A preparation method of an anti-low-temperature aluminum alloy applied to a base station

Abstract

This invention discloses a method for preparing a low-temperature resistant aluminum alloy for use in base stations, comprising the following steps: (1) dissolving aluminum nitrate and ammonium dihydrogen phosphate to form a solution, adjusting the pH to make the solution a slurry; separating the slurry into solid and liquid phases to obtain a filter cake; drying the filter cake to obtain amorphous aluminum phosphate hydrate loose powder; calcining the powder at high temperature to obtain scaly quartz-type aluminum phosphate; crushing the scaly quartz-type aluminum phosphate into aluminum phosphate micro powder; (2) mixing and ball milling the aluminum phosphate micro powder and zinc stearate powder to obtain modified powder; (3) activating the surface of a 3003-O aluminum alloy substrate; (4) adding a dispersion medium to the modified powder and then redispersing it to form a microcrystalline slurry; spraying the microcrystalline slurry onto the surface of the substrate and hot rolling the substrate; step five: stress-relief annealing. This invention provides a method for preparing a low-temperature resistant aluminum alloy for use in base stations, which improves the various properties of 3003-O aluminum alloy at low temperatures.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy processing technology, and more particularly to a method for preparing a low-temperature resistant aluminum alloy for use in base stations. Background Technology

[0002] With the rapid development of communication technology, base stations, as a crucial component of communication networks, bear the heavy responsibility of information transmission and exchange. To ensure the stable operation of base station equipment under various harsh environmental conditions, especially in extremely low-temperature environments, higher requirements are placed on the low-temperature resistance of materials used in base station external equipment. Particularly in northern regions, mountainous areas, and other cold regions, low temperatures pose a serious threat to the stability and lifespan of base station equipment. Therefore, developing materials with excellent low-temperature resistance has become a critical need in the field of communication base stations.

[0003] Currently, most aluminum alloys used in base station external equipment are standard aluminum alloys. These standard aluminum alloys have good mechanical and processing properties, but they exhibit a certain degree of brittleness in low-temperature environments. Especially at sub-zero temperatures (such as -60°C), the impact toughness and tensile strength of aluminum alloy materials will decrease significantly, which limits the service life and stability of base station equipment in cold environments.

[0004] To address this issue, some aluminum alloy materials with strong low-temperature resistance have been developed on the market. However, these aluminum alloy materials with strong low-temperature resistance still have certain drawbacks: Poor low-temperature impact performance: Existing aluminum alloy materials have poor impact toughness at low temperatures, which cannot meet the requirements for long-term stable operation of base stations in extremely cold environments. Especially at sub-zero temperatures, commonly used aluminum alloy materials are prone to brittle fracture, affecting the service life and safety of base station equipment; The surface modification layer is not tightly bonded to the substrate: Some aluminum alloys have their surfaces modified. Although the modification effectively improves the low-temperature performance of the aluminum alloy, the weak bonding force between the surface modification layer and the aluminum alloy substrate makes the modification layer easy to fall off or cause stress concentration during use, which in turn affects the long-term stability of the material. The balance between mechanical properties and low-temperature performance: Existing low-temperature resistant aluminum alloys often sacrifice other mechanical properties such as toughness and ductility when improving low-temperature performance, resulting in unsatisfactory overall performance in practical applications. Summary of the Invention

[0005] In view of this, the present invention proposes a method for preparing a low-temperature resistant aluminum alloy for use in base stations.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a low-temperature resistant aluminum alloy for use in base stations includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to make it a slurry. Perform solid-liquid separation on the slurry and retain the solid filter cake. Remove all by-products from the filter cake. Dry the filter cake to obtain amorphous aluminum phosphate hydrate loose powder. Calcine the powder at high temperature to obtain solid cristobalite-type aluminum phosphate. Crush the cristobalite-type aluminum phosphate into aluminum phosphate micro powder. Step 2: The aluminum phosphate micro powder and zinc stearate powder are mixed and ball-milled to obtain a modified powder. The zinc stearate forms a continuous, homogeneous, and flexible coating layer on the surface of the aluminum phosphate microcrystals. The mass of the zinc stearate is 4% to 5% of the mass of the aluminum phosphate. Step 3: Activate the surface of the 3003-O aluminum alloy; Step 4: Add a dispersion medium to the modified powder and then disperse it to form a microcrystalline slurry; uniformly spray the microcrystalline slurry onto the activated 3003-O aluminum alloy surface, with a surface loading of 14-17 mg / cm³. 2 After spraying, let it stand; preheat the hot rolling mill, raise the temperature of the 3003-O aluminum alloy to 180-190℃ and hold it at that temperature, then rapidly raise the temperature of the 3003-O aluminum alloy to 250-260℃; send the 3003-O aluminum alloy between the upper and lower rolls of the hot rolling mill to complete the rolling process, and the 3003-O aluminum alloy will exhibit a dense surface with metallic luster. Step 5: Stress-relief annealing of 3003-O aluminum alloy.

[0007] Furthermore, in step one, the pH of the solution is adjusted to 4-5.

