CROSS REFERENCE TO RELATED APPLICATIONS

[001] This application claims the benefit of United States Provisional Patent Application Serial Number 62/691,245, filed June 28, 2018, the content of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[002] This patent application relates to metal alloy products having fine eutectic-type structures and/or incorporating a high temperature vaporizable component within the alloy, and methods for making the same.

BACKGROUND

[003] The Aluminum Association Global Advisory Group defines“aluminum alloys” as “aluminum which contains alloying elements, where aluminum predominates by mass over each of the other elements and where the aluminum content is not greater than 99.00%.” (Global Advisory Group GAG - Guidance, GAG Guidance Document 001, Terms and Definitions, Edition 2009-01, March 2009, § 2.2.2.) An“alloying element” is a“metallic or non-metallic element which is controlled within specific upper and lower limits for the purpose of giving the aluminum alloy certain special properties” (§ 2.2.3). A casting alloy is defined as“alloy primarily intended for the production of castings,” (§ 2.2.5) and a“wrought alloy” is“alloy primarily intended for the production of wrought products by hot and/or cold working” (§ 2.2.5).

SUMMARY OF THE DISCLOSURE

[004] Broadly, the present patent application relates to new aluminum alloy products and other metal alloy products in which one or more components in the alloy product may have a tendency to evaporate during additive manufacturing melting, and methods for making the same. Examples of such components may include metals and alloys containing elements of Zn, Li, and/or Mg. Due to the unique compositions and/or manufacturing processes described herein, the new metal alloy products, such as aluminum alloy products, may realize, for instance, one or more specifically designed, tailored properties of the resulting product and/or preferential regions having tailored properties within the aluminum alloy products (e.g. differing properties tailored at certain locations of a product). Examples of tailored properties include, but are not limited to: (a) fine eutectic-type micro structures or precise desired chemistry, and/or (b) a high volume fraction of discrete intermetallic particles or (c) components having a vaporization temperature below an expected melting temperature anticipated during processing.

[005] In one approach, an alloy product in accordance with the present disclosure may be produced via additive manufacturing. As used herein,“additive manufacturing” means“a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies”, as defined in ASTM F2792-l2a entitled “Standard Terminology for Additively Manufacturing Technologies”. Alloy elements which lose more than 5% of their weight due to vaporization losses (at normal atmospheric pressure) are considered as being susceptible to vaporization. As used herein, evaporative losses during melting refers to losses of alloying elements in the liquid phase during which phase change from liquid to vapor phase occurs stochastically, well below the boiling point of the element. As disclosed herein and throughout the description of the various embodiments detailed herein, the pressurization above a predetermined threshold value (e.g. at least greater than 1 ATM) during additive manufacturing is configured to have a corresponding reduction in evaporative losses of one or more of the alloying elements and/or additions in the feedstock (e.g. which without pressurized AM would have a propensity for evaporation during AM). In some embodiments, the evaporative losses during melting are more significant / severe with alloying elements that have high vapor pressures. In one or more of the embodiments detailed herein, the application of external pressure is configured to proportionately reduce the propensity to have evaporative losses.

[006] During the additive manufacturing process, it is often necessary to superheat the alloy, i.e. raise its temperature above its melting point, which can result in vaporization losses which can affect the final product chemistry, contaminate the insides of the additive manufacture unit, and/or can create unwanted porosity in the product formed via the process. One or more of these effects (e.g. deleterious effects) can readily be reduced, eliminated, and/or prevented by processing in accordance with the various embodiments of the present disclosure. Processing in accordance with the present disclosure can include utilizing any heating technique that is compatible with elevated gas pressurization, such as laser or electron beam heating techniques.

[007] An exemplary method in accordance with the present disclosure of making an additively manufactured body includes the steps of: (a) placing an additive manufacturing feedstock material in a container and pressurizing the container to achieve a pressurized atmosphere maintained at, for example, at least above 1 atmosphere, and preferably above 1.5 atmosphere, corresponding to a pressure above a vaporization threshold pressure required to maintain an additive manufacturing feedstock component material in liquid form when heated above the liquidus temperature of the feedstock material, (b) selectively heating at least a portion of the additive manufacturing feedstock (e.g., via a laser) to a temperature above the liquidus temperature of the particular body to be formed, thereby forming a molten pool, and (c) cooling the molten pool thereby forming a solidified mass, the solidified mass having a correct desired chemistry, and repeating steps b and c for forming another portion of the particular body to be formed until the complete body is formed, whether it be an intermediate or final build body.

