Astronautical steel unqualified galvanizing layer stripping solution and method

Abstract

The application discloses a kind of aerospace steel piece unqualified zinc plating layer stripping solution and stripping method, and its stripping process is: sodium nitrite 80~150g / L, ammonium bicarbonate 100~180g / L, sodium chloride 50~100g / L, stripping solution pH is 6~8, normal temperature operation.Nitrite sodium is used as zinc plating layer oxidizing agent and steel matrix corrosion inhibitor, ammonium bicarbonate is used as zinc ion complexing agent and plating solution pH stabilizer, sodium chloride is used as the accelerator for dissolving zinc plating layer.When the pH of stripping solution is low, use sodium carbonate solution to raise pH to the process range, when the pH is high, use dilute nitric acid to reduce pH to the process range.The technical scheme of the application overcomes the high pollution problem of using chromium acid stripping method in the field of aerospace, and also overcomes the problem of hydrogen embrittlement of steel matrix and carbon hanging ash on the surface caused by using hydrochloric acid stripping method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal surface treatment, and particularly relates to a stripping solution and a stripping method for unqualified zinc plating layer of aerospace steel parts. BACKGROUND

[0002] Zinc plating is mainly used for preparing protective plating layer of steel parts, and is the largest one of plating species in electroplating processing, accounting for about 50%-60% of the total electroplating amount. Most of steel products in hardware industry are prepared from low-carbon steel, and unqualified zinc plating layer is mainly stripped by hydrochloric acid stripping method, which has fast stripping speed and low cost.

[0003] Carbon in high-strength steel exists in the form of cementite (Fe3C) in the steel base body, and the cementite is uniformly distributed in the steel base body after heat treatment. Aerospace steel parts are generally prepared from high-strength steel, and stripping the unqualified zinc plating layer on the surface of the steel by hydrochloric acid will cause hydrogen embrittlement of the base body, seriously affect the performance of the stripped part, and even cause the stripped part to be scrapped. The surface iron atoms of high-strength steel react with hydrochloric acid, and the cementite is attached or inlaid on the surface of the steel base body to form carbon hanging ash. The stripped part with carbon hanging ash has poor adhesion after being plated with zinc again, which is difficult to meet the standard requirements of the aerospace industry. Therefore, some aerospace enterprises have to use chromic acid stripping method to strip the zinc plating layer, but the method has the problem of high pollution of chromic acid. SUMMARY

[0004] In order to overcome the problems of hydrogen embrittlement and carbon hanging ash caused by stripping the unqualified zinc plating layer on the surface of high-strength steel by hydrochloric acid stripping method, and solve the problem of high pollution of chromic acid stripping method, the present application provides a stripping solution and a stripping method for unqualified zinc plating layer of aerospace steel parts. In order to achieve the above purpose, the present application adopts the following technical scheme:

[0005] A stripping solution for unqualified zinc plating layer of aerospace steel parts, comprising the following components and contents: 80-150 g / L of sodium nitrite, 100-180 g / L of ammonium bicarbonate, 50-100 g / L of sodium chloride, and the pH of the stripping solution is 6-8.

[0006] The sodium nitrite is used as an oxidizing agent to oxidize zinc into zinc oxide;

[0007] The ammonium bicarbonate is used as a complexing agent to react with zinc oxide to generate complex ions and dissolve in the stripping solution;

[0008] The ammonium bicarbonate is used as a stabilizing agent to keep the pH of the stripping solution stable;

[0009] The sodium chloride is used as an accelerator to improve the stripping speed of zinc plating layer.

[0010] In some embodiments, the stripping solution is prepared as follows: 4 / 5 water is added to the stripping tank according to the tank volume, and sodium nitrite, ammonium bicarbonate, and sodium chloride are added according to the composition and content requirements of the stripping solution. The mixture is stirred to dissolve the sodium nitrite, and water is added to the specified volume.

[0011] A method for stripping substandard zinc plating from aerospace steel parts includes the following steps:

[0012] (1) Prepare a membrane removal solution in a membrane removal tank, wherein the mass fraction of sulfuric acid is 3-7%;

[0013] (2) Prepare the stripping solution in the stripping tank according to the composition, content and preparation method of the stripping solution;

[0014] (3) Place the unqualified zinc-plated parts into the decoction tank to remove the passivation film. Operate at room temperature until the passivation film is completely removed.

