A micro-arc oxidation closed aging treatment method for aluminum alloy plates

Abstract

The present invention relates to the technical field of aluminum alloy processing, and in particular to a micro-arc oxidation sealing and aging treatment method for aluminum alloy plates. The micro-arc oxidation treatment process disclosed by the present invention is simple and has a short flow. There is no need to perform complex pre-treatment on the aluminum alloy plates, the oxidation process is pollution-free, non-toxic, harmless and long-lasting, and does not need to be replaced during the production process. Cleaning wastewater can be used as electrolyte replenishment water, and there is basically no wastewater discharge during the treatment process. The ceramic oxide film formed by micro-arc oxidation treatment has a dense film layer and has good wear resistance and corrosion resistance. There are many micropores on the surface of the oxide film, which is conducive to subsequent immersion sealing. It can make the organic silicate coating penetrate into the micropores of the oxide film to form an "anchoring effect", greatly improving the bonding force of the surface coating, strong processing capacity, high production efficiency, and is suitable for large-scale industrial production. The micro-arc oxidation electrolyte does not contain toxic substances and heavy metal elements, and the electrolyte has strong anti-pollution ability and a high regeneration reuse rate.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy processing, and particularly relates to a micro-arc oxidation closed aging treatment method for an aluminum alloy plate. Background Art

[0002] Micro-arc oxidation, also known as plasma oxidation, is a method that uses arc discharge to enhance and activate the reaction at the anode, building upon conventional anodic oxidation. This method creates a high-quality, reinforced ceramic film on the surface of workpieces made of aluminum, titanium, magnesium, and their alloys. A dedicated micro-arc oxidation power supply applies voltage to the workpiece, causing the metal on the workpiece surface to interact with an electrolyte solution, generating micro-arc discharges. Under the influence of high temperature and an electric field, a ceramic film forms on the metal surface, achieving surface strengthening. Sealing aluminum alloy anodic oxide films includes heat sealing (thermal hydration sealing), cold sealing, intermediate-temperature sealing, organic polymer coating sealing (organic acid or electrophoretic paint sealing), and other nickel-free sealing methods. Cold sealing, intermediate-temperature sealing, and electrophoretic paint sealing are the primary methods used for architectural aluminum alloys in my country. In recent years, intermediate-temperature sealing has rapidly developed to meet the performance requirements for thicker oxide films. Heat sealing (thermal hydration sealing) includes boiling water sealing and high-temperature steam sealing. Since boiling water sealing and high-temperature steam sealing are performed at high temperatures and consume a lot of energy, they are generally not used in the sealing process of architectural aluminum alloys. When sealing with nickel fluoride, a large amount of nickel-containing wastewater is generated during the production process, polluting the environment and causing public hazards; the surface of the aluminum alloy after sealing contains nickel hydroxide, which leaves users with a long-term carcinogenic risk. Medium-temperature sealing uses nickel acetate as the main component of the sealing agent, and its carcinogenicity is the same as that of low-temperature sealing. For example, on January 18, 2019, CN201811400926.4 A highly alkali-resistant sealant and sealing method for anodized films of aluminum and aluminum alloys, the sealant includes: nickel acetate, a dispersant, a surfactant, a fluoride, and the balance is deionized water. Those skilled in the art are in urgent need of developing a micro-arc oxidation sealing and aging treatment method for aluminum alloy plates to meet existing usage needs and performance requirements. Summary of the Invention

[0003] The purpose of the present invention is to provide a micro-arc oxidation closed aging treatment method for aluminum alloy plates in response to existing problems.

[0004] A method for micro-arc oxidation sealed aging treatment of aluminum alloy plates, comprising immersing the cleaned aluminum alloy plates in an electrolyte as an anode and using a stainless steel electrolyte tank as a cathode, further comprising the following steps:

[0005] Micro-arc oxidation is a coating technology that uses a combination of electrolyte and corresponding electrical parameters to grow ceramic materials mainly composed of matrix metal oxides on the surface of lightweight materials such as aluminum and their alloys by relying on the instantaneous high temperature and high pressure generated by arc discharge.

[0006] (1) Performing micro-arc oxidation treatment, rinsing the micro-arc oxidized aluminum alloy plate with 15-20°C cold water to remove the residue on the surface, and then air-drying at room temperature, wherein the electrolyte is: sodium dodecamolybdate phosphate with a concentration of 8-10 g / L, propylene glycol with a concentration of 0.5-1 g / L, potassium pyrophosphate with a concentration of 2-8 g / L, sodium metaborate with a concentration of 4-6 g / L, potassium metaaluminate with a concentration of 1-2 g / L, and sodium metavanadate with a concentration of 3-8 g / L;

[0007] Sodium dodecamolybdate phosphate is a corrosion inhibitor that has been used in water treatment and corrosion inhibition in the past.

