A gradient aluminum sacrificial anode material for marine corrosion protection and its preparation method

Abstract

This invention discloses a gradient aluminum sacrificial anode material for marine corrosion protection and its preparation method, belonging to the technical field of sacrificial anode materials for marine corrosion protection. The preparation method includes the following steps: S1, melting A21 aluminum alloy raw material and Sn particles at a temperature of 720-780℃ and stirring until homogeneous to obtain a uniform melt; S2, pouring the molten melt into a centrifuge mold for centrifugal casting, followed by air cooling to obtain a gradient aluminum alloy sacrificial anode. The aluminum alloy sacrificial anode of this invention forms a continuously varying gradient structure, with the discharge activity gradually changing with the gradient structure. The highly active outer layer can provide a large polarization current in the early stages of polarization. As the cathode polarization process progresses and the outer layer of the anode dissolves, the protective current output by the orderly activated gradient aluminum sacrificial anode gradually decreases, reducing the amount of sacrificial anode material used and achieving long-term cathodic protection for marine steel structures and efficient utilization of the sacrificial anode material.

Description

Technical Field

[0001] This invention relates to a gradient aluminum sacrificial anode material for marine corrosion protection and its preparation method, belonging to the technical field of sacrificial anode materials for marine corrosion protection. Background Technology

[0002] Due to the harshness of the marine environment, marine engineering equipment is prone to corrosion, and its operation, maintenance, and upkeep are challenging. Sacrificial anode cathodic protection is an effective method for preventing corrosion of large steel structures such as offshore wind turbine towers. Aluminum anodes are widely used in the field of corrosion protection for marine engineering equipment due to their advantages such as low density, high capacitance, and readily available raw materials. As is well known, aluminum is the most abundant metallic element on Earth, with a high theoretical specific capacity, suitable electrode potential, and relatively low specific gravity. Compared with magnesium sacrificial anodes, it outputs the most electrical charge for the same weight, has a longer service life, and can significantly reduce costs.

[0003] In current practical applications of sacrificial anodes, the number of anodes is typically increased to maintain the high current density required to induce cathodic polarization in the protected component. However, once the cathodic polarization stabilizes, the current required for cathodic protection decreases. At this point, too many anodes can lead to excessive current, resulting in significant waste of anode material and increased costs. Furthermore, it can place excessive additional loads on large steel structures, potentially causing safety accidents.

[0004] The mismatch between the protective current requirements of steel structure cathodes under different polarization states and the discharge capacity of conventional sacrificial anodes has been alleviated to some extent with the application of encapsulated composite sacrificial anodes. Encapsulated composite sacrificial anodes, commonly used in marine engineering corrosion protection, are fabricated in stages using two different materials for the outer shell and inner core: first, a high-current-efficiency alloy is used to prepare the sacrificial anode core, and then a high-drive-potential magnesium / aluminum / zinc alloy is coated on the outside of the alloy core to achieve rapid initial polarization of the protected cathode. According to literature reports, when Mg-Mn-coated Al-Zn-In-Mg-Ti composite sacrificial anodes are used for cathodic protection of circulating water pipelines in nuclear power plants, they significantly reduce the amount of anodes used, saving corrosion protection costs while reducing water resistance within the pipeline. CN100457975C provides a double-layer aluminum alloy composite sacrificial anode, where the outer low-potential aluminum alloy provides a larger polarization current, and the inner high-efficiency aluminum alloy provides a suitable sustaining current, reducing the amount of sacrificial anodes used in cathodic protection projects by 40%. However, the smelting of the magnesium alloy outer layer of magnesium-clad aluminum anodes requires high precision and involves significant losses. The incomplete cladding layer and susceptibility to cracking in clad composite sacrificial anodes severely restrict their widespread application. Furthermore, difficulties in controlling the composition of the transition zone and drastic fluctuations in the driving potential negatively impact the anode's performance. Moreover, the two-step preparation process for composite sacrificial anodes is cumbersome, increasing overall costs. Therefore, there is an urgent need to develop marine corrosion-resistant sacrificial anode materials that are easy to prepare, have stable driving potentials, and whose output current adapts to the polarization process of the protected steel structure. Summary of the Invention

[0005] To address the aforementioned problems of cumbersome preparation of encapsulated composite sacrificial anodes and mismatch between service performance and cathodic protection requirements, this invention proposes a gradient aluminum sacrificial anode material for marine corrosion protection that features stable driving potential and adaptive output current as the polarization process of the protected steel structure progresses.