[0015] (4) Place the unqualified galvanized parts after the film removal into the stripping tank for stripping at room temperature until the galvanized layer is completely removed.

[0016] In some embodiments, the mass ratio of sodium nitrite, ammonium bicarbonate, and sodium chloride added to the stripping bath during production is 1:(0.5-1):(0.3-0.7).

[0017] In some embodiments, the pH of the stripping solution is adjusted to 6-8 using dilute nitric acid with a mass fraction of 15%-25%.

[0018] In some embodiments, the pH of the stripping solution is adjusted to 6-8 using a sodium carbonate solution with a mass fraction of 15%-25%.

[0019] In some embodiments, the stripping solution is circulated and filtered during production using a filter to remove precipitates generated during the stripping process.

[0020] In the understanding of those skilled in the art, ammonia molecules can act as ligands, while ammonium ions do not possess liganding ability; only under alkaline conditions can some heavy metal ions form complexes with ammonia. However, this technical solution uses ammonium salts as ligands under near-neutral conditions, breaking through the general understanding of those skilled in the art. Nitrites typically possess oxidizing properties only under acidic conditions and cannot be used as oxidants under room temperature and neutral conditions. This technical solution uses sodium nitrite as an oxidant under room temperature and near-neutral conditions, overcoming the limitations of the understanding of those skilled in the art.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention provides a stripping solution and method for unqualified zinc plating on aerospace steel parts. It uses nitrite as an oxidant to oxidize the zinc plating metal and ammonium salt as a complexing agent to dissolve the zinc oxide. The zinc plating is effectively removed in a near-neutral stripping solution. This overcomes the problems of hydrogen embrittlement of the workpiece substrate and carbon ash buildup on the surface caused by hydrochloric acid stripping, and also overcomes the high pollution problem of the chromic acid stripping method currently used in the aerospace field.

[0023] 2. The stripping solution and stripping method for substandard zinc plating on aerospace steel parts of the present invention have the effect of nitrite inhibiting corrosion of the steel substrate, and the stripping solution does not corrode the steel substrate during the stripping process;

[0024] 3. The stripping solution and method for substandard zinc plating on aerospace steel parts of the present invention use ammonium bicarbonate as a stabilizer. During the stripping process, bicarbonate ions can release hydrogen ions to replenish the hydrogen ions consumed in the stripping reaction, thus keeping the pH of the stripping solution stable. When the pH is too low, bicarbonate ions react with hydrogen ions to generate carbon dioxide gas, which escapes from the stripping solution.

[0025] 4. The stripping solution and method for substandard zinc plating on aerospace steel parts of the present invention use sodium chloride as an accelerator, which effectively improves the removal speed of zinc plating. Attached Figure Description

[0026] Figure 1 This is a photo of a No. 45 steel screw placed in the stripping solution of this invention for 8 hours. Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0028] A stripping solution for substandard zinc plating on aerospace steel parts comprises the following components and contents: sodium nitrite 80-150 g / L, ammonium bicarbonate 100-180 g / L, sodium chloride 50-100 g / L, and the pH of the stripping solution is 6-8.

[0029] A method for stripping substandard zinc plating from aerospace steel parts includes the following steps:

[0030] (1) Prepare a membrane removal solution in a membrane removal tank, wherein the mass fraction of sulfuric acid is 3% to 7%;

[0031] (2) Calculate the volume of the stripping solution and add 4 / 5 of the water to the stripping tank. Add sodium nitrite, ammonium bicarbonate and sodium chloride according to the required composition and content of the stripping solution. Stir to dissolve and add water to the specified volume.

[0032] (3) Place the unqualified zinc-plated parts into the film removal tank to remove the passivation film. Operate at room temperature until the passivation film is completely removed. Observe that hydrogen bubbles are obviously escaping from the surface of the plated parts.

[0033] (4) Place the unqualified galvanized parts after the film removal into the stripping tank for stripping at room temperature until the galvanized layer is completely removed.