[0008] Furthermore, in step one, a vacuum filter is used to separate the solid and liquid components of the slurry; In step one, the method for removing the byproducts from the filter cake is as follows: first, wash the filter cake again with deionized water at 50-60℃ and filter it multiple times until the ammonium nitrate byproducts in the filter cake are completely removed; then wash it with anhydrous ethanol and filter it once. In step one, the filter cake is dried in a vacuum drying oven at a temperature of 100-120°C for 6-8 hours. In step one, the calcination method is as follows: the loose powder of amorphous aluminum phosphate hydrate is placed in a high-temperature muffle furnace and heated to 600-650°C at a rate of 5°C, and the calcination time is 2.5-3 hours. In step one, the crushing method is as follows: first, a crusher is used to crush the scaly quartz aluminum phosphate into particles <1mm, and then an air jet mill is used to crush the particles into micro powder with D50=12~20μm.

[0009] Furthermore, in step two, a dry mill is used for ball milling, with a milling speed of 150 rpm and a milling time of 35–45 min.

[0010] Furthermore, in step three, the method for surface activation of the 3003-O aluminum alloy is as follows: the 3003-O aluminum alloy is subjected to alkali washing, acid washing, and then drying. Alkaline washing was performed using a sodium hydroxide solution with a mass fraction of 5%–10%, at a temperature of 50–60°C, for a washing time of 30–60 seconds. Pickling was performed at room temperature using a nitric acid solution with a mass fraction of 15%–25% for 10–30 seconds.

[0011] Furthermore, in step four, the mass ratio of the modified powder to the dispersion medium is 3 to 5:1; In step four, the dispersion medium is isopropanol, and the dispersion is carried out using an ultrasonic disperser with an ultrasonic power of 150-300W and an ultrasonic time of 5-15min.

[0012] Furthermore, the microcrystalline slurry was uniformly sprayed onto the activated 3003-O aluminum alloy surface using a spray gun; In step four, the coated 3003-O aluminum alloy is left to stand at room temperature for 10 to 25 minutes.

[0013] Further, in step four, the rolls of the hot rolling mill are preheated to 150-180°C; the 3003-O aluminum alloy is heated to 180-190°C in a heating furnace and held for 10-20 minutes; then the temperature in another heating furnace is raised to 260°C, and the 3003-O aluminum alloy after holding is quickly placed into another heating furnace. When the 3003-O aluminum alloy reaches 250-260°C, it is sent between the upper and lower rolls of the hot rolling mill.

[0014] Furthermore, in step four, the rolling speed of the hot rolling mill is 0.1–0.2 m / s, the single-pass reduction rate is 8–12%, and the rolling pressure is 100–400 kN.

[0015] Furthermore, in step five, the stress-relief annealing method is as follows: place the 3003-O aluminum alloy in an annealing furnace and heat it to 300-350°C, hold it at that temperature for 1.5-2 hours, and then slowly cool it with the furnace.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention provides a method for preparing a low-temperature resistant aluminum alloy for base stations. During preheating at 190°C, zinc stearate melts into a liquid state and surrounds aluminum phosphate particles. During hot pressing at 260°C, the 3003-O aluminum alloy matrix, in a fluid-like manner, encapsulates aluminum phosphate microcrystals with a flexible layer. During rolling, as rolling pressure is applied, zinc stearate is pressed into the microscopic gaps between the aluminum phosphate microcrystals and the 3003-O aluminum alloy matrix. The hot rolling process generates dislocation strengthening on the surface of the 3003-O aluminum alloy, improving various properties of the 3003-O aluminum alloy at low temperatures, including tensile strength, yield strength, impact toughness, elongation, reduction of area, fracture toughness, and coefficient of linear expansion. The final low-temperature resistant aluminum alloy can be applied in base stations, communication fields, emergency communication metals, and other fields, and is suitable for outdoor applications. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Example 1

[0019] A method for preparing a low-temperature resistant aluminum alloy for use in base stations includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to 4.5. The solution will produce a large amount of white flocculent precipitate, which will then be converted into a slurry. A vacuum filter press is used to separate the solid and liquid components of the slurry, retaining the solid filter cake. First, wash the filter cake with 60℃ deionized water and filter it multiple times until the ammonium nitrate byproduct in the filter cake is completely removed (the conductivity of the filtrate is qualified); then wash it with anhydrous ethanol and filter it once. The filter cake was dried in a vacuum drying oven to obtain amorphous aluminum phosphate hydrate loose powder; the drying temperature was 110℃ and the drying time was 7h. Amorphous aluminum phosphate hydrate loose powder was placed in a high-temperature muffle furnace and heated to 650°C at a rate of 5°C for 3 hours to obtain solid cristobalite-type aluminum phosphate. First, a crusher is used to crush the scaly quartz aluminum phosphate into particles <1mm, and then an air jet mill is used to crush the particles into micro powder with D50=16μm.

[0020] Step 2: Mix aluminum phosphate micro powder and zinc stearate powder, and ball mill them using a dry mill at a speed of 150 rpm for 40 min to obtain modified powder. Zinc stearate forms a continuous, homogeneous, and flexible coating layer on the surface of aluminum phosphate microcrystals. The mass of zinc stearate is 5% of the mass of aluminum phosphate.