[0006] Meanwhile, this invention provides a method for preparing gradient aluminum sacrificial anode material for marine corrosion protection. This method obtains a gradient sacrificial anode with a highly activated outer layer and a highly efficient inner layer through centrifugal casting, and achieves the gradient activation effect without the need for the activation element Ga.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection includes the following steps:

[0009] S1, A21 aluminum alloy raw material and Sn particles are melted and stirred evenly at a temperature of 720-780℃ to obtain a uniform melt;

[0010] S2, the molten melt is poured into the mold of a centrifuge for centrifugal casting. After the process is completed, it is air-cooled to obtain a gradient aluminum alloy sacrificial anode.

[0011] A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection includes the following steps:

[0012] 1) Place the dried A21 aluminum alloy and 0.05-0.1 wt.% pure zinc raw material in a muffle furnace for melting at a temperature of 750-780℃. After the raw material is completely melted, stir thoroughly and let stand for at least 10 minutes, skimming off the slag. Lower the furnace temperature to 720℃, add 0.5-1 wt.% hexachloroethane refining agent, and refine the melt for 5-7 minutes until no bubbles emerge from the melt. Skim off the surface slag. After drying 0.05-0.15 wt.% pure tin wrapped in aluminum foil and replenishing the lost slag with 0.01-0.015 wt.% pure indium, 0.1-0.2 wt.% pure magnesium, and 0.1-0.15 wt.% Al-5.0 wt.% Ti master alloy, quickly press it into the lower layer of the molten aluminum and stir at a rate of 15-25 rpm for 3-5 minutes, then let stand for at least 5 minutes.

[0013] 2) Preheat the centrifuge mold to 100-200°C, pour the molten material into the mold after it has been set, and start the centrifuge at the same time to make the mold rotate. Gradually increase the speed from 0 rpm to 100-200 rpm within 15-30 seconds, and after 1-2 minutes increase the speed to 600-800 rpm and maintain it for 5 minutes. After centrifugation, remove the mold and air cool it to obtain the gradient aluminum anode.

[0014] In step 1), the drying temperature of the aluminum foil-wrapped pure tin and the replenished pure indium, pure magnesium, and Al-5.0wt.%Ti master alloy is 140-150℃.

[0015] The muffle furnace is a well-type muffle furnace.

[0016] The composition and proportions of A21 aluminum alloy are: 5.0 wt.% Zn, 0.036 wt.% In, 0.74 wt.% Mg, 0.02 wt.% Ti and the balance Al.

[0017] Step 2) is replaced with: preheat the centrifuge mold to 200°C, pour the molten material into the centrifuge mold after it has been set, and start the centrifuge at the same time to make the mold rotate. Within 45 seconds, the speed is gradually increased from 0 rpm to 300 rpm. After 2 minutes, the speed is increased to 1200 rpm and maintained for 3 minutes. The speed is then reduced to 800 rpm and maintained for 5 minutes. After centrifugation, the mold is removed and air-cooled to obtain a gradient aluminum anode.

[0018] The gradient aluminum sacrificial anode material for marine corrosion protection obtained by the preparation method of the present invention contains a continuous and obvious microstructure gradient, and the grain size of the inner, middle and outer sides of the gradient aluminum sacrificial anode material for marine corrosion protection varies continuously between 57.1 μm and 109.8 μm.

[0019] The initial coupling current density of the gradient aluminum sacrificial anode material for marine corrosion protection is 157.6 μA·cm. -2 ~358.3 μA·cm -2 .

[0020] Application of gradient aluminum sacrificial anode materials for marine corrosion protection in marine engineering equipment corrosion protection.

[0021] Offshore engineering equipment includes offshore wind turbine towers, offshore wind farms, or oil platforms.

[0022] A marine engineering equipment includes the gradient aluminum sacrificial anode material for marine corrosion protection according to the present invention.

[0023] In this invention, the synergistic effect of S1 and S2 has a crucial impact on improving the discharge performance of the fabricated gradient aluminum sacrificial anode. The introduction of Sn element in S1 can promote the activation of the aluminum alloy sacrificial anode, thereby improving the current output capability. At the same time, S2 can realize the gradient change of the internal structure of the sacrificial anode, thereby achieving a continuous and uniform change in the output current.

