A method for remelting and recycling aluminum alloy coarse powder

Abstract

This invention discloses a method for the remelting and recycling of coarse aluminum alloy powder, primarily for the remelting and recycling of coarse powder generated during the production of powder metallurgy aluminum alloys, powder metallurgy aluminum-based composite materials, and additive manufacturing aluminum alloy parts. The method includes steps such as batching of coarse aluminum alloy powder, remelting to form ingots, mixing furnace charge, atomization powder production, and powder sieving. The fine aluminum alloy powder obtained from powder sieving is used in the final product, while the coarse aluminum alloy powder can be further remelted to form ingots and atomized for powder production, achieving recycling. This method offers advantages such as high purity and uniform composition of the prepared alloy powder, ease of alloy composition adjustment, and ease of engineering and recycling. The remelted fine aluminum alloy powder prepared using this method has comparable composition and purity to the original fine aluminum alloy powder, and can be used for the research and production of high-performance powder metallurgy aluminum alloys, powder metallurgy aluminum-based composite materials, and additive manufacturing aluminum alloy products, meeting the development needs of weight reduction, vibration reduction, and cost reduction in the aerospace field.

Description

Technical Field

[0001] This invention relates to a method for remelting and recycling coarse aluminum alloy powder, belonging to the field of aluminum alloy remelting and recycling technology. Background Technology

[0002] Currently, aluminum alloy scrap recycling mainly focuses on the recycling of cast aluminum alloys and wrought aluminum alloys. Scrap is divided into process waste and final product waste, including coarse aluminum alloy powder generated during the aluminum alloy powder screening process in powder metallurgy, powder metallurgy aluminum-based composites, and additive manufacturing aluminum alloy powder products. There are two methods for recycling scrap: one is downgrading, where aluminum alloy scrap is used for parts in applications with lower quality requirements; the other is remelting for recycling. Currently, the vast majority of aluminum alloy castings and wrought product scrap is recycled through remelting. Statistics show that approximately 35% of aluminum alloy products currently use recycled aluminum, and this figure is projected to reach 50% by 2050 (see: Progress in Materials Science, 2022, 128:100947). The application of aluminum recycling technology can reduce primary aluminum resource consumption and energy consumption, reduce greenhouse gas emissions, and lower the production cost of aluminum alloy products, making it an important direction for achieving green and sustainable development of the aluminum alloy industry.

[0003] Currently, remelting methods are used to recycle process waste and final waste from aluminum alloy castings and wrought products, and are then used in the production of corresponding aluminum alloy castings and wrought products. After remelting, degassing, slag removal, modification, and refining are carried out during the melting process before finally being cast into ingots. This process also solves some defects that may appear inside and on the surface of recycled aluminum ingots.

[0004] In the field of aluminum alloy additive manufacturing, fine aluminum alloy powder can be reused. After the fine aluminum alloy powder used in the additive manufacturing of parts is screened to remove a small amount of coarse particles generated during the additive manufacturing process, the fine powder obtained is mixed with a certain proportion of new aluminum alloy powder of the same composition and particle size. The microstructure and properties of the parts produced by additive manufacturing are similar to those of the parts produced using 100% new aluminum alloy powder (see: Progress in Materials Science, 2022, 128:100947).

