Aluminum alloy anti-corrosion sacrificial anode for fresh water and manufacturing method thereof

Abstract

The invention discloses an aluminum alloy anti-corrosion sacrificial anode for fresh water and a manufacturing method thereof, and relates to the technical field of sacrificial anodes. According to the technical scheme, the aluminum alloy comprises, by mass, 12%-18% of zinc, 0.05%-1% of magnesium, 0.05%-0.15% of tin, 0.01%-0.04% of gallium, smaller than 0.1% of iron, smaller than 0.08% of silicon, smaller than 0.005% of copper, 0.05%-0.6% of cerium and the balance aluminum. The problems of existing magnesium alloy and zinc alloy sacrificial anodes in fresh water are solved, and the defects of existing aluminum alloy sacrificial anodes in composition and process are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of sacrificial anodes, and particularly to an aluminum alloy anti-corrosion sacrificial anode for fresh water and a manufacturing method thereof. Background Art

[0002] In the domestic fresh water anti-corrosion market, magnesium alloy sacrificial anodes are mainly used, but such anodes have obvious defects. The self-corrosion rate of magnesium alloy sacrificial anodes in fresh water is high, the current efficiency is usually lower than 50%, and hydrogen evolution corrosion is likely to occur, resulting in unstable protection effects.

[0003] Aluminum alloy sacrificial anodes have excellent electrochemical properties. The theoretical capacity can reach 2980 A·h / kg, and the driving potential can reach 1.1 V (vs. Ag / AgCl reference electrode) in the high electrical conductivity environment of seawater. At the same time, they have the advantages of light weight, high current efficiency, and uniform dissolution characteristics, and are ideal substitutes for magnesium alloy sacrificial anodes. However, the ion concentration in fresh water (such as river water and lake water) (such as Na + , Cl - ) is much lower than that in seawater (usually the electrical conductivity of seawater is 30 - 50 mS / cm, while that of fresh water is only 0.1 - 1 mS / cm), and the ion conduction ability is poor. When the aluminum alloy sacrificial anode undergoes an oxidation reaction, the released Al 3+ is difficult to be quickly diffused away, and it is easy to combine with OH - on the anode surface to form aluminum hydroxide, and further dehydrate to form a dense aluminum oxide passivation film. The mechanism is as follows: Anodic reaction: Al - 3e - → Al 3+ ; Solution reaction: Al 3+ + 3OH - → Al(OH)3↓; Passivation film formation: 2Al(OH)3 → Al2O3 + 3H2O. This leads to a significant decrease in the current conduction efficiency between the aluminum alloy sacrificial anode and the protected metal, a slowdown in the anodic corrosion reaction rate, inhibition of the continuous dissolution of the anode, resulting in a positive shift in potential, insufficient effective protection current density, and possibly unable to meet the cathodic protection potential requirements of metal structures (such as steel materials need to maintain a potential below -0.85 V (CSE) in fresh water), leading to an increased risk of local corrosion.

[0004] Currently, at home and abroad, in order to solve the problems of positive potential shift, formation of oxide film on the surface, uneven dissolution, and reduction of current efficiency of aluminum alloy sacrificial anodes in fresh water environments, the activating elements added are mostly elements harmful to fresh water environment pollution such as Hg, Cd, In, etc., which are closely related to fresh water environmental safety, human health, and fresh water ecological environment. In terms of manufacturing process, the existing production methods mostly adopt the method of metal mold casting, and there is a gap between the aluminum alloy sacrificial anode products and the international advanced level in terms of grain uniformity, and the precise control technology needs to be broken through. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, provide an aluminum alloy sacrificial anode for fresh water and its manufacturing method, solve the problems existing in the existing magnesium alloy and zinc alloy sacrificial anodes in fresh water, and the deficiencies in the composition and process of the existing aluminum alloy sacrificial anodes.