[0021] Step 3: The 3003-O aluminum alloy is subjected to alkaline washing, acid washing, and then dried. Alkaline washing was performed using an 8% sodium hydroxide solution at a temperature of 55°C for 45 seconds. Pickling was performed at room temperature using a 20% nitric acid solution for 20 seconds.

[0022] Step 4: Add isopropanol to the modified powder, and then disperse it using an ultrasonic disperser with an ultrasonic power of 200W and an ultrasonic time of 10min to form a microcrystalline slurry; the mass ratio of modified powder to isopropanol is 5:1. Isopropanol not only prevents the zinc stearate layer from peeling off, but also evaporates quickly after spraying; The microcrystalline slurry was evenly sprayed onto the activated 3003-O aluminum alloy surface using a spray gun in multiple passes, with a surface loading of 15 mg / cm³. 2 ; After the 3003-O aluminum alloy has been coated, let it stand at room temperature for 15 minutes until the isopropanol evaporates and disappears. The rolls of the hot rolling mill are preheated to 160°C; the 3003-O aluminum alloy is heated to 190°C in a heating furnace and held for 15 minutes; then the temperature in another heating furnace is raised to 260°C, and the 3003-O aluminum alloy after holding is quickly placed into another heating furnace. Once the 3003-O aluminum alloy reaches 260°C, it is sent between the upper and lower rolls of the hot rolling mill to complete the rolling process. After rolling, the powder on the surface of the 3003-O aluminum alloy disappears, revealing a dense surface with a metallic luster. This is because the microcrystalline slurry particles have been pressed into the surface of the 3003-O aluminum alloy. The hot rolling mill has a rolling speed of 0.15 m / s, a single-pass reduction rate of 10%, and a rolling pressure of 300 kN.

[0023] Step 5: Place the 3003-O aluminum alloy in an annealing furnace and heat it to 300℃. Hold it at that temperature for 2 hours, then slowly cool it in the furnace for stress-relief annealing to obtain the final aluminum alloy. The purpose of high-temperature annealing is to eliminate residual processing stress generated during the rolling and pressing process.

[0024] Finally, the aluminum phosphate microcrystals were forcefully pressed into the surface of the 3003-O aluminum alloy to a depth of about 200-300 μm, and zinc stearate filled the tiny gaps between the aluminum phosphate microcrystals and the 3003-O aluminum alloy.

[0025] The surface activation energy of 3003-O aluminum alloy can remove the oxide film on the surface of the aluminum alloy. The oxide film is brittle and has a weak bonding force with the modified particles.

[0026] The purity of aluminum nitrate and ammonium dihydrogen phosphate is AR grade; the purity of zinc stearate is GR grade; and the purity of isopropanol is AR grade.

[0027] When the ambient temperature drops sharply, the 3003-O aluminum alloy matrix contracts strongly, while the volume of the aluminum phosphate microcrystals embedded in the surface remains almost unchanged. This generates a local compressive stress field in the 3003-O aluminum alloy matrix, which neutralizes the tensile stress caused by cold contraction and effectively prevents the 3003-O aluminum alloy matrix from cold brittle fracture caused by low-temperature thermal stress.

[0028] At -60℃, zinc stearate acts as a buffer between aluminum phosphate microcrystals and the 3003-O aluminum alloy matrix. The long-chain organic components of zinc stearate are partially carbonized / decomposed under high-temperature extrusion, forming a composite transition phase with an elastic modulus between ceramics and metals, thereby achieving a flexible transition. Zinc stearate can also absorb the shear force caused by the mismatch of expansion coefficients through the micro-region movement of molecular chains, ensuring the integrity of the interface.

[0029] During preheating at 190℃, zinc stearate melts into a liquid state, surrounding aluminum phosphate particles. During hot pressing at 260℃, the 3003-O aluminum alloy matrix, resembling a fluid, encapsulates the aluminum phosphate microcrystals with a flexible layer. During rolling, with the application of rolling pressure, zinc stearate is pressed into the microscopic gaps between the aluminum phosphate microcrystals and the 3003-O aluminum alloy matrix. The hot rolling process induces dislocation strengthening on the surface of the 3003-O aluminum alloy, improving its resistance to deformation at low temperatures.

[0030] 3003-O aluminum alloy possesses excellent plasticity and low yield strength. During the hot rolling process of pressing aluminum phosphate microcrystals into the surface of the 3003-O aluminum alloy, the 3003-O aluminum alloy matrix surrounding the aluminum phosphate microcrystals undergoes plastic flow, smoothly dispersing the extrusion stress and effectively improving the toughness and impact resistance of the final aluminum alloy. Furthermore, when the 3003-O aluminum alloy is subjected to load impact, its good plasticity allows for slight displacement of the aluminum phosphate microcrystals without brittle peeling, ensuring that the compressive stress on the surface seals cracks while absorbing impact energy through the deformation of the 3003-O aluminum alloy matrix.

