Ultra-fine grain refining accelerator for smelting of waste aluminum and its preparation method

Abstract

The present application belongs to the technical field of aluminum alloy refiner, and particularly relates to a super-microcrystalline structure refining speed enhancer for waste aluminum recycling smelting and a preparation method thereof. The preparation method of the super-microcrystalline structure refining speed enhancer for waste aluminum recycling smelting comprises the following steps: S1, uniformly ball-milling and mixing waste aluminum ingot, boron powder, zirconium-aluminum alloy powder and rare earth oxide to obtain mixed raw material powder; S2, pressing and forming the mixed raw material powder in step S1, then wrapping with aluminum foil and drying to obtain the super-microcrystalline structure refining speed enhancer for waste aluminum recycling smelting. When the refining speed enhancer is applied to waste aluminum recycling smelting, the grain size of the aluminum alloy can be reduced, and the microhardness and tensile strength can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the technical field of aluminum alloy refining agents, specifically relating to an ultrafine crystal structure refining and accelerating agent for waste aluminum recycling and smelting, and its preparation method. Background Technology

[0002] Aluminum alloys possess excellent electrical and thermal conductivity, as well as corrosion resistance, making them widely used in machining, aerospace, marine, high-rise buildings, electrical appliances, and automobiles. However, the recycling and smelting of scrap aluminum often encounters the problem of coarse grain structure, which severely impacts the application of aluminum alloys. Therefore, addressing this coarse as-cast structure and improving the overall mechanical properties of the material is crucial. Therefore, grain refinement of aluminum has become an important industrial practice. Common methods for grain refinement include: (1) rapid cooling, which increases the degree of supercooling and improves the nucleation rate by controlling the casting process, such as by using rapid cooling technology, thereby obtaining fine grains; (2) mechanical vibration, which causes dendritic grains to break and thus refines the grains by vibration during the solidification of aluminum alloys; (3) electromagnetic stirring, which causes violent stirring when aluminum alloy melt solidifies in an electric or magnetic field, causing dendrites to break or re-nucleate, thus refining the grains; (4) ultrasonic vibration, which introduces ultrasonic vibration during the solidification of aluminum alloys, causing dendrites to break and thus obtaining a fine grain structure; (5) adding grain refiners, which is a widely used industrial method in the casting process of aluminum alloys.

[0003] Grain refiners, also known as grain refining accelerators, primarily refine the target material by utilizing the second-phase particles within the refiner as heterogeneous nucleation sites. These particles act as nucleation sites, promoting heterogeneous nucleation and inhibiting abnormal grain growth. While grain refiners provide heterogeneous nucleation sites and increase the nucleation rate, their refining effect is influenced by the type, amount, particle size, and uniformity of their distribution. Therefore, these factors need to be carefully controlled to ensure the stability of grain refinement.

[0004] Chinese patent (publication number CN112921203B) discloses a grain refiner for recycled aluminum alloys, its preparation method, and its application. This grain refiner consists of the following components by mass percentage: Ti: 3.8-4.2%, Ni: 0.9-1.1%, C: 0.7-0.9%, Fe≤0.15%, with the balance being Al and other unavoidable impurity elements. The individual content of these other impurity elements is ≤0.05%, and the total content is ≤0.15%. This refiner can transform the coarse dendritic α-Al grains of recycled aluminum alloys into fine, uniform equiaxed or near-spherical grains, solving the problem of difficult grain refinement in recycled aluminum alloys and improving their casting performance and mechanical properties. However, this patent lacks discussion on the effect of the refiner on the grain fineness of the aluminum alloy, and further research is needed on how to improve the hardness of the aluminum alloy by adding the refiner.

