Aluminum alloy hard anodizing method

Abstract

The invention proposes a method for hard anodizing of aluminum alloy, comprising the following steps: degreasing treatment, alkaline etching treatment, polishing treatment, hard anodizing treatment and sealing treatment. The hard anodizing treatment is to place the workpiece after the polishing treatment in an electrolytic bath liquid, the bath liquid temperature is ‑3-2°C, and the constant current method is used to supply electricity, and the current density is 0.5-1.8A / dm 2 The electrolytic bath solution contains 260-280 g / L sulfuric acid, 50-60 g / L glycerol and 5-10 g / L oxalic acid. The hard anodized film layer generated by the present invention has a thickness of more than 40 μm, a hardness of ≥300 HV, and an ablation rate of the product of about 3‰.

Description

Technical Field

[0001] The invention relates to the field of hard anodizing, in particular to a hard anodizing method for aluminum alloy. Background Art

[0002] Aluminum and aluminum alloys are amphoteric metals. They have a series of advantages such as low density, good shaping, easy strengthening, corrosion resistance, weldability, strong electrical and thermal conductivity, excellent mechanical properties and good machinability. They are widely used in aerospace, shipbuilding, construction, electrical, chemical, transportation, automobile and other fields. However, aluminum alloys will corrode to varying degrees in acid and alkali environments within a specific concentration range, and it is easy to form an oxide film with poor corrosion resistance on the surface of the aluminum alloy, especially in a humid environment. At the same time, the hardness and wear resistance of aluminum alloys are poor. Improvements through hard anodizing or surface coating just make up for these shortcomings and ensure the normal performance of the product.

[0003] The hard anodizing treatment of aluminum alloy is to form a hard anodized film on the surface of the material by electrolysis in an electrolyte with aluminum alloy as the anode. The hard anodized film has better performance than the naturally formed oxide film, and the film thickness, hardness and wear resistance are significantly improved. The hard anodized film is porous (with an average porosity of 10-15%) and is light gray, dark gray, gray-brown to black.

[0004] Most parts that have certain requirements for film hardness and thickness are hard anodized with sulfuric acid. If the workpiece is made of 2A12 aluminum alloy and the local thickness is less than 0.5mm, it is very easy to cause ablation or the film hardness and thickness cannot meet the technical requirements during sulfuric acid hard anodizing. Therefore, how to overcome the shortcomings of the existing technology is an urgent problem to be solved in the field of 2A12 hard anodizing technology. Summary of the invention

[0005] The invention provides a method for hard anodizing of aluminum alloy, wherein the thickness of the generated hard anodized film is above 40 μm, the hardness is ≥300 HV, and the ablation rate of the product is about 3‰.

[0006] The technical solution of the present invention is achieved as follows: a method for hard anodizing of aluminum alloy comprises the following steps:

[0007] (1) Degreasing: After degreasing the aluminum alloy workpiece, rinse it with 50-70℃ hot water, and then rinse it with running water;

[0008] (2) Alkali etching treatment: the aluminum alloy workpiece treated in step (1) is placed in an alkaline etching solution for alkaline etching treatment, and then rinsed with running water; this step removes the natural oxide film, impurities, slight rough marks and oil stains remaining from the previous process on the workpiece surface, so that the workpiece surface is evenly thinned;

[0009] (3) Polishing treatment: The aluminum alloy workpiece treated in step (2) is placed in a polishing tank for treatment at room temperature, and then rinsed with running tap water and then with running deionized water. This step removes dust on the workpiece surface after alkaline washing (residual copper, iron, magnesium and other particles that do not react with the alkaline etching solution), and neutralizes the alkaline etching solution remaining on the workpiece surface to prevent contamination by the hard anodizing solution, thereby obtaining an oxide film with a clean surface.

[0010] (4) Hard anodizing treatment: The aluminum alloy workpiece treated in step (3) is placed in an electrolytic bath with a bath temperature of -3 to 2°C and a constant current method with a current density of 0.5 to 1.8 A / dm 2 , stirring with air for 50-60 minutes; after the treatment, washing the electrolytic bath liquid on the surface with running water; the electrolytic bath liquid contains 260-280g / L sulfuric acid, 50-60g / L glycerol and 5-10g / L oxalic acid; through this step, an oxide film with a certain hardness and thickness is formed on the surface of the workpiece;

[0011] (5) Sealing treatment: The aluminum alloy workpiece treated in step (4) is placed in a sealing tank liquid for sealing, and then dried; the sealing tank liquid is deionized water with a conductivity of ≤30us / cm.