[0034] During the stripping process, as the oxidant, complexing agent, and accelerator are consumed and the stripping solution is carried out, sodium nitrite, ammonium bicarbonate, and sodium chloride need to be added to the stripping tank.

[0035] Preferably, the mass ratio of added sodium nitrite, ammonium bicarbonate, and sodium chloride is 1:(0.5-1):(0.3-0.7).

[0036] During the stripping process, hydrogen ions are consumed in the reaction of sodium nitrite oxidizing metallic zinc, and the pH of the stripping solution will gradually increase.

[0037] Preferably, the pH of the stripping solution is adjusted to 6-8 using dilute nitric acid with a mass fraction of 15%-25%, and the added nitrate is used as an oxidant for the zinc plating layer.

[0038] During the stripping process, the pH of the stripping solution may also be too low.

[0039] Preferably, the pH of the stripping solution is adjusted to 6-8 using a sodium carbonate solution with a mass fraction of 15%-25%.

[0040] During the stripping process, some metal oxide precipitates will appear in the stripping solution, and these precipitates need to be separated and removed.

[0041] Preferably, the filter is used to circulate and filter the stripping solution to remove the precipitates generated during the stripping process. Example 1

[0042] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0043] Sodium nitrite 100g / L, ammonium bicarbonate 100g / L, sodium chloride 60g / L, stripping solution pH 7.3, operate at room temperature, until the coating is completely removed.

[0044] 1. Prepare the film removal solution:

[0045] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 3%.

[0046] 2. Prepare the stripping solution:

[0047] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve and add water to the specified volume.

[0048] 3. Membrane removal:

[0049] Substandard galvanized parts are placed in a decoction tank to remove the passivation film. When hydrogen bubbles are clearly seen escaping from the surface of the part, the passivation film has been completely removed. After removing the part from the tank, it is washed with water three times.

[0050] 4. Stripping:

[0051] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0052] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank in a mass ratio of 1:0.6:0.3. After the pH rises, 20% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 20% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 2

[0053] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0054] Sodium nitrite 80g / L, ammonium bicarbonate 120g / L, sodium chloride 60g / L, stripping solution pH 7.1, operate at room temperature, and continue stripping until complete.

[0055] 1. Prepare the film removal solution:

[0056] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 4%.

[0057] 2. Prepare the stripping solution:

[0058] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve and add water to the specified volume.

[0059] 3. Membrane removal:

[0060] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed, and then washed with water three times.

[0061] 4. Stripping:

[0062] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0063] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank in a mass ratio of 1:0.8:0.3. After the pH rises, 15% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 15% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 3

[0064] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0065] Sodium nitrite 130g / L, ammonium bicarbonate 150g / L, sodium chloride 100g / L, stripping solution pH 7.2, room temperature operation, until the coating is completely removed.

[0066] 1. Prepare the film removal solution:

[0067] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 5%.

[0068] 2. Prepare the stripping solution:

[0069] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve and add water to the specified volume.

[0070] 3. Membrane removal:

[0071] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed. After removing them from the tank, they are washed with water three times.

[0072] 4. Stripping:

[0073] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0074] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping solution in a mass ratio of 1:0.7:0.5. After the pH rises, 25% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 25% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 4

[0075] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0076] Sodium nitrite 130g / L, ammonium bicarbonate 100g / L, sodium chloride 60g / L, stripping solution pH 7.4, operate at room temperature, until the coating is completely removed.

[0077] 1. Prepare the film removal solution:

[0078] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 6%.

[0079] 2. Prepare the stripping solution:

[0080] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve and add water to the specified volume.

[0081] 3. Membrane removal:

[0082] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed. After removing them from the tank, they are washed with water three times.

[0083] 4. Stripping:

[0084] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0085] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank in a mass ratio of 1:0.5:0.3. After the pH rises, 25% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 15% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 5

[0086] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0087] Sodium nitrite 80g / L, ammonium bicarbonate 100g / L, sodium chloride 70g / L, stripping solution pH 7.2, operate at room temperature, until the coating is completely removed.

[0088] 1. Prepare the film removal solution:

[0089] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 7%.