BRIEF DESCRIPTION OF THE DRAWING

[008] FIG. 1 is a phase diagram for an exemplary metal alloy additive feedstock that includes aluminum and zinc.

DETAILED DESCRIPTION

[009] The additive manufacturing process in accordance with the present disclosure particularly involves performing the processes in a pressurizable container, i.e. in a pressurized environment. Maintaining a threshold pressure (e.g. elevated pressure) during the manufacturing process is specifically configured to (a) result in maintaining improved alloy chemistry (e.g. in comparing the feedstock chemistry with the AM build chemistry), (b) reduce, prevent, and/or eliminate contamination of the build chamber/container; and/or prevent and/or minimize aberrations (e.g. porosity and/or voids) in the final additively manufactured product. The minimum pressurized atmosphere to be applied within the container during processing in accordance with the present disclosure is calculated by the Clausius-Clapeyron equation for any particular alloy element constituent in order to minimize vaporization of that particular alloy element during additive manufacturing. The Clausius- Clapeyron equation is set forth below: Clau te Qiaf>oyrqq Equation

[0010] The particular pressure maintained within the container during processing step (b) may be varied if necessary so as to obtain a desired chemistry of the alloy body formed, whether it be an intermediate build or a final build body. For example, additive manufacturing involves formation of a desired alloy formulation body in successively deposited layers. Hence a different pressure may be required to confirm desired chemistry/performance at specific locations of the intermediate or final build body. Hence the applied pressure may be varied depending on the particular alloying constituents.

[0011] In another embodiment, a method of making an additively manufactured body includes the steps of: (a) dispersing an additive manufacturing feedstock (e.g., a metal powder) in a pressurizable container (such as a pressurizable bed), wherein the additive manufacturing feedstock comprising a sufficient amount of aluminum, alloying elements, and optional additions to produce an aluminum alloy having a desired chemistry, (b) pressurizing the container (such as a suitable pressurizable bed) to a pressure of at least above one atmosphere and greater than a vaporization threshold pressure of any component of the additive manufacturing feedstock when the feedstock is heated to or above the liquidus temperature for the particular body to be formed (c) selectively heating at least a portion of the additive manufacturing feedstock (e.g., via an energy source such as an electron beam or laser) to a temperature above the liquidus temperature of the particular body to be formed, thereby forming a molten pool, and (d) cooling the molten pool thereby forming a solidified mass, the solidified mass having a fine eutectic-type structure, and repeating the selective heating and cooling steps in the pressurized environment until the complete body is formed.

[0012] In another embodiment, a method of making an additively manufactured body includes the steps of: (a) dispersing an additive manufacturing feedstock (e.g., a metal powder) in a pressurizable container (or other suitable container such as a pressurizable bed), wherein the additive manufacturing feedstock comprising a sufficient amount of aluminum, alloying elements, and optional additions to produce an aluminum alloy having a fine eutectic-type structure, (b) pressurizing the container (or other suitable container such as a pressurizable bed) to a pressure sufficient to preclude or minimize feedstock vaporization losses and selectively prevent or minimize vaporization of a desired alloying constituent when the feedstock is heated to or above the liquidus temperature for the particular body to be formed (c) selectively heating at least a portion of the additive manufacturing feedstock (e.g., via an energy source such as an electron beam or laser) to a temperature above the liquidus temperature of the particular body to be formed, thereby forming a molten pool, and (d) cooling the molten pool thereby forming a solidified mass, and repeating the selective heating and cooling steps in the pressurized environment until the complete intermediate or final build body is formed.

[0013] In one embodiment, the cooling comprises cooling at a rate of at least l000°C per second. In another embodiment, the cooling rate is at least l0,000°C per second. In yet another embodiment, the cooling rate is at least l00,000°C per second. In another embodiment, the cooling rate is at least l,000,000°C per second. Steps (b)-(d) may be repeated as necessary until the body is completed, i.e., until the final additively manufactured body is formed / completed. In some embodiments, the final additively manufactured body is an aluminum alloy which may also generally comprise a fine eutectic-type structure.

