Preparation process of high-current-efficiency rare earth micro-alloyed magnesium sacrificial anode

Abstract

The present application relates to the technical field of sacrificial anode material, in particular to a preparation process of high-current-efficiency rare earth micro-alloyed magnesium sacrificial anode, which comprises the following steps: (1) preparing raw materials: preparing according to Mg-Al-Zn-Ce-Mn-In alloy system, controlling the content of Ce to be 0.3-0.8wt%, the content of Mn to be 0.2-0.5wt%, the content of In to be 0.05-0.15wt%, and the rest being Mg and inevitable impurities; (2) vacuum smelting and ultrasonic refining; (3) low-temperature homogenization annealing; (4) preparation of conductive type micro-arc oxidation composite coating. Through the synergistic micro-alloying design of rare earth Ce and Mn and In, the present application realizes the effective inhibition of heterogeneous precipitation of β-Mg 17 Al 12 phase and significant refinement of grains, and solves the problem of low current efficiency caused by serious micro-electric couple corrosion of traditional magnesium sacrificial anode.

Description

Technical Field

[0001] This invention relates to the field of sacrificial anode material technology, specifically the preparation process of high current-efficiency rare-earth microalloyed magnesium sacrificial anodes. Background Technology

[0002] Magnesium sacrificial anodes are widely used for cathodic protection of metal structures such as buried pipelines, freshwater storage tanks, and heat exchange equipment due to their high driving potential and low specific gravity. However, traditional magnesium alloy sacrificial anodes (such as the AZ63 series) suffer from severe self-corrosion and low current efficiency (typically only 55%~65%). A large amount of current is consumed by the corrosion of their own micro-cells, which not only wastes materials but also leads to premature anode detachment and failure due to uneven surface dissolution, severely restricting the reliability and service life of the protection effect.

[0003] To improve the performance of magnesium anodes, methods such as alloying, plastic deformation, or heat treatment are commonly employed. Among these, adding rare earth elements can refine grains, purify the melt, and improve the distribution of the second phase, thus enhancing current efficiency to some extent. However, single rare earth alloying is ineffective in suppressing β-Mg... 17 Al 12 The effects of uneven phase precipitation and microgalvanic corrosion are still limited, and oxide inclusions and gases within the melt are difficult to completely remove, resulting in insufficient material purity and microstructure uniformity. Furthermore, matrix modification alone cannot simultaneously achieve high surface activity and corrosion resistance. Therefore, how to effectively reduce the self-corrosion rate while improving electrode activity is the core challenge in the development of magnesium sacrificial anodes. Summary of the Invention

[0004] This invention addresses the problems in the prior art by providing a process for preparing high-current-efficiency rare-earth microalloyed magnesium sacrificial anodes. The specific technical solution is as follows: This invention provides a process for preparing high-current-efficiency rare-earth microalloyed magnesium sacrificial anodes, comprising the following steps: (1) Preparation of raw materials: Prepared according to the Mg-Al-Zn-Ce-Mn-In alloy system, controlling the Ce content to be 0.3~0.8wt%, the Mn content to be 0.2~0.5wt%, the In content to be 0.05~0.15wt%, and the balance to be Mg and unavoidable impurities; (2) Vacuum melting and ultrasonic refining: The prepared raw materials are placed in a vacuum induction melting furnace and melted under a vacuum degree ≤5×10-3Pa; after all the raw materials are melted, a refining agent is added to the melt, and ultrasonic vibration with a frequency of 20~40kHz is applied to the melt for refining treatment; after refining, the ingot is obtained by step cooling casting. (3) Low-temperature homogenization annealing: The ingot obtained in step (2) is subjected to segmented low-temperature homogenization annealing. First, it is kept at 300℃ for 4 hours, then heated to 380℃ and kept for 8 hours, and then slowly cooled to below 150℃ in the furnace before being taken out of the furnace. (4) Preparation of conductive micro-arc oxidation composite coating: The annealed ingot is processed into an anode shape and placed in an electrolyte for micro-arc oxidation treatment. The electrolyte contains 6~8 g / L talc, 8~10 g / L sodium pyrophosphate and 7~9 g / L ferric oxide. The micro-arc oxidation process parameters are: current density 2.5~3.5 A / dm³. 2 The process involves a frequency of 400-600 Hz and a processing time of 25-30 min to form a micro-arc oxidation ceramic layer on the anode surface. Subsequently, a silane sealing treatment is performed to obtain a conductive composite coating, thus obtaining the high current efficiency rare earth microalloyed magnesium sacrificial anode.