[0090] 2. Prepare the stripping solution

[0091] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve and add water to the specified volume.

[0092] 3. Membrane removal:

[0093] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed. After removing them from the tank, they are washed with water three times.

[0094] 4. Stripping:

[0095] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0096] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank in a mass ratio of 1:0.7:0.4. After the pH rises, 15% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 25% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 6

[0097] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0098] Sodium nitrite 150g / L, ammonium bicarbonate 180g / L, sodium chloride 100g / L, stripping solution pH 7.2, operate at room temperature, until the coating is completely removed.

[0099] 1. Prepare the film removal solution

[0100] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 5%.

[0101] 2. Prepare the stripping solution

[0102] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve them. Adjust the pH of the stripping solution to 6.5 with 25% dilute nitric acid. Add water to the specified volume.

[0103] 3. Membrane removal

[0104] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed. After removing them from the tank, they are washed with water three times.

[0105] 4. Stripping

[0106] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0107] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank at a mass ratio of 1:0.8:0.4. After the pH rises, 25% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 20% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 7

[0108] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0109] Sodium nitrite 100g / L, ammonium bicarbonate 120g / L, sodium chloride 60g / L, stripping solution pH 6, operate at room temperature, until the coating is completely removed.

[0110] 1. Prepare the film removal solution:

[0111] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 5%.

[0112] 2. Prepare the stripping solution:

[0113] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve. Adjust the pH of the stripping solution to 6 with 15% dilute nitric acid. Add water to the specified volume.

[0114] 3. Membrane removal:

[0115] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed. After removing them from the tank, they are washed with water three times.

[0116] 4. Stripping:

[0117] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0118] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank in a mass ratio of 1:0.7:0.4. After the pH rises, 15% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 20% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter. Example 8

[0119] The following is a process for removing substandard zinc plating from aerospace steel parts:

[0120] Sodium nitrite 120g / L, ammonium bicarbonate 100g / L, sodium chloride 50g / L, stripping solution pH 6.5, room temperature operation, until the coating is completely removed.

[0121] 1. Prepare the film removal solution:

[0122] Add 4 / 5 water to the membrane removal tank according to the tank liquid volume, add concentrated sulfuric acid according to the process requirements, stir evenly, and then add water to the specified volume. The mass fraction of sulfuric acid in the prepared membrane removal solution is 5%.

[0123] 2. Prepare the stripping solution:

[0124] Add 4 / 5 water to the stripping tank according to the volume of the stripping solution. Add sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content requirements of the stripping solution. Stir to dissolve them. Adjust the pH of the stripping solution to 6.5 with 20% dilute nitric acid. Add water to the specified volume.

[0125] 3. Membrane removal:

[0126] The defective galvanized parts are placed in a descaling tank to remove the passivation film until it is completely removed. After removing them from the tank, they are washed with water three times.

[0127] 4. Stripping:

[0128] After removing the coating, unqualified galvanized parts are placed in a stripping tank for stripping until the coating is completely removed. After three water rinses, they are transferred to the galvanizing process.

[0129] During production, sodium nitrite, ammonium bicarbonate, and sodium chloride are added to the stripping tank in a mass ratio of 1:0.5:0.3. After the pH rises, 20% dilute nitric acid is added to the stripping tank to adjust the pH of the stripping solution to within the process range. If the pH is too low, 20% sodium carbonate solution is added to the plating tank to adjust the pH of the stripping solution to within the process range. The stripping solution is then circulated and filtered using a filter.

[0130] Experimental Example 1:

[0131] A 50mm × 100mm × 2mm No. 45 steel plate was quenched and tempered to form sorbitic steel. The heat-treated steel plate was then subjected to ultrasonic degreasing, sanding, chemical degreasing, and activation with 10% dilute sulfuric acid for 1 minute. A 10μm thick zinc-plated sample was prepared by potassium chloride zinc plating. The zinc-plated sample was passivated with hexavalent chromium low-chromium color. After removing the coating according to the process in Example 1, the zinc-plated sample was immersed in the stripping solution for 20 minutes. After removal, it was rinsed three times with water, dried, and the surface was observed. The zinc coating had been completely removed, and there was no carbon residue on the steel plate surface.

