Pretreatment process for solving problem of filamentous corrosion resistance in electrostatic spraying of aluminum alloy

Abstract

The invention discloses a pretreatment process for solving the problem of filamentous corrosion resistance of aluminum alloy electrostatic spraying, which is characterized by comprising the following steps: S1, polishing; s2, air gun dust removal; s3, degreasing is conducted; s4, washing for the first time; s5, alkali washing; s6, washing for the second time; s7, washing for the third time; s8, pickling and neutralizing; s9, washing for the fourth time; s10, washing with pure water for the first time; s11, anodic oxidation is conducted; s12, washing with pure water for the second time; s13, washing with pure water for the third time; s14, washing with pure water for the fourth time; s15, drying is conducted; s16, electrostatic spraying is carried out; and S17, baking and curing. The method has the advantages that the porous oxidation film formed through anodic oxidation provides a good adhesion basis for plastic spraying, the plastic spraying powder can be better embedded into pores of the oxidation film, the dual combination effect of mechanical locking and chemical bonding is formed, and the good filiform corrosion resisting effect is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy processing, and in particular to a pre-treatment process for solving the problem of aluminum alloy electrostatic spraying resistance to filamentary corrosion. Background Art

[0002] Filiform corrosion is the most stringent corrosion test, so its pre-treatment is very important. In the industry, passivation, silane, and phosphating are the most common pre-treatment processes. The present invention is to develop a new pre-treatment process. Anodizing itself is a corrosion-resistant surface treatment process, but the color is single. When customers require high resistance to filiform corrosion and the appearance needs to achieve a certain color gloss, it is necessary to change the conventional anodizing process, and the development of this process requires the adhesion of the plastic powder to be guaranteed. After continuous exploration of the oxidation process, the thickness of the anodized film can reach 4-15um, and the sealing process of the sealing agent is not performed. The sealing agent will affect the adhesion of the surface coating. Under this film thickness, it is N times that of the passivation film and the phosphating film, with good resistance to filiform corrosion, high hardness, and good adhesion of the electrostatic spraying plastic powder. Its resistance to filiform corrosion, salt spray resistance, high temperature and high humidity resistance are more advanced than pre-treatment processes such as passivation, silane, and phosphating. Studies have found that the thicker the oxide film, the lower the adhesion of its electrostatic powder spraying, and it will bring about the appearance defects of the powder spraying. Summary of the invention

[0003] The purpose of the present invention is to provide a pretreatment process for solving the problem of filamentary corrosion resistance of electrostatic spraying of aluminum alloy. The porous oxide film formed by anodizing provides a good adhesion basis for plastic spraying. The plastic spraying powder can be better embedded in the pores of the oxide film, forming a dual combination effect of mechanical locking and chemical bonding, thereby achieving good filamentary corrosion resistance.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions: A pretreatment process for solving the problem of aluminum alloy electrostatic spraying resistance to filiform corrosion, characterized by comprising the following steps: S1, grinding; S2, air gun dust removal; S3, skim; S4, first water wash; S5, alkali washing; S6, second water wash; S7, third water wash; S8, pickling and neutralization; S9, fourth wash; S10, first pure water wash; S11, anodized; S12, second pure water washing; S13, third pure water wash; S14, fourth pure water wash; S15, drying; S16, electrostatic spraying; S17, baking and curing.

[0005] Preferably, the step S1 specifically comprises: grinding the aluminum alloy using a gas grinder, and the mesh number of the grinding sandpaper is 180-240 meshes.

[0006] Preferably, in step S2, the air pressure of the air gun is 0.5-0.8 MPa.

[0007] Preferably, in step S3, the temperature of the degreasing acid solution is 40-50° C., the acid concentration is 100-140 g / L, and the degreasing time is 6-8 minutes.

[0008] Preferably, in step S4, the overflow rate of the first water washing is greater than 200 L / h, and the time is 1 min; The overflow rate of the second water washing in step S6 is greater than 400 L / h, and the time is 1 min; The overflow rate of the third water washing in step S7 is greater than 400 L / h, and the time is 1 min; The overflow rate of the fourth water washing in step S9 is greater than 200 L / h, and the time is 1 min.

[0009] Preferably, the concentration of the alkali washing solution used in the alkali washing in step S5 is 30-40 g / L, the aluminum ion concentration is 10-50 g / L, the alkali washing temperature is 40-45° C., and the alkali washing time is 5-6 min; The acid concentration of the pickling solution used in the pickling and neutralization in step S8 is 100-140 g / L, and the pickling time is 1-1.5 min.