[0005] As a further technical solution of the present invention, in step (1), the Al content in the Mg-Al-Zn-Ce-Mn-In alloy system is 5.5~6.5wt%, and the Zn content is 2.5~3.5wt%.

[0006] As a further technical solution of the present invention, in step (2), the refining agent is a MgCl2-KCl-NaF composite salt, the composition of which is as follows by mass percentage: MgCl2 40%~55%, KCl 35%~50%, NaF 5%~15%; the amount of refining agent added is 1%~2% of the total mass of the melt.

[0007] As a further technical solution of the present invention, in step (2), the ultrasonic vibration refining treatment time is 10~20min and the treatment temperature is 680~700℃.

[0008] As a further technical solution of the present invention, in step (2), the process of stepped cooling casting is as follows: after refining, the melt is cooled to 680°C and kept at that temperature for 10~20 minutes, then cooled to 620°C and poured into the mold, and cooled to room temperature.

[0009] As a further technical solution of the present invention, in step (4), the electrolyte uses deionized water as a solvent and also contains a pH adjuster to control the pH value of the electrolyte to 8~10.

[0010] As a further technical solution of the present invention, in step (4), the silane sealing treatment is as follows: the anode with the micro-arc oxidation ceramic layer is immersed in a silane coupling agent solution with a mass concentration of 5%~15% for 10~30 minutes, and then cured at 100~150℃ for 0.5~2 hours. The silane coupling agent is one of KH-550, KH-560 or KH-570.

[0011] The present invention also provides a high current-efficiency rare-earth microalloyed magnesium sacrificial anode, which is prepared by any one of the above-described technical solutions using the same preparation process.

[0012] The beneficial effects of this invention are as follows: (1) In this invention, the synergistic microalloying design of rare earth Ce with Mn and In was used to achieve the β-Mg 17 Al 12 The effective suppression of uneven phase precipitation and the significant refinement of grains solve the problem of low current efficiency caused by severe micro-galvanic corrosion in traditional magnesium sacrificial anodes.

[0013] (2) In this invention, the integrated process of vacuum induction melting and ultrasonic vibration-composite refining agent synergistic refining achieves efficient removal of oxidative inclusions and gaseous impurities in the melt, and solves the problem of structural defects and performance degradation caused by insufficient melt purity in traditional melting process.

[0014] (3) In this invention, by using stepped cooling casting and segmented low-temperature homogenization annealing of “300℃×4h+380℃×8h”, the stress in the casting state is fully eliminated and the second phase is dispersed and uniformly distributed, thus solving the problems of uneven surface dissolution and local severe corrosion leading to anode detachment failure during the anode discharge process.

[0015] (4) In this invention, a conductive composite coating is designed by combining a micro-arc oxidation ceramic layer and a silane sealing layer. The ratio of talc, sodium pyrophosphate and ferric oxide in the electrolyte and the micro-arc oxidation process parameters are optimized to achieve a balance between good conductivity and excellent corrosion resistance at a coating thickness of 50~80μm, thus solving the contradiction between the surface protection and discharge activity of traditional magnesium anodes. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0017] Example 1

[0018] (1) Raw materials: Weigh pure magnesium, pure aluminum, pure zinc, Mg-30Ce master alloy, Mg-10Mn master alloy and pure indium according to the alloy composition of Mg-6Al-3Zn-0.5Ce-0.35Mn-0.1In (wt%); the total amount of impurities is ≤0.2%.

[0019] (2) Vacuum melting and ultrasonic refining: Place the raw materials into a vacuum induction melting furnace and evacuate to 4×10 -3 Pa, heat to melt. After the melt is completely melted, cool to 690℃, add 1.5% of the composite refining agent (45%MgCl2+45%KCl+10%NaF) by mass of the melt, and simultaneously apply ultrasonic vibration at a frequency of 30kHz for 15 minutes; after refining, hold at 680℃ for 15 minutes, then cool to 620℃ and pour into a preheated metal mold, air cool to room temperature to obtain an ingot.

