Pickling process of α+β two-phase titanium alloy bolt

Abstract

The application discloses an acid pickling process of an alpha+beta type two-phase titanium alloy bolt, which comprises the following preparation steps: (1) preparing an acid pickling solution: one or more of concentrated nitric acid with a concentration of 63%, 24% hydrofluoric acid, 36% hydrochloric acid and 60% concentrated sulfuric acid are uniformly mixed with pure water according to a proportion to obtain an acid pickling solution; (2) adding an additive; (3) placing the titanium alloy bolt to be cleaned into a stainless steel material frame, immersing the titanium alloy bolt into the acid pickling solution and soaking for a period of time; (4) placing the cleaned titanium alloy bolt into a water tank to be cleaned, and then drying through a drying machine; (5) placing the titanium alloy bolt into an oven to be heat preserved, and the titanium alloy bolt is used for hydrogen removal treatment; (6) testing the oxidation film, the corrosion pollution layer and the hydrogen content performance of the product; through the above method, the oxidation film can be completely eliminated, the corrosion layer caused by the acid pickling can be maximally reduced, and the hydrogen embrittlement problem caused by the acid pickling can be effectively reduced through the hydrogen removal treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the pickling technology field of the alpha + beta type two-phase titanium alloy bolt, and specifically designs the type and proportion of the acid solution for deployment, and optimizes the pickling process. BACKGROUND

[0002] In the aviation industry, bolt fasteners are a type of mechanical part that is widely used in connection applications, and are a large number of important components that are indispensable in aircraft and other spacecraft. For all fastener designers and manufacturers, a major challenge is the availability of raw materials, such as titanium alloys and high-nickel-based alloys. Rare materials have caused cost increases, and the rapid development of today's aviation market makes it very important to obtain raw materials. In addition, the delivery period of the materials is very long, so it is also a challenge to provide customers with a suitable delivery period.

[0003] Titanium and its alloys have become a new type of metal material due to their high strength and corrosion resistance, and have been widely used in the fields of aerospace, national defense and military industry, petroleum and chemical industry, medical devices, etc. With the extensive use of composite materials, the advantages of titanium alloy fasteners are becoming more and more prominent. Titanium alloy, as a material for manufacturing aviation fasteners, fully demonstrates its advantages of high strength, high density, and lightweight.

[0004] The common heat treatment process for titanium alloy is solid solution + aging. After aging treatment at a temperature above 500℃, a blue or light blue oxide film is formed on the surface. This kind of high-hardness, high-brittleness, oxygen-containing contaminant is prone to crack during subsequent processing or use, which affects the performance of the product and reduces the service life of the material. Therefore, a surface treatment method is needed to remove this layer of oxide film.

[0005] There are already a wide range of applications for the process of surface treatment of titanium alloy. There are two methods for removing the oxide layer of titanium alloy in China: salt washing and acid pickling. Salt washing is a process of soaking in molten salt, with a temperature reaching above 400℃, and the reaction is relatively violent, which is difficult to control and can cause secondary oxidation or thin surface cracking. Acid pickling is a relatively mild reaction, but titanium has a strong affinity for hydrogen. After acid pickling, titanium alloy is prone to hydrogen embrittlement. When the hydrogen content in titanium alloy exceeds a certain value, the plasticity and toughness of the material will decrease significantly, and hydrogen embrittlement will occur. After hydrogen enters the material, it will dissolve in the crystal lattice in the form of interstitial atoms, which has little effect on performance. However, when the solid solution concentration reaches saturation, hydrogen will form titanium hydride, i.e. titanium hydride, and penetrate and diffuse in the titanium alloy, finally leading to hydrogen embrittlement fracture. SUMMARY

[0006] The technical problem solved by the present application is to provide an acid pickling process for alpha+beta two-phase titanium alloy bolts, which can effectively remove the oxide layer on the surface of the titanium alloy and reduce the performance decline caused by hydrogen absorption, so that the titanium alloy bolt has good surface quality, processing performance and mechanical properties.

