Processing technology of double-layer hard anodic oxide film on metal surface

Abstract

The invention discloses a processing technology of a double-layer hard anodic oxide film on a metal surface, relates to the technical field of aluminum alloy anodic oxidation, and provides the processing technology of the double-layer hard anodic oxide film on the metal surface in order to improve the surface hardness and high temperature resistance of aluminum alloy. The anodic oxide layers with different pores are prepared through different electrolyte components, the primary anodic oxide layer serves as a bottom layer, thermal stress between an aluminum alloy body and the oxide layers due to different thermal expansion coefficients is effectively reduced, expansion caused by thermal shock is relieved, the secondary anodic oxide layer on the surface layer has a small pore diameter, and the thermal shock resistance of the aluminum alloy body is improved. And the carbon fibers are subjected to modification treatment, so that the aluminum alloy material has relatively high hardness and a better corrosion-resistant effect, and the applicability of the aluminum alloy material to various environments is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy anodizing, in particular to a processing technology for a double-layer hard anodized film on a metal surface. Background Art

[0002] As a metal material, aluminum alloy has the characteristics of low density, high strength and excellent processing performance. It is widely used in aerospace and various transportation vehicle manufacturing fields. However, due to the nature of aluminum metal itself, the surface hardness of aluminum alloy material is low and it is easy to scratch. However, in the air environment, the surface of aluminum alloy will be passivated to form an oxide film. This oxide film can effectively improve the surface hardness of aluminum alloy material, thereby improving its wear resistance and chemical corrosion resistance. However, the oxide film naturally generated in the air environment is thin and contains more loose voids, which often cannot provide good protection for the aluminum alloy matrix. Therefore, in the existing process, anodizing technology is often used to form a dense oxide film on the surface of the aluminum alloy matrix to improve the protection of the aluminum alloy.

[0003] However, in the existing process, if you want the oxide film formed by the anodizing technology to have sufficient hardness, it must have a sufficient film thickness. However, there are different thermal expansion coefficients between the oxide film and the aluminum substrate. At high temperatures, the thicker the oxide film, the greater the thermal stress between it and the aluminum substrate, and the easier it is to cause the oxide film layer to crack, resulting in a decrease in protective performance. Summary of the invention

[0004] The purpose of the present invention is to provide a processing technology for a double-layer hard anodized film on a metal surface to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solution: a processing technology for a double-layer hard anodized film on a metal surface, comprising the following steps:

[0006] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0007] S2. The aluminum alloy body is immersed in an electrolyte as an anode, a graphite sheet is used as a cathode, and compressed air is stirred to perform an oxidation treatment. After the treatment, an anodic oxide layer is formed on the surface of the aluminum alloy body, the surface is removed, and the surface is washed with water to remove the electrolyte once, and then dried for use;

[0008] S3. The aluminum alloy body treated in step S2 is immersed in a secondary electrolyte as an anode, a graphite sheet as a cathode, and compressed air is stirred for secondary oxidation. After the treatment, a secondary anodized layer is obtained, and then the surface is washed with clean water to remove the secondary electrolyte, and then dried for standby use;

[0009] S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and vacuumed to 1-3×10 -2 Pa, take out after immersion for 10-30 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 1-3 minutes, take out, wash with deionized water, and dry for standby use;

[0010] S5. After repeating step S4 1-3 times, the aluminum alloy blank is heated to 180-220°C in an argon atmosphere and kept warm for 10-15 minutes, then heated to 480-550°C, kept warm for 30-45 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0011] Furthermore, in step S1, the acid solution is a 3-10wt% sulfuric acid solution, the pickling temperature is 70-85°C, and the pickling time is 3-8min.

[0012] Furthermore, in step S1, the alkali solution is a sodium hydroxide aqueous solution with a concentration of 5-10 wt%, the alkali etching temperature is 60-75° C., and the alkali etching time is 4-8 min.

[0013] Further, in step S2, during the primary oxidation treatment, the current density is 3-5A / dm 2 ; The thickness of the primary anodized layer is 25-40μm.

[0014] Further, in step S2, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0015] The concentration of sulfuric acid is 12-90 g / L, the concentration of sorbitol is 30-50 g / L, and the concentration of glycolic acid is 10-20 g / L.

[0016] Furthermore, in step S3, during the secondary oxidation treatment, the current density is 2-3A / dm 2 ; The thickness of the secondary anodized layer is 30-40μm.