[0006] The technical solution of the present invention is as follows: On the one hand, the present invention provides an aluminum alloy sacrificial anode for fresh water, which is composed of the following components by mass percentage: zinc 12-18%, magnesium 0.05-1%, tin 0.05-0.15%, gallium 0.01-0.04%, iron <0.1%, silicon <0.08%, copper <0.005%, cerium 0.05-0.6%, and the rest is aluminum. Among them, cerium has a purification effect and a preferential oxidation effect. It can combine with some impurity elements in the aluminum alloy to form high-melting-point compounds, reduce the content of segregation phases in the aluminum alloy, reduce local corrosion caused by segregation phases, make the corrosion rate of the anode more uniform, thereby reducing the electrochemical corrosion interference of impurities on the matrix, reducing corrosion caused by microcells, and improving the current efficiency of the anode. Compounds such as oxides and hydroxides formed by cerium on the anode surface can change the structure of the passivation film, make it more porous, inhibit the growth of the passivation film on the surface of the aluminum alloy sacrificial anode, thereby increasing the transmission rate of ions and electrons during the anodic reaction process, enhancing the activation performance of the anode, and facilitating the anodic reaction.

[0007] On the other hand, the present invention provides a manufacturing method for the above-mentioned aluminum alloy sacrificial anode for fresh water, including the following steps: S1 Preheating: Preheat the aluminum ingot to 200-220°C; S2 Melting: Put the preheated aluminum ingot into a crucible, transfer it to a melting furnace for aluminum and heat it until the aluminum ingot is completely melted, then add zinc metal, tin metal, aluminum-magnesium alloy, gallium metal and aluminum-cerium alloy to finally obtain an aluminum alloy melt; S3 Refining and impurity removal: Add a sodium-free flux, and after refining is completed, hold it at 730-760°C for 20-40 minutes for static impurity removal; S4 Directional solidification crystallization: Put the crucible into a crystallizer. First, perform primary cooling through the circulating cooling water in the jacket arranged outside the crystallizer, with a cooling rate of 150-180°C / s; at the same time, perform secondary cooling through the water holes arranged at intervals at the bottom of the crystallizer. The circulating cooling water jets and impacts the surface of the ingot through the water holes, with a cooling rate of 60-80°C / s; at the same time, apply an axial static magnetic field of 0.3-0.5T in the middle of the crystallizer to inhibit dendritic segregation, increase the proportion of equiaxed crystals, reduce the segregation of Sn and Ga elements, and improve the uniformity of anode dissolution; the casting rate is 180-200 mm / min to obtain a 6m long cylindrical ingot; Manufacturing of Aluminum Alloy Sacrificial Anodes for Freshwater Anti-Corrosion: Cut cylindrical ingots into blanks, perform extrusion molding under the conditions of an extrusion ratio of 20 - 60 and an extrusion rate of 0.5 - 1 m / min, and set water mist cooling at the extrusion outlet of the extrusion die with a water mist flow rate of 15 - 20 L / min to achieve rapid cooling, significantly reducing the diffusion distance of alloying elements, reducing elemental segregation between grain boundaries and dendrites. This homogenization effect reduces local micro-galvanic corrosion and inhibits self-corrosion hydrogen evolution, thereby improving current efficiency, and finally obtaining aluminum alloy sacrificial anodes for freshwater anti-corrosion.

[0008] Preferably, in step S2, the crucible is a silicon carbide crucible.

[0009] Preferably, in step S3, the addition amount of the sodium-free flux is 0.2 - 1% of the mass of the aluminum ingot.

[0010] Preferably, in step S3, the sodium-free flux is composed of 15 - 25% potassium fluoroaluminate, 5 - 15% calcium fluoride, 10 - 25% potassium carbonate, 10 - 25% potassium sulfate, 5 - 15% barium sulfate, 15 - 30% potassium chloride, and 3 - 5% anhydrous aluminum chloride by mass percentage.

[0011] Preferably, in step S4, the temperature of the circulating cooling water is 20 - 40 °C.

[0012] Preferably, in step S5, during extrusion molding, the extrusion die is preheated to 320 - 340 °C, and the temperature of the blank is 330 - 360 °C.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The manufacturing method of the aluminum alloy sacrificial anode for freshwater anti-corrosion of the present invention adopts processes such as impurity-free melting, flux purification and impurity removal, gradient water-cooled directional solidification crystallization, and low-temperature high-pressure extrusion molding, effectively solving the problem of grain uniformity of aluminum alloy sacrificial anodes and improving the electrochemical performance of the product. At the same time, the composition of the aluminum alloy sacrificial anode for freshwater anti-corrosion of the present invention does not use harmful elements such as Hg, Cd, and In, meeting environmental protection requirements and solving the pollution problem of existing aluminum alloy sacrificial anodes in freshwater environments. Description of the Drawings

[0014] Figure 1 is the corrosion state diagram of the aluminum alloy sacrificial anode for freshwater anti-corrosion manufactured in Example 1 of the present invention. Detailed Embodiments