[0132] Experimental Example 2:

[0133] The steel plate sample from Experiment 1, after being stripped of its zinc plating, was pickled and activated, then re-plated with potassium chloride zinc to a thickness of 10 μm, using hexavalent chromium low-chromium passivation. The adhesion of the plating was tested using the thermal shock method according to GB / T 5270-2005 "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Coatings on Metallic Substrates". The plated part was heated to 300°C in a furnace and held for 30 minutes, then removed and rapidly cooled in room temperature water. No blistering or peeling occurred, indicating good adhesion of the plating. The test shows that the method for stripping substandard zinc plating of this invention does not reduce the surface quality of steel parts.

[0134] Experimental Example 3:

[0135] The stripping solution was prepared according to Example 1. A stripping test was conducted on galvanized steel substrates that had been stored for six months. After removing the passivation film, galvanized M8×40 No. 45 steel screws were immersed in the stripping solution for 20 minutes, after which the coating was completely removed. The parts were then left in the stripping solution for another 8 hours. No rust was observed on the substrate surface. Figure 1 Experiments show that the sodium nitrite in the stripping solution of this invention has a good sustained-release effect on the steel substrate.

[0136] Experimental Example 4:

[0137] Preparation of the test solution: Sodium nitrite 100 g / L, ammonium bicarbonate 120 g / L, sodium chloride 60 g / L. Take 7 portions of the test solution and adjust the pH to 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5 respectively using 10% dilute nitric acid and 10% sodium hydroxide solution. The zinc plating sample prepared in Example 1 was used for stripping tests, and the results are listed in Table 1. Within the tested pH range, the zinc plating layer could be effectively removed. However, carbon dioxide gas was released from the test solution at pH 5.5, and ammonia gas was released at pH 8.5. Based on this, the pH process parameter is specified as 6–8 in this invention.

[0138] Table 1. Effect of pH on stripped parts and stripping solution

[0139] Sample No. pH Stripping time / min Zinc coating Carbon hang-up Gas evolution 1 5.5 20 None None Carbon dioxide 2 6.0 20 None None Negligible 3 6.5 20 None None None 4 7.0 20 None None None 5 7.5 20 None None None 6 8.0 20 None None Negligible 7 8.5 20 None None Ammonia

[0140] Experimental Example 5:

[0141] Prepare test solution A: 100 g / L sodium nitrite, 120 g / L ammonium bicarbonate, 60 g / L sodium chloride. Adjust the pH to 5 with 20% sulfuric acid. Under these conditions, ammonium ions cannot undergo hydrolysis to produce ammonia molecules.

[0142] Prepare test solution B: 100 g / L sodium nitrite, 120 g / L sodium bicarbonate, 60 g / L sodium chloride, and adjust the pH to 5 with 20% sulfuric acid.

[0143] The tests were conducted using unpassivated galvanized steel samples, specifically M8×40 screws. After 20 minutes in test solution A, the galvanized layer completely disappeared. After 20 minutes in test solution B, no observable change was observed in the galvanized layer.

[0144] In test solution A, sodium nitrite oxidizes metallic zinc into zinc oxide, while ammonium ions react with zinc oxide to form zinc complex ions that dissolve in test solution A, and finally the zinc plating layer is removed.

[0145] In test solution B, sodium nitrite oxidizes metallic zinc to zinc oxide. The zinc oxide forms a protective film on the zinc plating layer, preventing further reaction between sodium nitrite and metallic zinc. The experiment shows that, in the absence of ammonium ions for coordination, sodium nitrite alone cannot remove the zinc plating layer.

[0146] Comparative Example 1:

[0147] Preparation of the test stripping solution: sodium nitrite 100g / L, ammonium bicarbonate 120g / L, pH 7.3.

[0148] After removing the passivation film from an M8×40 carbon steel galvanized screw, it was placed in the above stripping solution for 20 minutes for observation. No steel substrate was exposed, and the galvanized layer was completely removed only after 40 minutes in the stripping solution. Comparative Example 1 and Experimental Example 3 show that the addition of sodium chloride to the stripping solution of the present invention significantly improves the removal speed of the galvanized layer.

