Low-temperature preparation method of phosphating solution for improving corrosion resistance of phosphating film on steel surface

Abstract

The present application relates to a kind of low-temperature preparation methods of phosphating solution for improving the corrosion resistance of steel surface phosphating film, specifically is the deionized water is cooled to 10-15 DEG C by water bath;Phosphoric acid, phosphate, nitrate, nitroguanidine and organic acid are sequentially dissolved in deionized water in order, then cooled to 1-5 DEG C, and maintain more than 20 min;Phosphating solution is heated to the operating temperature required by phosphating process.The present application method does not need to change the specific composition of phosphating solution, also does not need to adjust the temperature, time and other process conditions of phosphating process, only needs to ensure specific low-temperature conditions and the adding order of chemical reagent when preparing phosphating solution, can form thicker corrosion-resistant film layer on the surface of steel parts, and while greatly improving the stability of plating solution, also can maintain higher plating speed, thereby effectively control production cost and production efficiency.

Description

TECHNICAL FIELD

[0001] The application relates to a low-temperature preparation method of phosphating solution for improving the corrosion resistance of a phosphating film on a steel surface, and belongs to the technical field of metal surface treatment. BACKGROUND

[0002] Surface phosphating is a traditional process method for improving the corrosion resistance of steel materials, and can also play a lubricating role in reducing abrasion. The phosphating on the surface of steel materials forms a phosphating film which is a kind of chemical conversion film. The effective film-forming reaction lasts for a short time, thereby causing the thickness of the formed corrosion-resistant film layer to be relatively thin and the corrosion resistance to be relatively weak. Therefore, the phosphating film cannot be used as a corrosion protection layer alone, and is mostly used as a pretreatment process of other surface protection processes to improve the interfacial adhesion and corrosion resistance. However, compared with other surface corrosion protection methods, the chemical conversion film of phosphating is simple to operate and low in cost. How to prepare the chemical conversion film with relatively strong corrosion resistance through the method has been a direction of exploration. At present, most of the researches on the phosphating solution are concentrated on the optimization of the composition of the phosphating solution and the temperature, time and other process conditions in the phosphating process, and the influence of the preparation conditions on the performance of the phosphating solution is ignored. SUMMARY

[0003] In view of the status of the prior art, the application aims to provide a low-temperature preparation method of phosphating solution for improving the corrosion resistance of a phosphating film on a steel surface, so that the phosphating solution has stronger phosphating capacity, can form a thicker corrosion-resistant film layer on the surface of steel materials, and greatly improves the corrosion resistance of the phosphating film, simplifies the operation process of surface corrosion protection and greatly improves the production efficiency.

[0004] To solve the above technical problems, the application provides a low-temperature preparation method of phosphating solution for improving the corrosion resistance of a phosphating film on a steel surface, which is realized by controlling the preparation temperature of the phosphating solution and the adding sequence of chemical reagents, and the specific process is as follows:

[0005] Step 1: deionized water is cooled to 10-15 DEG C through water bath cooling;

[0006] Step 2: phosphoric acid, phosphate, nitrate, nitroguanidine and organic acid are sequentially added into the cooled deionized water, and are fully dissolved;

[0007] Step 3: the solution obtained in step 2 is cooled to 1-5 DEG C and maintained for more than 20 min to obtain the phosphating solution;

[0008] Step 4: the phosphating solution obtained in step 3 is warmed to the operating temperature required by the phosphating process, and the warming speed is controlled to be less than 3 DEG C / min.

[0009] The present application has the following advantages: the method of the present application does not need to change the specific components of the phosphating solution, nor to adjust the process conditions such as temperature and time of the phosphating process, but only needs to ensure the specific low-temperature condition and the adding sequence of the chemical agents when the phosphating solution is prepared, so that a thicker corrosion-resistant film layer can be formed on the surface of the steel part, the plating solution stability is greatly improved, the plating speed is maintained at a high level, and the production cost and production efficiency are effectively controlled. DETAILED DESCRIPTION

[0010] Example 1

[0011] The conventional phosphating solution formula: zinc dihydrogen phosphate 40 g / L, zinc nitrate 40 g / L, nickel nitrate 5 g / L, phosphoric acid 1.5 g / L, nitro guanidine 0.2 g / L and citric acid 1.5 g / L.