[0008] (2) Impregnation sealing: Add 4-5 wt% of aluminum salt to a 5-10% organic silicate solution with a pH value of 8-9, impregnate and seal the air-dried aluminum alloy plate at a temperature of 30-40°C for 10-20 min, and then dry it; (3) Aging: The dried aluminum alloy plate is aged in a room at a temperature of 35-45°C, containing 2-3% carbon dioxide and a relative humidity of 80-90% for 2-4 h.

[0009] Lithium methyl silicate has been used in the preparation of liquid concrete waterproofing agents.

[0010] Aging is the process of structural variation caused by the slow continuation of the sealing process.

[0011] Micro-arc oxidation film refers to a ceramic film formed on the surface of aluminum alloy objects by self-oxidation of the base metal through micro-arc discharge.

[0012] Furthermore, the drying in step (2) is performed at 60-80° C. for 0.5-1 h.

[0013] Sealing is a process of treating the holes in the oxide film by adsorption, chemical reaction or other mechanisms.

[0014] Furthermore, the organic silicate in step (2) is one of lithium methyl silicate or sodium phenyl silicate.

[0015] Furthermore, in step (1), the micro-arc oxidation power is 200~300kW, the current is: forward current 5~20A / dm2, negative current density 0~-5A / dm2, voltage: forward 500~540V, negative 0~-300V, frequency: 200Hz~600Hz, positive and negative duty cycle 5%~35%, and pulse width 50μs~2000μs.

[0016] Furthermore, the aluminum salt in step (2) is one or more of aluminum chloride and aluminum sulfate.

[0017] Furthermore, the aluminum alloy plate is one of 1050 aluminum alloy plate, 1100 aluminum alloy plate, 6010 aluminum alloy plate, and 6063 aluminum alloy plate.

[0018] Micro-arc oxidation (MAO) is a surface modification technique that grows ceramic films in situ under specific electrolyte and electric field conditions. The principle is to place an aluminum alloy in an aqueous electrolyte solution as the anode, and then electrochemically generate spark discharge spots on the surface of the material. Through the combined effects of thermochemistry, plasma chemistry, and electrochemistry, a metal oxide ceramic layer is formed.

[0019] The dried aluminum alloy plate is placed in a room with a temperature of 35-45°C, a carbon dioxide content of 2-3%, and a relative humidity of 80-90%, and reacts with water and carbon dioxide:

[0020]

[0021]

[0022] Beneficial effects of the present invention:

[0023] The micro-arc oxidation treatment process disclosed in the present invention is simple and has a short flow. There is no need for complex pre-treatment of the workpiece, the oxidation process is pollution-free, non-toxic, harmless and long-lasting, and does not need to be replaced during the production process. Cleaning wastewater can be used as electrolyte water, and there is basically no wastewater discharge during the treatment process. The ceramic oxide film formed by micro-arc oxidation treatment has a dense film layer and has good wear resistance and corrosion resistance. There are many micropores on the surface of the oxide film, which is conducive to subsequent impregnation and sealing. It can make the organic silicate coating penetrate into the micropores of the oxide film to form an "anchor effect", greatly improving the bonding force of the surface coating, strong processing ability, high production efficiency, and suitable for large-scale industrial production. The micro-arc oxidation electrolyte does not contain toxic substances and heavy metal elements, and the electrolyte has strong anti-pollution ability and high regeneration and reuse rate.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] Because the workpiece surface has a high oxidation voltage and a large electrolytic current during micro-arc oxidation (MAO), most of the heat generated is concentrated at the film interface, affecting the quality of the resulting film. Therefore, MAO requires the use of a heat exchange refrigeration system to promptly cool the electrolyte and ensure that MAO is carried out within the specified temperature range. The electrolyte is cooled using circulating convection, which not only controls the solution temperature but also achieves agitation. The organic silicate sealing formula and process completely eliminates water contamination caused by nickel salts. The combination of an organic silicate solution and an aluminum salt increases sealing speed and improves production efficiency. Using organic silicate as the primary sealing agent, the sealing temperature can be as low as 15°C, saving energy. The aging process, performed indoors at 35-45°C, with a carbon dioxide content of 2-3% and a relative humidity of 80-90%, results in a colorless and transparent sealed film, restoring the original color of the aluminum alloy sheet. No nickel wastewater is discharged. Operating at room temperature ensures a stable sealing bath solution and meets product quality standards. It is energy-saving and environmentally friendly, easy to treat wastewater, easy to mass-produce, and the cost is slightly lower than the traditional nickel salt sealing process. DETAILED DESCRIPTION

[0026] The present invention is described below with specific examples, but is not intended to be limiting of the present invention.