[0012] Furthermore, in step (4), the constant current method includes 5 stages of boosting, and the current intensity is 0.5-0.7A / dm 2 , 0.7-0.9 / dm 2 , 0.9-1.1 / dm 2 , 1.1-1.3 / dm 2 , 1.3-1.8 / dm 2 The first four stages lasted for 5 minutes each, and the fifth stage lasted for 30-32 minutes.

[0013] Furthermore, the aluminum alloy workpiece is made of 2A12 aluminum alloy, and the local thickness of the aluminum alloy workpiece is less than 0.5 mm.

[0014] Furthermore, in step (2), the alkaline etching solution contains 40-60 g / L of sodium hydroxide and 7-9 g / L of a long-life alkaline etching agent.

[0015] Furthermore, in step (2), the temperature of the alkaline etching treatment is 50-70° C. and the time is 1-3 min.

[0016] Furthermore, in step (3), the light output tank liquid contains 300-400 g / L nitric acid, and the treatment time is 1-3 min.

[0017] Furthermore, in step (5), the sealing bath solution is deionized water with a conductivity of ≤10 us / cm, and the sealing treatment temperature is 85-100° C. for 5-10 min.

[0018] Furthermore, in step (1), degreasing is performed using Tianyue New Materials' CT-256B alkaline degreasing agent, the degreasing temperature is 50-70°C, and the degreasing time is 3-5 minutes.

[0019] Furthermore, in step (4), after the treatment is completed, it is first rinsed with running tap water and then rinsed with deionized water.

[0020] Furthermore, in steps (1) and (2), the surface of the rinsed aluminum alloy workpiece is in a continuous water film state, and the water film time is maintained for 20 seconds.

[0021] Furthermore, in step (4), the stirring is performed using compressed air. The device for providing compressed air must have an oil-water separation function.

[0022] Beneficial effects of the present invention:

[0023] The invention is a stable and highly operable hard anodizing process method, which solves the defects of the traditional hard anodizing process of 2A12 material, and can effectively reduce the amount of workpiece ablation, and the obtained film layer has good hardness, thickness and corrosion resistance; the method of the invention is simple to operate, the solution system used is stable, and can be used for a long time; through the method of the invention, the hard anodized film layer generated on the surface of the 2A12 aluminum alloy material has a thickness of more than 40μm and a hardness of ≥300HV, and the ablation rate of the product is about 3‰. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is a microscopic morphology of the oxide film of the aluminum alloy workpiece of the present invention;

[0026] Figure 2 This is the macroscopic morphology of the oxide film of the aluminum alloy workpiece of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] A 2A12 aluminum alloy hard anodizing method comprises the following steps:

[0030] (1) Degreasing treatment: The aluminum alloy workpiece is placed in a special degreasing agent solution for aluminum parts for degreasing. The degreasing time is 3 minutes. After degreasing, the surface degreasing agent is first rinsed with 65°C hot water, and then rinsed with running tap water. The special degreasing agent solution for aluminum parts is an existing commercial product, and Shenzhen Tianyue New Materials CT-256B alkaline degreasing agent is preferably used. The material of the aluminum alloy workpiece is 2A12 aluminum alloy, and the local thickness is less than 0.5 mm.

[0031] (2) Alkali etching treatment: the aluminum alloy workpiece treated in step (1) is placed in an alkaline etching solution for alkaline etching treatment at a temperature of 60° C. for 2 min, and then rinsed with running tap water; the alkaline etching solution contains sodium hydroxide and a long-life alkaline etching agent for aluminum and aluminum alloy, the sodium hydroxide content is 45 g / L, and the long-life alkaline etching agent content is 8 g / L

[0032] (3) Light treatment: The aluminum alloy workpiece treated in (2) is placed in a light-emitting tank solution for treatment at room temperature for 1.5 min; then rinsed with running tap water and then rinsed with running deionized water; the light-emitting solution contains nitric acid, and the nitric acid content is 367 g / L;