[0005] Therefore, there is an urgent need for an ultrafine grain size refining and accelerator for waste aluminum recycling and smelting. By designing the components and introducing rare earth oxides, the effect of the refining and accelerator can be improved, ensuring that when applied to waste aluminum recycling and smelting, it can improve the hardness and strength of aluminum alloys and achieve an ultrafine grain size effect. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an ultrafine grain refiner and its preparation method for waste aluminum recycling and smelting. The invention involves ball milling and uniformly mixing waste aluminum ingots, boron powder, zirconium-aluminum alloy powder, and rare earth oxides to obtain a mixed raw material powder. This mixed raw material powder is then pressed into a mold, wrapped in aluminum foil, and dried to obtain the ultrafine grain refiner. When applied to waste aluminum recycling and smelting, this agent can reduce the grain size of aluminum alloys and effectively improve microhardness and tensile strength.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, this invention provides a method for preparing an accelerator for refining and accelerating the microcrystalline structure of recycled aluminum, comprising the following steps: S1. Ball mill and mix waste aluminum ingots, boron powder, zirconium aluminum alloy powder and rare earth oxides evenly to obtain mixed raw material powder; S2. Press the mixed raw material powder from step S1 into a mold, then wrap it with aluminum foil and dry it to obtain an ultra-fine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting.

[0008] As a preferred technical solution of the present invention, each component in step S1 includes, by weight: 50-60 parts of waste aluminum ingots, 5-10 parts of boron powder, 5-10 parts of zirconium aluminum alloy powder, and 2-4 parts of rare earth oxides.

[0009] As a preferred technical solution of the present invention, the weight parts of the waste aluminum ingots can be 50 parts, 52 parts, 54 parts, 56 parts, 58 parts or 60 parts, etc.

[0010] As a preferred embodiment of the present invention, the boron powder may be in the following weight proportions: 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts.

[0011] As a preferred technical solution of the present invention, the weight parts of the zirconium aluminum alloy powder can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc.

[0012] As a preferred embodiment of the present invention, the rare earth oxides may be present in 2, 3, or 4 parts by weight, etc.

[0013] As a preferred embodiment of the present invention, the zirconium-aluminum alloy powder mentioned in step S1 is Zr from Shanghai Gelin. 50 Al50 The Al content is 45-50%, and the mesh size is 100-200 mesh.

[0014] Zirconium (Zr) has a high melting point and strong deoxidation properties. It is a strong grain refiner and has a strong affinity for aluminum. It also has a good matching relationship with α-Al, making it a microalloying element of great strategic value in aluminum alloys.

[0015] In the zirconium-aluminum alloy powder of the present invention, some Zr combines with Al to form high-melting-point Al3Zr compound particles, allowing α-Al grains to preferentially precipitate on its surface, thereby significantly increasing the number of grains and reducing the grain size. At the same time, some Zr elements are dissolved into the aluminum matrix, and in subsequent processing, nanoscale dispersed phases will precipitate, strongly pinning grain boundaries and inhibiting recrystallization, thereby maintaining a fine grain structure.

[0016] As a preferred embodiment of the present invention, the rare earth oxide in step S1 is selected from one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, cerium oxide, and europium oxide.

[0017] The rare earth oxides of this invention are selected from lanthanum oxide, neodymium oxide, praseodymium oxide, cerium oxide, and europium oxide. Lanthanum oxide and neodymium oxide are preferred, and by controlling the mass ratio of the two, a good compounding effect is achieved, which effectively improves the comprehensive performance of the ultra-fine crystal structure refinement accelerator used in waste aluminum recycling and smelting.

[0018] As a preferred embodiment of the present invention, the rare earth oxides are lanthanum oxide and neodymium oxide.

[0019] As a preferred embodiment of the present invention, the mass ratio of lanthanum oxide to neodymium oxide in the rare earth oxide is (1~3):1, for example, it can be 1:1, 2:1 or 3:1.

[0020] This invention uses lanthanum oxide and neodymium oxide as a composite rare earth oxide. Lanthanum oxide dominates nucleation, melt purification and large-scale grain refinement, while neodymium oxide can strengthen grain boundary pinning, improve thermal stability and strictly control grain growth. The two work together to form multi-component composite nucleation particles, eliminate local abnormal grain coarsening caused by impurities, make the overall grain size more uniform, and effectively reduce the grain size of aluminum alloy.