[0010] Preferably, in step S10, the overflow rate of the first pure water washing is greater than 200 L / h, and the time is 1 min; In step S12, the overflow rate of the second pure water washing is greater than 400 L / h, and the time is 1 min; In step S13, the overflow rate of the third pure water washing is greater than 400 L / h, and the time is 1 min; In step S14, the overflow rate of the fourth pure water washing is greater than 400 L / h, and the time is 1 min.

[0011] Preferably, the anodization in step 11 is specifically as follows: temperature 23-27° C., time 5-10 min, acid concentration 170-190 g / L, voltage 12-18 V, aluminum ion concentration ≤15 g / L.

[0012] Preferably, the drying temperature in step S15 is 190-210° C., and the time is 30-60 min. The baking curing temperature in step 17 is 180-200° C., and the insulation time is 15-20 min.

[0013] Preferably, the specific parameters of the electrostatic powder spraying in step S16 are: input air pressure of 5.0~7.0 bar, fluidizing air pressure of 0.04~0.1 MPa, powder output of 20~40%, air supply of 3~5 bar, voltage of 30~70 kV, and current of 10~25 µA.

[0014] In summary, the beneficial effects of the present invention are: It effectively solves the problem of plastic spray adhesion on oxidized surfaces, and at the same time provides excellent resistance to acidic salt spray and filamentous corrosion. The porous oxide film formed by anodizing provides a good adhesion basis for plastic spraying. The plastic spraying powder can be better embedded in the pores of the oxide film, forming a dual bonding effect of mechanical locking and chemical bonding. The bonding between the passivation film and the plastic spraying layer mainly depends on physical adsorption and weaker chemical bonding, and the bonding strength is not as good as that of anodized plastic spraying. Secondly, after oxidized plastic spraying, when the plastic powder is destroyed, it can play a good anti-corrosion performance without corrosion expansion.

[0015] Traditional passivation and phosphating processes often use pollutants such as chromate and phosphate, which are harmful to the environment and human health. However, the anodizing spraying process can use a chromium-free electrolyte formula, which greatly reduces the use and emission of heavy metals. It can meet the European market with high environmental protection requirements, and the anodizing spraying process is more in line with environmental protection regulations.

[0016] The oxide film formed by anodizing has good chemical stability and shielding effect, which can effectively block the invasion of external corrosive media. Coupled with the further protection of the spray-coated layer, the corrosion resistance of the aluminum alloy after anodizing spray-coated is several times or even dozens of times higher than that of the passivated spray-coated in harsh corrosive environments, such as marine environments and industrial pollution areas. The anodized film itself has a high hardness of up to HV300~500, which can effectively resist friction and wear. The spray-coated layer further enhances the wear resistance of the surface, making the surface of the anodized spray-coated aluminum alloy products not easy to wear in occasions of frequent contact and friction, such as mechanical parts, furniture handles, etc., and maintain good appearance and performance. Anodizing can make the oxide film present a variety of colors, such as gold, black, blue, etc., by changing process parameters or using dyeing technology. The spray-coated layer also has a variety of colors and textures to choose from. The combination of the two can achieve more diverse decorative effects to meet the aesthetic needs of different customers. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1It is a flow chart of a pre-treatment process for solving the problem of filamentary corrosion resistance of electrostatic spraying of aluminum alloys according to the present invention; Figure 2 This is a material performance test result diagram of a pre-treatment process for solving the problem of filamentary corrosion resistance of aluminum alloy electrostatic spraying according to the present invention. DETAILED DESCRIPTION

[0018] The specific implementation manner of the present invention is further described below in conjunction with the accompanying drawings, and this embodiment does not constitute a limitation of the present invention.

[0019] like Figure 1 A pre-treatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying is shown, comprising the following steps: S1, grinding: Use an air grinder to grind the aluminum alloy workpiece, the grinding sandpaper mesh number is 180~240 mesh, and eliminate surface defects.

[0020] S2, air gun dust removal: The air pressure of the dust removal air gun is 0.5~0.8MPa. The air gun dust removal prevents dust from contaminating the degreasing tank.

[0021] S3, degreasing: The temperature of the degreasing acid solution is 40~50℃, the acid concentration is 100~140g / L, and the degreasing time is 6~8 minutes, so as to remove the surface animal fats and mineral oils to improve the adhesion of the coating. Test once every 4 hours to ensure the degreasing effect.