[0024] As a further improvement of the present invention, the centrifuge mold is first heated to 100-200°C. On the one hand, the preheating temperature of the mold affects the cooling rate of the melt, which in turn affects the formation of the alloy gradient structure. On the other hand, it makes the composition of the sacrificial anode surface uniform and smooth, avoiding the negative impact of defects such as segregation, porosity, and microcracks on the service performance of the sacrificial anode.

[0025] As a further improvement of this invention, the centrifuge mold begins to rotate simultaneously with the injection of the uniformly stirred molten metal. As the pouring process progresses, the centrifuge mold speed gradually increases from 0 rpm to the set speed, with a maximum speed of 800 rpm or 1200 rpm. The total centrifugation time is 7–10 minutes. Injecting the molten metal before starting centrifugation ensures a clear gradient structure between the inner and outer layers of the graded aluminum sacrificial anode. The gradient structure of the sacrificial anode can be adjusted by modifying the centrifuge speed and the total centrifugation time.

[0026] The sacrificial anode material prepared by this invention contains a continuous and distinct microstructure gradient, with grain size varying continuously between 57.1 μm and 109.8 μm in different locations, and a stable driving potential between -1.13 and -1.11 V. SCE When connected to a carbon steel cathode of the same size, the initial coupling current density of free polarization is increased to approximately 7 times the steady-state sustaining current, reaching 2.1 times that of a conventional A21 aluminum anode (an increase of approximately 117.6%), with a self-regulating range.

[0027] ~358.3 μA·cm -2 .

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] This invention modifies aluminum alloys by adding Sn, promoting alloy activation. More importantly, the centrifugal casting process creates a continuously varying gradient microstructure in the aluminum alloy sacrificial anode. The discharge activity gradually changes with the gradient microstructure. The highly active outer layer provides a large polarization current in the early stages of polarization. As the cathode polarization process progresses and the outer layer of the anode dissolves, the protective current output by the orderly activated gradient aluminum sacrificial anode gradually decreases, reducing the amount of sacrificial anode material used. This achieves long-term cathodic protection for marine steel structures and efficient utilization of sacrificial anode material. Furthermore, the centrifugal casting method for preparing gradient aluminum sacrificial anodes offers advantages such as controllable gradient microstructure, convenient production and use, and environmental friendliness and economy.

[0030] This invention discloses a gradient aluminum sacrificial anode material for marine corrosion protection and its preparation method. The method employs a one-time casting process, utilizing centrifugal force to control the microstructure gradient of the aluminum anode casting, thereby achieving a gradient change in its protective current. The prepared gradient A21-Sn aluminum anode exhibits a continuous grain size variation between 57.1 μm and 109.8 μm in different locations, with a stable driving potential between -1.13 and -1.11 V. SCE When connected to a carbon steel cathode of the same size, the initial coupling current density of free polarization is increased to approximately 7 times the steady-state sustaining current, reaching 2.1 times that of conventional A21 aluminum anodes. The protective current density output at different locations of the gradient aluminum anode varies continuously, perfectly matching the current density requirements at different stages of the polarization process of the protected cathode. Therefore, it has advantages such as high anode utilization, excellent protection effect, and environmentally friendly and economical preparation and use, making it particularly suitable for corrosion control of large marine steel structures. Attached Figure Description

[0031] Figure 1 This is a low-magnification cross-sectional photograph of the centrifugally cast A21-0.15Sn-2 gradient sacrificial anode of Embodiment 4 of the present invention;

[0032] Figure 2 These are metallographic photographs of different parts of the conventionally cast and centrifugally cast A21-0.15Sn-2 alloy obtained in Example 4 of this invention;

[0033] Figure 3 These are scanning electron microscope images of different parts of the conventionally cast and centrifugally cast A21-0.15Sn-2 alloy obtained in Example 4 of the present invention;

[0034] Figure 4 This is a coupling current curve of different parts of the A21-0.15Sn-2 alloy under the same conditions of conventional casting and centrifugal casting in Example 4 of the present invention;

[0035] Figure 5 These are the dissolved morphology images of different parts of the A21-0.15Sn-2 alloy after coupled discharge under the same conditions in Example 4 of this invention, using conventional casting and centrifugal casting. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0037] Example 1

[0038] A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection includes the following steps:

