GOST 1497 standard, cylindrical samples were cut from the printed part for tensile testing. The results are shown in Table 2.

[0072] Table 2

[0073]

[0074] By comparing the values listed in Table 2, a relatively high relative elongation value and satisfactory strength can be obtained with limited alloying, the optimal selection of alloying elements and their contents. All the tested alloys are suitable for 3D printing without quenching. It is worth noting that the strong over-alloying of alloy Y (Table 2) makes it unsuitable for 3D printing. Figure 1 Cubical samples with and without cracks are shown.

[0075] The typical content of the binary phase of element Y is up to 10% (except for scandium), which has very high strength.

[0076] Example 2

[0077] The method for preparing the aluminum alloy with the same material is similar to Example 1. Before atomization, carnallite flux was applied to the melt surface. After the flux completely covered the metal surface, magnesium was added to the melt. After the magnesium was melted, the melt was thoroughly stirred, the magnesium block was taken out, and the temperature was raised to no less than 40 °C above the liquidus temperature. The melt was atomized by an argon-oxygen jet containing 0.3 Vol.% oxygen. Thus, the Figure 2 shown spherical powders were produced. Their chemical compositions are listed in Table 3. The oxygen content in all the powders in the table varies between 0.01 and 0.3 (in weight percentage), depending on the oxygen content in the atomizing gas stream. The hydrogen content is 3 - 60 ppm.

[0078] Table 3

[0079]

[0080] The powders were sieved into sizes of D50 = 35 μm and D50 = 100 μm. The powders with D50 = 35 μm (particle size 15 - 45 μm) were used to print cylindrical samples for tensile testing. According to GOST 1497 standard, the tensile test was carried out at room temperature, and then annealing treatment was carried out to release stress and precipitate dispersoids. The test results are shown in Table 4. Table 4 also lists the porosity. Figure 3 The typical microstructure of the samples is shown.

[0081] Table 4

[0082]

[0083]

[0084] The addition of magnesium has a positive effect on strength but has little serious effect on relative elongation. However, a high concentration of magnesium will cause a significant decrease in the quality of printed parts, which is related to the fact that magnesium vapor is extremely easy to volatilize from the liquid melt. When the laser beam hits the powder layer, a large number of impurities will be formed in the powder. Therefore, the content of magnesium should also be limited.

[0085] Example 3

[0086] The casting (chemical composition is shown in Table 5) was processed in an induction furnace using A85 grade aluminum and furnace charges as alloy or commercially pure metals. The samples were loaded into the atomizer, melted, heated to a temperature at least 25 °C higher than the equilibrium liquidus temperature, and then atomized with a nitrogen stream. The resulting powder was classified, and the powder with a particle size of 20 - 63 μm was separated, and then cubic samples were printed with an EOS M290 SLM machine. The printing parameters were selected from Example 1. The cube was cut in half along the XZ plane, ground and polished for microstructure study and defect identification. The sections were examined using an inverted metallurgical microscope in bright field without etching. Table 5 summarizes the results of porosity and hot crack detection, and the hydrogen content was 10 - 50 ppm.

[0087] Table 5

[0088]

[0089] Higher impurity content has an adverse effect and reduces manufacturability depending on the alloying elements. Although hot cracks can be suppressed by correctly selecting printing parameters (such as reducing the scanning speed), excessive impurities will have an adverse effect. Another negative effect is that a higher content of charred particles contaminates the top layer of powder, resulting in an increase in porosity.

[0090] Example 4

[0091] Alloy No. 3 (Example 3) is made from Grade A7 aluminum and additives AlTi5, AlY10, AlZr10, and AlCr10. Iron and manganese are commercially pure. Cerium is replaced by dimercury. After aluminum is melted at 830 °C, all additives except dimercury are added. After smelting, it is stirred and precipitated at 870 °C for no less than 30 minutes. Then, a flux and copper pentoxide are added. The melt temperature is raised to 950 °C, the ingot is taken out, sampled for chemical composition analysis, and then atomization begins. The atomization uses a nitrogen-oxygen mixture (oxygen content: 2 vol.%). The oxygen content of the metal powder produced by atomization is 0.075 wt.%. The powder with a particle size of 15 - 63 μm is poured into an EOS M290 machine for printing various components and test samples. The samples are annealed in a forced convection furnace at 350 - 420 °C. Subsequently, the specimens are immersed in a 1N aqueous sodium chloride (NaCl) solution containing 0.3% hydrogen peroxide (H2O2) for 45 days to test their tensile properties and corrosion resistance. The corrosion rate is estimated by weighing the samples before and after testing. The results are shown in Table 6.

