Environment-friendly titanium alloy surface alkali-acid washing treatment method

Abstract

This invention discloses an environmentally friendly alkaline pickling treatment method for titanium alloy surfaces, comprising: immersing the titanium alloy sheet in a molten alkaline solution for 10-30 minutes at a temperature of 420-450°C; removing the titanium alloy sheet and letting it stand for 5 minutes, then immediately immersing it in a cold water bath for rapid cooling to cause residual iron oxide scale to crack and fall off; immersing the water-washed titanium alloy sheet in a fluorine-free pickling reagent for 3-10 minutes at a temperature of 30-60°C; immersing the pickled titanium alloy sheet in a nitric acid solution for 1-3 minutes within 30 seconds; and after whitening, rinsing and drying the titanium alloy sheet. The method of this invention uses a fluorine-free pickling reagent, and no harmful gases are generated during the alkaline pickling process. By controlling the selection, ratio, temperature, and time of compounds in the alkaline acid solution, the rapid increase in hydrogen content after alkaline pickling is suppressed.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy surface treatment technology, specifically relating to an environmentally friendly alkaline pickling treatment method for titanium alloy surfaces. Background Technology

[0002] Titanium alloys possess numerous advantages, including high specific strength, excellent corrosion resistance, and good biocompatibility, leading to their widespread application in various fields. Consequently, their surface treatment technology has attracted considerable attention. The removal of oxide scale and hard α-oxygen layer from titanium alloy surfaces mainly falls into two categories: mechanical treatment and chemical etching. Mechanical treatments (such as sandblasting, polishing, and water grinding) have poor adaptability to workpiece shape and size, and the difficulty in achieving uniform thickness control during the process limits their application range.

[0003] Chemical etching is more widely applicable, and the industry generally adopts a process combining alkaline pretreatment with subsequent acid pickling. Commonly used acid pickling systems include: alkaline pickling + hydrofluoric acid (HF) system and alkaline pickling + three-acid mixture (H2SO4, HCl, HNO3). The first system is the most widely used and mature, but the extremely corrosive and volatile nature of hydrofluoric acid itself poses significant inhalation health risks. More importantly, in the currently mainstream HF-HNO3 acid pickling system, the reaction easily produces the byproduct nitric oxide. NO is rapidly oxidized by oxygen in the air to generate toxic nitrogen dioxide, forming characteristic yellow-brown fumes (yellow smoke), polluting the environment. To address these serious safety and environmental hazards, industrial applications must be equipped with closed pickling lines, advanced safety protection facilities, and specialized wastewater treatment systems, resulting in extremely high initial investment and subsequent operation and maintenance costs for the entire system. The second system, alkaline washing combined with a mixture of three acids (H2SO4, HCl, and HNO3), avoids some of the risks associated with the hydrofluoric acid system. However, it faces problems such as wrinkles, grain boundary corrosion pits, and increased hydrogen content on the titanium alloy surface after alkaline and acid washing, which can damage the product's appearance quality and potential performance.

[0004] To address the problems existing in the two mainstream systems mentioned above, there is still a need for an environmentally friendly alkaline pickling surface treatment method for titanium alloys that requires less hydrogen absorption, produces a smooth surface after pickling, and does not generate industrial waste gas. Summary of the Invention

[0005] To address the shortcomings of the existing technology, an environmentally friendly alkaline pickling treatment method for titanium alloy surfaces is provided. This method effectively avoids environmental pollution caused by "yellow fumes" generated during the pickling process, while also suppressing pickling defects and hydrogen absorption on the titanium alloy surface, thus reducing production line investment and maintenance costs.

[0006] To achieve the above objectives, the following technical solution is adopted: This invention provides an environmentally friendly alkaline pickling treatment method for titanium alloy surfaces, comprising the following steps: S101, Alkali washing: Immerse the titanium alloy sheet in a molten alkaline solution for alkaline washing. The alkaline washing time is 10~30 minutes and the alkaline washing temperature is 420~450℃. S102. Water washing: After taking out the titanium alloy sheet, let it stand for 5-10 minutes, then immediately immerse the titanium alloy sheet in a cold water tank for rapid cooling, so that the residual iron oxide scale will crack and fall off. S103. Pickling: The water-washed titanium alloy sheet is immersed in a fluorine-free pickling reagent for pickling. The pickling time is 3~10 minutes and the pickling temperature is 30~60℃. S104, Whitening: Immerse the pickled titanium alloy sheet in a nitric acid solution for 30 seconds, and soak for 1 to 3 minutes; S105. Post-treatment: After whitening, the titanium alloy sheet is washed with water and dried.