[0027] Example 1

[0028] Micro-arc oxidation sealed aging treatment method for aluminum alloy plate: QC12Y CNC shearing machine is used to process 6063 aluminum alloy plates with a length of 1500mm, a width of 2000mm and a thickness of 1.5mm. The first step is degreasing and cleaning: the clamped 6063 aluminum alloy plate is placed in a 40KHz800W ultrasonic cleaning tank for cleaning for 30 minutes. The surface is 100mm away from the liquid surface of the cleaning liquid. The cleaning agent is an alkaline water-based cleaning agent WP-751 with a dilution ratio of 1:30 with water. After the degreasing step is completed, take it out and put it into a 20℃ pure water rinsing tank for cleaning to remove the surface cleaning agent. The rinsed parts are blown dry with pure 0.4MPa compressed air and the parts are kept warm in a drying oven at a temperature of 90℃ for 10 minutes to complete the cleaning. The second step is to remove the mechanical deformation and mechanical damage of the cleaned surface and to prevent oxidation quality. An aluminum alloy plate with defects such as skin, spots, pits, nodules, burrs, scratches, etc. and a roughness of Ra≤6.3 is immersed in an electrolyte as an anode, and a stainless steel electrolyte tank is used as a cathode. Guangdong Kairui SMDF (S) micro-arc oxidation power supply is used to perform micro-arc oxidation treatment. The aluminum alloy plate after micro-arc oxidation is hung into a cleaning tank, and the residual solution on the surface of the part is cleaned. It is rinsed with 20°C cold water to remove the surface residue and placed at room temperature to air dry. The electrolyte is: sodium dodecamolybdate with a concentration of 10g / L, propylene glycol with a concentration of 1g / L, potassium pyrophosphate with a concentration of 8g / L, sodium metaborate with a concentration of 6g / L, potassium metaaluminate with a concentration of 2g / L, and sodium metavanadate with a concentration of 8g / L. In step (1), a DC square wave pulse is output, the micro-arc oxidation power is 300kW, and the current is: forward current 20A / dm2, negative current density -5A / dm 2 , voltage: positive 540V, negative -300V, frequency: 600Hz, positive and negative duty cycle 35%, pulse width 2000μs; (2) Impregnation and sealing: add 5wt% of the mass of aluminum chloride to a sealing tank filled with a 10% mass fraction of lithium methyl silicate solution with a pH value of 9, and impregnate and seal the air-dried aluminum alloy plate at a temperature of 30℃ for 20min and then dry it at 80℃ for 1h; (3) Aging: the dried aluminum alloy plate is aged for 4h in a room with a temperature of 35℃, 3% carbon dioxide and a relative humidity of 90%. The electrolyte tank, cleaning tank, spray tank and sealing tank are transported by auxiliary equipment gantry car.

[0029] Product: The average thickness of the oxide film is 40μm, the average thickness of the sealing coating is 132μm, the porosity is zero, the appearance is uniform and continuous, there is no peeling, sand holes, powdering areas, no marks and slight water stains, the appearance color is uniform, and the microhardness is ≥800HV 0.05 The corrosion resistance is in accordance with GB / T10125 (NSS test) and after 336h neutral salt spray test, there is no corrosion or shedding phenomenon.

[0030] Example 2

[0031] A method for micro-arc oxidation sealing and aging treatment of aluminum alloy plates:

[0032] QC12Y CNC shearing machine is used to process 1100 aluminum alloy plates with a length of 3000mm, a width of 900mm and a thickness of 1mm.