[0017] Furthermore, in step S3, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0018] Wherein, the concentration of oxalic acid is 90-128 g / L, and the concentration of sulfuric acid is 2-8 g / L.

[0019] Furthermore, in step S4, the concentration of acrylonitrile in the acrylonitrile solution is 4-15 wt %, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.005-0.1 wt %.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In order to improve the surface hardness and high temperature resistance of aluminum alloy, the present invention provides a processing technology for a double-layer hard anodized film on the metal surface, and changes the single-layer anodized film into a double-layer film structure. The present invention first uses a primary electrolyte composed of sulfuric acid, sorbitol, glycolic acid and deionized water as a treatment agent, and then uses a secondary electrolyte composed of sulfuric acid, oxalic acid and deionized water as a treatment agent, and corrodes at high and low current densities respectively to prepare oxide layers with different pore sizes, thereby improving the compatibility between the oxide layer and the aluminum alloy substrate, effectively reducing the thermal stress between the aluminum alloy and the oxide layer caused by different thermal expansion coefficients, and relieving the expansion caused by thermal shock;

[0022] On this basis, the present invention further uses acrylonitrile as a treating agent, and immerses the aluminum alloy substrate in it. Under negative pressure conditions, the acrylonitrile solution will fully penetrate into the tiny pores of the secondary anodized layer, and then the acrylonitrile will be cross-linked under the action of ammonium persulfate initiator, and finally carbon fibers will be generated under high temperature conditions to fill the tiny pores of the secondary anodized layer, thereby further improving the hardness and corrosion resistance of the anodized film. DETAILED DESCRIPTION

[0023] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0024] Embodiment 1. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0025] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0026] The acid solution is a 3wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 8min;

[0027] The alkali solution is a 5wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 8 minutes;

[0028] S2. Immerse the aluminum alloy blank in the primary electrolyte as the anode, use the graphite sheet as the cathode, and set the current density to 3A / dm2 , stirring with compressed air, and performing an oxidation treatment. After the treatment, a primary anodized layer with a thickness of 30 μm is formed on the surface of the aluminum alloy blank, the blank is taken out, washed with clean water to remove the primary electrolyte on the surface, and dried for use;

[0029] Wherein, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0030] In the primary electrolyte, the concentration of sulfuric acid is 45 g / L, the concentration of sorbitol is 30 g / L, and the concentration of glycolic acid is 20 g / L;

[0031] S3. The aluminum alloy blank treated in step S2 is immersed in a secondary electrolyte as an anode, and a graphite sheet is used as a cathode, and the current density is set to 2A / dm 2 , stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 35 μm is obtained, and then the layer is taken out, washed with clean water to remove the secondary electrolyte on the surface, and then dried for use;

[0032] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0033] The oxalic acid concentration in the secondary electrolyte is 120 g / L and the sulfuric acid concentration is 2 g / L;

[0034] S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and evacuated to 1.5×10 -2 Pa, take out after immersion for 15 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 3 minutes, take out, wash with deionized water, and dry for standby use;

[0035] Wherein, the concentration of acrylonitrile in the acrylonitrile solution is 4wt%, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.01wt%;

[0036] S5. After repeating step S4 for 3 times, the aluminum alloy blank is heated to 210°C in an argon atmosphere and kept warm for 15 minutes, then heated to 500°C and kept warm for 5 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0037] Embodiment 2. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0038] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0039] The acid solution is a 10wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 3 minutes;

[0040] The alkali solution is a 10wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 4 minutes;

[0041] S2. Immerse the aluminum alloy blank in the primary electrolyte as the anode, use the graphite sheet as the cathode, and set the current density to 5A / dm 2 , stirring with compressed air, and performing an oxidation treatment. After the treatment, a primary anodized layer with a thickness of 30 μm is formed on the surface of the aluminum alloy blank, the blank is taken out, washed with clean water to remove the primary electrolyte on the surface, and dried for use;

[0042] Wherein, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0043] In the primary electrolyte, the concentration of sulfuric acid is 90 g / L, the concentration of sorbitol is 30 g / L, and the concentration of glycolic acid is 20 g / L;

[0044] S3. The aluminum alloy blank treated in step S2 is immersed in a secondary electrolyte as an anode, and a graphite sheet is used as a cathode, and the current density is set to 3A / dm 2 , stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 35 μm is obtained, and then the layer is taken out, washed with clean water to remove the secondary electrolyte on the surface, and then dried for use;