[0014] FIG. 1 illustrates a phase diagram for an exemplary metal alloy additive feedstock that includes aluminum and zinc, at normal atmospheric pressure. An exemplary additive feedstock alloys such as an aluminum -zinc alloy has between 1 and 10% zinc. The vaporization threshold, for example, for a 5% zinc alloy is shown to be around 1450 degrees Kelvin. At normal pressure, additive manufacturing methods utilizing a laser melt apparatus produce temperatures far exceeding this vaporization threshold. Consequently at normal pressures the liquid and gas phase would volatilize a greater portion of the zinc compared to the aluminum, resulting in a product having a different composition or chemistry than the feedstock. However, if the additive manufacturing alloy feedstock is first placed in a container that is maintained in a pressurized environment in accordance with the present disclosure, and then melted at a pressure above the vaporization threshold for the zinc component, the resultant molten pool will retain the percentage composition in the liquid phase as it had when solid and is expected to retain desired characteristics in the solid form. Thus, the feedstock composition or chemistry matches and/or substantially corresponds to the chemistry of the additively manufactured product. In some embodiments, the feedstock composition is specifically configured and/or uniquely tailored to promote certain characteristics, via the additive manufacturing process, in the final AM product (e.g. a fine eutectic-type structure, among others). In this instance, volatilization of these components may create one or more deleterious consequences in the final AM part (e.g. chemistry is different from feedstock, cracking in the part, grain structure not in accordance with target grain structure, among others).

[0015] An exemplary method of producing a metal alloy product in accordance with the present disclosure may include operations of (a) selecting an additive manufacturing alloy feedstock that includes a component susceptible to vaporization, (b) placing the additive manufacturing feedstock in a pressurizable container, (c) pressurizing the container to a predetermined pressure of at least two atmospheres and sufficient to preclude vaporization losses from the component thereby minimizing evaporative losses, volatization and vaporization of the component, and (d) selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock. This heating forms a molten pool. Next, the exemplary method includes (e) cooling the molten pool to form a solidified mass, wherein the solidified mass comprises a portion of a final additively manufactured product, and (f) repeating steps (d) and (e) until a desired product is formed. A predetermined pressure of at least two atmospheres is sufficient to maintain the component in liquid form at the liquidus temperature for the additive manufacturing feedstock. In addition, at this pressure and above, evaporative as well as boiling losses will be minimized if not completely prevented, as evaporation is a stochastic process in which phase change occurs randomly. Evaporation is substantively slowed by pressure application. A pressure of at least 2 atmospheres or above, depending on the component, is also believed to be sufficient to prevent porosity in the manufactured product, and/or prevent at least partial vaporization of the component during formation of the molten pool.

[0016] The additive manufacturing feedstock(s) used to create the final additively manufactured body may be of any of the exemplary compositions given below. In some embodiments, the additive manufacturing feedstock is a powder. As used herein,“powder” means a material comprising a plurality of particles suited to produce an aluminum alloy product via additive manufacturing. In the context of additive manufacturing powder feedstocks,“particle” means a minute fragment of matter having a size suitable for use in the powder of the powder bed (e.g., a size from 5 microns to 100 microns). Shavings are types of particles. Suitable methods for producing powders include, for instance, atomization (e.g. gas atomization, plasma atomization), and impingement of a molten liquid (e.g., solidification of an impinging molten metal droplet on a cold substrate), among others. In this aspect, the additive manufacturing powder feedstock may be comprised of any combination of metallic powders, alloy powders, and non-metallic powders (e.g., ceramic powders; intermetallic powders). Furthermore, an additive manufacturing feedstock powder may comprise metallic powders and/or alloy powders, where the particles comprising the metallic powders and/or alloy particles have additions therein (e.g., ceramic materials, among others). In one embodiment, the additive manufacturing feedstock comprises aluminum and at least one other alloying component such as zinc. In another embodiment, the additive manufacturing feedstock comprises at least one addition. In another embodiment, the additive manufacturing feedstock comprises at least one grain refiner. In some embodiments, the grain refiner comprises at least one ceramic material. In some embodiments, the additive manufacturing feedstock is an alloy powder comprised of alloy particles, wherein the alloy particles themselves have non-metallic particles therein. By way of non-limiting example, an additive manufacturing feedstock powder may be comprised of alloy particles, and the alloy particles may include a plurality of non-metallic particles or additions therein, wherein the non- metallic particles or additions have a smaller size than the alloy particles therein.

