Pickling paste, preparation method of pickling paste and application of pickling paste in removal of alpha layer of titanium alloy

Abstract

The invention relates to pickling paste, a preparation method thereof and application of the pickling paste to removal of an alpha layer on the surface of titanium alloy, and belongs to the technical field of alloy surface treatment. Based on 100 parts by mass, the pickling paste is prepared from the following raw materials in parts by mass: 10-20 parts of nitric acid; 30-40 parts of hydrofluoric acid; 10 to 20 parts of magnesium nitrate; 2 to 5 parts of an associative polyurethane emulsion; and the balance of solvent. The invention further discloses a preparation method of the titanium alloy pickling paste and application of the titanium alloy pickling paste to removal of an alpha layer on the surface of titanium alloy. The titanium alloy pickling paste is used for treating the titanium alloy surface, the removal rate of an alpha layer on the titanium alloy surface is 100%, the harmful surface layer on the titanium alloy surface can be effectively removed in time, and the product quality and the production schedule are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy surface treatment, and particularly relates to a pickling paste, a preparation method thereof, and an application in removing the α layer of a titanium alloy. Background Art

[0002] The α layer on the surface of a titanium alloy is mainly composed of a rich α phase (hexagonal close-packed structure, HCP) and titanium oxides (such as TiO 2 )). The α layer on the surface of a titanium alloy is usually formed during high-temperature oxidation, heat treatment, or machining processes; the α layer on the surface of a titanium alloy may contain trace amounts of nitrides (formed by the reaction of nitrogen with titanium at high temperatures) or carbides (formed by the reaction of carbon dioxide with titanium at high temperatures); although the α layer on the surface of a titanium alloy has certain corrosion resistance and hardness, it may also cause problems such as increased brittleness, stress concentration, interface weakening, and uneven corrosion resistance; therefore, removing the α layer on the surface of a titanium alloy is of great significance for improving the comprehensive performance of the titanium alloy, optimizing subsequent processes, and extending the service life.

[0003] Currently, for the removal of the α layer on the surface of a titanium alloy, the commercially available products mainly include: bright cleaning agents for titanium alloy oxide scales, stainless steel pickling and passivation pastes, carbon steel pickling pastes, etc.; the bright cleaning agent for titanium alloy oxide scales is a liquid, and the corrosion area is uncontrollable, making it difficult to achieve the purpose of local removal; the stainless steel pickling and passivation paste is mainly used to remove oxides on the surface of stainless steel (the main components are chromium oxide, nickel oxide, etc.); the carbon steel pickling paste is used to remove the oxide scales on the surface of carbon steel, such as rust, carbonate, etc.; although both the stainless steel pickling and passivation paste and the carbon steel pickling paste contain acidic substances and can react with oxides to achieve the purpose of local removal, since the corrosion resistance of the α layer on the surface of a titanium alloy is higher than that of chromium oxide on the surface of stainless steel or iron oxide on carbon steel, the commercially available pickling paste cannot completely remove the α layer on the surface of a titanium alloy; and increasing the content of acidic substances in the stainless steel pickling and passivation paste and the carbon steel pickling paste is likely to cause excessive corrosion on the surface of the titanium alloy, and there are always defects such as bulging, pitting, ash hanging, residue, and mottling; the acidic substances in the commercially available pickling paste are difficult to determine, and titanium alloy forgings are mainly used in aviation, and chemical reagents containing chlorine ions are prohibited; in view of this, it is still necessary to obtain a special pickling paste for removing the α layer on the surface of a titanium alloy without chlorine ions through self-production.

[0004] In the prior art, CN86101522A and CN1124788A both disclose stainless steel pickling pastes and solve the problem of removing the oxide layer on the surface of stainless steel; however, the effect of using them to remove the α layer on the surface of titanium alloy is still difficult to determine; in addition, the polyvinylpyrrolidone and cellulose ether carriers used in CN1124788A float on the surface of the acid solution and are immiscible with the acid solution; the magnesium stearate used in CN86101522A can react with the acid to form stearic acid, which is also insoluble in the acid solution and will also float on the surface of the acid solution; both of them cannot effectively control the corrosion reaction, and the surface of the titanium alloy is prone to corrosion and form defective defects. Summary of the Invention

[0005] In order to solve the above technical problems, a pickling paste, its preparation method and application in removing the α layer of titanium alloy are provided. The pickling paste has a removal rate of 100% for the α layer on the surface of titanium alloy, a controllable corrosion area, and can ensure the production quality and production progress of titanium alloy products.