[0022] S4, first water washing: overflow rate> 200L / h, time is 1min, remove residual chemical solvents and impurity particles on the surface, and check once every 4 hours to ensure the water washing effect.

[0023] S5, alkali washing: the concentration of alkali washing solution is 30~40g / L, the aluminum ion concentration is 10~50g / L, the alkali washing temperature is 40~45℃, the alkali washing time is 5~6min, adjust the surface state of aluminum alloy, remove the surface oxide film, and check once every 4 hours to ensure the surface adjustment effect.

[0024] S6, second water washing: water washing overflow > 400L / h, time is 1min, remove residual chemical solvents on the surface, test once every 4 hours to ensure the water washing effect.

[0025] S7, third water washing: water washing overflow > 400L / h, time is 1min, remove residual chemical solvents on the surface, test once every 4 hours to ensure the water washing effect.

[0026] S8, pickling and neutralization: the acid concentration of the pickling solution is 100~140g / L, the pickling time is 1~1.5min, and the residual chemical solvents on the surface are neutralized. Test once every 4 hours to ensure the pickling effect.

[0027] S9, the fourth water washing: overflow rate> 200L / h, time is 1min, remove residual chemical solvents on the surface, and check once every 4 hours to ensure the water washing effect.

[0028] S10, first pure water washing: overflow rate> 200L / h, time is 1min, remove residual chemical solvents on the surface, and check once every 4 hours to ensure the washing effect.

[0029] S11, anodizing: temperature 23~27℃, time 5~10min, acid concentration 170~190g / L, voltage 12~18V, aluminum ion concentration ≤15g / L. An oxide film is formed on the surface of the aluminum alloy to improve the adhesion and corrosion resistance of the coating. Test once every 4 hours to ensure the passivation effect.

[0030] S12, second pure water washing: overflow rate> 400L / h, time is 1min, remove residual solution on the surface, and check once every 4 hours to ensure the washing effect.

[0031] S13, third pure water washing: overflow rate> 400L / h, time is 1min, remove residual solution on the surface, and check once every 4 hours to ensure the washing effect.

[0032] S14, the fourth pure water washing: overflow rate> 400L / h, time is 1min, remove the residual solution on the surface, can wash away the agent in the hole, avoid the agent on the spray adhesion product influence, test once every 4 hours to ensure the washing effect.

[0033] S15, drying: temperature is 190~210℃, time is 30~60min, to remove surface moisture.

[0034] S16, electrostatic spraying: input air pressure is 5.0~7.0bar, fluidizing air pressure is 0.04~0.1MPa, powder output is 20~40%, air supply is 3~5bar, voltage is 30~70kv, current is 10~25µA, and electrostatic powder spraying is performed on the surface of aluminum alloy workpiece at 30-50℃. This temperature can quickly apply powder, save spraying time, reduce the problem of no powder application in dead corners, and improve product qualification rate.

[0035] S17, baking and curing: the temperature is 180~200℃, and the insulation time is 15~20min to ensure that the plastic powder is fully cured.

[0036] Follow-up appearance inspections are conducted to prevent defective products from reaching customers, avoid customer complaints, and improve customer satisfaction.

[0037] The present invention effectively solves the problem of plastic spray adhesion on the oxidized surface, and at the same time provides excellent resistance to acid salt spray and filamentous corrosion. The porous oxide film formed by anodizing provides a good adhesion basis for plastic spraying, and the plastic spraying powder can be better embedded in the pores of the oxide film to form a dual combination effect of mechanical locking and chemical bonding. The aluminum alloy prepared by the pretreatment of the present application is tested according to the standard ISO 4632-2-2016, and the anodizing in the present application is replaced by ordinary passivation treatment as a comparative test. The specific test data are as follows: Figure 2 As shown in the figure, the combination of the passivation film and the spray coating mainly relies on physical adsorption and weak chemical bonding, and the bonding strength is not as good as that of anodized spray coating. Secondly, after anodized spray coating, when the plastic powder is destroyed, it can play a good anti-corrosion performance without corrosion expansion. Anodized spray coating uses an electrochemical method to form an oxide film on the surface of the aluminum alloy that is transformed from the aluminum alloy matrix itself. This oxide film is tightly bonded to the matrix and is part of the matrix metal, while passivation spray coating mainly forms a passivation film on the metal surface through chemical reaction. The combination of this film layer and the matrix relies more on chemical adsorption, and the bonding force is relatively weak. The oxide film formed by anodization can better adapt to complex processing and use environments and is not easy to peel off.