[0017] For powder additive manufacturing feedstocks, the powder itself may comprise a fine eutectic-type structure, among other characteristics. In this regard, the feedstock itself may realize any of the characteristics of the aluminum alloy products described herein (e.g. one or more of the described characteristics including: equiaxed grains, an average grain size, volume percentage of discrete intermetallic particles, cell size of the cellular structures, spacing between eutectic structures, among others). For instance, the feedstock may comprise equiaxed grains, an average grain size of not greater than 20 microns (i.e., micrometers), discrete intermetallic particles, cellular structures having a cell size of not greater than 1 micron, spacing between eutectic structures of not greater than 1 micron, among others. In this aspect of the present invention, the powders may be produced via any suitable method. In one embodiment, the powder is produced via a process having rapid solidification of the powder. In some embodiments, the aluminum alloy powder is produced via a method having a sufficient solidification rate to facilitate production of the fine eutectic- type structure. In this regard, the aluminum alloy powder may be produced via any one of plasma atomization, gas atomization, or impingement of a molten aluminum alloy (e.g., solidification of an impinging molten metal droplet on a cold substrate). In some embodiments, the powder is configured for use in an additive manufacturing process.

[0018] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure greater than or equal to 1.5 atmospheres, for example, 2 atmospheres, wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure, pressurizing the container to at least at or above 1.5 atmospheres, such as 2 atmospheres, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selectively heating and cooling steps until a desired product is formed.

[0019] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure in a range greater than or equal to 2 atmospheres up to and including 5 atmospheres wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure, pressurizing the container to a range at least or above 2 atmospheres up to about 5 atmospheres, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selective heating and cooling steps until a desired product is formed.

[0020] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure in a range greater than or equal to 2 atmospheres up to and including 10 atmospheres wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure, pressurizing the container to a range at least or above 2 atmospheres up to about 10 atmospheres, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selective heating and cooling steps until a desired product is formed.

[0021] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure in a range greater than or equal to 2 atmospheres up to and including 20 atmospheres wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure, pressurizing the container to a range at least or above 2 atmospheres up to about 20 atmospheres, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selective heating and cooling steps until a desired product is formed.

[0022] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure in a range greater than or equal to 5 atmospheres up to and including 10 atmospheres wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure, pressurizing the container to a range at least or above 5 atmospheres up to about 10 atmospheres, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selective heating and cooling steps until a desired product is formed.

[0023] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure in a range greater than or equal to 10 atmospheres up to and including 20 atmospheres wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure, pressurizing the container to a range at least or above 10 atmospheres up to about 20 atmospheres,, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selective heating and cooling steps until a desired product is formed.

[0024] In another aspect, a method is provided, comprising: additively manufacturing from an aluminum alloy feedstock an aluminum alloy product at a threshold pressure in a range greater than or equal to 2 atmospheres up to and including 20 atmospheres or higher wherein the aluminum alloy feedstock has a first composition comprising a plurality of components, wherein each component has a corresponding vaporization pressure,

pressurizing the container to a range at least or above 2 atmospheres up to about 20 atmospheres or higher, selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; cooling the molten pool to form a solidified mass wherein the solidified mass comprises a portion of a final additively manufactured product, and repeating the selective heating and cooling steps until a desired product is formed.

[0025] In some embodiments, one or more of the alloys of the present disclosure include an alloy having a characteristic or property specifically configured and/or tailored for an end use application (e.g. industrial or commercial). Some non-limiting examples of such alloys include: structural alloys, functional alloys, bulk metallic glasses, and/or combinations thereof. For example, structural alloys can be considered as alloys primarily developed to provide structural support through combination various attributes (e.g. including, but not limited to: strength (both room temperature and/or elevated/high temperatures); toughness, fatigue resistance; corrosion resistance; and/or other characteristics as may be required for a tailored structural use. For example functional alloys can be considered as alloys developed to primarily perform a specific function (e.g. including but not limited to: magnetic performance/capabilities (e.g. high magnetic permeability), chemical storage (e.g. solid state hydrogen storage), tailored effects (e.g. Magneto-Caloric effect, Thermo-electric effect), and/or combinations thereof. For example, bulk metallic glasses can be considered to be alloys developed to primarily provide a particular structure and affiliated/associated benefits thereof (e.g. an amorphous or nano-crystalline structure), where the associated benefits include one or more non-limiting properties like: high hardness, high strength, ease of formability, high coefficient of restitution, and/or combinations thereof.