[0005] However, there is currently no method for remelting, recycling, or reusing coarse aluminum alloy powder. In recent years, the application of high-performance powder metallurgy aluminum alloys, powder metallurgy aluminum-based composites, and additive manufacturing aluminum alloys in the aerospace field has become increasingly widespread, with their annual production continuously increasing. The aluminum alloy powders used in these materials are typically fine powders, usually -150 mesh, -200 mesh, -250 mesh, -270 mesh, -300 mesh, or -325 mesh aluminum alloy powder products; the yield of these fine powders is typically 30-70%. During the sieving process, these aluminum alloy powder products simultaneously generate coarse powders of +150 mesh, +200 mesh, +250 mesh, +270 mesh, +300 mesh, or +325 mesh, with particle sizes typically ranging from 45 to 200 μm. The proportion of these coarse powders is approximately 30-70%. With the increasing annual production of powder metallurgy aluminum alloys and aluminum-based composite parts, as well as additive manufacturing aluminum alloy parts, the amount of coarse aluminum alloy powder generated during the production process is also increasing. Due to the limited availability of aluminum ore resources and the high resource and energy consumption in producing aluminum ingots, coupled with the high cost of high-performance aluminum alloys, downgrading their use—such as ball milling them into flake powder for formulating functional coatings or disposing of them as waste—would lead to significant cost losses and resource waste. It would also increase the cost of powder metallurgy aluminum alloys, aluminum-based composite materials, and additive manufacturing aluminum alloy products. Furthermore, aluminum alloy powder reacts exothermically when exposed to water or moisture, and is prone to combustion or explosion when exposed to open flames or electrical sparks, posing a certain degree of danger. Therefore, from the perspectives of resource utilization, cost, and safety, there is a pressing need to address the issue of recycling and utilizing coarse aluminum alloy powder. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a method for remelting and recycling aluminum alloy coarse powder. Its purpose is to realize the recycling of aluminum alloy coarse powder generated during the powder screening process of powder metallurgy aluminum alloys, powder metallurgy aluminum-based composite materials, and additive manufacturing aluminum alloy products.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] The steps of this method for remelting and recycling aluminum alloy coarse powder are as follows:

[0009] Step 1: Batch production of coarse powder

[0010] The aluminum alloy coarse powder produced after screening is grouped into batches according to its composition, and the batches are divided into 2xxx, 3xx, 5xxx, 6xxx, 7xxx, and 8xxx series aluminum alloy coarse powders.

[0011] Step 2: Remelting and Ingot Formation

[0012] A medium-frequency induction furnace was used to remelt the same batch of aluminum alloy coarse powder into remelted alloy ingots. For 2xxx, 3xx, 5xxx, 6xxx, and 7xxx series aluminum alloy coarse powder, the melting temperature was 700–900℃ and the holding time was 15–30 min; for 8xxx series aluminum alloy coarse powder, the melting temperature was 1000–1300℃ and the holding time was 15–30 min.

[0013] Step 3: Prepare the mixed furnace charge

[0014] According to the capacity of the atomizing furnace, the above-mentioned remelted alloy ingots and new furnace charge or pre-made alloy ingots of the same composition are mixed in proportion to prepare mixed furnace charge, and the weight percentage of remelted alloy ingots in mixed furnace charge is 20-45%.

[0015] Step 4: Atomization and Powder Production

[0016] The mixed furnace charge is atomized into spherical powder using nitrogen and supersonic gas atomization technology. For mixed furnace charge of 2xxx, 3xx, 5xxx, 6xxx, and 7xxx series aluminum alloys, the atomization temperature is 750–850℃; for mixed furnace charge of 8xxx series aluminum alloys, the atomization temperature is 1000–1300℃.

[0017] Step 5: Powder Sieving

[0018] According to the particle size requirements, the spherical powder produced by atomization is sieved through a 150-mesh, 200-mesh, 250-mesh, 270-mesh, 300-mesh, or 325-mesh stainless steel sieve using a sieve separator. The resulting aluminum alloy fine powder (-150-mesh, -200-mesh, -250-mesh, -270-mesh, -300-mesh, or -325-mesh) and the remaining aluminum alloy coarse powder are used to prepare powder metallurgy aluminum alloys, aluminum-based composite materials, or additive manufacturing aluminum alloy parts. The remaining aluminum alloy coarse powder continues to participate in the remelting and reuse process in steps one through five above.

[0019] In practice, the particle size of the spherical powder produced by atomization in step four is 45–200 μm.

[0020] In practice, the new furnace charge and precast alloy ingots mentioned in step three include pure aluminum, other pure metals, and aluminum-based master alloys.

[0021] The features and advantages of the technical solution of this invention are as follows:

[0022] 1. The prepared alloy powder has high purity. The coarse aluminum alloy powder is produced during the powder screening process and has essentially the same purity as the fine aluminum alloy powder. Furthermore, both the remelting and atomization powdering processes utilize a medium-frequency induction furnace for melting, which, along with thorough stirring, facilitates the flotation of gases and inclusions such as oxide films. Additionally, the nitrogen used in the atomization powdering process has a purity exceeding 99.99%. Therefore, the atomized aluminum alloy powder prepared from remelted coarse aluminum alloy powder has high purity.