[0031] Emergency communication equipment made from this final aluminum alloy, when subjected to frequent loading and unloading, impacts, and outdoor hot and cold cycles, and hot-pressed at 260℃, shows that the aluminum phosphate microcrystalline modified layer does not easily peel off. This is because the aluminum phosphate microcrystalline modified layer and the 3003-O aluminum alloy may form a trace amount of Al-OP chemical bond coupling. Example 2

[0032] Compared with Example 1, the differences are as follows: the mass of zinc stearate is 4% of the mass of aluminum phosphate; the mass ratio of modified powder to isopropanol is 4:1; and the surface loading of 3003-O aluminum alloy is 17 mg / cm³. 2 .

[0033] Everything else is the same as in Example 1. Example 3

[0034] Compared with Example 1, the differences are as follows: the mass of zinc stearate is 5% of the mass of aluminum phosphate; the mass ratio of modified powder to isopropanol is 3:1; and the surface loading of 3003-O aluminum alloy is 14 mg / cm³. 2 .

[0035] Everything else is the same as in Example 1. Example 4

[0036] Compared with Example 1, the differences are as follows: the mass of zinc stearate is 4.5% of the mass of aluminum phosphate; the mass ratio of modified powder to isopropanol is 5:1; and the surface loading of 3003-O aluminum alloy is 16 mg / cm³. 2 .

[0037] Everything else is the same as in Example 1.

[0038] Comparative Example 1 A method for preparing a low-temperature resistant aluminum alloy for use in base stations includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to 4.5. The solution will produce a large amount of white flocculent precipitate, which will then be converted into a slurry. A vacuum filter press is used to separate the solid and liquid components of the slurry, retaining the solid filter cake. First, wash the filter cake with 60℃ deionized water and filter it multiple times until the ammonium nitrate byproduct in the filter cake is completely removed (the conductivity of the filtrate is qualified); then wash it with anhydrous ethanol and filter it once. The filter cake was dried in a vacuum drying oven to obtain amorphous aluminum phosphate hydrate loose powder; the drying temperature was 110℃ and the drying time was 7h. Amorphous aluminum phosphate hydrate loose powder was placed in a high-temperature muffle furnace and heated to 650°C at a rate of 5°C for 3 hours to obtain solid cristobalite-type aluminum phosphate. First, a crusher is used to crush the scaly quartz aluminum phosphate into particles <1mm, and then an air jet mill is used to crush the particles into micro powder with D50=16μm.

[0039] Step 2: The 3003-O aluminum alloy is subjected to alkaline washing, acid washing, and then dried. Alkaline washing was performed using an 8% sodium hydroxide solution at a temperature of 55°C for 45 seconds. Pickling was performed at room temperature using a 20% nitric acid solution for 20 seconds.

[0040] Step 3: Add isopropanol to the modified powder and then disperse it using an ultrasonic disperser with an ultrasonic power of 200W and an ultrasonic time of 10min to form a microcrystalline slurry; the mass ratio of modified powder to isopropanol is 5:1. The microcrystalline slurry was evenly sprayed onto the activated 3003-O aluminum alloy surface using a spray gun in multiple passes, with a surface loading of 15 mg / cm³. 2 ; After the 3003-O aluminum alloy has been coated, let it stand at room temperature for 15 minutes until the isopropanol evaporates and disappears. The rolls of the hot rolling mill are preheated to 160°C; the 3003-O aluminum alloy is heated to 190°C in a heating furnace and held for 15 minutes; then the temperature in another heating furnace is raised to 260°C, and the 3003-O aluminum alloy after holding is quickly placed into another heating furnace. Once the 3003-O aluminum alloy reaches 260°C, it is sent between the upper and lower rolls of the hot rolling mill to complete the rolling process. After rolling, the powder on the surface of the 3003-O aluminum alloy disappears, revealing a dense surface with a metallic luster. This is because the microcrystalline slurry particles have been pressed into the surface of the 3003-O aluminum alloy. The hot rolling mill has a rolling speed of 0.15 m / s, a single-pass reduction rate of 10%, and a rolling pressure of 300 kN.

[0041] Step 4: Place the 3003-O aluminum alloy in an annealing furnace and heat it to 300℃. Hold it at that temperature for 2 hours, then slowly cool it in the furnace for stress-relief annealing to obtain the final aluminum alloy.

[0042] Comparative Example 2 A method for preparing a low-temperature resistant aluminum alloy for use in base stations includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to 4.5. The solution will produce a large amount of white flocculent precipitate, which will then be converted into a slurry. A vacuum filter press is used to separate the solid and liquid components of the slurry, retaining the solid filter cake. First, wash the filter cake with 60℃ deionized water and filter it multiple times until the ammonium nitrate byproduct in the filter cake is completely removed (the conductivity of the filtrate is qualified); then wash it with anhydrous ethanol and filter it once. The filter cake was dried in a vacuum drying oven to obtain amorphous aluminum phosphate hydrate loose powder; the drying temperature was 110℃ and the drying time was 7h. First, a crusher is used to break the loose powder of amorphous aluminum phosphate hydrate into particles <1mm, and then an air jet mill is used to break the particles into micro powder with D50=16μm.