[0045] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0046] The concentration of oxalic acid in the secondary electrolyte is 90 g / L and the concentration of sulfuric acid is 8 g / L;

[0047] S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and evacuated to 1.5×10 -2 Pa, take out after immersion for 15 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 3 minutes, take out, wash with deionized water, and dry for standby use;

[0048] Wherein, the concentration of acrylonitrile in the acrylonitrile solution is 15wt%, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.01wt%;

[0049] S5. After repeating step S4 for 3 times, the aluminum alloy blank is heated to 210°C in an argon atmosphere and kept warm for 15 minutes, then heated to 550°C and kept warm for 5 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0050] Embodiment 3. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0051] Compared with Example 1, this embodiment increases the thickness of the primary anodized layer in step S2;

[0052] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0053] The acid solution is a 10wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 3 minutes;

[0054] The alkali solution is a 10wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 4 minutes;

[0055] S2. Immerse the aluminum alloy blank in the primary electrolyte as the anode, use the graphite sheet as the cathode, and set the current density to 5A / dm 2 , stirring with compressed air, and performing an oxidation treatment. After the treatment, a primary anodized layer with a thickness of 40 μm is formed on the surface of the aluminum alloy blank, the blank is taken out, washed with clean water to remove the primary electrolyte on the surface, and dried for use;

[0056] Wherein, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0057] In the primary electrolyte, the concentration of sulfuric acid is 45 g / L, the concentration of sorbitol is 30 g / L, and the concentration of glycolic acid is 20 g / L;

[0058] S3. The aluminum alloy blank treated in step S2 is immersed in a secondary electrolyte as an anode, and a graphite sheet is used as a cathode, and the current density is set to 2A / dm 2 , stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 35 μm is obtained, and then the layer is taken out, washed with clean water to remove the secondary electrolyte on the surface, and then dried for use;

[0059] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0060] The oxalic acid concentration in the secondary electrolyte is 120 g / L and the sulfuric acid concentration is 2 g / L;

[0061] S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and evacuated to 1.5×10 -2Pa, take out after immersion for 15 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 3 minutes, take out, wash with deionized water, and dry for standby use;

[0062] Wherein, the concentration of acrylonitrile in the acrylonitrile solution is 15wt%, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.01wt%;

[0063] S5. After repeating step S4 for 3 times, the aluminum alloy blank is heated to 210°C in an argon atmosphere and kept warm for 15 minutes, then heated to 550°C and kept warm for 5 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0064] Embodiment 4. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0065] Compared with Example 1, this embodiment increases the thickness of the secondary anodized layer in step S3;

[0066] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0067] The acid solution is a 3wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 8min;

[0068] The alkali solution is a 5wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 8 minutes;

[0069] S2. Immerse the aluminum alloy blank in the primary electrolyte as the anode, use the graphite sheet as the cathode, and set the current density to 3A / dm 2 , stirring with compressed air, and performing an oxidation treatment. After the treatment, a primary anodized layer with a thickness of 30 μm is formed on the surface of the aluminum alloy blank, the blank is taken out, washed with clean water to remove the primary electrolyte on the surface, and dried for use;

[0070] Wherein, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0071] In the primary electrolyte, the concentration of sulfuric acid is 45 g / L, the concentration of sorbitol is 30 g / L, and the concentration of glycolic acid is 20 g / L;

[0072] S3. The aluminum alloy blank treated in step S2 is immersed in a secondary electrolyte as an anode, and a graphite sheet is used as a cathode, and the current density is set to 2A / dm 2, stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 40 μm is obtained, and then the layer is taken out, washed with clean water to remove the secondary electrolyte on the surface, and dried for use;

[0073] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0074] The oxalic acid concentration in the secondary electrolyte is 120 g / L and the sulfuric acid concentration is 2 g / L;

[0075] S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and evacuated to 1.5×10 -2 Pa, take out after immersion for 15 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 3 minutes, take out, wash with deionized water, and dry for standby use;

[0076] Wherein, the concentration of acrylonitrile in the acrylonitrile solution is 4wt%, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.01wt%;