[0007] In some embodiments, the alkaline solution consists of 70-80 wt% sodium hydroxide and 20-30 wt% sodium nitrate.

[0008] In some embodiments, the fluorine-free pickling reagent comprises industrial-grade sulfuric acid, inorganic potassium salt, and water; wherein the mass concentration of the industrial-grade sulfuric acid is 60% to 70%, and the inorganic potassium salt is selected from one or both of potassium chloride and potassium nitrate.

[0009] In some embodiments, the fluorine-free pickling reagent consists of 400-500 ml / L industrial grade sulfuric acid, 60-100 ml / L potassium chloride, 120-200 ml / L potassium nitrate, and the balance being water.

[0010] In some embodiments, the nitric acid-containing solution in step S104 consists of 15-20 wt% nitric acid and the remainder water.

[0011] In some embodiments, the post-processing in step S105 includes the following steps: Water cleaning: After whitening, the titanium alloy sheet is immersed in a cold water tank, then in a hot water tank, and finally rinsed with high pressure water to remove residual acid from the surface of the sheet. Drying: The titanium alloy plates that have been washed with water are sent into a drying oven and dried by flowing hot air.

[0012] In some embodiments, the water temperature in the hot water tank is 60~80℃; the temperature of the flowing hot air is 70~100℃.

[0013] In some embodiments, in step S101, the alkaline washing time is 16~22 min and the alkaline washing temperature is 430~450℃.

[0014] In some embodiments, the titanium alloy plates are framed before alkaline washing. The titanium alloy plates to be acid-washed are placed into a special alkaline washing frame and fixed. The interval between each titanium alloy plate is greater than 150mm, and they are fixed with titanium clips.

[0015] In some embodiments, the titanium alloy sheet is a TC4, TA15, or TA17 titanium alloy sheet, and the sheet thickness is 2~10mm.

[0016] The present invention has the following beneficial technical effects: The environmentally friendly alkaline pickling method for titanium alloy surfaces disclosed in this invention uses fluorine-free pickling reagents. No harmful gases are generated during the alkaline pickling process, effectively avoiding safety hazards and environmental pollution, and reducing equipment investment and maintenance costs. By controlling the selection, ratio, temperature, and time of compounds in the alkaline acid solution, the rapid increase in hydrogen content after alkaline pickling is suppressed, preventing preferential corrosion of grain boundaries on the plate surface during pickling, slowing down the corrosion rate, achieving a dynamic balance between corrosion and passivation, and obtaining a smooth, silvery-white surface. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to the present invention; Figure 2 This is a comparison chart showing the hydrogen content detected by the inert gas melting-thermal conductivity method before and after pickling in the embodiments and comparative examples of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0020] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0021] To achieve the above objectives, one aspect of the present invention provides an environmentally friendly method for alkaline pickling treatment of titanium alloy surfaces. Figure 1 The diagram shown is a schematic flowchart of the method.

[0022] like Figure 1 As shown, the processing method may include the following steps: S101, Alkali washing: Immerse the titanium alloy sheet in a molten alkaline solution for alkaline washing. The alkaline washing time is 10~30 minutes and the alkaline washing temperature is 420~450℃. S102. Water washing: After taking out the titanium alloy sheet, let it stand for 5-10 minutes, then immediately immerse the titanium alloy sheet in a cold water tank for rapid cooling, so that the residual iron oxide scale will crack and fall off. S103. Pickling: The water-washed titanium alloy sheet is immersed in a fluorine-free pickling reagent for pickling. The pickling time is 3~10 minutes and the pickling temperature is 30~60℃. S104, Whitening: Immerse the pickled titanium alloy sheet in a nitric acid solution for 30 seconds, and soak for 1 to 3 minutes; S105. Post-treatment: After whitening, the titanium alloy sheet is washed with water and dried.

[0023] The environmentally friendly alkaline pickling method for titanium alloy surfaces disclosed in this invention uses fluorine-free pickling reagents. No harmful gases are generated during the alkaline pickling process, effectively avoiding safety hazards and environmental pollution, and reducing equipment investment and maintenance costs. By controlling the selection, ratio, temperature, and time of compounds in the alkaline acid solution, the rapid increase in hydrogen content after alkaline pickling is suppressed, preventing preferential corrosion of grain boundaries on the plate surface during pickling, slowing down the corrosion rate, achieving a dynamic balance between corrosion and passivation, and obtaining a smooth, silvery-white surface.