[0033] The first step is degreasing and cleaning: place the clamped 1100 aluminum alloy plate into a 40KHz800W ultrasonic cleaning tank for cleaning for 30 minutes, with the surface 100mm away from the cleaning liquid level. The cleaning agent is an alkaline water-based cleaning agent WP-751 with a dilution ratio of 1:30 with water. After the degreasing step is completed, take it out and place it in a 20℃ pure water rinsing tank for cleaning to remove the surface cleaning agent. Blow dry the rinsed parts with pure 0.4MPa compressed air and keep the parts in a drying oven at 80℃ for 5 minutes to complete the cleaning. The second step is to immerse the aluminum alloy plate with no mechanical deformation and mechanical damage on the surface after cleaning, and no defects such as oxide scale, spots, pits, nodules, burrs, scratches, etc. that affect the oxidation quality and a roughness of Ra≤6.3 in an electrolytic The electrolyte is used as the anode, the electrolyte is cooled by circulating convection, and the stainless steel electrolyte tank is used as the cathode. Guangdong Kairui SMDF (S) micro-arc oxidation power supply is used for micro-arc oxidation treatment. The aluminum alloy plate after micro-arc oxidation is hung into the cleaning tank, the residual solution on the surface of the part is cleaned, and it is rinsed with 18°C ​​cold water to remove the surface residue. It is placed at room temperature and air-dried. The electrolyte is: sodium dodecamolybdate with a concentration of 9g / L, propylene glycol with a concentration of 0.8g / L, potassium pyrophosphate with a concentration of 5g / L, sodium metaborate with a concentration of 5g / L, potassium metaaluminate with a concentration of 1.5g / L, and sodium metavanadate with a concentration of 6g / L. In step (1), a DC square wave pulse is output, the micro-arc oxidation power is 250kW, and the current is: forward current 15A / dm2, negative current density 0A / dm 2 , voltage: positive 500V, negative -300V, frequency: 400Hz, positive and negative duty cycle 25%, pulse width 50μs; (2) Impregnation and sealing: add 4wt% of the mass of aluminum sulfate to a sealing tank filled with a 5% mass fraction of phenyl sodium silicate solution with a pH value of 8, and impregnate and seal the air-dried aluminum alloy plate at a temperature of 30℃ for 10min and then dry it at 60℃ for 0.75h; (3) Aging: the dried aluminum alloy plate is placed in a room with a temperature of 40℃, 2.5% carbon dioxide and a relative humidity of 80% for 3h, wherein the electrolyte tank, cleaning tank, spray tank and sealing tank are transported by auxiliary equipment gantry car.

[0034] Product: The average thickness of the oxide film is 34μm, the average thickness of the sealing coating is 110μm, the porosity is zero, the appearance is uniform and continuous, there is no peeling, sand holes, powdering areas, no marks and slight water stains, the appearance color is uniform, and the microhardness is 1243.6HV 0.05The corrosion resistance is in accordance with GB / T10125 (NSS test) and after 336h neutral salt spray test, there is no corrosion or shedding phenomenon.

[0035] Example 3

[0036] A micro-arc oxidation closed aging treatment method for aluminum alloy plates,

[0037] The first step, degreasing and cleaning: QC12Y CNC shearing machine is used to process 6010 aluminum alloy plates with a length of 1000mm, a width of 2000mm and a thickness of 2mm. Before micro-arc oxidation treatment, 400#, 600#, 800#, 1000# and 1200# water sandpaper are used to grind the workpiece step by step. The clamped 6010 aluminum alloy plate is placed in a 40KHz800W ultrasonic cleaning tank for cleaning for 30 minutes. The surface is 100mm away from the liquid surface of the cleaning liquid. The cleaning agent is an alkaline water-based cleaning agent WP-751 with a dilution ratio of 1:30 with water. After the degreasing step is completed, take it out and put it into a 20℃ pure water rinsing tank for cleaning to remove the surface cleaning agent. The rinsed parts are blown dry with pure 0.4MPa compressed air and the parts are kept warm for 5min in a drying oven at a temperature of 70℃. The cleaning is completed; the second step, the cleaned parts are placed in a 20℃ pure water rinsing tank for cleaning to remove the surface cleaning agent. The surface of the aluminum alloy plate has no mechanical deformation and mechanical damage, no defects such as oxide scale, spots, pits, nodules, burrs, scratches, etc. that affect the oxidation quality, and the roughness Ra≤6.3 is immersed in the electrolyte as the anode, and the stainless steel electrolyte tank is used as the cathode. Guangdong Kairui SMDF (S) micro-arc oxidation power supply is used for micro-arc oxidation treatment. The aluminum alloy plate after micro-arc oxidation is hung into the cleaning tank, the residual solution on the surface of the part is cleaned, and it is rinsed with 15°C cold water to remove the surface residue, and placed at room temperature to air dry. The electrolyte is: sodium dodecamolybdate with a concentration of 8g / L, propylene glycol with a concentration of 0.5g / L, potassium pyrophosphate with a concentration of 2g / L, sodium metaborate with a concentration of 4g / L, potassium metaaluminate with a concentration of 1g / L, and sodium metavanadate with a concentration of 3g / L. In step (1), a DC square wave pulse is output, the micro-arc oxidation power is 200kW, and the current is: forward current 5A / dm 2 , negative current density -5A / dm 2 , voltage: positive 500V, negative -300V, frequency: 200Hz, positive and negative duty cycle 5%, pulse width 2000μs; (2) Impregnation and sealing: add 4wt% of aluminum chloride salt to a sealing tank filled with 5% lithium methyl silicate solution with a pH value of 8, and immerse and seal the air-dried aluminum alloy plate at a temperature of 30℃ for 10~20min and then dry it at 60℃ for 0.5h; (3) Aging: the dried aluminum alloy plate is placed in a room with a temperature of 35~45℃, 2% carbon dioxide and 80% relative humidity for 2h, and the electrolyte tank, cleaning tank, spray tank and sealing tank are transported by auxiliary equipment gantry car.