[0033] (4) Hard anodizing treatment: The aluminum alloy workpiece treated in (3) was placed in a hard anodizing bath with a bath temperature of -1.3°C and a constant current method with a current density of 1.3A / dm 2 The current is increased in 5 stages, with current intensities of 0.6A / dm 2 , 0.75 / dm 2 , 0.9 / dm 2 , 1.1 / dm 2 , 1.3 / dm 2The first four stages lasted for 5 minutes respectively, and the fifth stage lasted for 32 minutes. The whole process was stirred with compressed air. After the treatment, the surface electrolyte was cleaned within 1 minute. When cleaning, it was first rinsed with running tap water and then with deionized water. The electrolyte solution contained sulfuric acid, glycerol and oxalic acid, with a sulfuric acid content of 267g / L, a glycerol content of 55g / L, and an oxalic acid content of 6g / L.

[0034] (5) Sealing treatment: The aluminum alloy workpiece subjected to the hard anodizing treatment in (4) is placed in a sealing tank for sealing treatment. After sealing, it can be blown dry with compressed air, naturally dried, or baked. The sealing tank liquid is deionized water with a conductivity of ≤30us / cm, the sealing temperature is 90°C, and the sealing treatment time is 9min.

[0035] The oxide film thickness of the aluminum alloy workpiece prepared in this embodiment is 44 μm, the hardness is 330 HV, and the test solution does not change color after being dripped with a corrosive liquid at 25°C for 40 minutes, and the corrosion resistance meets the standard: WJ 538-20074.4.4 (hard anodized aluminum alloy E); the microscopic morphology of the workpiece oxide film is as follows Figure 1 As shown, the macroscopic morphology is Figure 2 shown.

[0036] Example 2

[0037] A method for hard anodizing of aluminum alloy comprises the following steps:

[0038] (1) Degreasing treatment: The aluminum alloy workpiece is placed in a special degreasing agent solution for aluminum parts for degreasing. The degreasing time is 3 minutes. After degreasing, the surface degreasing agent is first rinsed with 60°C hot water, and then rinsed with running tap water. The special degreasing agent solution for aluminum parts is an existing commercial product, and Shenzhen Tianyue New Materials CT-256B alkaline degreasing agent is preferably used. The material of the aluminum alloy workpiece is 2A12 aluminum alloy, and the local thickness is less than 0.5 mm.

[0039] (2) Alkali etching treatment: the aluminum alloy workpiece treated in step (1) is placed in an alkaline etching solution for alkaline etching treatment, the alkaline etching treatment temperature is 55° C., and the time is 2.5 min; then it is rinsed with running tap water; the alkaline etching solution contains sodium hydroxide and a long-life alkaline etching agent for aluminum and aluminum alloy, the sodium hydroxide content is 50 g / L, and the long-life alkaline etching agent content is 7.5 g / L

[0040] (3) Light treatment: The aluminum alloy workpiece treated in step (2) is placed in a light-emitting tank solution for treatment at room temperature for 2 minutes; then rinsed with running tap water and then rinsed with running deionized water; the light-emitting solution contains nitric acid, and the nitric acid content is 337 g / L;

[0041] (4) Hard anodizing treatment: The aluminum alloy workpiece treated in step (3) is placed in a hard anodizing bath with a bath temperature of -0.3°C and a constant current method with a current density of 1.5 A / dm 2 The current is increased in 5 stages, with current intensities of 0.6A / dm 2 , 0.85 / dm 2 , 1.0 / dm 2 , 1.3 / dm 2 , 1.5 / dm 2 The first four stages lasted for 5 minutes respectively, and the fifth stage lasted for 30 minutes. The whole process was stirred with compressed air. After the treatment, the surface electrolyte was cleaned within 1 minute. When cleaning, it was first rinsed with running tap water and then rinsed with deionized water. The electrolyte solution contained sulfuric acid, glycerol and oxalic acid, with a sulfuric acid content of 278g / L, a glycerol content of 53g / L, and an oxalic acid content of 8g / L.

[0042] (5) Sealing treatment: The aluminum alloy workpiece subjected to hard anodizing treatment in step (4) is placed in a sealing tank for sealing treatment. After sealing, the workpiece may be dried by blowing with compressed air, naturally air-dried, or baked. The sealing tank liquid may be deionized water with a conductivity of ≤30 us / cm. The sealing treatment temperature is 95° C. and the sealing treatment time is 7 min.