[0024] In a preferred embodiment of the present invention, the alkaline solution is composed of 70-80 wt% sodium hydroxide and 20-30 wt% sodium nitrate.

[0025] A binary molten alkaline solution of sodium hydroxide and sodium nitrate works synergistically to achieve highly efficient alkaline etching and removal of oxide scale: Sodium hydroxide acts as the main alkaline agent, undergoing a saponification reaction with the oxide scale on the titanium alloy surface, thus destroying the oxide scale layer structure; Sodium nitrate acts as an oxidant, assisting in enhancing the separation effect between the oxide scale and the substrate. Furthermore, the optimized ratio results in an alkaline etching efficiency far exceeding that of a single sodium hydroxide solution. The alkaline solution with the above ratio maintains a stable molten state at 420~450℃, without local solidification or coking, ensuring uniform contact of the reagent with the plate surface during alkaline washing and avoiding local oxide scale residue. The binary alkaline solution system contains no other additives, has a simple composition, and uses conventional industrial reagents that are easy to procure and prepare. The reaction is mild in the molten state, preventing over-corrosion of the titanium alloy substrate, and simultaneously inhibiting the hydrogen absorption tendency of the titanium alloy during alkaline washing.

[0026] In a preferred embodiment of the present invention, the fluorine-free pickling reagent comprises industrial-grade sulfuric acid, inorganic potassium salt and water; wherein the mass concentration of industrial-grade sulfuric acid is 60%~70%, and the inorganic potassium salt is selected from one or both of potassium chloride and potassium nitrate.

[0027] In a preferred embodiment of the present invention, the fluorine-free pickling reagent consists of 400-500 ml / L industrial grade sulfuric acid, 60-100 ml / L potassium chloride, 120-200 ml / L potassium nitrate, and the balance being water.

[0028] The pickling reagent is a fluorine-free system of industrial-grade sulfuric acid, inorganic potassium salt, and water, eliminating the need for hydrofluoric acid and preventing fluoride pollution and yellow fumes at the reagent level. Sulfuric acid, as the primary acid, effectively reacts with residual oxide layers on the titanium alloy surface for chemical removal. Furthermore, the corrosiveness of sulfuric acid is controllable, minimizing over-corrosion of the substrate. The concentration of industrial-grade sulfuric acid is limited to 60%–70%, ensuring pickling efficiency while avoiding problems such as excessively rapid reaction rates, uneven surface corrosion, and a sudden increase in hydrogen absorption caused by excessively high sulfuric acid concentrations. Potassium chloride and / or potassium nitrate are selected as the inorganic potassium salts. Potassium ions regulate the corrosion rate of the pickling system, synergistically achieving a balance between corrosion and passivation with sulfuric acid, preventing preferential corrosion at grain boundaries, and inhibiting hydrogen adsorption on the titanium alloy during pickling, thus reducing hydrogen absorption and solving the problem of high hydrogen absorption in traditional three-acid systems.

[0029] In a preferred embodiment of the present invention, the nitric acid-containing solution in step S104 consists of 15-20 wt% nitric acid and the remainder water.

[0030] In a preferred embodiment of the present invention, the post-processing in step S105 includes the following steps: Water cleaning: After whitening, the titanium alloy sheet is immersed in a cold water tank, then in a hot water tank, and finally rinsed with high pressure water to remove residual acid from the surface of the sheet. Drying: The titanium alloy plates that have been washed with water are sent into a drying oven and dried by flowing hot air.

[0031] The temperature of the cold water tank is ≤30℃, preferably 15~25℃; the temperature of the hot water tank is 60~80℃; and the water pressure of the high-pressure water is 2~5MPa.

[0032] In a preferred embodiment of the present invention, the water temperature in the hot water tank is 60~80℃; the temperature of the flowing hot air is 70~100℃.

[0033] In a preferred embodiment of the present invention, in step S101, the alkaline washing time is 16~22 min and the alkaline washing temperature is 430~450℃.

[0034] In a preferred embodiment of the present invention, the titanium alloy plates are first framed before alkaline washing. The titanium alloy plates to be acid-washed are placed into a special alkaline washing frame and fixed. The interval between each titanium alloy plate is greater than 150mm and they are fixed with titanium clips.