[0039] 1) Weigh the raw materials using A21 aluminum alloy (5.0 wt.% Zn, 0.036 wt.% In, 0.74 wt.% Mg, 0.02 wt.% Ti, Al balance), pure zinc (99.95 wt.%), pure tin (99.99 wt.%), pure indium (99.99 wt.%), pure magnesium (99.95 wt.%), and Al-5.0 wt.% Ti master alloy raw materials. A21 and 0.05wt.% pure zinc raw materials dried at 150℃ were placed in a pit-type muffle furnace for smelting at 750℃. After the raw materials were completely melted, they were stirred thoroughly and allowed to stand for 10 minutes, and the scum was skimmed off. The furnace temperature was lowered to 720℃, and 0.5wt.% hexachloroethane refining agent was added. The melt was refined for 5 minutes until no bubbles emerged from the melt, and the surface scum was skimmed off. 0.15wt.% pure tin wrapped in aluminum foil and 0.01wt.% pure indium, 0.15wt.% pure magnesium, and 0.1wt.% Al-5.0wt.% Ti master alloy were dried at 150℃ and quickly pressed into the lower layer of the molten aluminum and stirred at 15rpm for 5 minutes, and allowed to stand for 5 minutes.

[0040] The method of supplementing the amount of elements lost during burning was adopted, and pure indium, pure magnesium, and Al-5.0wt.%Ti master alloy were added to the melt of A21 aluminum alloy (5.0wt.%Zn, 0.036wt.%In, 0.74wt.%Mg, 0.02wt.%Ti)+Zn.

[0041] 2) Preheat the centrifuge mold to 150℃. Pour the settled melt into the centrifuge mold while simultaneously starting the centrifuge, gradually increasing the speed from 0 rpm. At 30 seconds, the speed stabilizes at 200 rpm, and all the melt is poured into the mold. After 2 minutes, increase the speed to 800 rpm and maintain this speed for 5 minutes. After centrifugation, remove the mold and air-cool it to obtain a gradient aluminum anode. Simultaneously, pour a portion of the melt into a preheated steel mold and use conventional casting methods (without centrifugation) to obtain a homogeneous aluminum alloy sacrificial anode ingot, denoted as A21-0.15Sn-1 as-cast. Its average grain size is 130.6 μm, and the driving potential is -1.09V. SCE The initial coupling current density under free polarization when coupled to carbon steel of equal area is 319.6 μA·cm. -2 The current efficiency is 93.8%.

[0042] 3) The test sample was cut from the centrifugal ingot using an electrical discharge wire cutter in a direction perpendicular to the centrifugal force. The cuts, from the inside out, were designated as the inner side of A21-0.15Sn-1, the middle of A21-0.15Sn-1, and the outer side of A21-0.15Sn-1, with corresponding average grain sizes of 70.5 μm, 82.9 μm, and 63.4 μm, respectively. The driving potential...

[0043] ~-1.12VSCE The initial coupling current density under free polarization when coupled to a carbon steel of equal area is 326.7 μA·cm. -2 341.2 μA·cm -2 369.7 μA·cm -2 The current efficiencies were 82.3%, 78.6%, and 67.4%, respectively.

[0044] The preparation method of this embodiment yields a gradient aluminum sacrificial anode material for marine corrosion protection, which contains a continuously changing and distinct microstructure gradient.

[0045] Application of gradient aluminum sacrificial anode materials for marine corrosion protection in marine engineering equipment corrosion protection.

[0046] Offshore engineering equipment includes offshore wind turbine towers, offshore wind farms, or oil platforms.

[0047] A marine engineering equipment includes the gradient aluminum sacrificial anode material for marine corrosion protection, as described in this embodiment.

[0048] Example 2

[0049] A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection includes the following steps:

[0050] 1) Weigh the raw materials using A21 aluminum alloy (5.0 wt.% Zn, 0.036 wt.% In, 0.74 wt.% Mg, 0.02 wt.% Ti, Al balance), pure zinc (99.95 wt.%), pure indium (99.99 wt.%), pure tin (99.99 wt.%), pure magnesium (99.95 wt.%), and Al-5.0 wt.% Ti master alloy raw materials. A21 and 0.1 wt.% pure zinc raw materials dried at 150℃ were placed in a pit-type muffle furnace for smelting at 780℃. After the raw materials were completely melted, they were stirred thoroughly and allowed to stand for 10 minutes, and the scum was skimmed off. The furnace temperature was lowered to 720℃, and 0.5 wt.% hexachloroethane refining agent was added. The melt was refined for 7 minutes until no bubbles emerged from the melt, and the surface scum was skimmed off. 0.10 wt.% pure tin wrapped in aluminum foil and 0.015 wt.% pure indium, 0.2 wt.% pure magnesium, and 0.15 wt.% Al-5.0 wt.% Ti master alloy were dried at 150℃ and quickly pressed into the lower layer of the molten aluminum and stirred at 25 rpm for 3 minutes, and allowed to stand for 5 minutes.