[0043] Step 2: Mix aluminum phosphate micro powder and zinc stearate powder, and ball mill them using a dry mill at a speed of 150 rpm for 40 min to obtain modified powder. Zinc stearate forms a continuous, homogeneous, and flexible coating layer on the surface of aluminum phosphate particles. The mass of zinc stearate is 5% of the mass of aluminum phosphate.

[0044] Step 3: The 3003-O aluminum alloy is subjected to alkaline washing, acid washing, and then dried. Alkaline washing was performed using an 8% sodium hydroxide solution at a temperature of 55°C for 45 seconds. Pickling was performed at room temperature using a 20% nitric acid solution for 20 seconds.

[0045] Step 4: Add isopropanol to the modified powder, and then disperse it using an ultrasonic disperser with an ultrasonic power of 200W and an ultrasonic time of 10min to form a slurry; the mass ratio of modified powder to isopropanol is 5:1. Isopropanol not only prevents the zinc stearate layer from peeling off, but also evaporates quickly after spraying; The slurry was evenly sprayed onto the activated 3003-O aluminum alloy surface in multiple passes using a spray gun, with a surface loading of 15 mg / cm³. 2 ; After the 3003-O aluminum alloy has been coated, let it stand at room temperature for 15 minutes until the isopropanol evaporates and disappears. The rolls of the hot rolling mill are preheated to 160°C; the 3003-O aluminum alloy is heated to 190°C in a heating furnace and held for 15 minutes; then the temperature in another heating furnace is raised to 260°C, and the 3003-O aluminum alloy after holding is quickly placed into another heating furnace. Once the 3003-O aluminum alloy reaches 260°C, it is sent between the upper and lower rolls of the hot rolling mill to complete the rolling process. After rolling, the powder on the surface of the 3003-O aluminum alloy disappears, revealing a dense surface with a metallic luster. This is because the slurry particles have been pressed into the surface of the 3003-O aluminum alloy. The hot rolling mill has a rolling speed of 0.15 m / s, a single-pass reduction rate of 10%, and a rolling pressure of 300 kN.

[0046] Step 5: Place the 3003-O aluminum alloy in an annealing furnace and heat it to 300℃. Hold it at that temperature for 2 hours, then slowly cool it in the furnace for stress-relief annealing to obtain the final aluminum alloy.

[0047] Comparative Example 3 A method for preparing a low-temperature resistant aluminum alloy for use in base stations includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to 4.5. The solution will produce a large amount of white flocculent precipitate, which will then be converted into a slurry. A vacuum filter press is used to separate the solid and liquid components of the slurry, retaining the solid filter cake. First, wash the filter cake with 60℃ deionized water and filter it multiple times until the ammonium nitrate byproduct in the filter cake is completely removed (the conductivity of the filtrate is qualified); then wash it with anhydrous ethanol and filter it once. The filter cake was dried in a vacuum drying oven to obtain amorphous aluminum phosphate hydrate loose powder; the drying temperature was 110℃ and the drying time was 7h. Amorphous aluminum phosphate hydrate loose powder was placed in a high-temperature muffle furnace and heated to 650°C at a rate of 5°C for 3 hours to obtain solid cristobalite-type aluminum phosphate. First, a crusher is used to crush the scaly quartz aluminum phosphate into particles <1mm, and then an air jet mill is used to crush the particles into micro powder with D50=16μm.

[0048] Step 2: Mix aluminum phosphate micro powder and zinc stearate powder, and ball mill them using a dry mill at a speed of 150 rpm for 40 min to obtain modified powder. Zinc stearate forms a continuous, homogeneous, and flexible coating layer on the surface of aluminum phosphate microcrystals. The mass of zinc stearate is 5% of the mass of aluminum phosphate.

[0049] Step 3: The 3003-O aluminum alloy is subjected to alkaline washing, acid washing, and then dried. Alkaline washing was performed using an 8% sodium hydroxide solution at a temperature of 55°C for 45 seconds. Pickling was performed at room temperature using a 20% nitric acid solution for 20 seconds.

[0050] Step 4: Add isopropanol to the modified powder, and then disperse it using an ultrasonic disperser with an ultrasonic power of 200W and an ultrasonic time of 10min to form a microcrystalline slurry; the mass ratio of modified powder to isopropanol is 5:1. Isopropanol not only prevents the zinc stearate layer from peeling off, but also evaporates quickly after spraying; The microcrystalline slurry was evenly sprayed onto the activated 3003-O aluminum alloy surface using a spray gun in multiple passes, with a surface loading of 15 mg / cm³. 2 ; After the 3003-O aluminum alloy has been coated, let it stand at room temperature for 15 minutes until the isopropanol evaporates and disappears. After the 3003-O aluminum alloy is coated, it is left to stand at room temperature for a full 24 hours to complete the curing process.

[0051] Step 5: Place the cured 3003-O aluminum alloy in an annealing furnace and heat it to 300℃. Hold it at that temperature for 2 hours, then slowly cool it in the furnace for stress-relief annealing to obtain the final aluminum alloy.