[0007] To solve the above technical problems, one technical solution of the present application is to provide an acid pickling process for alpha+beta two-phase titanium alloy bolts, comprising the following preparation steps:

[0008] (1) Preparation of acid pickling solution:

[0009] According to the volume ratio, one or more of 63% concentrated nitric acid, 24% hydrofluoric acid, 36% hydrochloric acid and 60% concentrated sulfuric acid are mixed with pure water in proportion to obtain an acid pickling solution;

[0010] (2) Additives are added;

[0011] (3) The titanium alloy bolt to be cleaned is placed in a stainless steel material frame and immersed in the acid pickling solution for a period of time;

[0012] (4) The cleaned titanium alloy bolt is placed in a water tank for rinsing and then dried by a spin dryer;

[0013] (5) The titanium alloy bolt is placed in an oven for hydrogen removal treatment;

[0014] (6) The product is tested for oxidation film, corrosion pollution layer and hydrogen content performance.

[0015] Preferably, in the above step (1), the concentration of 63% concentrated nitric acid, 24% hydrofluoric acid, 36% hydrochloric acid and 60% concentrated sulfuric acid used in the solution of 1L volume is as follows:

[0016]

[0017]

[0018] Preferably, the additive in the above step (2) is one or a combination of potassium nitrate, ethanol, surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and sodium dodecyl sulfonate.

[0019] Preferably, the temperature of the acid pickling solution in the above step (3) is 20-40℃, and the acid pickling time is 5-10min.

[0020] Preferably, the temperature for hydrogen removal in the above step (5) is 150-250℃, and the time is 2-10h.

[0021] The beneficial effects of the present application are:

[0022] The pickling process of the alpha + beta two-phase titanium alloy bolt provided by the present application can effectively remove the oxide scale on the surface of the titanium alloy by matching the processes of solution preparation, pickling, rinsing, and hydrogen removal, while minimizing the corrosion layer caused by pickling, effectively reducing the performance degradation caused by hydrogen absorption, and making the titanium alloy bolt have good surface quality, better processing performance and mechanical properties, and good technical popularization value. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present application are described in detail below to make the advantages and features of the present application more easily understood by those skilled in the art, so as to make the protection scope of the present application more clearly defined.

[0024] Conventional titanium alloys are divided into alpha, beta, and alpha + beta according to major categories, among which Ti6Al4V is an alpha + beta titanium alloy, which has physical and chemical properties of both alpha and beta titanium alloys. The total amount of Ti6Al4V in current industrial production accounts for more than 50% of the total amount of all titanium alloys, and the total amount of titanium alloy in aerospace accounts for more than 2 / 3. Other titanium alloys are relatively small, so the titanium alloy type selected in the embodiments of the present application is Ti6Al4V. In addition, water needs to be added to mix the acid in the present application, and the preparation method is to add water first and then add acid. Because the densities of different acid solutions are different, the actual density cannot be calculated after mixing with water, and only ml can be added, then water is added to a fixed solvent, and mL / L is used as a reference.

[0025] Example 1

[0026] A Ti6Al4V titanium alloy with model AL10AG-8-6BK2 is selected. After machining and heat treatment, a layer of scaly gray oxide film is formed on the surface. 1L of acid solution is prepared by mixing 300mL / L of concentrated nitric acid with a concentration of 63% and 80mL / L of hydrofluoric acid with a concentration of 24% with pure water, and adding 10g / L of potassium nitrate, 2% of ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, and 2g / L of sodium dodecyl sulfonate as additives.

[0027] Then, the titanium alloy bolt to be cleaned is placed in a stainless steel frame and immersed in the 20℃ pickling solution for 10min, and the following chemical reaction occurs:

[0028] TiO2+6HF=H2TiF6+2H2O

[0029] During the pickling process, HNO3 provides the hydrogen ions and acidity required for the reaction, and the oxide film removal effect is obvious and rapid, but after the oxide film is removed, the following reactions will continue to occur, and titanium tetrafluoride will be formed on the surface, which is dark gray:

[0030] Ti + 4HF = TiF4+ 2H2↑

[0031] 3Ti + 4HNO3+ 12HF = 3TiF4+ 8H2O + 4NO↑.

[0032] After pickling, the acid solution is drained, then rinsed to remove H + attached to the surface of the titanium alloy bolt, prevent the hydrogen ions from reacting with the base material at high temperature during the solid solution process, then perform spin-drying treatment on the surface moisture, and then place the product in a 200°C oven, heat for 4h, and then take it out and air cool.

[0033] In this embodiment, the concentration of hydrofluoric acid is too high, and the reaction is too rapid, causing corrosion on the surface of the titanium alloy bolt.