[0051] 2) Preheat the centrifuge mold to 200℃. Pour the settled melt into the centrifuge mold while simultaneously starting the centrifuge, gradually increasing the speed from 0 rpm. After 30 seconds, all the melt is poured into the mold. At 45 seconds, the speed stabilizes at 300 rpm. After 2 minutes, the speed is increased to 1200 rpm and maintained for 3 minutes. The speed is then reduced to 800 rpm and maintained for 5 minutes. After centrifugation, the melt is removed and air-cooled to obtain a gradient aluminum anode. Simultaneously, a portion of the melt is poured into a preheated steel mold to obtain a homogeneous aluminum alloy sacrificial anode ingot, denoted as A21-0.10Sn as-cast, using conventional casting methods. Its average grain size is 118.6 μm, and the driving potential is -1.09V. SCE The initial coupling current density under free polarization when coupled to carbon steel of equal area is 326.5 μA·cm. -2 The current efficiency is 90.3%.

[0052] 3) The test sample was cut from the centrifugal ingot using an electrical discharge wire cutter in a direction perpendicular to the centrifugal force. The cuts, from the inside out, were designated as the inner side of A21-0.10Sn, the middle of A21-0.10Sn, and the outer side of A21-0.10Sn, respectively. The corresponding average grain sizes were 65.2 μm, 78.1 μm, and 59.6 μm, with a driving potential of ~-1.11V. SCE The initial coupling current density when freely polarized and coupled to a carbon steel of equal area is 315.7 μA·cm. -2 339.5 μA·cm -2 350.8 μA·cm -2 The current efficiencies were 87.7%, 79.3%, and 71.1%, respectively.

[0053] The preparation method of this embodiment yields a gradient aluminum sacrificial anode material for marine corrosion protection, which contains a continuously changing and distinct microstructure gradient.

[0054] Application of gradient aluminum sacrificial anode materials for marine corrosion protection in marine engineering equipment corrosion protection.

[0055] Offshore engineering equipment includes offshore wind turbine towers, offshore wind farms, or oil platforms.

[0056] A marine engineering equipment includes the gradient aluminum sacrificial anode material for marine corrosion protection, as described in this embodiment.

[0057] Example 3

[0058] A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection includes the following steps:

[0059] 1) Weigh the raw materials using A21 aluminum alloy (5.0 wt.% Zn, 0.036 wt.% In, 0.74 wt.% Mg, 0.02 wt.% Ti, Al balance), pure zinc (99.95 wt.%), pure indium (99.99 wt.%), pure tin (99.99 wt.%), pure magnesium (99.95 wt.%), and Al-5.0 wt.% Ti master alloy raw materials. A21 and 0.05wt.% pure zinc raw materials dried at 150℃ were placed in a pit-type muffle furnace for smelting at 750℃. After the raw materials were completely melted, they were stirred thoroughly and allowed to stand for 12 minutes, and the scum was skimmed off. The furnace temperature was lowered to 720℃, and 1wt.% hexachloroethane refining agent was added. The melt was refined for 7 minutes until no bubbles emerged from the melt, and the surface scum was skimmed off. 0.05wt.% pure tin wrapped in aluminum foil and 0.01wt.% pure indium, 0.1wt.% pure magnesium, and 0.1wt.% Al-5.0wt.% Ti master alloy were dried at 140℃ and quickly pressed into the lower layer of the molten aluminum and stirred at 25rpm for 3 minutes, and allowed to stand for 6 minutes.

[0060] 2) Preheat the centrifuge mold to 100℃. Pour the settled melt into the centrifuge mold while simultaneously starting the centrifuge to rotate the mold. Gradually increase the speed from 0 rpm to 100 rpm after 15 seconds. After 30 seconds, all the melt is poured into the mold. After 1 minute, increase the speed to 600 rpm and maintain this for 5 minutes. After centrifugation, remove the mold and air-cool it to obtain a gradient aluminum anode. Simultaneously, pour a portion of the melt into a preheated steel mold to obtain a homogeneous aluminum alloy sacrificial anode ingot using conventional casting methods, denoted as A21-0.05Sn in the as-cast state. Its average grain size is 216.4 μm, and the driving potential is -1.10V. SCE The initial coupling current density under free polarization when coupled to carbon steel of equal area is 170.6 μA·cm. -2 The current efficiency is 89.6%.