[0052] Comparative Example 4 A method for preparing a low-temperature resistant aluminum alloy for use in base stations includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to 4.5. The solution will produce a large amount of white flocculent precipitate, which will then be converted into a slurry. A vacuum filter press is used to separate the solid and liquid components of the slurry, retaining the solid filter cake. First, wash the filter cake with 60℃ deionized water and filter it multiple times until the ammonium nitrate byproduct in the filter cake is completely removed (the conductivity of the filtrate is qualified); then wash it with anhydrous ethanol and filter it once. The filter cake was dried in a vacuum drying oven to obtain amorphous aluminum phosphate hydrate loose powder; the drying temperature was 110℃ and the drying time was 7h. Amorphous aluminum phosphate hydrate loose powder was placed in a high-temperature muffle furnace and heated to 650°C at a rate of 5°C for 3 hours to obtain solid cristobalite-type aluminum phosphate. First, a crusher is used to crush the scaly quartz aluminum phosphate into particles <1mm, and then an air jet mill is used to crush the particles into micro powder with D50=16μm.

[0053] Step 2: Mix aluminum phosphate micro powder and zinc stearate powder, and ball mill them using a dry mill at a speed of 150 rpm for 40 min to obtain modified powder. Zinc stearate forms a continuous, homogeneous, and flexible coating layer on the surface of aluminum phosphate microcrystals. The mass of zinc stearate is 5% of the mass of aluminum phosphate.

[0054] Step 3: The 3003-O aluminum alloy is subjected to alkaline washing, acid washing, and then dried. Alkaline washing was performed using an 8% sodium hydroxide solution at a temperature of 55°C for 45 seconds. Pickling was performed at room temperature using a 20% nitric acid solution for 20 seconds.

[0055] Step 4: Add isopropanol to the modified powder, and then disperse it using an ultrasonic disperser with an ultrasonic power of 200W and an ultrasonic time of 10min to form a microcrystalline slurry; the mass ratio of modified powder to isopropanol is 5:1. Isopropanol not only prevents the zinc stearate layer from peeling off, but also evaporates quickly after spraying; The microcrystalline slurry was evenly sprayed onto the activated 3003-O aluminum alloy surface using a spray gun in multiple passes, with a surface loading of 15 mg / cm³. 2 ; After the 3003-O aluminum alloy has been coated, let it stand at room temperature for 15 minutes until the isopropanol evaporates and disappears. The rolls of the hot rolling mill are preheated to 400℃; the 3003-O aluminum alloy is heated to 190℃ in a heating furnace and held for 15 minutes; then the temperature in another heating furnace is raised to 430℃, and the 3003-O aluminum alloy after holding is quickly placed into another heating furnace. When the 3003-O aluminum alloy reaches 400℃, it is sent between the upper and lower rolls of the hot rolling mill to complete the rolling process. After rolling, the powder on the surface of the 3003-O aluminum alloy disappears, and a dense surface with metallic luster is revealed. This is because the microcrystalline slurry particles have been pressed into the surface of the 3003-O aluminum alloy. The hot rolling mill has a rolling speed of 0.15 m / s, a single-pass reduction rate of 10%, and a rolling pressure of 300 kN.

[0056] Step 5: Place the 3003-O aluminum alloy in an annealing furnace and heat it to 300℃. Hold it at that temperature for 2 hours, then slowly cool it in the furnace for stress-relief annealing to obtain the final aluminum alloy.

[0057] According to GB / T228.2-2015 "Metallic materials - Tensile testing - Part 2: High temperature test method" and ISO6892-3 (Low temperature test), a universal testing machine equipped with a low temperature environment chamber was used to measure the tensile strength, yield strength, elongation, and reduction of area of ​​the specimens after holding them at -60℃ for 30 minutes. The aluminum alloy specimens prepared in Examples 1-4 and Comparative Examples 1-4 were all cut into standard specimens by wire cutting. All specimens were polished with sandpaper to remove cutting burrs (care was taken to preserve the integrity of the modified layer surface). Three parallel specimens were taken from each group, and the average value of the test results was taken.

[0058] According to GB / T229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials", a standard impact specimen with a V-notch (the modified layer is located on the tensile surface behind the notch) was prepared, and the impact toughness was measured. The specimen was placed in a cryogenic cooling medium at -60℃ for 15 min, and the impact test was completed within 5 seconds after removal. The energy absorbed by the specimen at fracture was measured, and the impact toughness value (α) was calculated. k The aluminum alloy samples prepared in Examples 1-4 and Comparative Examples 1-4 were all cut into standard samples by wire cutting. All samples were polished with sandpaper to remove cutting burrs (taking care to preserve the integrity of the modified layer surface). Three parallel samples were taken from each group, and the test results were averaged.