[0035] In a preferred embodiment of the present invention, the titanium alloy plate is a TC4, TA15 or TA17 titanium alloy plate, and the plate thickness is 2~10mm.

[0036] The present invention will be further illustrated by the following examples.

[0037] Example 1 An environmentally friendly alkaline pickling treatment method for titanium alloy surfaces, taking the pickling of oxide scale on the surface of a 2mm thick TC4 titanium alloy sheet as an example, includes the following steps; (1) Frame: Place the TC4 titanium alloy plates into a special frame for alkali and acid washing, with a spacing of more than 150mm between each plate, and fix them with titanium clips.

[0038] (2) Alkali washing: Immerse the pickling frame from step (1) into the molten alkaline solution for 16 minutes at a temperature of 430°C.

[0039] (3) Water washing: After the alkaline pot is removed from the plate, it is left for 5 minutes. Then the plate is immediately immersed in a cold water tank for rapid cooling, so that the residual iron oxide scale cracks and falls off.

[0040] (4) Pickling: Immerse the washed titanium alloy plate in an acidic solution for 4 minutes at a temperature of 48°C. (5) Whitening: Immerse the board after pickling in step (4) in a solution containing nitric acid within 30 seconds for 1 minute.

[0041] (6) Water rinsing: After completing step (5), rinse the residual acid by immersing in cold water tank - immersing in hot water tank - high pressure water rinsing.

[0042] (7) Drying: The boards are sent into the drying oven and dried quickly by flowing hot air.

[0043] No harmful gases are generated during the pickling process. After alkaline pickling, the oxide scale on the surface of the TC4 titanium alloy sheet is removed, leaving a smooth surface without pickling "wrinkles," pits, or other defects. The surface has a uniform silvery-white metallic luster. The hydrogen content was tested using the inert gas melting-thermal conductivity method, and the results are as follows: Figure 2 As shown, it meets the national standard requirements.

[0044] Example 2 An environmentally friendly alkaline pickling treatment method for titanium alloy surfaces, taking the pickling of oxide scale on the surface of a 10mm thick TA15 titanium alloy sheet as an example, includes the following steps; (1) Frame: Place the TA15 titanium alloy plates into a special frame for alkali and acid washing, with a spacing of more than 150mm between each plate, and fix them with titanium clips.

[0045] (2) Alkali washing: Immerse the pickling frame from step (1) into the molten alkaline solution for 22 minutes at a temperature of 450°C.

[0046] (3) Water washing: After the alkaline pot is removed from the plate, it is left for 5 minutes. Then the plate is immediately immersed in a cold water tank for rapid cooling, so that the residual iron oxide scale cracks and falls off.

[0047] (4) Pickling: Immerse the washed titanium alloy plate in an acidic solution for 8 minutes at a temperature of 55°C. (5) Whitening: Immerse the board after pickling in step (4) in a solution containing nitric acid within 30 seconds for 7 minutes.

[0048] (6) Water rinsing: After completing step (5), rinse the residual acid by immersing in cold water tank - immersing in hot water tank - high pressure water rinsing.

[0049] (7) Drying: The boards are sent into the drying oven and dried quickly by flowing hot air.

[0050] No harmful gases were generated during the pickling process. After alkaline pickling, the oxide scale on the surface of the TA15 titanium alloy sheet was removed, leaving a smooth and uniform surface with no visible pickling defects. The hydrogen content was tested before and after pickling using the inert gas melting-thermal conductivity method, and the results are as follows: Figure 2 As shown, it meets the national standard requirements.

[0051] Example 3 An environmentally friendly alkaline pickling treatment method for titanium alloy surfaces, taking the pickling of oxide scale on the surface of an 8mm thick TA17 titanium alloy sheet as an example, includes the following steps; (1) Frame: Place the TA17 titanium alloy plates into a special frame for alkali and acid washing, with a spacing of more than 150mm between each plate, and fix them with titanium clips.

[0052] (2) Alkali washing: Immerse the pickling frame from step (1) into the molten alkaline solution for 18 minutes at a temperature of 450°C.

[0053] (3) Water washing: After the alkaline pot is removed from the plate, it is left for 5 minutes. Then the plate is immediately immersed in a cold water tank for rapid cooling, so that the residual iron oxide scale cracks and falls off.

[0054] (4) Pickling: Immerse the washed titanium alloy plate in an acidic solution for 6 minutes at a temperature of 45°C.