[0021] As a preferred embodiment of the present invention, the conditions for ball milling and mixing in step S1 are as follows: nitrogen atmosphere; ball diameter of 2-6 mm, for example, 2 mm, 3 mm, 4 mm, 5 mm, or 6 mm; ball-to-material ratio of (5-10):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1; ball milling speed of 200-300 r / min, for example, 200 r / min, 210 r / min, 220 r / min, 230 r / min, 240 r / min, 250 r / min, 260 r / min, 270 r / min, 280 r / min, 290 r / min, or 300 r / min; and ball milling time of 60-80 min, for example, 60 min, 65 min, 70 min, 75 min, or 80 min.

[0022] This invention uses a high-purity nitrogen sealed atmosphere throughout the ball milling process to isolate the air from oxidation and prevent the failure of rare earth and boron components. The diameter of the ball milling beads, the ball-to-material ratio, the ball milling speed, and the ball milling time are strictly controlled to avoid uneven mixing or excessively fine powder agglomeration. This achieves ultra-fine dispersion of multiple components, full interface bonding, avoids segregation, and improves the efficiency of synchronous smelting reaction.

[0023] As a preferred technical solution of the present invention, the pressing conditions in step S2 are as follows: the pressing pressure is 14~16MPa, for example, it can be 14MPa, 15MPa, or 16MPa; the holding time is 100~120s, for example, it can be 100s, 110s, or 120s.

[0024] As a preferred technical solution of the present invention, the drying conditions in step S2 are as follows: the drying temperature is 140~160℃, for example, 140℃, 150℃, or 160℃; the drying time is 40~50min, for example, 40min, 42min, 44min, 46min, 48min, or 50min.

[0025] In a second aspect, the present invention provides a method for preparing an ultrafine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting, as described in the first aspect.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses waste aluminum ingot powder, elemental boron powder, zirconium aluminum alloy powder and compound rare earth oxides as core raw materials to prepare a refining and speed-up agent. Among them, waste aluminum ingots serve as a carrier matrix to improve melt wettability, reduce burn-off, and ensure rapid melting into aluminum liquid; boron components rapidly construct boride nucleation cores, improve the initial nucleation rate, and refine the surface layer and surface grains; zirconium aluminum alloy powder effectively pins grain boundaries and inhibits grain growth; compound rare earth oxides purify aluminum liquid and eliminate needle-like brittle iron phases; multi-element nucleation superposition and strong grain boundary pinning form an ultra-microcrystalline uniform equiaxed crystal structure, optimizing the comprehensive performance of recycled aluminum.

[0027] (2) Some Zr atoms in the zirconium aluminum alloy powder of the present invention are dissolved into the aluminum lattice, which distorts the lattice structure and enhances the matrix’s resistance to indentation deformation. At the same time, it can combine with harmful impurities in waste aluminum to weaken brittle impurity phases and reduce soft segregation areas. The combined effect ensures that the overall hardness uniformity is greatly improved. In addition, by adding zirconium aluminum alloy powder, stable Al3Zr nucleation particles are generated in the melt, which greatly refines the cast grains and increases the grain boundaries to hinder dislocation movement. The nano-sized Al3Zr particles are uniformly dispersed in the grains, pinning dislocations and grain boundaries and inhibiting deformation slip, thereby increasing the tensile deformation resistance of the matrix and improving the tensile strength of the aluminum alloy material.

[0028] (3) In this invention, the lanthanum element in the compound rare earth oxide can preferentially remove non-metallic inclusions in the melt, providing a pure matrix for hardness improvement. The neodymium element precipitate can effectively pin the grain boundaries, resist grain coarsening at high temperature, and ensure that the hardness of the material does not decrease under heating conditions, thus synergistically improving the microhardness of the aluminum alloy. At the same time, the compound rare earth oxide can form fine rare earth intermetallic compounds that are uniformly dispersed in the grain and pin the grain boundaries and dislocations, inhibiting grain slip and crack initiation during tensile deformation, and significantly improving the ultimate tensile strength of the aluminum alloy. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] The sources of some components in the examples and comparative examples are as follows: Boron powder, product number B163016, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Zirconium aluminum alloy powder, Zr 50 Al 50 The Al content is 50%, the mesh size is 200, and it was purchased from Shanghai Gelin Technology Co., Ltd. Lanthanum oxide, product number L431806, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Neodymium oxide, product number N299296, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Cerium oxide, item number C103981, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0031] Example 1 This embodiment provides a method for preparing an ultrafine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting, including the following steps: S1. By weight, mix 60 parts of waste aluminum ingots, 10 parts of boron powder, and 10 parts of zirconium-aluminum alloy powder (Zr). 50 Al 50 Four parts of rare earth oxides (three parts of lanthanum oxide and one part of neodymium oxide) were ball-milled and mixed evenly to obtain a mixed raw material powder. The ball milling conditions were: nitrogen atmosphere, ball bead diameter of 6 mm, ball-to-material ratio of 5:1, ball milling speed of 300 r / min, and ball milling time of 60 min.