[0061] 3) The test sample was cut from the centrifugal ingot using an electrical discharge wire cutter in a direction perpendicular to the centrifugal force. The cuts, from the inside out, were designated as the inner side of A21-0.05Sn, the middle of A21-0.05Sn, and the outer side of A21-0.05Sn, respectively. The corresponding average grain sizes were 86.5 μm, 109.8 μm, and 77.6 μm, with a driving potential of ~-1.12V. SCE The initial coupling current density when freely polarized and coupled to carbon steel of equal area is 173.7 μA·cm. -2 169.5 μA·cm -2 188.1 μA·cm -2 The current efficiencies were 87.5%, 76.4%, and 69.7%, respectively.

[0062] The preparation method of this embodiment yields a gradient aluminum sacrificial anode material for marine corrosion protection, which contains a continuously changing and distinct microstructure gradient.

[0063] Application of gradient aluminum sacrificial anode materials for marine corrosion protection in marine engineering equipment corrosion protection.

[0064] Offshore engineering equipment includes offshore wind turbine towers, offshore wind farms, or oil platforms.

[0065] A marine engineering equipment includes the gradient aluminum sacrificial anode material for marine corrosion protection, as described in this embodiment.

[0066] Example 4

[0067] A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection includes the following steps:

[0068] 1) Weigh the raw materials using A21 aluminum alloy (5.0 wt.% Zn, 0.036 wt.% In, 0.74 wt.% Mg, 0.02 wt.% Ti, Al-balance), pure zinc (99.95 wt.%), pure tin (99.99 wt.%), pure indium (99.99 wt.%), pure magnesium (99.95 wt.%), and Al-5.0 wt.% Ti master alloy raw materials. A21 and 0.05wt.% pure zinc raw materials dried at 150℃ were placed in a pit-type muffle furnace for smelting at 750℃. After the raw materials were completely melted, they were stirred thoroughly and allowed to stand for 10 minutes, and the scum was skimmed off. The furnace temperature was lowered to 720℃, and 0.5wt.% hexachloroethane refining agent was added. The melt was refined for 5 minutes until no more bubbles emerged from the melt, and the surface scum was skimmed off. 0.15wt.% pure tin wrapped in aluminum foil and 0.01wt.% pure indium, 0.15wt.% pure magnesium, and 0.1wt.% Al-5.0wt.% Ti master alloy were dried at 150℃ and quickly pressed into the lower layer of the molten aluminum and stirred at 15rpm for 5 minutes, and allowed to stand for 5 minutes.

[0069] 2) Preheat the centrifuge mold to 200℃. Pour the settled melt into the centrifuge mold while simultaneously starting the centrifuge, gradually increasing the speed from 0 rpm. After 30 seconds, all the melt is poured into the mold. After 45 seconds, the speed stabilizes at 300 rpm. After 2 minutes, the speed is increased to 1200 rpm and maintained for 3 minutes. The speed is then reduced to 800 rpm and maintained for 5 minutes. After centrifugation, the melt is removed and air-cooled to obtain a gradient aluminum anode. Simultaneously, a portion of the melt is poured into a preheated steel mold to obtain a homogeneous aluminum alloy sacrificial anode ingot, denoted as A21-0.15Sn-2 as-cast, using conventional casting methods. Its average grain size is 133.9 μm, and its driving potential is -1.09V. SCEThe initial coupling current density under free polarization when coupled to carbon steel of equal area is 314.1 μA·cm. -2 The current efficiency is 94.3%.

[0070] 3) The test sample was cut from the centrifugal ingot using an electrical discharge wire cutter in a direction perpendicular to the centrifugal force. The cuts, from the inside out, were designated as the inner side, middle, and outer side of A21-0.15Sn-2, respectively. The corresponding average grain sizes were 61.8 μm, 72.9 μm, and 57.1 μm, with a driving potential of ~-1.13V. SCE The initial coupling current density under free polarization when coupled to a carbon steel of equal area is 358.1 μA·cm. -2 363.0 μA·cm -2 397.1 μA·cm -2 The current efficiencies were 80.5%, 76.8%, and 69.6%, respectively.

[0071] The preparation method of this embodiment yields a gradient aluminum sacrificial anode material for marine corrosion protection, which contains a continuously changing and distinct microstructure gradient.

[0072] Application of gradient aluminum sacrificial anode materials for marine corrosion protection in marine engineering equipment corrosion protection.