[0055] (5) Whitening: Immerse the board after pickling in step (4) in a solution containing nitric acid within 30 seconds for 3 minutes.

[0056] (6) Water rinsing: After completing step (5), rinse the residual acid by immersing in cold water tank - immersing in hot water tank - high pressure water rinsing.

[0057] (7) Drying: The boards are sent into the drying oven and dried quickly by flowing hot air.

[0058] No harmful gases are generated during the pickling process. After alkaline pickling, the oxide scale on the surface of the TA17 titanium alloy sheet is removed, leaving a smooth and uniform surface with no pickling "wrinkles," pits, or other defects. The hydrogen content was measured before and after pickling using the inert gas melting-thermal conductivity method. Figure 2 As shown, it meets the national standard requirements.

[0059] Comparative Example 1 Taking the pickling of the oxide scale on the surface of a 2mm thick TC4 titanium alloy plate as an example, the alkaline pickling steps are similar to those in Specific Example 1. The difference is that the alkaline pickling time in step (2) is 25min and the alkaline pickling temperature is 470℃, while the pickling time in step (4) is 12min.

[0060] After alkali and acid washing, the oxide scale on the surface of the TC4 titanium alloy sheet was removed, and visible corrosion pits were found on the surface. The hydrogen content of the sheet was determined using the inert gas melting-thermal conductivity method, and the results are as follows. Figure 2 As shown, the hydrogen content increased by 0.0026% before and after pickling.

[0061] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0062] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. An environmentally friendly alkaline-acid pickling treatment method for titanium alloy surfaces, characterized in that, Includes the following steps: S101, Alkali washing: Immerse the titanium alloy sheet in a molten alkaline solution for alkaline washing. The alkaline washing time is 10~30 minutes and the alkaline washing temperature is 420~450℃. S102. Water washing: After taking out the titanium alloy sheet, let it stand for 5-10 minutes, then immediately immerse the titanium alloy sheet in a cold water tank for rapid cooling, so that the residual iron oxide scale will crack and fall off. S103. Pickling: The water-washed titanium alloy sheet is immersed in a fluorine-free pickling reagent for pickling. The pickling time is 3~10 minutes and the pickling temperature is 30~60℃. S104, Whitening: Immerse the pickled titanium alloy sheet in a nitric acid solution for 30 seconds, and soak for 1 to 3 minutes; S105. Post-treatment: After whitening, the titanium alloy sheet is washed with water and dried.

2. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 1, characterized in that, The alkaline solution consists of 70-80 wt% sodium hydroxide and 20-30 wt% sodium nitrate.

3. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 1, characterized in that, The fluorine-free pickling reagent contains industrial-grade sulfuric acid, inorganic potassium salt, and water; wherein, the mass concentration of industrial-grade sulfuric acid is 60%~70%, and the inorganic potassium salt is selected from one or both of potassium chloride and potassium nitrate.

4. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 3, characterized in that, The fluorine-free pickling reagent consists of 400-500 ml / L industrial grade sulfuric acid, 60-100 ml / L potassium chloride, 120-200 ml / L potassium nitrate, and the remainder water.

5. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 1, characterized in that, The nitric acid solution in step S104 consists of 15-20 wt% nitric acid and the remainder water.

6. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 1, characterized in that, The post-processing in step S105 includes the following steps: Water cleaning: After whitening, the titanium alloy sheet is immersed in a cold water tank, then in a hot water tank, and finally rinsed with high pressure water to remove residual acid from the surface of the sheet. Drying: The titanium alloy plates that have been washed with water are sent into a drying oven and dried by flowing hot air.

7. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 6, characterized in that, The water temperature in the hot water tank is 60~80℃; the temperature of the flowing hot air is 70~100℃.

8. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 1, characterized in that, In step S101, the alkaline washing time is 16~22 min and the alkaline washing temperature is 430~450℃.

9. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to claim 1, characterized in that, Before alkaline washing, the titanium alloy plates are first framed. The titanium alloy plates to be acid-washed are placed into a special alkaline washing frame and fixed. The spacing between each titanium alloy plate is greater than 150mm, and they are fixed with titanium clips.

10. The environmentally friendly alkaline pickling treatment method for titanium alloy surfaces according to any one of claims 1-9, characterized in that, The titanium alloy sheet is a TC4, TA15, or TA17 titanium alloy sheet, with a thickness of 2-10 mm.

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