[0038] Traditional passivation and phosphating processes often use pollutants such as chromate and phosphate, which are harmful to the environment and human health. However, the anodizing spraying process can use a chromium-free electrolyte formula, which greatly reduces the use and emission of heavy metals. It can meet the European market with high environmental protection requirements, and the anodizing spraying process is more in line with environmental protection regulations.

[0039] The oxide film formed by anodizing has good chemical stability and shielding effect, which can effectively block the invasion of external corrosive media. Coupled with the further protection of the spray-coated layer, the corrosion resistance of the aluminum alloy after anodizing spray-coated is several times or even dozens of times higher than that of the passivated spray-coated in harsh corrosive environments, such as marine environments and industrial pollution areas. The anodized film itself has a high hardness of up to HV300~500, which can effectively resist friction and wear. The spray-coated layer further enhances the wear resistance of the surface, making the surface of the anodized spray-coated aluminum alloy products not easy to wear in occasions of frequent contact and friction, such as mechanical parts, furniture handles, etc., and maintain good appearance and performance. Anodizing can make the oxide film present a variety of colors, such as gold, black, blue, etc., by changing process parameters or using dyeing technology. The spray-coated layer also has a variety of colors and textures to choose from. The combination of the two can achieve more diverse decorative effects to meet the aesthetic needs of different customers.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A pre-treatment process for solving the problem of filamentary corrosion resistance of aluminum alloy electrostatic spraying, characterized in that: The steps include: S1, grinding; S2, air gun dust removal; S3, skim; S4, first water wash; S5, alkali washing; S6, second water wash; S7, third water wash; S8, pickling and neutralization; S9, fourth wash; S10, first pure water wash; S11, anodized; S12, second pure water washing; S13, third pure water wash; S14, fourth pure water wash; S15, drying; S16, electrostatic spraying; S17, baking and curing.

2. A pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1, characterized in that: The step S1 specifically comprises: using a gas grinder to grind the aluminum alloy, and the mesh number of the grinding sandpaper is 180-240 meshes.

3. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized in that: In step S2, the air gun air pressure is 0.5-0.8 MPa.

4. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized in that: In step S3, the temperature of the degreasing acid solution is 40-50° C., the acid concentration is 100-140 g / L, and the degreasing time is 6-8 minutes.

5. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized in that: In step S4, the overflow rate of the first water washing is greater than 200 L / h, and the time is 1 min; The overflow rate of the second water washing in step S6 is greater than 400 L / h, and the time is 1 min; The overflow rate of the third water washing in step S7 is greater than 400 L / h, and the time is 1 min; The overflow rate of the fourth water washing in step S9 is greater than 200 L / h, and the time is 1 min.

6. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized by: In step S5, the concentration of the alkali washing solution used for alkali washing is 30-40 g / L, the aluminum ion concentration is 10-50 g / L, the alkali washing temperature is 40-45° C., and the alkali washing time is 5-6 min; The acid concentration of the pickling solution used in the pickling and neutralization in step S8 is 100-140 g / L, and the pickling time is 1-1.5 min.

7. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized by: In step S10, the overflow rate of the first pure water washing is greater than 200 L / h, and the time is 1 min; In step S12, the overflow rate of the second pure water washing is greater than 400 L / h, and the time is 1 min; In step S13, the overflow rate of the third pure water washing is greater than 400 L / h, and the time is 1 min; In step S14, the overflow rate of the fourth pure water washing is greater than 400 L / h, and the time is 1 min.

8. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized by: The specific anodization in step 11 is: temperature 23-27° C., time 5-10 min, acid concentration 170-190 g / L, voltage 12-18 V, aluminum ion concentration ≤15 g / L.

9. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized by: In the step S15, the drying temperature is 190-210° C. and the time is 30-60 min. In the step 17, the baking curing temperature is 180-200° C. and the heat preservation time is 15-20 min.

10. The pretreatment process for solving the filiform corrosion resistance of aluminum alloy electrostatic spraying according to claim 1 is characterized in that: The specific parameters of the electrostatic powder spraying in step S16 are: input air pressure of 5.0-7.0 bar, fluidizing air pressure of 0.04-0.1 MPa, powder output of 20-40%, air supply of 3-5 bar, voltage of 30-70 kV, and current of 10-25 µA.

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