[0073] Offshore engineering equipment includes offshore wind turbine towers, offshore wind farms, or oil platforms.

[0074] A marine engineering equipment includes the gradient aluminum sacrificial anode material for marine corrosion protection, as described in this embodiment.

[0075] Performance Analysis

[0076] like Figure 1 A low-magnification cross-sectional photograph of the centrifugally cast A21-0.15Sn-2 gradient sacrificial anode shows that after 0.15Sn alloying and centrifugal casting, the A21-0.15Sn-2 sacrificial anode material forms a distinct gradient microstructure. The microstructure gradually changes along the direction of centrifugal force: the outer region of the centrifugal ingot has the smallest grain size, the middle region has larger coarse grains, and the inner region has grain sizes between the outer and middle regions, with no obvious interfaces between the regions.

[0077] Figure 2The images show the metallographic structures of different parts of the A21-0.15Sn-2 gradient sacrificial anode material in both the as-cast and centrifugally cast states. The metallographic images reveal that the as-cast and centrifugally cast A21-0.15Sn-2 alloys are primarily composed of α-Al, exhibiting a typical as-cast microstructure. The average grain size of the as-cast A21-0.15Sn-2 is 133.9 μm, with the inner grain size at 61.8 μm, the middle grain size at 72.9 μm, and the outer grain size at 57.1 μm. Figure 3 It can be seen that the alloy contains a small amount of precipitates, mainly distributed in the grain boundary region. Compared with the as-cast state, the inner and middle regions, the outer region has more precipitates, and the morphology changes from granular to short rod-shaped.

[0078] Electrochemical and discharge performance tests were conducted on the A21 base alloy and the prepared aluminum alloy sacrificial anode in simulated seawater medium using a saturated calomel electrode (SCE) as the reference electrode. The coupling current density curves under free polarization of the sacrificial anode coupled to an equal-area carbon steel cathode are shown in the figure. Figure 4 As shown in a), in the initial stage of polarization, compared with the A21 base alloy, the coupling current density of the as-cast sacrificial anode of A21-0.15Sn-2 increased by 72.5%, the coupling current density of the inner sacrificial anode of A21-0.15Sn-2 increased by 96.7%, the coupling current density of the middle sacrificial anode of A21-0.15Sn-2 increased by 98.9%, and the coupling current density of the outer sacrificial anode of A21-0.15Sn-2 increased by 117.6%. After 168 hours of coupling, the carbon steel cathode is fully polarized, at which point the sacrificial anode only needs to output a small sustaining current (35-45 μA·cm). -2 This can meet the requirements for cathodic protection. From the coupling potential curve ( Figure 4 As shown in b), during the initial stage of free polarization of the coupled connection (3–6 h), the alloy sacrificial anode with added Sn exhibits a more negative operating potential, with the outer side of A21-0.15Sn-2 showing the lowest operating potential of -1.13 V during the initial polarization stage. SCE All sacrificial anodes operated at potentials ranging from -1.07 to 1.13 V during the 168-hour coupling free polarization period. SCE The current efficiency of the A21-0.15Sn-2 cast sacrificial anode can reach 94.3%, while the current efficiencies of the centrifugally cast A21-0.15Sn-2 gradient sacrificial anode, from the outside to the inside, are 69.6%, 76.8%, and 80.5%, respectively, with a self-adjusting range for coupling current density exceeding 358.34 μA·cm. -2This method meets the requirements for sacrificial cathodic protection of marine steel structures such as offshore wind farms and oil platforms, while reducing the number of sacrificial anodes in the initial polarization stage and improving the utilization rate of anode materials.

[0079] Figure 5 The figures show the discharge morphology of different parts of A21-0.15Sn-2 gradient sacrificial anode materials in the as-cast and centrifugally cast states after 168 hours of discharge and removal of corrosion products. The figures show that the Sn-added alloy sacrificial anode exhibits an active dissolution discharge morphology. Specifically, the grain boundary precipitates on the outer surface of A21-0.15Sn-2 promote the dissolution of the nearby aluminum matrix, resulting in a certain number of corrosion pits distributed along the grain boundaries. The middle and inner surfaces of A21-0.15Sn-2 show uniform dissolution characteristics, with the number and area of ​​corrosion pits gradually decreasing. The centrifugally cast A21-0.15Sn-2 exhibits overall uniform dissolution, and the relatively smooth discharge morphology indicates that corrosion products do not form a crust and are easily detached during discharge, which is conducive to active discharge.