[0077] S5. After repeating step S4 for 3 times, the aluminum alloy blank is heated to 210°C in an argon atmosphere and kept warm for 15 minutes, then heated to 500°C and kept warm for 5 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0078] Embodiment 5. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0079] Compared with Example 1, this embodiment reduces the number of repetitions in step S5;

[0080] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0081] The acid solution is a 3wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 8min;

[0082] The alkali solution is a 5wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 8 minutes;

[0083] S2. Immerse the aluminum alloy blank in the primary electrolyte as the anode, use the graphite sheet as the cathode, and set the current density to 3A / dm 2, stirring with compressed air, and performing an oxidation treatment. After the treatment, a primary anodized layer with a thickness of 30 μm is formed on the surface of the aluminum alloy blank, the blank is taken out, washed with clean water to remove the primary electrolyte on the surface, and dried for use;

[0084] Wherein, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0085] In the primary electrolyte, the concentration of sulfuric acid is 45 g / L, the concentration of sorbitol is 30 g / L, and the concentration of glycolic acid is 20 g / L;

[0086] S3. The aluminum alloy blank treated in step S2 is immersed in a secondary electrolyte as an anode, and a graphite sheet is used as a cathode, and the current density is set to 2A / dm 2 , stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 35 μm is obtained, and then the layer is taken out, washed with clean water to remove the secondary electrolyte on the surface, and then dried for use;

[0087] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0088] The oxalic acid concentration in the secondary electrolyte is 120 g / L and the sulfuric acid concentration is 2 g / L;

[0089] S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and evacuated to 1.5×10 -2 Pa, take out after immersion for 15 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 3 minutes, take out, wash with deionized water, and dry for standby use;

[0090] Wherein, the concentration of acrylonitrile in the acrylonitrile solution is 4wt%, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.01wt%;

[0091] S5. After repeating step S4 once, the aluminum alloy blank is heated to 210°C in an argon atmosphere and kept warm for 15 minutes, then heated to 500°C and kept warm for 5 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0092] Comparative Example 1. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0093] Compared with Example 1, this comparative example did not perform the original step S2 treatment;

[0094] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0095] The acid solution is a 3wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 8min;

[0096] The alkali solution is a 5wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 8 minutes;

[0097] S2. The aluminum alloy blank is immersed in the secondary electrolyte as the anode, the graphite sheet is used as the cathode, and the current density is set to 2A / dm 2 , stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 35 μm is obtained, and then the layer is taken out, washed with clean water to remove the secondary electrolyte on the surface, and then dried for use;

[0098] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0099] The oxalic acid concentration in the secondary electrolyte is 120 g / L and the sulfuric acid concentration is 2 g / L;

[0100] S3. The aluminum alloy blank treated in step S32 is immersed in an acrylonitrile solution at 2-4°C and evacuated to 1.5×10 -2 Pa, take out after immersion for 15 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 3 minutes, take out, wash with deionized water, and dry for standby use;

[0101] Wherein, the concentration of acrylonitrile in the acrylonitrile solution is 4wt%, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.01wt%;

[0102] S4. After repeating step S3 for 3 times, the aluminum alloy blank is heated to 210°C in an argon atmosphere and kept warm for 15 minutes, then heated to 500°C and kept warm for 5 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

[0103] Comparative Example 2. A process for producing a double-layer hard anodized film on a metal surface, comprising the following steps:

[0104] Compared with Example 1, this comparative example did not perform steps S4 and S5;

[0105] S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank;

[0106] The acid solution is a 3wt% sulfuric acid solution, the pickling temperature is 70°C, and the pickling time is 8min;

[0107] The alkali solution is a 5wt% sodium hydroxide aqueous solution, the alkali etching temperature is 70°C, and the alkali etching time is 8 minutes;

[0108] S2. Immerse the aluminum alloy blank in the primary electrolyte as the anode, use the graphite sheet as the cathode, and set the current density to 3A / dm 2 , stirring with compressed air, and performing an oxidation treatment. After the treatment, a primary anodized layer with a thickness of 30 μm is formed on the surface of the aluminum alloy blank, the blank is taken out, washed with clean water to remove the primary electrolyte on the surface, and dried for use;

[0109] Wherein, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water;

[0110] In the primary electrolyte, the concentration of sulfuric acid is 45 g / L, the concentration of sorbitol is 30 g / L, and the concentration of glycolic acid is 20 g / L;

[0111] S3. The aluminum alloy blank treated in step S2 is immersed in a secondary electrolyte as an anode, and a graphite sheet is used as a cathode, and the current density is set to 2A / dm 2 , stirring with compressed air, and performing secondary oxidation treatment. After the treatment, a secondary anodized layer with a thickness of 35 μm is obtained, and then the aluminum alloy material containing a double-layer hard anodized film on the surface is obtained after the secondary anodized layer is taken out and washed with clean water to remove the secondary electrolyte on the surface, and then dried;

[0112] Wherein, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water;

[0113] The oxalic acid concentration in the secondary electrolyte is 120 g / L, and the sulfuric acid concentration is 2 g / L.