[0032] S2. Press the mixed raw material powder from step S1 into a mold (molding pressure is 16MPa, holding time is 100s), then wrap it with aluminum foil and dry it (drying temperature is 160℃, drying time is 40min) to obtain an ultra-fine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting.

[0033] Example 2 This embodiment provides a method for preparing an ultrafine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting, including the following steps: S1. By weight, mix 50 parts of waste aluminum ingots, 5 parts of boron powder, and 5 parts of zirconium-aluminum alloy powder (Zr). 50 Al 50 Two parts of rare earth oxides (one part of lanthanum oxide and one part of neodymium oxide) were ball-milled and mixed evenly to obtain a mixed raw material powder. The ball milling conditions were: nitrogen atmosphere, ball bead diameter of 2 mm, ball-to-material ratio of 10:1, ball milling speed of 200 r / min, and ball milling time of 80 min.

[0034] S2. Press the mixed raw material powder from step S1 into a mold (molding pressure is 14MPa, holding time is 120s), then wrap it with aluminum foil and dry it (drying temperature is 140℃, drying time is 50min) to obtain an ultra-fine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting.

[0035] Example 3 This embodiment provides a method for preparing an ultrafine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting, including the following steps: S1. By weight, 55 parts of waste aluminum ingots, 8 parts of boron powder, and 8 parts of zirconium-aluminum alloy powder Zr 50 Al 50Three parts of rare earth oxides (two parts of lanthanum oxide and one part of neodymium oxide) were ball-milled and mixed evenly to obtain a mixed raw material powder. The ball milling conditions were: nitrogen atmosphere, ball bead diameter of 4 mm, ball-to-material ratio of 8:1, ball milling speed of 250 r / min, and ball milling time of 70 min.

[0036] S2. Press the mixed raw material powder from step S1 into a mold (molding pressure is 15MPa, holding time is 110s), then wrap it with aluminum foil and dry it (drying temperature is 150℃, drying time is 45min) to obtain an ultra-fine crystal structure refinement and acceleration agent for waste aluminum recycling and smelting.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that zirconium aluminum alloy powder is not added in step S1.

[0038] Comparative Example 2 The difference between this comparative example and Example 1 is that the rare earth oxides in step S1 are replaced with 3.5 parts of lanthanum oxide and 0.5 parts of neodymium oxide.

[0039] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S1, the rare earth oxide is replaced by 1 part lanthanum oxide and 3 parts neodymium oxide.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S1, the rare earth oxide is replaced with 4 parts of cerium oxide.

[0041] Comparative Example 5 The difference between this comparative example and Example 1 is that rare earth oxides are not added in step S1.

[0042] Performance testing Waste aluminum is heated to 720°C and melted into recycled aluminum alloy liquid. Then, 0.5% of the refining and accelerators of the examples and comparative examples are added to the recycled aluminum alloy liquid, and after stirring and melting evenly, it is poured into a metal mold to cast recycled aluminum alloy.

[0043] Grain size test: The test shall be conducted in accordance with the requirements of GB / T 6394-2017 Method for determination of average grain size of metals.

[0044] Microhardness test: The microhardness of the examples and comparative examples was measured using an HXD-1000TMC microhardness tester. The test force was 0.9807N and the pressure time was 30s. Five points were measured for each sample and the average value was taken.