[0006] In order to solve the above technical problems, the first object of the present invention is to provide a pickling paste. Calculated by 100 parts by mass, the titanium alloy pickling paste is made of the following raw materials in parts by mass:

[0007] Nitric acid 10 - 20 parts; hydrofluoric acid 30 - 40 parts; magnesium nitrate 10 - 20 parts; associative polyurethane emulsion 2 - 5 parts; the balance is solvent.

[0008] In a specific embodiment of the present invention, the molecular weight of the associative polyurethane emulsion is 10000 - 50000Da.

[0009] In a specific embodiment of the present invention, the pH value of the pickling paste ≤ 2.0.

[0010] In a specific embodiment of the present invention, the density of the pickling paste is 1.3 - 1.6 g / mL.

[0011] In a specific embodiment of the present invention, the solvent is water.

[0012] In a specific embodiment of the present invention, the concentration of the hydrofluoric acid is 30% - 40%.

[0013] The second object of the present invention is to provide a preparation method of the above titanium alloy pickling paste, including the following steps:

[0014] Take the solvent, and at normal temperature and under stirring, sequentially add 10 - 20 parts of nitric acid, 30 - 40 parts of hydrofluoric acid, 10 - 20 parts of magnesium nitrate and 2 - 5 parts of associative polyurethane emulsion to the solvent, mix well and then stand still to obtain the titanium alloy pickling paste.

[0015] In a specific embodiment of the present invention, the standing time is 30 to 50 minutes.

[0016] The third object of the present invention is to provide the application of the above-mentioned titanium alloy pickling paste or the titanium alloy pickling paste prepared by the above-mentioned preparation method in removing the α layer on the surface of the titanium alloy.

[0017] In a specific embodiment of the present invention, the thickness of the α layer ≤ 100 μm.

[0018] In the present invention, the operation process of applying the titanium alloy pickling paste to remove the α layer on the surface of the titanium alloy is as follows: degreasing - water washing - applying the pickling paste - scrubbing - neutralizing - water washing - drying; among them, the thickness of the applied titanium alloy pickling paste is controlled at 1 mm; the removal time of the α layer on the surface of the titanium alloy is determined according to the thickness of the α layer on the surface of the titanium alloy. Usually, the removal time ≥ 30 minutes. During this period, the application can be appropriately repeated until the applied surface of the titanium alloy shows metallic luster.

[0019] The functions of each raw material in the formula of the titanium alloy pickling paste of the present invention in removing the α layer on the surface of the titanium alloy:

[0020] Function of nitric acid: Nitric acid (HNO 3 ) can react with aluminum oxide, vanadium oxide, etc. in the α layer on the surface of the titanium alloy to promote the decomposition of the α layer; since hydrogen gas is generated when hydrofluoric acid reacts with titanium, nitric acid can oxidize hydrogen gas to form water, inhibiting hydrogen embrittlement of the titanium alloy; since the reaction between hydrofluoric acid and titanium metal is violent, in order to avoid excessive corrosion of the surface of the titanium alloy, the addition of nitric acid can passivate the titanium alloy and slow down the excessive corrosion of the surface of the titanium alloy; nitric acid can provide an acidic environment for fluoride ions and extend the service life of the corrosion agent.

[0021] Function of hydrofluoric acid: At room temperature, titanium metal does not react with the three major strong acids (hydrochloric acid, nitric acid, and sulfuric acid). Although hydrofluoric acid (HF) is a weak acid, fluoride ions can change the standard electrode potential through coordination with titanium metal and become the best solvent for titanium metal. The two react to form hexafluorotitanate ions and hydrogen gas.

[0022] Function of magnesium nitrate: Magnesium nitrate can provide nitrate ions. Nitrate ions have certain oxidizing properties and can play a part of the role of nitric acid; since water is always present in nitric acid and hydrofluoric acid, even in the most concentrated state, the water content in the entire formula can reach 30 to 50%. Magnesium nitrate is a dehydrating agent of medium strength and can effectively absorb the water in the mixed acid, which can weaken the reaction between hydrofluoric acid and titanium to a certain extent, achieve the purpose of controlling the time for pickling to remove the α layer, and avoid the appearance of bad defects on the surface of the titanium alloy after the α layer on the surface of the titanium alloy is removed; magnesium nitrate can also ensure the viscosity of the pickling paste and is beneficial to the long-term preservation of the pickling paste.