[0059] According to GB / T4161-2007 "Plane Strain Fracture Toughness K of Metallic Materials" IC The test method employed a three-point bending (SEB) specimen. First, fatigue cracks were pre-induced at room temperature. Then, the specimens were placed in a -60°C cryogenic chamber and loaded until fracture. Load-displacement curves were recorded, and the plane strain fracture toughness K was calculated. IC The aluminum alloy samples prepared in Examples 1-4 and Comparative Examples 1-4 were all cut into standard samples by wire cutting. All samples were polished with sandpaper to remove cutting burrs (taking care to preserve the integrity of the modified layer surface). Three parallel samples were taken from each group, and the test results were averaged.

[0060] According to GB / T4339-2008 "Determination of Thermal Expansion Characteristic Parameters of Metallic Materials", a pusher-type thermal dilatometer was used. Cylindrical specimens (or stacked sheet specimens) with a diameter of 6 mm × 25 mm were prepared from the aluminum alloys obtained in Examples 1-4 and Comparative Examples 1-4. The temperature program was set from -60℃ to +40℃ at a heating rate of 5℃ / min, and the operation was carried out under a pure argon protective atmosphere. The curve of specimen length versus temperature was recorded, and the average linear expansion coefficient within this temperature range was calculated. Three parallel sets of specimens were taken from each group, and the average value of the test results was taken.

[0061] The test results of various properties of the samples in Examples 1-4 and Comparative Examples 1-4 are shown in Tables 1 and 2.

[0062] Table 1. Test results of various properties of aluminum alloy samples in Examples 1-4 project Example 1 Example 2 Example 3 Example 4 Tensile strength (MPa) 148.5 148.3 147.1 146.5 Yield strength (MPa) 68.4 68.0 66.9 67.3 Elongation (%) 42.5 41.8 41.5 41.3 Reduction of area (%) 65.0 65.5 65.2 64.4 impact strength (J / cm 2 ) 165.2 163.7 165.4 166.8 fracture toughness (MPa-m 1 / 2 )]> 42.1 42.5 42.9 41.8 <![CDATA[Coefficient of linear expansion (10 -6 / °C)]]> 21.8 21.7 21.5 21.4 Table 2 shows the test results of various properties of the aluminum alloy samples from Comparative Examples 1-4. project Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength (MPa) 135.2 140.1 132.4 125.6 Yield strength (MPa) 59.2 61.5 55.8 50.1 Elongation (%) 26.8 32.4 28.5 18.2 Reduction of area (%) 48.5 55.2 50.1 35.4 <![CDATA[Impact toughness (J / cm 2 )]]> 82.5 110.4 35.6 48.2 <![CDATA[Fracture toughness (MPa·m 1 / 2 ).]]> 31.5 35.8 28.2 22.4 <![CDATA[Coefficient of linear expansion (10 -6 / °C)]]> 22.9 23.1 27.5 23.3 As shown in Table 1, the aluminum alloys prepared in Examples 1-4 have higher tensile strength, yield strength, elongation and reduction of area; the aluminum alloy prepared in Comparative Example 4 has the lowest tensile strength, yield strength, elongation and reduction of area, because the decomposition of zinc stearate produces pores, which reduces the effective cross-sectional area under stress.

[0063] The aluminum alloys prepared in Examples 1-4 maintained a high elongation because the zinc stearate buffer prevented the formation of crack initiation. In contrast, the aluminum alloy prepared in Comparative Example 1 showed a significant decrease in elongation because, without the zinc stearate coating, the particles would pierce the aluminum matrix during stretching, becoming a large number of surface microcrack initiation points, leading to premature fracture of the sample.

[0064] The aluminum alloys prepared in Examples 1-4 exhibited good impact toughness; the aluminum alloy prepared in Comparative Example 3 had the lowest impact toughness because it was not hot-rolled, and the modified powder was only loosely deposited on the surface of the 3003-O aluminum alloy. In the impact test at -60℃, the interface lacked effective physical anchoring, and the modified microcrystalline slurry underwent large-area collapse and detachment upon impact, hence its lowest impact toughness; the aluminum alloy prepared in Comparative Example 4 had relatively low impact toughness because it contained internal pores, had a loose structure, and poor energy absorption capacity.

[0065] The aluminum alloys prepared in Examples 1-4 exhibit higher fracture toughness because the aluminum phosphate particles pressed in during hot rolling in Examples 1-4 are distributed on the surface of the 3003-O aluminum alloy. When cracks attempt to propagate from the surface inward, the strong mechanical anchoring between the aluminum phosphate particles and the 3003-O aluminum alloy matrix, along with the viscoelastic effect of zinc stearate, causes the cracks to deflect when they encounter the hard particles, greatly consuming the energy required for crack propagation. In contrast, the aluminum alloy prepared in Comparative Example 3, which was not hot rolled, has lower fracture toughness because the modified aluminum phosphate powder is only loosely deposited on the surface of the 3003-O aluminum alloy.

[0066] Comparative Example 2 did not include a high-temperature calcination step, i.e., the following step was omitted: Amorphous aluminum phosphate hydrate loose powder was placed in a high-temperature muffle furnace and heated to 650°C at a rate of 5°C for 3 hours to obtain solid cristobalite-type aluminum phosphate. The linear expansion coefficient of amorphous aluminum phosphate differs significantly from that of the aluminum matrix. When the rolling temperature is lowered to -60°C, due to the large temperature difference, high residual thermal tensile stress is generated at the interface between the amorphous particles and the 3003-O aluminum alloy matrix. This internal tensile stress promotes crack propagation, resulting in significantly lower fracture toughness and impact toughness compared to Examples 1-4.