[0023] 2. The prepared alloy powder has a uniform composition. Both the remelting and atomization processes of the aluminum alloy coarse powder are carried out using a medium-frequency induction furnace, which facilitates thorough stirring of the alloy melt. Therefore, the aluminum alloy atomized powder prepared from the remelted aluminum alloy coarse powder ingot has a uniform composition.

[0024] 3. Easy adjustment of alloy composition. This method allows for the addition of pure metal or aluminum-based master alloy ingots during the remelting process to adjust the composition of the remelted aluminum alloy ingot. Simultaneously, this method also allows for the adjustment of the aluminum alloy atomized powder composition during the atomization process by adding pure metal or aluminum-based master alloy ingots to meet composition requirements.

[0025] 4. Easy to implement in engineering. Remelting coarse aluminum alloy powder can be done using a medium-frequency induction furnace with a capacity of 50kg to 200kg of aluminum. Furthermore, by batching remelted alloy ingots for atomization production, batches of 500 to 1000kg of remelted aluminum alloy atomized powder can be obtained. This meets the requirements for the engineering production and application of remelted aluminum alloy powder.

[0026] 5. It enables the recycling of aluminum alloy coarse powder. The aluminum alloy coarse powder undergoes a first remelting to produce remelted alloy ingots. These ingots are then mixed with new furnace charge or pre-formed alloy ingots of the same composition in a specific ratio and atomized with gas to obtain atomized aluminum alloy powder. This powder is then screened to obtain fine and coarse aluminum alloy powder. The fine powder is used as the final product powder. The coarse powder undergoes a second remelting to produce remelted alloy ingots. These ingots are then mixed with new furnace charge or pre-formed alloy ingots of the same composition in a specific ratio and atomized with gas to obtain atomized aluminum alloy powder again. This powder is then screened to obtain fine and coarse aluminum alloy powder. The coarse powder is then further remelted and atomized to produce powder, thus achieving the recycling of aluminum alloy coarse powder. Attached Figure Description

[0027] Figure 1 The flowchart illustrates the remelting and recycling of aluminum alloy coarse powder according to the method of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0029] Appendix Figure 1This is a flowchart of the aluminum alloy coarse powder remelting and recycling method of the present invention. It can be seen that the aluminum alloy fine powder produced by powder screening is the product powder, while the aluminum alloy coarse powder can be recycled after batching, remelting and ingot making, mixing furnace charge and atomizing powder making, and powder screening.

[0030] This embodiment takes 2xxx series aluminum alloy as an example. Table 1 shows two examples of preparing Al94.7Cu3.8Mg1.5 (wt.%) aluminum alloy atomized powder by remelting and atomizing aluminum alloy coarse powder and the chemical composition of the powder.

[0031] Table 1

[0032]

[0033] Example 1: Coarse powder of Al94.7Cu3.8Mg1.5 aluminum alloy was remelted into ingots using a medium-frequency induction furnace. The melting temperature was 840℃, the holding time was 15 min, followed by stirring, slag removal, casting, and cooling to obtain the coarse powder remelted alloy ingot. The coarse powder remelted alloy ingot was mixed with a fresh batch of furnace charge (composed of pure aluminum, pure magnesium, and Al-Cu master alloy ingots) of the same composition to form a mixed furnace charge, with the coarse powder remelted alloy ingot accounting for 24% of the mass of the mixed furnace charge. Then, the mixed furnace charge was pulverized using a supersonic gas atomization process, and after sieving, a powder with a micrometer diameter of -100 μm was obtained.

[0034] Example 2: Coarse powder of Al94.7Cu3.8Mg1.5 aluminum alloy was remelted into ingots using a medium-frequency induction furnace. The melting temperature was 840℃, the holding time was 15 minutes, followed by stirring, slag removal, casting, and cooling to obtain the coarse powder remelted alloy ingot. The coarse powder remelted alloy ingot was mixed with a fresh batch of furnace charge (composed of pure aluminum, pure magnesium, and Al-Cu master alloy ingots) of the same composition to form a mixed furnace charge, with the coarse powder remelted alloy ingot accounting for 45% of the mass of the mixed furnace charge. Then, a supersonic gas atomization process was used to pulverize the mixed furnace charge into powder, which was then sieved to obtain powder with a particle size of less than 100 μm.