[0034] Example 2:

[0035] A Ti6Al4V titanium alloy, model AL10AG-8-6BK2, is selected, after machining and heat treatment, a layer of scaly gray oxide film is formed on the surface, 1L of acid solution is prepared by mixing 300mL / L of concentrated nitric acid with a concentration of 63% and 40mL / L of hydrofluoric acid with a concentration of 24% with pure water, and adding 10g / L of potassium nitrate, 2% of ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, and 2g / L of sodium dodecyl sulfonate as additives;

[0036] The titanium alloy bolt to be cleaned is placed in a stainless steel frame and immersed in a 20°C pickling solution for 10 minutes, and the following reactions occur:

[0037] TiO2+ 6HF = H2TiF6+ 2H2O

[0038] During the pickling process, after the oxide film is removed, a small amount of hydrofluoric acid also slows down the following reaction rate:

[0039] Ti + 4HF = TiF4+ 2H2↑

[0040] 3Ti + 4HNO3+ 12HF = 3TiF4+ 8H2O + 4NO↑.

[0041] After pickling, the acid solution is drained, then rinsed to remove H +, prevent the hydrogen ion in the solid solution process at high temperature and the base material reaction, finally, the surface moisture of the product is treated by spin-drying, and then the product is put into a 200°C oven, kept for 4h, and taken out for air cooling.

[0042] In this embodiment, after pickling, the surface of the titanium alloy product is bright, and there is a residual oxide film on part of the product.

[0043] Example 3

[0044] A Ti6Al4V titanium alloy, model AL10AG-8-6BK2, is selected. After machining and heat treatment, a scale-like gray oxide film is formed on the surface. A 1L acid solution is prepared by mixing 600mL / L of concentrated nitric acid with a concentration of 63% and 80mL / L of hydrofluoric acid with a concentration of 24% with pure water, and adding 10g / L of potassium nitrate, 2% of ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, and 2g / L of sodium dodecyl sulfonate as additives.

[0045] The titanium alloy bolts to be cleaned are placed in a stainless steel frame and immersed in the 20°C pickling solution for 10 minutes, and the following reactions occur:

[0046] TiO2+6HF=H2TiF6+2H2O;

[0047] During the pickling process, after the oxide film is removed, a small amount of hydrofluoric acid also slows down the following reaction rate:

[0048] Ti+4HF=TiF4+2H2↑

[0049] 3Ti+4HNO3+12HF=3TiF4+8H2O+4NO↑.

[0050] After pickling is completed, the pickling is drained, rinsed, and H + , prevent the hydrogen ion in the solid solution process at high temperature and the base material reaction, finally, the surface moisture of the product is treated by spin-drying, and then the product is put into a 200°C oven, kept for 4h, and taken out for air cooling.

[0051] In this embodiment, the concentration of nitric acid is too high, and the reaction is too violent, causing surface contamination of the product;

[0052] From the combination of Example 1, Example 2 and Example 3, in order to prevent the chemical reaction from being too fast and causing corrosion, 300mL / L of concentrated nitric acid with a concentration of 63% and 40mL / L of hydrofluoric acid with a concentration of 24% are mixed with pure water, and in order to fully remove the oxide film, the above-mentioned additives are added to optimize the pickling process.

[0053] Example 4

[0054] A Ti6Al4V titanium alloy, model AL10AG-8-6BK2, was selected. After machining and heat treatment, a scaly gray oxide film was formed on the surface. A 1L acid solution was prepared by mixing 300mL / L of 63% concentrated nitric acid, 40mL / L of 24% hydrofluoric acid, and 100mL / L of 36% hydrochloric acid with pure water. At the same time, 10g / L of potassium nitrate, 2% ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, and 2g / L of sodium dodecyl sulfonate were added.

[0055] The titanium alloy bolts to be cleaned are placed in a stainless steel pickling frame and immersed in a 20°C pickling solution for 20 minutes, resulting in the following reaction:

[0056] TiO2 + 6HF = H2TiF6 + 2H2O;

[0057] Cl in HCl - It can increase the reaction rate, remove the oxide scale on the surface more quickly, and improve the reaction efficiency. The main reaction is as follows:

[0058] Ti + 4HF = TiF4 + 2H2↑

[0059] 3Ti+4HNO3+12HF=3TiF4+8H2O+4NO↑;

[0060] After pickling, the acid solution is drained and rinsed to remove the H2 residue adhering to the surface of the titanium alloy bolts. + To prevent hydrogen ions from reacting with the base material at high temperatures during the solution treatment process, the surface moisture is then removed by spin drying. The product is then placed in a 200℃ oven and kept at that temperature for 4 hours before being air-cooled.