[0012] Preparation process:

[0013] Step 1: 1000 ml of deionized water was placed in a beaker and placed in a water bath cooling device, and the temperature was reduced to 10℃.

[0014] Step 2: 1.5 g of phosphoric acid, 40 g of zinc dihydrogen phosphate, 40 g of zinc nitrate, 5 g of nickel nitrate, 0.2 g of nitro guanidine and 1.5 g of citric acid were sequentially added to the deionized water. When adding, wait for each chemical agent to completely dissolve before adding the next chemical agent.

[0015] Step 3: Control the temperature of the water bath cooling device, cool the solution of step 2 to 5℃, and maintain 5℃ for 20 min to obtain the phosphating solution.

[0016] Step 4: The above phosphating solution was transferred to a heating device, and was first allowed to naturally warm up to 30℃, which took about 20 min. Then the temperature of the heating device was controlled to allow the phosphating solution to warm up from 30℃ to 65℃, the operating temperature required for the phosphating process, within 15 min.

[0017] To show the effect of low-temperature preparation conditions on the performance of the phosphating solution, a comparison solution was prepared by directly adding 1.5 g of phosphoric acid, 40 g of zinc dihydrogen phosphate, 40 g of zinc nitrate, 5 g of nickel nitrate, 0.2 g of nitro guanidine and 1.5 g of citric acid to 1000 ml of deionized water at room temperature of 30℃.

[0018] The comparison of the promoting effect of the phosphating solution prepared under low-temperature conditions and the phosphating solution prepared under room temperature conditions on the corrosion resistance of the phosphating film on the surface of the 30CrMnSi steel part is as follows:

[0019] The process conditions of the phosphating treatment: temperature 65℃, phosphating time 20 min.

[0020] In the above two phosphating solutions, 30CrMnSi sheets with a size of 50 mm x 50 mm x 2 mm and a surface pretreatment were placed, and the phosphating time was 20 min. After phosphating, the samples were taken out, washed and dried.

[0021] The weight gain of the samples before and after phosphating was measured by weighing method to obtain the weight of the phosphating film. Thus, the thickness of the phosphating film can be compared.

[0022] The corrosion resistance of the phosphating film layers obtained by the two phosphating solutions was compared by drop test. The drop liquid composition was: 40 g / L of copper sulfate pentahydrate, 33 g / L of sodium chloride and 13 mL / L of 0.1N hydrochloric acid solution. The discoloration time of the drop test was compared to compare the corrosion resistance of the film layers.

[0023] The comparative experiment found that under room temperature (30°C) conditions, the weight gain of the sample treated in the prepared phosphating solution was 9.72 g / m 2 , and the weight gain of the sample treated in the phosphating solution prepared under low temperature conditions was 12.7 g / m 2 , representing a significant increase in film thickness.

[0024] The drop test comparison found that the discoloration time of the sample treated in the phosphating solution prepared under room temperature (30°C) conditions was 40 seconds, and the discoloration time of the sample treated in the phosphating solution prepared under low temperature conditions was 70 seconds, and the corrosion resistance was greatly increased.

[0025] Example 2

[0026] The conventional phosphating solution formula: zinc dihydrogen phosphate 40 g / L, zinc nitrate 40 g / L, nickel nitrate 5 g / L, phosphoric acid 1.5 g / L, nitro guanidine 0.2 g / L and citric acid 1.5 g / L.

[0027] Configuration process:

[0028] Step 1: Place 1000 ml of deionized water in a beaker and place it in a water bath cooling device to cool to 15°C.