[0092] This alloy has high strength and ductility. Its corrosion resistance is similar to that of 6XXX series aluminum alloys. The printed components can be applied in many fields such as aerospace, automotive, and mechanical engineering.

[0093] Table 6

[0094]

[0095] According to the scope of the disclosed claims, legal protection is sought for a powdered aluminum alloy that includes iron and cerium; at least one element from Group A, including manganese, lanthanum, and yttrium; at least one element from Group B, including zirconium, vanadium, chromium, hafnium, and scandium; optionally: hydrogen and magnesium; and aluminum and inevitable impurities, including silicon, copper, and zinc; the content of each of the above elements (by weight percentage) is as follows:

[0096] Iron 0.3 - 1.5,

[0097] Cerium 0.35 - 2.6,

[0098] Titanium 0.15 - 0.4;

[0099] At least one element from Group A, where Group A includes:

[0100] Manganese, lanthanum, and yttrium 0.2 - 2.0 (total or individual);

[0101] At least one element from Group B, where Group B includes:

[0102] Vanadium, chromium, hafnium, and scandium 0.6 - 1.5 (total or individual);

[0103] Optionally:

[0104] Hydrogen 3 - 60 ppm

[0105] Magnesium 1.5 - 4.5; and

[0106] Aluminum and inevitable impurities, including:

[0107] Silicon, copper and zinc, the balance

[0108] wherein the contents of silicon, copper and zinc are as follows:

[0109] Silicon at most 0.2

[0110] Copper at most 0.05

[0111] Zinc at most 0.05,

[0112] The structure contains an aluminum solid solution, eutectics and nanoscale dispersed phases of not more than 10% of the AlB - type phase, and the dispersed phases are formed by group B elements.

[0113] A preferred embodiment is an alloy containing 0.3 - 1.0 wt.% of iron, 0.35 - 1.0 weight percent of cerium, 0.15 - 0.25 wt.% of titanium, 0.5 - 2.0 wt.% of at least one group A element, 0.6 - 0.8 wt.% of at least one group B element and 2.0 - 4.0 wt.% of magnesium. The aluminum alloy powder is produced by gas atomization using nitrogen or argon or a mixture of these gases and oxygen. Therefore, the powder also contains 0.01 - 0.3 wt.% of oxygen. Generally, the average particle size of the powder is 20 - 100 μm. The strength of the parts made from the powder by additive technology after annealing is at least 320 MPa.

[0114] The aluminum alloy of the present invention can be used as a powder to manufacture parts by additive manufacturing technology. It can obtain high strength without quenching or artificial aging. It is suitable for 3D printing and has excellent corrosion resistance in harsh environments.

Claims

1. An aluminum powder alloy comprising iron and cerium; at least one element from Group A including manganese, lanthanum, and yttrium; at least one element from Group B including zirconium, vanadium, chromium, hafnium, and scandium; optionally also: hydrogen and magnesium; and aluminum and inevitable impurities including silicon, copper, and zinc; the contents of the above elements (by weight percentage) are as follows: Iron 0.3–1.5, Cerium 0.35–2.6, Titanium 0.15–0.4; At least one element from Group A, Group A includes: Manganese, lanthanum, and yttrium 0.2 - 2.0 (total amount or individual); At least one element from Group B, Group B includes: Vanadium, chromium, hafnium, and scandium 0.6 - 1.5 (total amount or individual); Optionally: Hydrogen 3 - 60 ppm Magnesium 1.5 - 4.5; and Aluminum and inevitable impurities including: Silicon, copper, and zinc, the balance, wherein the contents of silicon, copper, and zinc are as follows: Silicon at most 0.2 Copper at most 0.05 Zinc at most 0.05 And the structure includes an aluminum solid solution, eutectic, and a nanoscale dispersion of no more than 10% of the AlB-type phase formed by the Group B elements.

2. The aluminum alloy according to claim 1, wherein the aluminum alloy comprises:

3. The aluminum alloy according to claim 2, wherein the aluminum alloy comprises manganese of Group A elements, and zirconium and vanadium of Group B elements.

4. A powder made from the aluminum alloy according to any one of claims 1 - 3, wherein the powder is prepared by gas atomization using nitrogen, argon, or a mixture thereof with oxygen, and the powder further contains 0.01 to 0.3 wt.% of oxygen.

5. The powder according to claim 4, wherein the average particle size of the powder is 20 - 100 μm.

6. A component manufactured from aluminum alloy powder using additive technology, wherein the component is made from the powder of claim 4, and the strength of the component after annealing is not less than 320 MPa.

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