[0015] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0016] Example 1 The sacrificial aluminum alloy anode for freshwater corrosion prevention in this embodiment is composed of the following components by mass percentage: zinc 12%, magnesium 0.05%, tin 0.05%, gallium 0.01%, cerium 0.05%, iron 0.06%, silicon 0.03%, copper 0.001%, and the rest is aluminum. Its manufacturing method includes the following steps: S1 Preheating: Preheat the aluminum ingot to 220°C; S2 Melting: Clean the silicon carbide crucible, put the preheated aluminum ingot into the silicon carbide crucible, transfer it to the aluminum melting furnace and heat it to 760°C to completely melt the aluminum ingot, and then add zinc metal, tin metal, aluminum-magnesium alloy, gallium metal and aluminum-cerium alloy according to the formula ratio to finally obtain an aluminum alloy melt; S3 Refining and impurity removal: Add a sodium-free flux, which accounts for 0.5% of the mass of the aluminum ingot. The sodium-free flux is composed of potassium fluoroaluminate 25%, calcium fluoride 15%, potassium carbonate 15%, potassium sulfate 15%, barium sulfate 10%, potassium chloride 15% and anhydrous aluminum chloride 5% by mass percentage; after refining, keep it at 730°C for 20 minutes for static impurity removal; S4 Directional solidification and crystallization: Put the silicon carbide crucible into the crystallizer, first perform primary cooling through the circulating cooling water in the jacket outside the crystallizer, the temperature of the circulating cooling water is 20°C, and the cooling rate is 150°C / s; at the same time, perform secondary cooling through the water holes arranged at intervals at the bottom of the crystallizer. The circulating cooling water jets and impacts the surface of the ingot through the water holes, and the cooling rate is 80°C / s. At the same time, apply an axial static magnetic field of 0.5T in the middle of the crystallizer; the casting rate is 200mm / min to obtain a 6m long cylindrical ingot; S5 Manufacturing the sacrificial aluminum alloy anode for freshwater corrosion prevention: Cut the cylindrical ingot into blanks, and perform extrusion molding under the conditions that the extrusion die is preheated to 320°C, the blank temperature is 330°C, the extrusion ratio is 20, and the extrusion rate is 0.5m / min. And water mist cooling is set at the extrusion outlet of the extrusion die, and the water mist flow rate is 20L / min to obtain the sacrificial aluminum alloy anode for freshwater corrosion prevention.

[0017] Example 2 The sacrificial aluminum alloy anode for freshwater corrosion prevention in this embodiment is composed of the following components by mass percentage: zinc 18%, magnesium 1%, tin 0.15%, gallium 0.04%, cerium 0.6%, iron 0.07%, silicon 0.04%, copper 0.001%, and the rest is aluminum. Its manufacturing method includes the following steps: S1 Preheating: Preheat the aluminum ingot to 200°C; S2 Melting: Clean the silicon carbide crucible, put the preheated aluminum ingot into the silicon carbide crucible, transfer it to the aluminum melting furnace and heat it to 760°C to completely melt the aluminum ingot, and then add zinc metal, tin metal, aluminum-magnesium alloy, gallium metal and aluminum-cerium alloy according to the formula ratio to finally obtain an aluminum alloy melt; S3 Refining and impurity removal: Add a sodium-free flux, which accounts for 1% of the mass of the aluminum ingot. The sodium-free flux is composed of potassium hexafluoroaluminate at 15% by mass, calcium fluoride at 5% by mass, potassium carbonate at 25% by mass, potassium sulfate at 10% by mass, barium sulfate at 15% by mass, potassium chloride at 25% by mass, and anhydrous aluminum chloride at 5% by mass. After refining, hold at 760 °C for 40 min for static impurity removal; S4 Directional solidification crystallization: Place the silicon carbide crucible in the crystallizer. First, perform primary cooling through the circulating cooling water in the jacket outside the crystallizer. The temperature of the circulating cooling water is 40 °C, and the cooling rate is 180 °C / s. At the same time, perform secondary cooling through the water holes arranged at intervals at the bottom of the crystallizer. The circulating cooling water jets and impacts the surface of the ingot through the water holes, and the cooling rate is 60 °C / s. At the same time, apply an axial static magnetic field of 0.3 T in the middle of the crystallizer. The casting rate is 180 mm / min to obtain a 6-m-long cylindrical ingot; S5 Manufacturing an aluminum alloy sacrificial anode for freshwater corrosion prevention: Cut the cylindrical ingot into blanks, and perform extrusion molding under the conditions that the extrusion die is preheated to 340 °C, the blank temperature is 360 °C, the extrusion ratio is 60, and the extrusion rate is 1 m / min, and water mist cooling is provided at the extrusion outlet of the extrusion die, and the water mist flow rate is 15 L / min to obtain an aluminum alloy sacrificial anode for freshwater corrosion prevention.