[0067] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-temperature resistant aluminum alloy for use in base stations, characterized in that, Includes the following steps: Step 1: Dissolve aluminum nitrate and ammonium dihydrogen phosphate in deionized water at a molar ratio of 1:1 to form a solution. Adjust the pH of the solution to make it a slurry. Perform solid-liquid separation on the slurry and retain the solid filter cake. Remove all by-products from the filter cake. Dry the filter cake to obtain amorphous aluminum phosphate hydrate loose powder. Calcine the powder at high temperature to obtain solid cristobalite-type aluminum phosphate. Crush the cristobalite-type aluminum phosphate into aluminum phosphate micro powder. Step 2: The aluminum phosphate micro powder and zinc stearate powder are mixed and ball-milled to obtain a modified powder. The zinc stearate forms a continuous, homogeneous, and flexible coating layer on the surface of the aluminum phosphate microcrystals. The mass of the zinc stearate is 4% to 5% of the mass of the aluminum phosphate. Step 3: Activate the surface of the 3003-O aluminum alloy; Step 4: Add a dispersion medium to the modified powder and then disperse it to form a microcrystalline slurry; uniformly spray the microcrystalline slurry onto the activated 3003-O aluminum alloy surface, with a surface loading of 14-17 mg / cm³. 2 After spraying, let it stand; preheat the hot rolling mill, raise the temperature of the 3003-O aluminum alloy to 180-190℃ and hold it at that temperature, then rapidly raise the temperature of the 3003-O aluminum alloy to 250-260℃; send the 3003-O aluminum alloy between the upper and lower rolls of the hot rolling mill to complete the rolling process, and the 3003-O aluminum alloy will exhibit a dense surface with metallic luster. Step 5: Stress-relief annealing of 3003-O aluminum alloy.

2. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step one, the pH of the solution is adjusted to 4-5.

3. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step one, a vacuum filter is used to separate the solid and liquid components of the slurry. In step one, the method for removing the byproducts from the filter cake is as follows: first, wash the filter cake again with deionized water at 50-60℃ and filter it multiple times until the ammonium nitrate byproducts in the filter cake are completely removed; then wash it with anhydrous ethanol and filter it once. In step one, the filter cake is dried in a vacuum drying oven at a temperature of 100-120°C for 6-8 hours. In step one, the calcination method is as follows: the loose powder of amorphous aluminum phosphate hydrate is placed in a high-temperature muffle furnace and heated to 600-650°C at a rate of 5°C, and the calcination time is 2.5-3 hours. In step one, the crushing method is as follows: first, a crusher is used to crush the scaly quartz aluminum phosphate into particles <1mm, and then an air jet mill is used to crush the particles into micro powder with D50=12~20μm.

4. The method for preparing a low-temperature resistant aluminum alloy for base stations according to claim 1, characterized in that, In step two, a dry mill is used for ball milling, with a milling speed of 150 rpm and a milling time of 35–45 min.

5. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step three, the method for surface activation of 3003-O aluminum alloy is as follows: the 3003-O aluminum alloy is subjected to alkali washing, acid washing, and then drying. Alkaline washing was performed using a sodium hydroxide solution with a mass fraction of 5%–10%, at a temperature of 50–60°C, for a washing time of 30–60 seconds. Pickling was performed at room temperature using a nitric acid solution with a mass fraction of 15%–25% for 10–30 seconds.

6. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step four, the mass ratio of the modified powder to the dispersion medium is 3 to 5:

1. In step four, the dispersion medium is isopropanol, and the dispersion is carried out using an ultrasonic disperser with an ultrasonic power of 150-300W and an ultrasonic time of 5-15min.

7. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, Use a spray gun to evenly spray the microcrystalline slurry onto the activated 3003-O aluminum alloy surface; In step four, the coated 3003-O aluminum alloy is left to stand at room temperature for 10 to 25 minutes.

8. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step four, the rolls of the hot rolling mill are preheated to 150-180°C; the 3003-O aluminum alloy is heated to 180-190°C in a heating furnace and held for 10-20 minutes; then the temperature in another heating furnace is raised to 260°C, and the 3003-O aluminum alloy after holding is quickly placed into another heating furnace. When the 3003-O aluminum alloy reaches 250-260°C, it is sent between the upper and lower rolls of the hot rolling mill.

9. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step four, the rolling speed of the hot rolling mill is 0.1 to 0.2 m / s, the single-pass reduction rate is 8 to 12%, and the rolling pressure is 100 to 400 kN.

10. The method for preparing a low-temperature resistant aluminum alloy for use in base stations according to claim 1, characterized in that, In step five, the stress-relief annealing method is as follows: place the 3003-O aluminum alloy in an annealing furnace and heat it to 300-350°C, hold it at that temperature for 1.5-2 hours, and then slowly cool it with the furnace.