[0043] The oxide film thickness of the aluminum alloy workpiece prepared in this embodiment is 42 μm, the hardness is 342 HV, and the test solution does not change color after being dripped with a corrosive liquid at 25° C. for 40 minutes, and the corrosion resistance meets the standard: WJ 538-20074.4.4 (hard anodized aluminum alloy E).

[0044] The aluminum alloy workpieces prepared by using Example 1 and Example 2 have an ablation rate of about 3‰.

[0045] Comparative Example 1

[0046] This embodiment is basically the same as embodiment 1, except that in step (4), the electrolytic cell solution contains sulfuric acid and glycerol, the sulfuric acid content is 256 g / L, and the glycerol content is 15 g / L.

[0047] The oxide film thickness of the aluminum alloy workpiece prepared in this embodiment is 24 μm and the hardness is 233 HV.

[0048] Comparative Example 2

[0049] This embodiment is basically the same as embodiment 1, except that in step (4), the bath liquid temperature is -3.7°C.

[0050] The oxide film thickness of the aluminum alloy workpiece prepared in this embodiment is 29 μm and the hardness is 343 HV.

[0051] Comparative Example 3

[0052] This embodiment is basically the same as embodiment 1, except that in step (4), the current is increased in five stages, namely 1A / dm 2 , 1.3A / dm 2 , 1.5A / dm 2 , 1.7A / dm 2 , 2A / dm 2 ,The first four stages last for 5 minutes respectively, and the fifth stage lasts for 30 minutes.

[0053] The oxide film thickness of the aluminum alloy workpiece prepared in this embodiment is 25 μm and the hardness is 357 HV.

[0054] The aluminum alloy workpieces prepared by Comparative Examples 1-3 had a product ablation rate of about 2%.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for hard anodizing of aluminum alloy, characterized in that: The following steps are involved: (1) Degreasing: After degreasing the aluminum alloy workpiece, rinse it with 50-70℃ hot water, and then rinse it with running water; (2) Alkaline etching treatment: placing the aluminum alloy workpiece treated in step (1) in an alkaline etching solution for alkaline etching treatment, and then rinsing with running water; (3) Polishing treatment: The aluminum alloy workpiece treated in step (2) is placed in a polishing tank liquid for treatment at room temperature, and then rinsed with running tap water and then with running deionized water; (4) Hard anodizing treatment: the aluminum alloy workpiece treated in step (3) is placed in an electrolytic bath with a bath temperature of -3 to 2°C, and is powered by a constant current method. The entire process is stirred by compressed air. After the treatment is completed, the electrolytic bath liquid on the surface is immediately cleaned with running water. The electrolytic cell solution contains 260-280 g / L of sulfuric acid, 50-60 g / L of glycerol and 5-10 g / L of oxalic acid; (5) Sealing treatment: the aluminum alloy workpiece treated in step (4) is placed in a sealing tank liquid for sealing, and then dried; the sealing tank liquid is deionized water with a conductivity of ≤30us / cm; In step (4), the constant current method includes 5 stages of boosting, with current intensities ranging from 0.5 to 0.7 A / dm 2 , 0.7-0.9 / dm 2 , 0.9-1.1 / dm 2 , 1.1-1.3 / dm 2 , 1.3-1.8 / dm 2 , the first four stages lasted for 5-6 minutes, and the fifth stage lasted for 30-35 minutes; The aluminum alloy workpiece is made of 2A12 aluminum alloy, and the local thickness of the aluminum alloy workpiece is less than 0.5 mm; In step (2), the alkaline etching solution contains 40-60 g / L of sodium hydroxide and 7-9 g / L of long-life alkaline etching agent; the temperature of the alkaline etching treatment is 50-70°C and the time is 1-3 min; In step (3), the light emitting tank liquid contains 300-400 g / L nitric acid, and the treatment time is 1-3 min; In step (5), the sealing treatment temperature is 85-100°C and the time is 5-10 minutes.

2. The method for hard anodizing of aluminum alloy according to claim 1, characterized in that: In step (4), after treatment, rinse with running tap water first and then with deionized water.

3. The method for hard anodizing of aluminum alloy according to claim 1, characterized in that: In steps (1) and (2), the surface of the rinsed aluminum alloy workpiece presents a continuous water film state, and the water film time is maintained for 20 seconds.

Images