[0018] Example 3 The aluminum alloy sacrificial anode for freshwater corrosion prevention in this example is composed of the following components by mass percentage: zinc 15%, magnesium 0.55%, tin 0.1%, gallium 0.025%, cerium 0.3%, iron 0.08%, silicon 0.03%, copper 0.002%, and the rest is aluminum. Its manufacturing method includes the following steps: S1 Preheating: Preheat the aluminum ingot to 210 °C; S2 Melting: Clean the silicon carbide crucible, place the preheated aluminum ingot in the silicon carbide crucible, transfer it to the aluminum melting furnace and heat it to 760 °C to completely melt the aluminum ingot, and then add zinc metal, tin metal, aluminum-magnesium alloy, gallium metal, and aluminum-cerium alloy according to the formula ratio to finally obtain an aluminum alloy melt; S3 Refining and impurity removal: Add a sodium-free flux, which accounts for 0.6% of the mass of the aluminum ingot. The sodium-free flux is composed of potassium hexafluoroaluminate at 18% by mass, calcium fluoride at 6% by mass, potassium carbonate at 13% by mass, potassium sulfate at 25% by mass, barium sulfate at 5% by mass, potassium chloride at 30% by mass, and anhydrous aluminum chloride at 3% by mass. After refining, hold at 740 °C for 30 min for static impurity removal; S4 Directional solidification crystallization: Place the silicon carbide crucible into the crystallizer. First, perform primary cooling through the circulating cooling water in the jacket outside the crystallizer. The temperature of the circulating cooling water is 30°C, and the cooling rate is 160°C / s. At the same time, perform secondary cooling through the water holes arranged at intervals at the bottom of the crystallizer. The circulating cooling water jets and impacts the surface of the ingot from the water holes, and the cooling rate is 70°C / s. Meanwhile, apply an axial static magnetic field of 0.4 T in the middle of the crystallizer. The casting rate is 190 mm / min to obtain a 6-m long cylindrical ingot. S5 Fabricate the aluminum alloy sacrificial anode for freshwater corrosion prevention: Cut the cylindrical ingot into blanks, and perform extrusion molding under the conditions that the extrusion die is preheated to 330°C, the blank temperature is 350°C, the extrusion ratio is 40, and the extrusion rate is 0.8 m / min. And water mist cooling is set at the extrusion outlet of the extrusion die, and the water mist flow rate is 18 L / min to obtain the aluminum alloy sacrificial anode for freshwater corrosion prevention.

[0019] Comparative Example 1 The difference from Example 1 is that after the refining and impurity removal in step S3, it is directly poured into the metal mold, and after natural cooling and forming, the aluminum alloy sacrificial anode for freshwater corrosion prevention is obtained.

[0020] Comparative Example 2 The difference from Example 1 is that in step S3, a sodium-containing flux composed of 40% KCl, 35% NaCl, 5% CaF2, 8% Na3AlF6, 8% Mg2N3, 3.5% C2Cl6, and 0.5% CeF3 by mass percentage is used to replace the sodium-free flux in Example 1.

[0021] Comparative Example 3 The difference from Example 1 is that in step S4, only primary cooling is performed, and secondary cooling is not performed.

[0022] Comparative Example 4 The difference from Example 1 is that in step S4, no axial static magnetic field is applied.

[0023] Comparative Example 5 The difference from Example 1 is that in step S5, the blank temperature is 450°C and the extrusion ratio is 10.

[0024] Comparative Example 6 The difference from Example 1 is that in step S5, water mist cooling is not set at the extrusion outlet of the extrusion die.

[0025] Comparative Example 7 The difference from Example 1 is that the addition amounts of various raw materials are adjusted so that the finally obtained sacrificial aluminum alloy anode for freshwater anti-corrosion is composed of the following components by mass percentage: zinc 12%, magnesium 0.03%, tin 0.02%, gallium 0.005%, iron 0.07%, silicon 0.04%, copper 0.001%, cerium 0.01%, and the balance is aluminum.