[0038] Product: average oxide film thickness 30μm, average sealing coating thickness 80μm, zero porosity, uniform and continuous appearance, no peeling, sand holes, powdering areas, no marks and slight water stains, uniform appearance color, microhardness ≥800HV 0.05 The corrosion resistance is in accordance with GB / T10125 (NSS test) and after 336h neutral salt spray test, there is no corrosion or shedding phenomenon.

[0039] Example 4

[0040] The 1100 aluminum alloy in Example 2 is replaced with 1050 aluminum alloy plate, and the remaining steps are the same.

[0041] Product: The average thickness of the oxide film is 33μm, the average thickness of the sealing coating is 108μm, the porosity is zero, the appearance is uniform and continuous, there is no peeling, sand holes, powdering areas, no marks and slight water stains, the appearance color is uniform, and the microhardness is ≥800HV 0.05 The corrosion resistance is in accordance with GB / T10125 (NSS test) and after 1000h neutral salt spray test, there is no corrosion or shedding phenomenon.

[0042] Note: The wear resistance of the micro-arc oxidation film is tested using the wheel abrasion method specified in GB / T12967.2-2008. The neutral salt spray test for corrosion resistance is conducted using the method specified in GB / T10125-2021. The corrosion sample rating is conducted in accordance with GB / T6461-2002. The hardness is tested by holding for 15 seconds according to GB / T9790-2021. The porosity is tested according to GB / T17720-1999, "Test and Evaluation of Porosity of Metallic Coatings."

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for micro-arc oxidation sealing aging treatment of aluminum alloy plates, wherein the cleaned aluminum alloy plates are immersed in an electrolyte as an anode and a stainless steel electrolyte tank is used as a cathode, characterized in that: The following steps are also included: (1) Performing micro-arc oxidation treatment, rinsing the micro-arc oxidized aluminum alloy plate with 15-20°C cold water to remove surface residues, and air-drying at room temperature, wherein the electrolyte is: sodium dodecamolybdate phosphate with a concentration of 8-10 g / L, propylene glycol with a concentration of 0.5-1 g / L, potassium pyrophosphate with a concentration of 2-8 g / L, sodium metaborate with a concentration of 4-6 g / L, potassium metaaluminate with a concentration of 1-2 g / L, and sodium metavanadate with a concentration of 3-8 g / L; the micro-arc oxidation power is 200-300 kW, and the current is: forward current 5-20 A / dm 2 , negative current density 0~-5A / dm 2 , voltage: positive 500~540V, negative 0~-300V, frequency: 200Hz~600Hz, positive and negative duty cycle 5%~35%, pulse width 50μs~2000μs; (2) Impregnation sealing: add 4~5wt% of aluminum salt to the organic silicate solution with a mass fraction of 5~10% and a pH value of 8~9, and impregnate the air-dried aluminum alloy plate at a temperature of 30~40℃ for 10~20min and then dry it; (3) Aging: the dried aluminum alloy plate is aged in a room at a temperature of 35~45℃, containing 2%~3% carbon dioxide and a relative humidity of 80~90% for 2~4h.

2. The method for micro-arc oxidation closed aging treatment of aluminum alloy plate according to claim 1, characterized in that: The drying in step (2) is performed at 60-80° C. for 0.5-1 h.

3. The method for micro-arc oxidation closed aging treatment of aluminum alloy plate according to claim 1, characterized in that: The organic silicate in step (2) is one of lithium methyl silicate or sodium phenyl silicate.

4. The method for micro-arc oxidation closed aging treatment of aluminum alloy plate according to claim 1, characterized in that: The aluminum salt in step (2) is one or more of aluminum chloride and aluminum sulfate.

5. The method for micro-arc oxidation closed aging treatment of aluminum alloy plate according to claim 1, characterized in that: The aluminum alloy plate is one of 1050 aluminum alloy plate, 1100 aluminum alloy plate, 6010 aluminum alloy plate and 6063 aluminum alloy plate.

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