[0023] Associative polyurethane emulsion: Although magnesium nitrate can cure the mixed acid, when a large amount of magnesium nitrate is added, the mixed acid will become jelly-like, which is not conducive to spreading and construction. If the amount is small, the pickling paste is prone to flow; introducing associative polyurethane emulsion, which not only has the characteristics of anti-microbial degradation, insensitivity to PH, and effectively improving medium shear viscosity, its viscosity is nearly 14,000 CP, which can enhance the viscosity of the pickling paste, make the pickling paste spread smoothly, and does not flow and does not pollute other surfaces of the titanium alloy.

[0024] The beneficial effects of the present invention are:

[0025] 1. The self-made pickling paste of the present invention is used to treat the surface of titanium alloy. After metallographic test, the removal rate of the α layer on the surface of titanium alloy is 100%, which indicates that the harmful surface layer on the surface of titanium alloy can be removed in time and effectively through the self-made pickling paste, ensuring product quality and production progress;

[0026] 2. The titanium alloy pickling paste of the present invention has good adhesion, does not flow, does not pollute other surfaces, can control the corrosion area, and can reduce acid waste and environmental pollution;

[0027] 3. After removing the α layer on the surface of titanium alloy with the pickling paste of the present invention, there are no bad defects such as bulges, pits, ash hanging, residues, and mottles on the surface of the titanium alloy. Using the pickling paste is simple in operation, low in cost, the construction environment is not restricted by the site, and it is practical and reliable. Description of the drawings

[0028] Figure 1 It is a photo of the titanium alloy before removing the surface α layer in Example 1 of the specific embodiment of the present invention;

[0029] Figure 2 It is a metallographic structure diagram of the titanium alloy before removing the surface α layer in Example 1 of the specific embodiment of the present invention;

[0030] Figure 3 It is a photo of the titanium alloy after removing the surface α layer in Example 1 of the specific embodiment of the present invention;

[0031] Figure 4 It is a metallographic structure diagram of the titanium alloy after removing the surface α layer in Example 1 of the specific embodiment of the present invention;

[0032] Figure 5 It is a photo of the titanium alloy before removing the surface α layer in Example 2 of the specific embodiment of the present invention;

[0033] Figure 6 It is a metallographic structure diagram of the titanium alloy before removing the surface of the titanium alloy in Example 2 of the specific embodiment of the present invention;

[0034] Figure 7 It is a photo of the titanium alloy after removing the surface α layer in Example 2 of the specific embodiment of the present invention;

[0035] Figure 8 It is the metallographic structure after removing the surface α layer in Example 2 of the specific implementation mode of the present invention;

[0036] Figure 9 It is a photo of the titanium alloy before removing the surface α layer in Example 3 of the specific implementation mode of the present invention;

[0037] Figure 10 It is a photo of the titanium alloy after removing the surface α layer in Example 3 of the specific implementation mode of the present invention. Specific implementation mode

[0038] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other implementation manners obtained by those of ordinary skill in the art without making creative efforts belong to the scope protected by the present invention.

[0039] Pickling paste. Calculated by 100 parts by mass, the titanium alloy pickling paste is made of the following raw materials in parts by mass:

[0040] Nitric acid 10 - 20 parts; hydrofluoric acid 30 - 40 parts; magnesium nitrate 10 - 20 parts; associative polyurethane emulsion 2 - 5 parts; the balance is solvent.

[0041] In some examples, the molecular weight of the associative polyurethane emulsion is 10000 - 50000 Da.

[0042] In some examples, the pH value of the pickling paste ≤ 2.0.

[0043] In some examples, the density of the pickling paste is 1.3 - 1.6 g / mL.

[0044] In some examples, the solvent is water.

[0045] In some examples, the concentration of hydrofluoric acid is 30% - 40%; it should be noted that the nitric acid can be selected as analytical pure or chemical pure.

[0046] The preparation method of the above-mentioned titanium alloy pickling paste includes the following steps:

[0047] Take the solvent. Under normal temperature and stirring state, add 10 - 20 parts of nitric acid, 30 - 40 parts of hydrofluoric acid, 10 - 20 parts of magnesium nitrate and 2 - 5 parts of associative polyurethane emulsion to the solvent in sequence, mix well and then stand still to obtain the titanium alloy pickling paste.

[0048] In some examples, the standing time is 30 - 50 min.

[0049] Use of the above-mentioned titanium alloy pickling paste or the titanium alloy pickling paste prepared by the above-mentioned preparation method in removing the α layer on the surface of the titanium alloy.