[0080] The self-adjustment range is the difference between the initial coupling current density after free polarization when connected to a carbon steel cathode of the same size and the coupling current density after reaching steady state after 168 hours (7 days) of polarization. In all embodiments, the coupling current density after reaching steady state after 168 hours (7 days) is approximately (30–45 μA·cm). -2 A larger self-adjusting range of coupling current density reflects a larger initial coupling current, which allows for the use of fewer sacrificial anodes to meet the initial current requirements of the protected cathode, thus improving the utilization rate of the sacrificial anode material. The self-adjusting ranges of Embodiments 1, 2, 3, and 4 of this invention are 332.5 μA·cm⁻¹, respectively. -2 309.5 μA·cm -2 157.6 μA·cm -2 358.3 μA·cm -2 .

[0081] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0082] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a gradient aluminum sacrificial anode material for marine corrosion protection, characterized in that, The steps include the following: S1, A21 aluminum alloy raw material and Sn particles are melted and stirred evenly at a temperature of 720~780℃ to obtain a uniform melt; S2, the molten melt is poured into the mold of a centrifuge for centrifugal casting. After the process is completed, it is air-cooled to obtain a gradient aluminum alloy sacrificial anode. The specific steps are as follows: 1) Place the dried A21 aluminum alloy and 0.05~0.1wt.% Sn granules in a muffle furnace for melting at a temperature of 750~780℃. After the raw materials are completely melted, stir thoroughly and let stand for at least 10 minutes, skimming off the slag. Reduce the furnace temperature to 720℃, add 0.5~1wt.% hexachloroethane refining agent, and refine the melt for 5~7 minutes until no bubbles emerge from the melt. Skim off the surface slag. After drying 0.05~0.15wt.% pure tin wrapped in aluminum foil and replenishing the lost 0.01~0.015wt.% pure indium, 0.1~0.2wt.% pure magnesium, and 0.1~0.15wt.% Al-5.0wt.% Ti master alloy, quickly press them into the lower layer of the molten aluminum and stir at a rate of 15~25 rpm for 3~5 minutes, then let stand for at least 5 minutes. 2) Preheat the centrifuge mold to 100~200℃, pour the molten material into the mold after it has been settling, and start the centrifuge at the same time to make the mold rotate. Gradually increase the speed from 0 rpm to 100~200 rpm within 15~30 seconds, and after 1~2 minutes increase the speed to 600~800 rpm and maintain it for 5 minutes. After centrifugation, remove the mold and air cool it to obtain the gradient aluminum anode.

2. The preparation method according to claim 1, characterized in that, The composition and proportions of A21 aluminum alloy are: 5.0 wt.% Zn, 0.036 wt.% In, 0.74 wt.% Mg, 0.02 wt.% Ti and the balance Al.

3. The preparation method according to claim 1, characterized in that, Step 2) is replaced with: preheating the centrifuge mold to 200°C, pouring the molten material into the centrifuge mold after it has been set, and starting the centrifuge at the same time to make the mold rotate. Within 45 seconds, the speed is gradually increased from 0 rpm to 300 rpm. After 2 minutes, the speed is increased to 1200 rpm and maintained for 3 minutes. The speed is then reduced to 800 rpm and maintained for 5 minutes. After centrifugation, the mold is removed and air-cooled to obtain a gradient aluminum anode.

4. The gradient aluminum sacrificial anode material for marine corrosion protection obtained by the preparation method according to any one of claims 1 to 3, characterized in that, The gradient aluminum sacrificial anode material for marine corrosion protection contains a continuous and obvious microstructure gradient. The grain size of the inner, middle and outer sides of the gradient aluminum sacrificial anode material for marine corrosion protection varies continuously between 57.1 μm and 109.8 μm.

5. The gradient aluminum sacrificial anode material for marine corrosion protection according to claim 4, characterized in that, The initial coupling current density of the gradient aluminum sacrificial anode material for marine corrosion protection is 157.6 μA·cm. -2 ~358.3 μA·cm -2 .

6. The application of the gradient aluminum sacrificial anode material for marine corrosion protection according to claim 4 in the corrosion protection of marine engineering equipment.

7. The application according to claim 6, characterized in that, Offshore engineering equipment includes offshore wind turbine towers, offshore wind farms, or oil platforms.

8. A marine engineering equipment, characterized in that, Includes the gradient aluminum sacrificial anode material for marine corrosion protection as described in claim 4.

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