[0061] In this embodiment, the product surface is bright after pickling, and the oxide film is completely removed. However, the concentrations of nitric acid and hydrochloric acid are too high, the acid solution darkens in color, and a pungent odor is produced, resulting in the following reaction:

[0062] HNO3 + 3HCl = 2H2O + Cl2 + NOCl.

[0063] Example 5:

[0064] A Ti6Al4V titanium alloy, model AL10AG-8-6BK2, after machining and heat treatment, a layer of scaly gray oxide film is formed on the surface, according to the concentration of 63% of concentrated nitric acid with 300mL / L and the concentration of 24% of hydrofluoric acid with 40mL / L and the concentration of 60% of sulfuric acid with 100mL / L and pure water to prepare 1L acid solution, while adding 10g / L of potassium nitrate, 2% of ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, 2g / L of sodium dodecyl sulfonate;

[0065] The titanium alloy bolts to be cleaned are placed in a stainless steel frame and immersed in the 20℃ pickling solution for 10 minutes, and the following reactions occur:

[0066] TiO2+6HF=H2TiF6+2H2O;

[0067] Sulfuric acid mainly provides acidity and has little effect on the reaction, and the main reaction is:

[0068] Ti+4HF=TiF4+2H2↑

[0069] 3Ti+4HNO3+12HF=3TiF4+8H2O+4NO↑;

[0070] After pickling is completed, the acid solution is drained and rinsed to remove H + on the surface of the titanium alloy bolts, prevent hydrogen ions from reacting with the base material at high temperature during solid solution, and finally perform spin-drying treatment to remove surface moisture, then place the product in a 200℃ oven, heat for 4h and take out for air cooling.

[0071] In this embodiment, the product surface is bright after pickling, and there is a part of the product with residual oxide film.

[0072] From the combination of example 3, example 4 and example 5, it can be seen that new pickling solution components are sought, sulfuric acid has little effect on the pickling process, Cl - in hydrochloric acid can increase the reaction rate, remove the surface oxide skin as soon as possible, and improve the reaction efficiency, but too high concentration of hydrochloric acid will make the acid solution color dark, produce irritating gas, and the hydrogen element on the product surface is too high, so the concentration of hydrochloric acid in the acid solution is gradually reduced.

[0073] Example 6:

[0074] A Ti6Al4V titanium alloy, model AL10AG-8-6BK2, after machining and heat treatment, a layer of scaly gray oxide film is formed on the surface, according to the concentration of 63% of concentrated nitric acid with 300mL / L and the concentration of 24% of hydrofluoric acid with 40mL / L and the concentration of 36% of hydrochloric acid with 50mL / L and pure water to prepare 1L acid solution, while adding 10g / L of potassium nitrate, 2% of ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium salt, and 2g / L of sodium dodecyl sulfonate;

[0075] The titanium alloy bolts to be cleaned are placed in a stainless steel frame and immersed in the 20℃ pickling solution for 10 minutes, and the following reactions occur:

[0076] TiO2+6HF=H2TiF6+2H2O;

[0077] Among them: Cl in HCl - The reaction rate can be increased to remove the oxide skin on the surface as soon as possible and improve the efficiency, but the increase of hydrochloric acid content will increase the tendency of hydrogen absorption, and HNO3 can effectively reduce the hydrogen absorption reaction in the pickling process. When the content of nitric acid in the pickling solution exceeds 20%, the hydrogen absorption effect is greatly reduced, and nitric acid can make the surface of the titanium alloy bolt more bright, and the main reaction is:

[0078] Ti+4HF=TiF4+2H2↑

[0079] 3Ti+4HNO3+12HF=3TiF4+8H2O+4NO↑;

[0080] After pickling is completed, the acid solution is drained, rinsed, and H + is removed from the surface of the titanium alloy bolt to prevent the reaction of hydrogen ions with the base material at high temperature during solid solution, and finally the surface moisture is spun dry, and the product is placed in a 200℃ oven, heated for 4h and taken out for air cooling.

[0081] In this embodiment, after pickling is completed, the product surface is bright and the oxide film is completely removed, and the relevant tests meet the requirements.