[0050] It should be noted that the pickling paste has the best effect on removing the α layer on the surface of the titanium alloy. Of course, the pickling paste can also be used to remove the oxide layer or passivation layer on the surface of other alloys. However, due to the large difference in corrosion resistance from the α layer itself, it may be difficult to control the removal time when using the pickling paste to remove the oxide layer or passivation layer on the surface of other alloys, and there may be a situation where bad defects are generated due to over-corrosion.

[0051] In some examples, the thickness of the α layer ≤ 100 μm; by applying the pickling paste on the surface of the titanium alloy, the removal of the α layer with a thickness ≤ 100 μm can be achieved.

[0052] In some examples, the operation process of the application is: degreasing, water washing, applying the pickling paste, scrubbing, neutralizing, water washing and drying.

[0053] In some examples, after degreasing, sandpaper is used for grinding or sandblasting to remove the black skin on the surface of the titanium alloy to be treated, and the dust is blown / swept away.

[0054] In some examples, the thickness of the applied pickling paste is controlled at 1 mm, and the local area of the α layer to be removed on the surface of the titanium alloy is evenly covered; the application is carried out with a brush.

[0055] In some examples, after applying the pickling paste, the titanium alloy needs to be left standing, and during this period, the pickling paste of the titanium alloy can be stirred with a brush or another layer of pickling paste can be applied.

[0056] In some examples, before scrubbing, it is necessary to wait until the applied pickling paste of the titanium alloy removes the α layer on the surface of the titanium alloy and shows a metallic luster; for the above-mentioned titanium alloy pickling paste, after applying the pickling paste of the titanium alloy, the time for removing the α layer on the surface of the titanium alloy ≥ 30 min. It is necessary to determine the removal time according to the thickness of the α layer to be removed on the surface of the titanium alloy. The thicker the thickness of the α layer, the longer the removal time should be appropriately extended; when the thickness of the α layer on the surface of the titanium alloy is 50 - 100 μm, the removal time of the α layer is 2 - 3 h.

[0057] In some examples, alkali liquor is used for neutralization during neutralization; the alkali liquor can be an alkali containing hydroxide or an alkali that shows alkalinity after dissolution; preferably, the alkali liquor is a low-concentration sodium carbonate solution.

[0058] To further prove the effect of the titanium alloy pickling paste of the present invention in removing the α layer on the surface of the titanium alloy, the following examples and comparative examples are provided:

[0059] Example 1

[0060] This embodiment provides a preparation method of pickling paste, including: at room temperature, using 48 parts by mass of deionized water as a solvent, adding 10 parts by mass of 68% nitric acid, 30 parts by mass of 40% hydrofluoric acid, 10 parts by mass of magnesium nitrate, and 2 parts by mass of associative polyurethane emulsion, stirring and mixing evenly, and standing for 30 min to obtain a viscous pickling paste for titanium alloy.

[0061] Degrease the surface of the titanium alloy to be treated, use sandpaper to polish off the black skin on the surface of the titanium alloy, and purge; use a brush to apply the pickling paste for titanium alloy obtained in this embodiment on the surface of the α layer of the titanium alloy to be treated to form a pickling paste layer for titanium alloy with a thickness of 1 mm; the time from application to scrubbing is 2.5 h; when metallic luster appears in the applied area of the titanium alloy, wipe off the pickling paste layer for titanium alloy, and rinse it with clean water; then clean and neutralize the surface of the titanium alloy with a low-concentration sodium carbonate solution; finally, rinse with clean water until the pH value of the titanium alloy surface is the same as that of the rinsing water, and dry it.

[0062] The photo of the titanium alloy before removing the surface α layer in this embodiment is as shown in the appendix Figure 1 shown; the metallographic structure before removing the surface α layer of the titanium alloy is as shown in the appendix Figure 2 shown;

[0063] The photo of the titanium alloy after removing the surface α layer in this embodiment is as shown in the appendix Figure 3 shown; the metallographic structure after removing the surface α layer of the titanium alloy is as shown in the appendix Figure 4 shown.

[0064] As can be seen from the appendix Figures 1-4 shown, the removal rate of the surface α layer after applying the pickling paste prepared in this embodiment on the surface of the titanium alloy is 100%, and there are no surface defects.

[0065] Example 2

[0066] This embodiment provides a preparation method of pickling paste for titanium alloy, including: at room temperature, using 43 parts by mass of deionized water as a solvent, adding 10 parts by mass of 68% nitric acid, 40 parts by mass of 40% hydrofluoric acid, 5 parts by mass of magnesium nitrate, and 3 parts by mass of associative polyurethane emulsion, stirring and mixing evenly, and standing for 30 min to obtain a viscous pickling paste for titanium alloy.