[0035] Comparative Examples 1 and 2 were prepared by using 100% (freshly prepared furnace charge) and 100% (pre-made alloy ingots), respectively, and the mixed furnace charge was made into powder by supersonic gas atomization process. The powder was then sieved to obtain powder with a particle size of less than 100 μm.

[0036] Samples of the -100 μm powders from Examples 1, 2, Comparative Example 1, and Comparative Example 2 were taken for chemical composition analysis. The contents of Cu, Mg, Si, Fe, and Zn in the powders were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) according to HB 6731-2005; the O content in the powders was determined using an oxygen, nitrogen, and hydrogen analyzer.

[0037] As shown in Table 1, the Cu, Mg, Si, Fe, Zn, and O content of the aluminum alloy powders prepared using [24% (coarse powder remelted alloy ingot) + 76% (fresh furnace charge)] and [45% (coarse powder remelted alloy ingot) + 55% (fresh furnace charge)] in the two examples are basically equivalent to the corresponding element content of the aluminum alloy powders prepared using 100% (fresh furnace charge) and 100% (pre-made alloy ingot). This indicates that the composition of aluminum alloy atomized powder prepared using 24%–45% coarse powder remelted alloy ingot can meet the composition requirements of aluminum alloy powder products.

[0038] Table 2 presents the room temperature tensile properties of extruded bars from four examples and two comparative examples of Al94.7Cu3.8Mg1.5 aluminum alloy prepared by aluminum alloy coarse remelting / powder metallurgy process.

[0039] Table 2

[0040]

[0041]

[0042] In this embodiment, a medium-frequency induction furnace is used to remelt coarse powder of Al94.7Cu3.8Mg1.5 aluminum alloy into remelted alloy ingots. The melting temperature is 840℃, the holding time is 15 minutes, followed by stirring, slag removal, and casting. Simultaneously, the same process is used in a medium-frequency induction furnace to melt new furnace charge (including pure aluminum, pure magnesium, and Al-Cu master alloy ingots) of Al94.7Cu3.8Mg1.5 aluminum alloy into pre-formed alloy ingots. Examples 3 and 4 use Al94.7Cu3.8Mg1.5 coarse powder remelted alloy ingots and new furnace charge of the same composition to prepare two mixed furnace charges, with the remelted alloy ingots accounting for 24% and 45% of the mixed furnace charge by mass, respectively. Examples 5 and 6 use Al94.7Cu3.8Mg1.5 coarse powder remelted alloy ingots and pre-formed alloy ingots to prepare another two mixed furnace charges, with the remelted alloy ingots accounting for 24% and 42% of the mixed furnace charge by mass, respectively. Then, the four mixed furnace charges were separately powdered using a supersonic gas atomization process, and after sieving, powder with a particle size of -100μm was obtained. Using the same process, two comparative examples of -100μm powders with the same composition were prepared: 100% (freshly prepared furnace charge) and 100% (pre-made alloy ingot).

[0043] Four examples and two comparative examples of -100μm Al94.7Cu3.8Mg1.5 powder were respectively encased in aluminum sleeves, with a powder weight of approximately 730g each; then, they were degassed separately. The powder was extruded into Φ25mm rods using a small press, and tensile test specimens, 75mm in length, were then cut from the head and longitudinal end of these rods. Finally, a T4 heat treatment was performed, with the following conditions: solution treatment at 498℃ for 4 hours, followed by quenching in room temperature water; and then natural aging at room temperature for at least 96 hours.