[0082] Example 7:

[0083] A Ti6Al4V titanium alloy, model AL10AG-8-6BK2, after machining and heat treatment, a layer of scaly gray oxide film is formed on the surface, according to the concentration of 63% of concentrated nitric acid with 300mL / L and the concentration of 24% of hydrofluoric acid with 40mL / L and the concentration of 36% of hydrochloric acid with 30mL / L and pure water to prepare 1L acid solution, while adding 10g / L of potassium nitrate, 2% of ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium salt, and 2g / L of sodium dodecyl sulfonate;

[0084] The titanium alloy bolts to be cleaned are placed in a stainless steel frame and immersed in the 20℃ pickling solution for 10 minutes, and the following reactions occur:

[0085] TiO2+6HF=H2TiF6+2H2O;

[0086] Among them, Cl - in HCl can increase the reaction rate, remove the surface oxide scale as soon as possible, and improve the efficiency, but the increase of hydrochloric acid content will increase the tendency of hydrogen absorption, and HNO3 can effectively reduce the hydrogen absorption reaction in the pickling process. When the nitric acid content in the pickling solution exceeds 20%, the hydrogen absorption effect is greatly reduced, and nitric acid can make the surface of titanium alloy bolts brighter, and the main reaction is:

[0087] Ti+4HF=TiF4+2H2↑

[0088] 3Ti+4HNO3+12HF=3TiF4+8H2O+4NO↑;

[0089] After pickling is completed, the acid solution is drained, rinsed, and H + attached to the surface of the titanium alloy bolt is removed to prevent the reaction of hydrogen ions with the base material at high temperature during solid solution, and finally the surface moisture is removed by spin-drying treatment, and the product is placed in a 200℃ oven, heated for 4h, and then taken out and air-cooled.

[0090] In this embodiment, after pickling is completed, the surface of the product is bright, most of the products are free of oxide film, and a small number of products have some residual oxide film.

[0091] Comparative Example 1:

[0092] The difference from Example 6 is that the pickling time is 5 minutes;

[0093] Comparative Example 2:

[0094] The difference from Example 6 is that the pickling solution temperature is 40℃;

[0095] Comparative Example 3:

[0096] The difference from Example 6 is that the oven temperature of the hydrogen removal step is 250℃, and the time is 10h;

[0097] Comparative Example 4:

[0098] The difference from Example 6 is that the oven temperature of the hydrogen removal step is 150℃, and the time is 2h;

[0099] Comparative Example 5:

[0100] The difference from Example 6 is that no potassium nitrate, ethanol, 3g / L of surfactant octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, and 2g / L of sodium dodecyl sulfonate are added;

[0101] Comparative Example 6:

[0102] The difference from Example 6 is that the pickling time is 15 minutes;

[0103] Comparative Example 7:

[0104] The difference from Example 6 is that the auxiliary agent is 10g / L of potassium nitrate and 2% by mass of ethanol, and no octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate and sodium dodecyl sulfonate are added;

[0105] Comparative Example 8:

[0106] The difference from Example 6 is that the pickling solution temperature is 10℃;

[0107] Comparative Example 9:

[0108] The difference from Example 6 is that the oven temperature of the hydrogen removal step is 200℃, and the time is 20h;

[0109] Comparative Example 10:

[0110] The difference from Example 6 is that the oven temperature of the hydrogen removal step is 200℃, and the time is 1h.

[0111] The titanium alloy bolt products after pickling in the above Examples 1-7 and Comparative Examples 1-10 are tested for oxide film, corrosion contamination layer, and hydrogen content, and the test standards and test results are shown below:

[0112] 1. Surface oxide film:

[0113] The surface oxide film test uses product inlay polishing, and after 10s of corrosion with kroll's reagent, it is observed and measured with an optical microscope. The bright edge is the oxide film, and the center is the titanium alloy substrate after being corroded by the reagent. The test data are shown in Table 1 below:

[0114] Table 1. Surface oxide film test results

[0115] Example Thickness (pm) Example Thickness (pm) Example 1 0 pm Comparative Example 1 13 pm Example 2 17 pm Comparative Example 2 0 pm Example 3 0 pm Comparative Example 3 10 pm Example 4 0 pm Comparative Example 4 0 pm Example 5 13 pm Comparative Example 5 0 pm Example 6 0 pm Comparative Example 6 0 pm Example 7 8 pm Comparative Example 7 11 pm Comparative Example 8 10 pm Comparative Example 9 8 pm Comparative Example 10 0 pm

