Die-casting aluminum anode technology resistant to high-strength salt spray test

Abstract

The invention discloses a high-strength salt spray test resistant die-casting aluminum anode process which is characterized by comprising the following steps: step 1, hanging die-casting aluminum on processing equipment, driving the die-casting aluminum to be soaked in a degreasing agent to remove oil stains, and washing the die-casting aluminum after degreasing; secondly, the degreased die-casting aluminum is soaked in a neutralizing solution, acid and alkali of the die-casting aluminum are neutralized, a leather film of the die-casting aluminum is removed, and the die-casting aluminum is washed with water again; 3, the die-casting aluminum is placed in an anode tank and soaked in the electrolyte, the die-casting aluminum is located at an anode under the action of external stable current or stable voltage, so that an oxidation film is formed, and the die-casting aluminum is washed with water; compared with the prior art, the surface effect of the product subjected to three times of sealing is not different from that of a product produced by a normal common process, a salt spray test can meet the requirement of a continuous neutral salt spray test of 720 H or above, and the requirement of a neutral salt spray test of 960 H or above can be met under the condition that the third time of sealing is increased.

Description

Technical Field

[0001] The invention relates to the technical field of die-casting aluminum anode processing, and in particular to a die-casting aluminum anode process resistant to high-intensity salt spray test. Background Art

[0002] In response to market demand: automotive die-cast aluminum parts need to withstand more than 720 hours of continuous neutral salt spray test after anodizing, and some customers even require more than 960 hours of continuous neutral salt spray test requirements; the existing anode process cannot meet this requirement, so a new process is specially developed to meet this demand;

[0003] Due to the high content of impurity elements in die-cast aluminum, only the surface aluminum element will form a film during the anode process. After anode, the film thickness is uneven due to the residual trace elements in the local area, resulting in failure to completely seal during sealing, thus affecting the service life of the product. The existing technology can only meet the requirements of neutral salt spray continuous salt spray test for about 240H-360H, and is completely unable to meet the 720H ​​and 960H continuous salt spray tests proposed by customers. Summary of the invention

[0004] The purpose of the present invention is to provide a die-cast aluminum anode process resistant to high-intensity salt spray test, which can solve at least one of the above technical problems. The technical solution of the present invention is as follows:

[0005] A die-cast aluminum anode process resistant to high-intensity salt spray test, characterized by comprising the following steps:

[0006] Step 1: Hang the die-cast aluminum onto the processing equipment, and drive the die-cast aluminum to soak in the degreasing agent to remove the oil stains, and then wash the die-cast aluminum with water after degreasing;

[0007] Step 2: Soak the degreased die-cast aluminum in a neutralizing solution to neutralize the acid and alkali of the die-cast aluminum and remove the film of the die-cast aluminum, and then wash the die-cast aluminum again;

[0008] Step 3: Place the die-cast aluminum in the anode tank and immerse it in the electrolyte. By applying a stable current or a stable voltage, the die-cast aluminum is at the anode to form an oxide film, and the die-cast aluminum is washed with water;

[0009] Step 4: The die-cast aluminum is repeatedly immersed in different sealants. The processing temperature and processing time of various sealants are different, so that the oxide film pores on the die-cast aluminum are closed. The die-cast aluminum is washed with water after each immersion in the sealant and processing;

[0010] Step 5: Dry the processed die-cast aluminum to evaporate the moisture on the product.

[0011] Furthermore, the degreasing agent in step 1 is an acidic degreasing agent, and its percentage concentration is 5%-10%.

[0012] Furthermore, the neutralization solution in step 2 is nitric acid, and its percentage concentration is 10%-20%.

[0013] Furthermore, the stable current mode in step 3 is processing temperature 19°C-21°C, time 60min-100min, current density 0.75A / dm 2 -1.5A / dm 2 , oxidation film, and the stable voltage method is as follows: processing temperature 19℃-21℃, time 80min-120min, voltage size 12V-13V, oxidation film.