[0026] Comparative Example 8 The difference from Example 1 is that the addition amounts of various raw materials are adjusted so that the finally obtained sacrificial aluminum alloy anode for freshwater anti-corrosion is composed of the following components by mass percentage: zinc 12%, magnesium 1.5%, tin 0.2%, gallium 0.05%, iron 0.08%, silicon 0.04%, copper 0.002%, cerium 1%, and the balance is aluminum.

[0027] Comparative Example 9 The difference from Example 1 is that the addition amounts of various raw materials are adjusted so that the finally obtained sacrificial aluminum alloy anode for freshwater anti-corrosion is composed of the following components by mass percentage: zinc 12%, magnesium 0.05%, tin 0.05%, gallium 0.01%, iron 0.06%, silicon 0.03%, copper 0.002%, and the balance is aluminum.

[0028] Comparative Example 10 Comparative Example 10 uses the magnesium alloy sacrificial anode AZ31B of Zibo Deyuan Metal Materials Co., Ltd.

[0029] Performance tests were carried out on the sacrificial aluminum alloy anodes for freshwater anti-corrosion manufactured in Examples 1-3 and Comparative Examples 1-9 and the magnesium alloy sacrificial anode of Comparative Example 10. The tests were carried out with reference to "ASTM G97-18(2022), Standard Test Method for Laboratory Evaluation of Magnesium Sacrificial Anode Specimens for Subsurface Applications". The test results are shown in Table 1: Table 1 Performance test results of the sacrificial anodes in Examples 1-3 and Comparative Examples 1-10

[0030] It can be seen from the test data in Table 1 that the performance indexes of the sacrificial aluminum alloy anodes for freshwater anti-corrosion manufactured in Examples 1-3 are better than those of the sacrificial aluminum alloy anodes for freshwater anti-corrosion manufactured in Comparative Examples 1-9 and the magnesium alloy sacrificial anode of Comparative Example 10. And by Figure 1It can be seen that the sacrificial aluminum alloy anode for freshwater corrosion prevention manufactured in Example 1 has uniform corrosion and the corrosion products are easily detached. In Comparative Example 1, after refining and impurity removal, direct metal die casting was carried out, resulting in a high inclusion content in the melt and coarse grains, leading to non-uniform corrosion and fast self-corrosion. In Comparative Example 2, the sodium-containing flux easily forms Na-Mg compounds with magnesium in the aluminum alloy, resulting in an increase in the flux viscosity, and the residual sodium will adsorb hydrogen, increasing the risk of sodium embrittlement, triggering intergranular corrosion, and reducing the current efficiency. In Comparative Example 3, only primary cooling was carried out without secondary cooling. For aluminum alloys with a high zinc content, due to their complex composition, the solidification range becomes wider, and the liquid phase between dendrites is "sealed" to produce shrinkage porosity, and the dendrite segregation is serious. In Comparative Example 4, when no axial static magnetic field was applied, the grain size of the ingot was coarse, the dendrite segregation was serious, and the defect rates such as cracks and pores increased significantly, which led to slag inclusion and crack defects and non-uniform corrosion in the follow-up. In Comparative Example 5, the extrusion temperature was too high and the extrusion ratio was too small. The high temperature promoted the segregation of elements such as zinc and tin at the grain boundaries to form coarse β phases (Al-Zn), and the small extrusion ratio led to the segregation of impurity elements such as Fe and Si at the grain boundaries to form cathode phases such as Al6Fe and Al5FeSi. These phases, as cathode phases, would accelerate local corrosion. In Comparative Example 6, no water mist cooling was provided at the extrusion outlet, and the anode would cool down slowly through natural heat dissipation, resulting in significant grain growth. The coarse grains would cause "local preferential corrosion" during the dissolution of the anode, reducing the current efficiency. In Comparative Example 7, the contents of magnesium, tin, gallium, and cerium in the sacrificial aluminum alloy anode for freshwater corrosion prevention were too low, resulting in potential shift, insufficient activation ability, tissue deterioration, and non-uniform corrosion, reducing the current efficiency. In Comparative Example 8, the contents of magnesium, tin, gallium, and cerium in the sacrificial aluminum alloy anode for freshwater corrosion prevention were too high, resulting in abnormal potential, tissue deterioration, increased self-corrosion, and enhanced passivation tendency, reducing the current efficiency. In Comparative Example 9, the sacrificial aluminum alloy anode for freshwater corrosion prevention did not contain cerium, resulting in an increase in the segregation degree of elements such as zinc and tin between dendrites, forming a continuous β phase (Al-Zn) network, an increase in the formation of brittle phases (such as Al3Fe), a larger difference in local corrosion current density, and a reduction in the current efficiency. In Comparative Example 10, during the casting of the magnesium alloy sacrificial anode, dendrite segregation was easily generated, and Al was enriched at the grain boundaries to form a continuous network phase, leading to intergranular corrosion and a reduction in the current efficiency. In summary, the manufacturing method and composition design of the sacrificial aluminum alloy anode for freshwater corrosion prevention of the present invention can effectively improve the performance of the sacrificial aluminum alloy anode for freshwater corrosion prevention and meet the requirements of freshwater corrosion prevention.