[0029] Step 2: Add 1.5 g of phosphoric acid, 40 g of zinc dihydrogen phosphate, 40 g of zinc nitrate, 5 g of nickel nitrate, 0.2 g of nitro guanidine and 1.5 g of citric acid to the deionized water in order. When adding, wait for each of the above chemical agents to completely dissolve before adding the next chemical agent.

[0030] Step 3: Control the temperature of the water bath cooling device, cool the solution of step 2 to 3°C, and maintain 3°C for 30 min to obtain the phosphating solution.

[0031] Step 4: The phosphating solution is transferred into the heating device, and is allowed to naturally warm up to 30°C, which takes about 20 minutes. The temperature of the heating device is then controlled to allow the phosphating solution to warm up from 30°C to the operating temperature of 65°C required by the phosphating process within 15 minutes.

[0032] To show the effect of low-temperature preparation conditions on the performance of the phosphating solution, and for easy performance comparison, a comparative phosphating solution is prepared at room temperature of 30°C by directly adding 1.5 g of phosphoric acid, 40 g of zinc dihydrogen phosphate, 40 g of zinc nitrate, 5 g of nickel nitrate, 0.2 g of nitro guanidine, and 1.5 g of citric acid into 1000 ml of deionized water.

[0033] The comparison of the promoting effect of the phosphating solution prepared under low-temperature conditions and the phosphating solution prepared at room temperature on the corrosion resistance of the phosphating film on the surface of the 30CrMnSi steel piece is as follows:

[0034] The process conditions of the phosphating treatment are: temperature 65°C, and phosphating time 20 minutes.

[0035] In the above two phosphating solutions, the 30CrMnSi sheet after surface pretreatment is placed, with the size specification being 50mm x 50mm x 2mm, and the phosphating time being 20 minutes. After the phosphating is completed, it is taken out, washed, and dried.

[0036] The weight gain of the sample before and after phosphating is measured by weighing, and the weight of the phosphating film is obtained. Thus, the thickness of the phosphating film can be compared.

[0037] The corrosion resistance of the phosphating film layer obtained by the two kinds of phosphating solutions is compared by the drop test. The drop liquid is composed of 40g / L of copper sulfate pentahydrate, 33g / L of sodium chloride, and 13mL / L of 0.1N hydrochloric acid solution. The discoloration time of the drop test is compared to determine the corrosion resistance of the film layer.

[0038] The comparative experiment shows that the weight gain of the sample treated in the phosphating solution prepared at room temperature (30°C) is 11.1g / m 2 , and the weight gain of the sample treated in the phosphating solution prepared under low-temperature conditions is 14.3g / m 2 , representing a significant increase in film thickness.

[0039] The drop test comparison shows that the discoloration time of the sample treated in the phosphating solution prepared at room temperature (30°C) is 53 seconds, and the discoloration time of the sample treated in the phosphating solution prepared under low-temperature conditions is 90 seconds, representing a significant increase in corrosion resistance.

Claims

1. A method for preparing a phosphating solution at low temperature to improve the corrosion resistance of phosphating film on steel surfaces, characterized in that: The specific process is as follows: Step 1: Cool 1000 ml of deionized water to 10-15℃ in a water bath; Step 2: Add 1.5 g phosphoric acid, 40 g zinc dihydrogen phosphate, 40 g zinc nitrate, 5 g nickel nitrate, 0.2 g nitroguanidine, and 1.5 g citric acid to deionized water in sequence; when adding, wait for each chemical to dissolve completely before adding the next chemical. Step 3: Cool the solution obtained in Step 2 to 1-5℃ and maintain it for more than 20 minutes to obtain the phosphating solution; Step 4: First, naturally heat the phosphating solution obtained in Step 3 to 30°C, which takes 20 minutes. Then, heat the phosphating solution from 30°C to 65°C, which is required for the phosphating process. The heating rate should be controlled to be less than 3°C / min. The preparation process was carried out at room temperature of 30°C.