[0014] Furthermore, the electrolyte in step three is divided into a sulfuric acid system and a mixed acid system, wherein the sulfuric acid system has a sulfuric acid concentration of 180g / L-200g / L, and the mixed acid system has oxalic acid 20g / L-40g / L, phosphoric acid 10g / L-20g / L, and sulfuric acid 20g / L-25g / L.

[0015] Furthermore, the number of repeated immersions in the step four is three times, and the sealants for the first sealing, the second sealing and the third sealing processes are trivalent chromium sealant, chromium nitrate sealant and nickel acetate sealant, respectively. The processing temperatures are 30°C-35°C, 50°C-55°C and 90°C-95°C, respectively, and the processing times are 300 seconds-600 seconds, 600 seconds-900 seconds and 600 seconds-1500 seconds, respectively.

[0016] Furthermore, the concentrations of the trivalent chromium sealant, the chromium nitrate sealant and the nickel acetate sealant are 15%-20%, 20%-25% and 6g / L-12g / L respectively.

[0017] Preferably, the temperature of the drying treatment in step 5 is 80-120° C., and the drying time is 600 seconds to 900 seconds.

[0018] Preferably, the water washing treatment in steps 1 to 4 uses pure water for washing, and the conductivity of the pure water is less than 50 us / cm.

[0019] In summary, the present invention has the following beneficial effects compared with the prior art:

[0020] The invention provides a die-cast aluminum anode process resistant to high-intensity salt spray test. During production, the die-cast aluminum is immersed in an anode tank, and the electrolyte component in the anode tank can be sulfuric acid or a mixed acid. The anodic oxidation parameters are controlled in the form of low current or low voltage, so that the film forming speed at the anode is more uniform and dense. The invention uses a three-step sealing process. The first step of sealing uses a sealing agent containing trivalent chromium, so that the trivalent chromium solution penetrates into the bottom of the oxide film layer to play a role as a bottom line protection barrier. The second step of sealing uses a chromium nitrate sealing agent, and the third step uses a high-temperature nickel acetate sealing agent. Compared with the prior art, the surface effect of the product after the three-step sealing is no different from that of the product produced by the normal ordinary process, and the salt spray test can meet the continuous neutral salt spray test requirement of more than 720 hours, and the neutral salt spray test requirement of more than 960 hours can be met by increasing the third step of sealing time. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0023] like Figure 1 A die-cast aluminum anode process resistant to high-intensity salt spray test is shown, characterized in that it includes the following steps:

[0024] Step 1: Hang the die-cast aluminum onto the processing equipment, and drive the die-cast aluminum to soak in a degreasing agent to remove oil stains. After degreasing, the die-cast aluminum is washed with water. The die-cast aluminum degreasing agent can be divided into acid degreasing and alkaline degreasing. The present invention adopts acid degreasing, which is mostly carried out at room temperature compared to alkaline degreasing, and has easy production control and low cost;

[0025] Step 2: Soak the degreased die-cast aluminum in a neutralizing solution to neutralize the acid and alkali of the die-cast aluminum and remove the film of the die-cast aluminum, and then wash the die-cast aluminum again. The main purpose of the neutralization treatment is to ensure that the surface of the die-cast aluminum is clean, remove the residual acidic and alkaline substances in the die-cast aluminum, and improve the overall performance and service life of the die-cast aluminum;

[0026] Step 3: Place the die-cast aluminum in the anode tank and immerse it in the electrolyte. By applying a stable current or a stable voltage, the die-cast aluminum is at the anode to form an oxide film. The die-cast aluminum is washed with water. The main functions of the anodizing of die-cast aluminum include corrosion prevention, wear resistance enhancement, and improved decorative and insulating properties of die-cast aluminum. The anodizing significantly improves the corrosion resistance and wear resistance of the material by forming a dense oxide film on the surface of the die-cast aluminum. At the same time, various bright colors can be obtained through dyeing, and even a ceramic-like coating effect can be achieved.