[0149] Comparative Example 2:

[0150] Preparation of hydrochloric acid stripping solution: The volume ratio of concentrated hydrochloric acid to water is 2:5.

[0151] A comparative test was conducted using the galvanized sample prepared in Example 1. The galvanized sample was placed in the above-mentioned hydrochloric acid stripping solution for stripping. After the galvanized layer was completely removed, the sample was taken out, rinsed with water, and dried. A layer of gray-black carbon ash was observed on the surface of the sample.

[0152] As can be seen from Experimental Example 1 and Comparative Example 2, for the stripping of zinc plating on medium carbon steel workpieces, the technical solution of the present invention overcomes the defect of carbon ash buildup caused by the traditional hydrochloric acid stripping method.

[0153] Comparative Example 3:

[0154] The steel plate sample with carbon residue after the plating of Comparative Example 2 was pickled and activated, then re-plated with potassium chloride zinc to a thickness of 10 μm, and passivated with hexavalent chromium low-chromium color. The adhesion of the plating was tested using the thermal shock method according to GB / T 5270-2005 "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Coatings on Metallic Substrates". The plated part was heated to 300℃ in a furnace and held for 30 minutes, then removed and rapidly cooled in room temperature water. A small number of bubbles appeared in the plating, indicating that its adhesion did not meet the requirements of this standard.

[0155] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. The protection scope of this invention patent should be determined by the appended claims.

Claims

1. An aerospace steel part unqualified galvanized layer stripping solution, characterized in that, The composition and content of the solution include: 80-150 g / L of sodium nitrite, 100-180 g / L of ammonium bicarbonate, and 50-100 g / L of sodium chloride, and the pH of the solution is 6-8; The sodium nitrite is used as an oxidizing agent to oxidize zinc into zinc oxide; The ammonium bicarbonate is used as a complexing agent to react with zinc oxide to form complex ions and dissolve in the stripping solution; The ammonium bicarbonate is used as a stabilizing agent to keep the pH of the stripping solution stable; The sodium chloride is used as an accelerator to increase the stripping speed of the zinc coating.

2. The aerospace steel part unqualified galvanized layer stripping solution according to claim 1, characterized in that, The stripping solution is prepared by adding 4 / 5 of water in the stripping tank according to the volume of the tank, adding sodium nitrite, ammonium bicarbonate, and sodium chloride according to the composition and content of the stripping solution, stirring to dissolve, and adding water to the specified volume.

3. A method for stripping off a non-conforming zinc coating of an aerospace steel part, characterized in that, The process includes the following steps: (1) preparing a film removal solution in a film removal tank, wherein the mass fraction of sulfuric acid is 3-7%; (2) preparing a stripping solution in a stripping tank, wherein the stripping solution contains 80-150 g / L of sodium nitrite, 100-180 g / L of ammonium bicarbonate, and 50-100 g / L of sodium chloride, and the pH of the solution is 6-8; (3) putting the unqualified zinc-plated parts into the film removal tank to remove the passivation film, operating at room temperature until the passivation film is completely removed; (4) putting the unqualified zinc-plated parts after film removal into the stripping tank to strip the zinc coating, operating at room temperature until the zinc coating is completely removed.

4. The method of deplating of non-conforming galvanizing layer of aerospace steel parts according to claim 3, characterized in that: In production, the mass ratio of sodium nitrite, ammonium bicarbonate, and sodium chloride added to the stripping tank is 1:(0.5-1):(0.3-0.7).

5. The method of deplating of non-conforming galvanizing layer of aerospace steel parts according to claim 3, characterized in that: The pH of the stripping solution is adjusted to 6-8 by using 15-25% dilute nitric acid.

6. The method of deplating of non-conforming galvanizing layer of aerospace steel parts according to claim 3, characterized in that: The pH of the stripping solution is adjusted to 6-8 by using 15-25% sodium carbonate solution.

7. The aerospace steel part unqualified galvanizing layer stripping method according to claim 3, characterized in that: In production, the stripping solution is filtered by a filter to remove the precipitates generated during the stripping process.

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