[0114] Testing: According to GB / T 4340.1-2009, the samples prepared in Examples 1-5 and Comparative Examples 1-2 were tested for HV5 Vickers hardness;

[0115] According to GB / T8013.1-2018, the samples prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to a neutral salt spray test;

[0116] The samples prepared in Examples 1-5 and Comparative Examples 1-2 were heated to 250° C., kept at this temperature for 5 min, cooled to room temperature at a rate of 3° C. / min, kept at this temperature for 5 min, and repeated the cycle 10 times before being subjected to a neutral salt spray test again.

[0117] The test results are shown in the table below;

[0118]

[0119] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for producing a double-layer hard anodized film on a metal surface, characterized in that: The following steps are involved: S1. After the aluminum alloy is polished to a smooth surface by CNC process, it is immersed in an acid solution for degreasing, taken out and washed with clean water, immersed in an alkali solution again for alkaline etching, and then washed again on the surface and dried to obtain an aluminum alloy blank; S2. The aluminum alloy body is immersed in an electrolyte as an anode, a graphite sheet is used as a cathode, and compressed air is stirred to perform an oxidation treatment. After the treatment, an anodic oxide layer is formed on the surface of the aluminum alloy body, the surface is removed, and the surface is washed with water to remove the electrolyte once, and then dried for use; S3. The aluminum alloy body treated in step S2 is immersed in a secondary electrolyte as an anode, a graphite sheet as a cathode, and compressed air is stirred for secondary oxidation. After the treatment, a secondary anodized layer is obtained, and then the surface is washed with clean water to remove the secondary electrolyte, and then dried for standby use; S4. The aluminum alloy blank treated in step S3 is immersed in an acrylonitrile solution at 2-4°C and vacuumed to 1-3×10 - 2 Pa, take out after immersion for 10-30 minutes, immerse the aluminum alloy blank again in an ammonium persulfate solution at a temperature of 80-85°C, react for 1-3 minutes, take out, wash with deionized water, and dry for standby use; S5. After repeating step S4 1-3 times, the aluminum alloy blank is heated to 180-220°C in an argon atmosphere and kept warm for 10-15 minutes, then heated to 480-550°C, kept warm for 30-45 minutes, and then cooled to room temperature in the furnace to obtain an aluminum alloy material with a double-layer hard anodized film on the surface.

2. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S1, the acid solution is a 3-10wt% sulfuric acid solution, the pickling temperature is 70-85°C, and the pickling time is 3-8min.

3. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S1, the alkali solution is a sodium hydroxide aqueous solution with a concentration of 5-10 wt%, the alkali etching temperature is 60-75° C., and the alkali etching time is 4-8 min.

4. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S2, during the primary oxidation treatment, the current density is 3-5A / dm 2 ; The thickness of the primary anodized layer is 25-40μm.

5. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S2, the primary electrolyte is a mixture of sulfuric acid, sorbitol, glycolic acid and deionized water; The concentration of sulfuric acid is 12-90 g / L, the concentration of sorbitol is 30-50 g / L, and the concentration of glycolic acid is 10-20 g / L.

6. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S3, during the secondary oxidation treatment, the current density is 2-3A / dm 2 ; The thickness of the secondary anodized layer is 30-40μm.

7. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S3, the secondary electrolyte is a mixture of sulfuric acid, oxalic acid and deionized water; Wherein, the concentration of oxalic acid is 90-128 g / L, and the concentration of sulfuric acid is 2-8 g / L.

8. The process for producing a double-layer hard anodized film on a metal surface according to claim 1, characterized in that: In step S4, the concentration of acrylonitrile in the acrylonitrile solution is 4-15 wt %, and the concentration of ammonium persulfate in the ammonium persulfate solution is 0.005-0.1 wt %.

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