Claims

1. Aluminum alloy sacrificial anode for freshwater corrosion prevention, characterized in that, It consists of the following components by mass percentage: zinc 12 - 18%, magnesium 0.05 - 1%, tin 0.05 - 0.15%, gallium 0.01 - 0.04%, iron < 0.1%, silicon < 0.08%, copper < 0.005%, cerium 0.05 - 0.6%, and the balance is aluminum.

2. The manufacturing method of the aluminum alloy sacrificial anode for freshwater anti-corrosion according to claim 1, characterized in that, It includes the following steps: S1 Preheating: Preheat the aluminum ingot to 200 - 220 °C; S2 Melting: Put the preheated aluminum ingot into a crucible, transfer it to an aluminum melting furnace and heat until the aluminum ingot is completely melted, then add zinc metal, tin metal, aluminum - magnesium alloy, gallium metal and aluminum - cerium alloy to finally obtain an aluminum alloy melt; S3 Refining and impurity removal: Add a sodium - free flux. After refining, hold it at 730 - 760 °C for 20 - 40 min for static impurity removal; S4 Directional solidification crystallization: Put the crucible into a crystallizer. First, conduct primary cooling through the circulating cooling water in the jacket outside the crystallizer, with a cooling rate of 150 - 180 °C / s; at the same time, conduct secondary cooling through the water holes arranged at intervals at the bottom of the crystallizer. The circulating cooling water jets and impacts the surface of the ingot through the water holes, with a cooling rate of 60 - 80 °C / s; at the same time, apply an axial static magnetic field of 0.3 - 0.5 T in the middle of the crystallizer; the casting rate is 180 - 200 mm / min to obtain a 6 - m - long cylindrical ingot; S5 Manufacturing an aluminum alloy sacrificial anode for freshwater corrosion prevention: Cut the cylindrical ingot into blanks, perform extrusion molding under the conditions of an extrusion ratio of 20 - 60 and an extrusion rate of 0.5 - 1 m / min, and set water mist cooling at the extrusion outlet of the extrusion die, with a water mist flow rate of 15 - 20 L / min to obtain an aluminum alloy sacrificial anode for freshwater corrosion prevention.

3. The manufacturing method of the aluminum alloy sacrificial anode for fresh water as described in claim 2, characterized in that, In step S2, the crucible is a silicon carbide crucible.

4. The manufacturing method of the aluminum alloy sacrificial anode for fresh water as claimed in claim 2, characterized in that, In step S3, the addition amount of the sodium - free flux is 0.2 - 1% of the mass of the aluminum ingot.

5. The manufacturing method of the aluminum alloy sacrificial anode for fresh water as described in claim 2, characterized in that, In step S3, the sodium - free flux consists of potassium hexafluoroaluminate 15 - 25% by mass percentage, calcium fluoride 5 - 15%, potassium carbonate 10 - 25%, potassium sulfate 10 - 25%, barium sulfate 5 - 15%, potassium chloride 15 - 30% and anhydrous aluminum chloride 3 - 5%.

6. The manufacturing method of the aluminum alloy sacrificial anode for fresh water corrosion prevention according to claim 2, characterized in that, In step S4, the temperature of the circulating cooling water is 20 - 40 °C.

7. The manufacturing method of the sacrificial aluminum alloy anode for freshwater anti-corrosion according to claim 2, characterized in that In step S5, during extrusion molding, the extrusion die is preheated to 320 - 340 °C and the blank temperature is 330 - 360 °C.

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