[0020] (3) Low-temperature homogenization annealing: Place the ingot in a heat treatment furnace, raise the temperature to 300°C at 10°C / min, hold for 4 hours, raise the temperature to 380°C at the same rate, hold for 8 hours, and then cool it down to below 150°C in the furnace before taking it out of the furnace.

[0021] (4) Conductive micro-arc oxidation composite coating: After annealing, the ingot is machined into a cylindrical anode sample. Electrolyte preparation: talc powder 7g / L, sodium pyrophosphate 9g / L, ferric oxide 8g / L, deionized water as solvent, pH adjusted to 9 with NaOH; pulsed micro-arc oxidation power supply, current density 3A / dm 2 At a frequency of 500Hz and a duty cycle of 30%, the treatment lasted for 28 minutes to obtain a dark gray ceramic layer. After anodic rinsing, the ceramic layer was immersed in an 8% KH-550 silane aqueous solution for 20 minutes. After removal, it was cured at 120℃ for 1 hour to form a composite coating. The total thickness of the coating was approximately 65μm.

[0022] Testing showed that the magnesium sacrificial anode prepared in this embodiment had a current efficiency of 86.2% (GB / T17848-1999 standard) and a self-corrosion rate of 0.118 mg / (cm²). 2 ·d), compared to uncoated and unannealed cast anodes of the same composition (0.301 mg / (cm³) 2 •d)) The corrosion rate decreased by 61%, and after 2000 hours of neutral salt spray testing, the surface corrosion was uniform with no deep peeling observed.

[0023] Example 2

[0024] The difference from Example 1 is: In step (1), the raw materials are weighed according to the following formula: Mg-5.8Al-2.8Zn-0.3Ce-0.2Mn-0.15In (wt%). In step (2) vacuum melting and ultrasonic refining, the vacuum degree is 5×10 -3 Pa, after melting and clearing, cool to 700℃, add 1% of refining agent by mass of the melt, the composition of which is 50%MgCl2+40%KCl+10%NaF, apply ultrasonic frequency of 20kHz, and treat for 20min; the stepped cooling casting process is the same as in Example 1. In step (3) low-temperature homogenization annealing, the process is the same as in Example 1; In step (4), during the preparation of the conductive micro-arc oxidation composite coating, the electrolyte contains 6 g / L talc, 10 g / L sodium pyrophosphate, and 9 g / L ferric oxide; the micro-arc oxidation process parameters are a current density of 2.5 A / dm³. 2 The frequency was 600Hz and the processing time was 25min; the silane sealing treatment involved immersion in 10% KH-560 solution for 30min and curing at 150℃ for 0.5h, resulting in a coating thickness of approximately 50μm.

[0025] The magnesium sacrificial anode prepared in this embodiment has a current efficiency of 85.5% and a self-corrosion rate of 0.127 mg / (cm²). 2 ·d), No local perforation was observed after 1800 hours of salt spray testing.

[0026] Example 3

[0027] The difference from Example 1 is: In step (1), the raw materials are weighed according to the following ratio: Mg-6.5Al-3.5Zn-0.8Ce-0.5Mn-0.05In (wt%). In step (2) vacuum melting and ultrasonic refining, the vacuum degree is 3×10 -3 Pa, after melting and clearing, add 2% of the refining agent by mass of the melt, which has the composition of 40%MgCl2+50%KCl+10%NaF, apply ultrasonic frequency of 40kHz, and treat for 10min; the stepped cooling casting process is the same as in Example 1. In step (3) low-temperature homogenization annealing, the process is the same as in Example 1; In step (4), during the preparation of the conductive micro-arc oxidation composite coating, the electrolyte contains 8 g / L talc, 8 g / L sodium pyrophosphate, and 7 g / L ferric oxide; the micro-arc oxidation process parameters are a current density of 3.5 A / dm³. 2 The frequency was 400Hz and the processing time was 30min; the silane sealing treatment involved immersion in 5% KH-570 solution for 10min and curing at 100℃ for 2h, resulting in a coating thickness of approximately 80μm.

[0028] The magnesium sacrificial anode prepared in this embodiment has a current efficiency of 87.1% and a self-corrosion rate of 0.104 mg / (cm²). 2 ·d), the service life estimated by constant current accelerated life test is greater than 15.5 years.

[0029] Comparative Example 1 The process was the same as in Example 1, but without the addition of Ce and In, and without ultrasonic refining and segmented annealing; only conventional refining and annealing at 420°C for 12 hours were used. The resulting anodic current efficiency was 62%, and the self-corrosion rate was 0.288 mg / (cm²). 2 ·d), severe pitting and localized flaking occurred after 800 hours of salt spray testing.