[0045] Tensile strength test: The test shall be conducted in accordance with the requirements of GB / T 16865-2023 Specimens and methods for tensile testing of wrought aluminum, magnesium and their alloy processed products.

[0046] The performance test data above are shown in Table 1.

[0047] Table 1 Performance Test Results

[0048] As can be seen from the above, the present invention ball-mills and mixes waste aluminum ingots, boron powder, zirconium aluminum alloy powder and rare earth oxides to obtain a mixed raw material powder, which is then pressed into shape, wrapped in aluminum foil and dried to obtain an ultrafine crystal structure refinement accelerator. This accelerator has a good effect when applied to waste aluminum recycling and smelting.

[0049] Compared to Example 1, in step S1, no zirconium-aluminum alloy powder was added. The lack of zirconium resulted in poor refining and accelerator effects, leading to larger grain sizes and reduced mechanical properties in the recycled aluminum alloy (Comparative Example 1). Compared to Example 1, in step S1, the rare earth oxides were replaced with 3.5 parts lanthanum oxide and 0.5 parts neodymium oxide. Excessive lanthanum oxide usage reduced the refining and accelerator effects, resulting in larger grain sizes and reduced mechanical properties in the recycled aluminum alloy (Comparative Example 2). Compared to Example 1, in step S1, the rare earth oxides were replaced with 1 part lanthanum oxide and 3 parts neodymium oxide. Excessive neodymium usage reduces the refining and accelerator effect, resulting in larger grain size and reduced mechanical properties in the recycled aluminum alloy (Comparative Example 3). Compared to Example 1, in step S1, 4 parts of cerium oxide were used instead of rare earth oxide. Using cerium oxide alone reduced the refining and accelerator effect, resulting in larger grain size and reduced mechanical properties in the recycled aluminum alloy (Comparative Example 4). Compared to Example 1, no rare earth oxide was added in step S1. The lack of rare earth oxide resulted in poor refining and accelerator effect, resulting in larger grain size and reduced mechanical properties in the recycled aluminum alloy (Comparative Example 5).

Claims

1. A method for preparing an ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting, characterized in that, Includes the following steps: S1. Ball mill and mix waste aluminum ingots, boron powder, zirconium aluminum alloy powder and rare earth oxides evenly to obtain mixed raw material powder; S2. Press the mixed raw material powder from step S1 into a mold, then wrap it with aluminum foil and dry it to obtain an ultra-microcrystalline structure refinement and acceleration agent for waste aluminum recycling and smelting.

2. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 1, characterized in that, The components in step S1, by weight, include: 50-60 parts of waste aluminum ingots, 5-10 parts of boron powder, 5-10 parts of zirconium-aluminum alloy powder, and 2-4 parts of rare earth oxides.

3. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 1, characterized in that, The zirconium-aluminum alloy powder mentioned in step S1 is Zr from Shanghai Gelin. 50 Al 50 The Al content is 45-50%, and the mesh size is 100-200 mesh.

4. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 1, characterized in that, The rare earth oxides mentioned in step S1 are selected from one or more of lanthanum oxide, neodymium oxide, praseodymium oxide, cerium oxide, and europium oxide.

5. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 4, characterized in that, The rare earth oxides are lanthanum oxide and neodymium oxide.

6. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 5, characterized in that, The mass ratio of lanthanum oxide to neodymium oxide in the rare earth oxide is (1~3):

1.

7. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 1, characterized in that, The conditions for ball milling in step S1 are: nitrogen atmosphere, ball diameter of 2-6 mm, ball-to-material ratio of (5-10):1, ball milling speed of 200-300 r / min, and ball milling time of 60-80 min.

8. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 1, characterized in that, The conditions for pressing in step S2 are: molding pressure of 14~16MPa and holding time of 100~120s.

9. The preparation method of the ultrafine crystal structure refinement accelerator for waste aluminum recycling and smelting according to claim 1, characterized in that, The drying conditions in step S2 are: drying temperature of 140~160℃ and drying time of 40~50min.

10. A microcrystalline structure refinement and acceleration agent for waste aluminum recycling and smelting, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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