[0067] Degrease the surface of the titanium alloy to be treated, use sandpaper to polish off the black skin on the surface of the titanium alloy, and purge; use a brush to apply the pickling paste for titanium alloy obtained in this embodiment on the surface of the α layer of the titanium alloy to be treated to form a pickling paste layer for titanium alloy with a thickness of 1 mm; the time from application to scrubbing is 3 h; when metallic luster appears in the applied area of the titanium alloy, wipe off the pickling paste layer for titanium alloy, and rinse it with clean water; then clean and neutralize the surface of the titanium alloy with a low-concentration sodium carbonate solution; finally, rinse with clean water until the pH value of the titanium alloy surface is the same as that of the rinsing water, and dry it.

[0068] The photo of the titanium alloy before removing the surface α layer in this embodiment is as shown in the appendix Figure 5 ; the metallographic structure before removing the surface α layer is as shown in the appendix Figure 6 .

[0069] The photo of the titanium alloy after removing the surface α layer in this embodiment is as shown in the appendix Figure 7 ; the metallographic structure after removing the surface α layer is as shown in the appendix Figure 8 .

[0070] Example 3

[0071] This embodiment provides a preparation method of a pickling paste for titanium alloy, including: at room temperature, using 39 parts by mass of deionized water as a solvent, adding 20 parts by mass of 68% nitric acid, 30 parts by mass of 40% hydrofluoric acid, 8 parts by mass of magnesium nitrate, and 3 parts by mass of an associative polyurethane emulsion, stirring and mixing evenly, and standing for 30 min to obtain a viscous pickling paste for titanium alloy.

[0072] Degrease the surface of the titanium alloy to be treated, use sandpaper to polish and remove the black skin on the surface of the titanium alloy, and blow it; use a brush to apply the pickling paste for titanium alloy obtained in this embodiment on the surface of the α layer of the titanium alloy to be treated to form a pickling paste layer with a thickness of 1 mm; after the application is completed, the reaction starts violently, and stir the pickling paste with a brush during this period; when a metallic luster appears in the applied area of the titanium alloy, wipe off the pickling paste layer, and wash it clean with clean water; then wash and neutralize the surface of the titanium alloy with a low-concentration sodium carbonate solution; finally, wash it with clean water until the pH value of the surface of the titanium alloy is the same as that of the rinsing water, and dry it.

[0073] The photo of the titanium alloy before removing the surface α layer in this embodiment is as shown in the appendix Figure 9 .

[0074] The photo of the titanium alloy after removing the surface α layer in this embodiment is as shown in the appendix Figure 10 .

Claims

1. A pickling paste, characterized in that: Based on 100 parts by mass, the titanium alloy pickling paste is made of the following raw materials in parts by mass: 10-20 parts of nitric acid; 30-40 parts of hydrofluoric acid; 10-20 parts of magnesium nitrate; 2-5 parts of associative polyurethane emulsion; the balance is solvent.

2. The pickling paste according to claim 1, characterized in that: The molecular weight of the associative polyurethane emulsion is 10000-50000Da.

3. The pickling paste according to claim 1, characterized in that: The pH value of the pickling paste is ≤2.

0.

4. The pickling paste according to claim 1, characterized in that: The density of the pickling paste is 1.3-1.6 g / ml.

5. The pickling paste according to claim 1, characterized in that: The solvent is water.

6. The pickling paste according to claim 1, characterized in that: The concentration of the hydrofluoric acid is 30% to 40%.

7. The method for preparing the pickling paste according to any one of claims 1 to 6, characterized in that: The following steps are involved: Take a solvent, and add 10 to 20 parts of nitric acid, 30 to 40 parts of hydrofluoric acid, 10 to 20 parts of magnesium nitrate and 2 to 5 parts of associative polyurethane emulsion into the solvent in sequence at room temperature and under stirring, mix well and let stand to obtain a titanium alloy pickling paste.

8. The preparation method according to claim 7, characterized in that: The standing time is 30 to 50 minutes.

9. Use of the pickling paste according to any one of claims 1 to 6 or the pickling paste prepared by the preparation method according to claims 7 and 8 in removing the α layer on the surface of titanium alloy.

10. The application according to claim 9, characterized in that: The thickness of the α layer is ≤100 μm.

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