[0030] The comparative results show that the synergistic effect of the microalloying design, vacuum ultrasonic refining, segmented low-temperature annealing and conductive composite coating disclosed in this invention is the key to improving the current efficiency of magnesium sacrificial anodes and extending their lifespan.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A process for preparing high-current-efficiency rare-earth microalloyed magnesium sacrificial anodes, characterized in that, Includes the following steps: (1) Preparation of raw materials: Prepared according to the Mg-Al-Zn-Ce-Mn-In alloy system, controlling the Ce content to be 0.3~0.8wt%, the Mn content to be 0.2~0.5wt%, the In content to be 0.05~0.15wt%, and the balance to be Mg and unavoidable impurities; (2) Vacuum melting and ultrasonic refining: The prepared raw materials are placed in a vacuum induction melting furnace, and the vacuum degree is ≤5×10 -3 Melt at Pa; after all the raw materials have melted, add refining agent to the melt, and at the same time apply ultrasonic vibration at a frequency of 20~40kHz to the melt for refining treatment; after refining, perform stepped cooling and casting to obtain ingots; (3) Low-temperature homogenization annealing: The ingot obtained in step (2) is subjected to segmented low-temperature homogenization annealing. First, it is kept at 300℃ for 4 hours, then heated to 380℃ and kept for 8 hours, and then slowly cooled to below 150℃ in the furnace before being taken out of the furnace. (4) Preparation of conductive micro-arc oxidation composite coating: The annealed ingot is processed into an anode shape and placed in an electrolyte for micro-arc oxidation treatment. The electrolyte contains 6~8 g / L talc, 8~10 g / L sodium pyrophosphate and 7~9 g / L ferric oxide. The micro-arc oxidation process parameters are: current density 2.5~3.5 A / dm³. 2 The process involves a frequency of 400-600 Hz and a processing time of 25-30 min to form a micro-arc oxidation ceramic layer on the anode surface. Subsequently, a silane sealing treatment is performed to obtain a conductive composite coating, thus obtaining the high current efficiency rare earth microalloyed magnesium sacrificial anode.

2. The preparation process of the high current efficiency rare earth microalloyed magnesium sacrificial anode according to claim 1, characterized in that: In step (1), the Al content in the Mg-Al-Zn-Ce-Mn-In alloy system is 5.5~6.5wt%, and the Zn content is 2.5~3.5wt%.

3. The preparation process of the high current efficiency rare earth microalloyed magnesium sacrificial anode according to claim 1, characterized in that: In step (2), the refining agent is a MgCl2-KCl-NaF composite salt, and its composition by mass percentage is: MgCl2 40%~55%, KCl 35%~50%, NaF 5%~15%; the amount of refining agent added is 1%~2% of the total mass of the melt.

4. The preparation process of the high current efficiency rare earth microalloyed magnesium sacrificial anode according to claim 1, characterized in that: In step (2), the ultrasonic vibration refining process takes 10 to 20 minutes and the processing temperature is 680 to 700°C.

5. The preparation process of the high current efficiency rare earth microalloyed magnesium sacrificial anode according to claim 1, characterized in that: In step (2), the stepped cooling casting process is as follows: after refining, the melt is cooled to 680°C and held for 10-20 minutes, then cooled to 620°C and poured into the mold, and cooled to room temperature.

6. The preparation process of the high current efficiency rare earth microalloyed magnesium sacrificial anode according to claim 1, characterized in that: In step (4), the electrolyte uses deionized water as a solvent and also contains a pH adjuster to control the pH value of the electrolyte to 8~10.

7. The preparation process of the high current efficiency rare earth microalloyed magnesium sacrificial anode according to claim 1, characterized in that: In step (4), the silane sealing treatment is as follows: the anode with the micro-arc oxidation ceramic layer is immersed in a silane coupling agent solution with a mass concentration of 5%~15% for 10~30 minutes, and then cured at 100~150℃ for 0.5~2 hours. The silane coupling agent is one of KH-550, KH-560 or KH-570.

8. A high current-efficiency rare-earth microalloyed magnesium sacrificial anode, characterized in that, It is prepared by any one of the preparation processes according to claims 1 to 7.