[0027] Step 4: Repeatedly immerse the die-cast aluminum in different sealants. The processing temperature and processing time of various sealants are different, so that the oxide film pores on the die-cast aluminum are closed. The die-cast aluminum is washed with water after each immersion in the sealant and processing. Through multiple sealing process treatments, the customer's test requirements for different adjustments of high salt spray after die-cast aluminum anode are met;

[0028] Step 5: Dry the processed die-cast aluminum to evaporate the moisture on the product.

[0029] In some embodiments of the present invention, the degreasing agent in step 1 is an acidic degreasing agent with a percentage concentration of 5%-10%. The nitric acid concentration of 5%-10% is suitable for cleaning heavy oil stains and can quickly remove stubborn oil stains. In addition, in the acidic degreasing solution, the oil will undergo a hydrolysis reaction to generate glycerol and corresponding higher fatty acids. Adding a small amount of wetting agent and emulsifier to the acidic degreasing solution is conducive to the softening, freeing, dissolving and emulsifying of the oil, and significantly improves the degreasing effect.

[0030] In some embodiments of the present invention, the neutralizing solution in step 2 is nitric acid with a percentage concentration of 10%-20%. The 10%-20% nitric acid solution is immersed at room temperature to improve the removal of metallic copper attached to the surface of the die-cast aluminum during the chemical polishing process.

[0031] In some embodiments of the present invention, the stable current mode in step 3 is processing temperature 19°C-21°C, time 60min-100min, current density 0.75A / dm 2 -1.5A / dm 2 , oxidation film, and the stable voltage mode is processing temperature 19 ℃ -21 ℃, time 80min-120min, voltage size 12V-13V, oxidation film (where dm 2 The unit of area is square decimeter). Stable current can ensure the constancy of current and make the color of the electroplating layer consistent. At the same time, the longer the processing time, the thicker the oxide film formed. The advantage of voltage stabilization is that it can reduce the uneven thickness of the electroplating layer caused by current changes.

[0032] In some embodiments of the present invention, the electrolyte in step three is divided into a sulfuric acid system and a mixed acid system, wherein the sulfuric acid system has a sulfuric acid concentration of 180g / L-200g / L, and the mixed acid system has oxalic acid 20g / L-40g / L, phosphoric acid 10g / L-20g / L, and sulfuric acid 20g / L-25g / L. The acid concentration of 180g / L-200g / L can effectively improve the surface oxidation effect and corrosion resistance of die-cast aluminum after anodizing, and the concentration of the mixed acid system can significantly improve the quality and performance of the oxide film.

[0033] In some embodiments of the present invention, the number of repeated immersions in step 4 is three times, and the sealants for the first sealing, the second sealing and the third sealing processes are trivalent chromium sealant, chromium nitrate sealant and nickel acetate sealant, respectively, and the processing temperatures are 30°C-35°C, 50°C-55°C and 90°C-95°C, respectively, and the processing times are 300 seconds-600 seconds, 600 seconds-900 seconds and 600 seconds-1500 seconds, respectively. By using trivalent chromium sealing, chromium nitrate sealing and nickel acetate three-stage sealing processes, the customer's requirements for high salt spray test after die-casting aluminum anode are met (continuous neutral salt spray test for more than 720H, if the sealing time of 3 is 1500 seconds, the continuous neutral salt spray test for more than 960H can be met), and the closed product has no effect on appearance and environmental protection, and meets ELV and Rohs requirements.

[0034] In some embodiments of the present invention, the concentrations of the trivalent chromium sealer, chromium nitrate sealer and nickel acetate sealer are 15%-20%, 20%-25% and 6g / L-12g / L respectively, and the concentration components of the above-mentioned sealers work together to form a protective film. The sealing treatment can not only improve the corrosion resistance of the passivation film, but also improve the color of the passivation film, reduce the friction coefficient, and increase the blackness of the black passivation.