[0026] A method for producing an alloy product in accordance with this disclosure may comprise (a) placing an additive manufacturing alloy feedstock in a pressurizable container, (b) pressurizing the container to a predetermined pressure of at least above 1 atmosphere up to about 5 atmospheres, (c) selectively heating at least a portion of the additive manufacturing feedstock to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool, (d) cooling the molten pool, thereby forming a solidified mass, wherein the solidified mass comprises a portion of a final additively manufactured product; and (e) repeating steps (c)-(d), thereby producing a final additively manufactured product. The additive manufacturing alloy feedstock preferably comprises aluminum and at least one other alloying component. This additive manufacturing feedstock preferably comprises zinc. The predetermined pressure is preferably above two atmospheres and the predetermined pressure maintains a selected component of the feedstock above a vaporization pressure threshold for the selected component when heated above a liquidus temperature of the manufacturing alloy feedstock and minimizes volatilization and vaporization of the selected component. In an exemplary embodiment the additive manufacturing alloy feedstock comprises aluminum and the selected component is at least one other alloying element. Particularly advantageously the additive manufacturing feedstock alloy comprises zinc. The predetermined pressure is preferably above 1.25 times the vaporization pressure threshold for the selected component.

[0027] A method of producing a metal alloy product in accordance with this disclosure may be viewed as comprising: (a) selecting an additive manufacturing alloy feedstock that includes a component having a predetermined vaporization threshold temperature and pressure; (b) placing the additive manufacturing feedstock in a pressurizable container; (c) pressurizing the container to a pressure above 2 atmospheres and greater than the predetermined vaporization threshold pressure for the component; (d) selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; and (e) cooling the molten pool to form a solidified mass. The solidified mass preferably comprises a portion of a final additively manufactured product. The process preferably includes repeating steps (d) and (e) until a desired product is formed. The predetermined pressure is preferably sufficient to maintain the component in liquid form at the liquidus temperature for the additive manufacturing feedstock. The alloy preferably is an aluminum alloy and the component is preferably zinc. The predetermined pressure is preferably sufficient to preclude vaporization losses in a selected component of the feedstock when the feedstock is heated above a liquidus temperature of the manufacturing alloy feedstock.

[0028] Alternatively an embodiment of the present disclosure may be viewed as a method for producing a metal alloy product comprising: (a) selecting an additive manufacturing alloy feedstock that includes a component having a predetermined vaporization threshold temperature and pressure; (b) placing the additive manufacturing feedstock in a pressurizable container; (c) pressurizing the container to a pressure in a range between 2 and 10 atmospheres and greater than the predetermined vaporization threshold pressure for the component; (d) selectively heating at least a portion of the additive manufacturing feedstock in the container to a temperature above the liquidus temperature of the additive manufacturing feedstock, thereby forming a molten pool; (e) cooling the molten pool to form a solidified mass, wherein the solidified mass comprises a portion of a final additively manufactured product; and (f) repeating steps (d) and (e) until a desired product is formed. The predetermined pressure is preferably sufficient to maintain the component in liquid form at the liquidus temperature for the additive manufacturing feedstock. The alloy is preferably an aluminum alloy and the component preferably is zinc. The predetermined pressure is sufficient to preclude vaporization losses in a selected component of the feedstock when the feedstock is heated above a liquidus temperature of the manufacturing alloy feedstock. Preferably the additive manufacturing alloy feedstock comprises aluminum and the selected component is at least one other alloying element.

[0029] While the present disclosure generally relates to metal alloy products such as aluminum alloy products produced via powder-based additive manufacturing methods in a pressurized environment, in some embodiments, one or more of the below aluminum alloy compositions may also find utility in wire-based additive manufacturing methods in such a pressurized environment. For instance, wire-based additive manufacturing methods that utilize an electron beam and/or plasma arc may be used in the heating steps of the methods described.