[0044] The above-mentioned sample blocks (T4 state) were longitudinally processed into Φ5mm standard tensile specimens, and their room temperature tensile properties and elastic modulus were tested according to HB 5143-1996. Table 2 shows the room temperature longitudinal tensile properties of extruded bars of Al94.7Cu3.8Mg1.5 aluminum alloy prepared by aluminum alloy rough remelting / powder metallurgy process. In Table 2, σb, σ0.2, and δ5 represent tensile strength, 0.2% conditional yield strength, and elongation, respectively. The comparison shows that the room temperature σb, σ0.2, δ5, and E of the extruded bars prepared by 100% (fresh furnace charge) and 100% (pre-made alloy ingot) reach 390-425 MPa, 265-295 MPa, and 28-33%, respectively. The longitudinal room temperature tensile properties of extruded bars prepared using [24% (coarse powder remelted alloy ingot) + 76% (fresh furnace charge)] and [24% (coarse powder remelted alloy ingot) + 76% (precast alloy ingot)] are comparable, i.e., σb, σ0.2, and δ5 are 425–430 MPa, 280–295 MPa, and 25–27%, respectively. Their strength and elongation are comparable to those of extruded bars prepared using 100% (precast alloy ingot) and 100% (fresh furnace charge). When the proportion of coarse powder remelted alloy ingot increases to 42%–45%, its σb, σ0.2, and δ5 are in the range of 335–450 MPa, 270–335 MPa, and 17–22%, respectively, and the elongation decreases. This may be related to the increase in oxygen content / oxide film in the prepared atomized powder with the increase of the remelted ingot proportion (from 0.038% to 0.042%, see Table 1). However, in general, when the proportion of coarse powder remelted alloy ingot does not exceed 42%, the composition of the prepared atomized powder and the room temperature tensile strength and yield strength of the prepared extruded bars are basically equivalent to those of atomized powder extruded bars prepared using 100% (pre-made alloy ingot) and 100% (new furnace charge).

[0045] The above provides examples of six preferred methods and parameters for the remelting and recycling of aluminum alloy coarse powder. However, the present invention is not limited to the above examples, but can be modified by different hot working forming methods and parameters.

[0046] This invention can be used for the remelting and recycling of coarse powder generated during the production of high-performance powder metallurgy aluminum alloys, powder metallurgy aluminum-based composite materials, and additive manufacturing aluminum alloys for aerospace applications. High-performance powder aluminum alloys, aluminum-based composite materials, and additive manufacturing parts produced using alloy ingots containing remelted coarse powder can be used for platform and support components in aircraft, satellites, etc., meeting the development needs of the aerospace field for weight reduction, vibration reduction, and long service life.

Claims

1. A method for remelting and recycling aluminum alloy coarse powder, characterized in that: The steps of this method are as follows: Step 1: Batch production of coarse powder The aluminum alloy coarse powder produced after screening is grouped into batches according to its composition, and the batches are divided into 2xxx, 3xx, 5xxx, 6xxx, 7xxx, and 8xxx series aluminum alloy coarse powders. Step 2: Remelting and Ingot Formation A medium-frequency induction furnace was used to remelt the same batch of aluminum alloy coarse powder into remelted alloy ingots. For 2xxx, 3xx, 5xxx, 6xxx, and 7xxx series aluminum alloy coarse powder, the melting temperature was 700–900℃ and the holding time was 15–30 min; for 8xxx series aluminum alloy coarse powder, the melting temperature was 1000–1300℃ and the holding time was 15–30 min. Step 3: Prepare the mixed furnace charge According to the capacity of the atomizing furnace, the above-mentioned remelted alloy ingots and new furnace charge or pre-made alloy ingots of the same composition are mixed in proportion to prepare mixed furnace charge, and the weight percentage of remelted alloy ingots in mixed furnace charge is 20-45%. Step 4: Atomization and Powder Production The mixed furnace charge is atomized into spherical powder using nitrogen and supersonic gas atomization technology. For mixed furnace charge of 2xxx, 3xx, 5xxx, 6xxx, and 7xxx series aluminum alloys, the atomization temperature is 750–850℃; for mixed furnace charge of 8xxx series aluminum alloys, the atomization temperature is 1000–1300℃. Step 5: Powder Sieving According to the particle size requirements, the spherical powder produced by atomization is sieved through a 150-mesh, 200-mesh, 250-mesh, 270-mesh, 300-mesh, or 325-mesh stainless steel sieve using a sieve separator. The resulting aluminum alloy fine powder (-150-mesh, -200-mesh, -250-mesh, -270-mesh, -300-mesh, or -325-mesh) and the remaining aluminum alloy coarse powder are used to prepare powder metallurgy aluminum alloys, aluminum-based composite materials, or additive manufacturing aluminum alloy parts. The remaining aluminum alloy coarse powder continues to participate in the remelting and reuse process in steps one through five above.

2. The method for remelting and recycling aluminum alloy coarse powder according to claim 1, characterized in that: The particle size of the spherical powder produced by atomization in step four is 45–200 μm.

3. The method for remelting and recycling aluminum alloy coarse powder according to claim 1, characterized in that: The new furnace charge and precast alloy ingots mentioned in step three include pure aluminum, other pure metals, and aluminum-based master alloys.

Images