[0035] In some embodiments of the present invention, the temperature of the drying treatment in step five is 80-120° C., and the drying time is 600 seconds to 900 seconds.

[0036] In some embodiments of the present invention, the water washing treatment in steps 1 to 4 uses pure water for washing, and the conductivity of the pure water is less than 50 us / cm.

[0037] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A die-cast aluminum anode process resistant to high-intensity salt spray test, characterized in that: The following steps are involved: Step 1: Hang the die-cast aluminum onto the processing equipment, and drive the die-cast aluminum to soak in the degreasing agent to remove the oil stains, and then wash the die-cast aluminum with water after degreasing; Step 2: Soak the degreased die-cast aluminum in a neutralizing solution to neutralize the acid and alkali of the die-cast aluminum and remove the film of the die-cast aluminum, and then wash the die-cast aluminum again; Step 3: Place the die-cast aluminum in the anode tank and immerse it in the electrolyte. By applying a stable current or a stable voltage, the die-cast aluminum is at the anode to form an oxide film, and the die-cast aluminum is washed with water; Step 4: The die-cast aluminum is repeatedly immersed in different sealants. The processing temperature and processing time of various sealants are different, so that the oxide film pores on the die-cast aluminum are closed. The die-cast aluminum is washed with water after each immersion in the sealant and processing; Step 5: Dry the processed die-cast aluminum to evaporate the moisture on the product.

2. A die-cast aluminum anode process resistant to high-intensity salt spray test according to claim 1, characterized in that The degreasing agent in step 1 is an acidic degreasing agent, and its percentage concentration is 5%-10%.

3. The die-cast aluminum anode process for high-intensity salt spray test resistance according to claim 1, characterized in that The neutralization solution in step 2 is nitric acid, and its percentage concentration is 10%-20%.

4. The die-cast aluminum anode process for high-intensity salt spray test resistance according to claim 1, characterized in that The stable current mode in step 3 is processing temperature 19°C-21°C, time 60min-100min, current density 0.75A / dm 2 -1.5A / dm 2 , oxidation film, and the stable voltage method is as follows: processing temperature 19℃-21℃, time 80min-120min, voltage size 12V-13V, oxidation film.

5. The die-cast aluminum anode process for high-intensity salt spray test resistance according to claim 1, characterized in that The electrolyte in step three is divided into a sulfuric acid system and a mixed acid system, wherein the sulfuric acid system has a sulfuric acid concentration of 180g / L-200g / L, and the mixed acid system has oxalic acid 20g / L-40g / L, phosphoric acid 10g / L-20g / L, and sulfuric acid 20g / L-25g / L.

6. The die-cast aluminum anode process for high-intensity salt spray test resistance according to claim 1, characterized in that The number of repeated immersions in the step 4 is three times, and the sealants for the first sealing, the second sealing and the third sealing processes are trivalent chromium sealant, chromium nitrate sealant and nickel acetate sealant, respectively. The processing temperatures are 30°C-35°C, 50°C-55°C and 90°C-95°C, respectively, and the processing times are 300 seconds-600 seconds, 600 seconds-900 seconds and 600 seconds-1500 seconds, respectively.

7. A die-cast aluminum anode process resistant to high-intensity salt spray test according to claim 6, characterized in that The concentrations of the trivalent chromium sealant, the chromium nitrate sealant and the nickel acetate sealant are 15%-20%, 20%-25% and 6g / L-12g / L respectively.

8. The die-cast aluminum anode process for high-intensity salt spray test resistance according to claim 1, characterized in that The temperature of the drying treatment in step 5 is 80-120° C., and the drying time is 600 seconds to 900 seconds.

9. The die-cast aluminum anode process for high-intensity salt spray test resistance according to claim 1, characterized in that The water washing treatment in steps 1 to 4 is performed using pure water, and the conductivity of the pure water is less than 50 us / cm.

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