[0116] According to the detection data in Table 1, it can be seen that the surfaces of the products of Example 1, Example 3, Example 4, Example 6, Comparative Example 2, Comparative Example 4, Comparative Example 5, Comparative Example 6 and Comparative Example 10 have no oxide layer, the products of Example 2, Example 5 and Example 7 fail to completely remove the oxide film due to non-optimal acid solution ratio, short pickling time in Comparative Example 1, no addition of surfactant in Comparative Example 7, low pickling temperature in Comparative Example 8, high oven temperature and long time in Comparative Example 3 and Comparative Example 9, and a new oxide film is formed again.

[0117] 2. Test of corrosion pollution layer

[0118] The pollution layer test is carried out by cutting the product in the middle, inlaying and then polishing, and then corroding for 10-30 s with 1% hydrofluoric acid solution, observing the edge of the sample, and the darker color is the corrosion pollution layer generated by pickling, and the lighter color is the substrate. The test data are shown in Table 2.

[0119] Table 2. Test results of corrosion pollution layer

[0120] Example Thickness (pm) Example Thickness (pm) Example 1 11 pm Comparative Example 1 0 pm Example 2 0 pm Comparative Example 2 10 pm Example 3 17 pm Comparative Example 3 0 pm Example 4 23 pm Comparative Example 4 0 pm Example 5 0 pm Comparative Example 5 17 pm Example 6 0 pm Comparative Example 6 10 pm Example 7 0 pm Comparative Example 7 0 pm Comparative Example 8 0 pm Comparative Example 9 0 pm Comparative Example 10 0 pm

[0121] According to the detection data in Table 2, it can be seen that the surfaces of the products of Example 2, Example 5, Example 6 and Example 7, Comparative Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 7, Comparative Example 8, Comparative Example 9 and Comparative Example 10 have no oxide layer, the acid solution concentration is high in Example 1, Example 3 and Example 4, the acid solution temperature is high in Comparative Example 2, no additive is added in Comparative Example 5, the pickling time is too long in Comparative Example 6, and the product is corroded.

[0122] 3. Test of hydrogen content

[0123] Test method: according to standard ASTM E1447 "Determination of Hydrogen Content in Titanium Alloys", the extraction method is to maximize the test surface area; part of the product sample is cut into a triangular or fan-shaped sample, the weight must be between 0.150 g and 0.300 g, the coverage area is maximized, and the most accurate hydrogen content reading is obtained, and the device used is Leco ROH 600 hydrogen detector, and the test results are shown in Table 3.

[0124] Table 3. Test results of hydrogen content

[0125] Example Hydrogen Content (ppm) Example Hydrogen Content (ppm) Example 1 70 ppm Comparative Example 1 38 ppm Example 2 50 ppm Comparative Example 2 87 ppm Example 3 24 ppm Comparative Example 3 3 ppm Example 4 154 ppm Comparative Example 4 51 ppm Example 5 41 ppm Comparative Example 5 21 ppm Example 6 38 ppm Comparative Example 6 46 ppm Example 7 29 ppm Comparative Example 7 43 ppm Comparative Example 8 20 ppm Comparative Example 9 21 ppm Comparative Example 10 64 ppm

[0126] As can be seen from Table 3 above, the increase in the amount of hydrochloric acid and the increase in the reaction temperature will cause the hydrogen content to increase, and the hydrogen content of Example 2, Example 3, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 8, Comparative Example 9, Comparative Example 4 and Comparative Example 10 is low. As can be seen from Comparative Example 4 and Comparative Example 10, short hydrogenation time and low temperature will also increase the hydrogen content.

[0127] 4. Double shear test (mechanical property):

[0128] Test method: NASM 1312-13 "Fastener test method-double shear", ASTM E4 "Standard specification for load force verification of testing equipment", using INSTRON 3369 tensile testing machine, serial number Q3836;

[0129] The test method is to place the sample in the test fixture, and the shear test is carried out in the rod diameter area of the fastener. The double shear force test load is pressurized at a rate of 100,000 pounds per square inch (100,000 psi) per minute, and the lb / min load is maintained at 100,000 psi / min. When the product deforms, the program will automatically stop the load force and stop testing, and the corresponding shear force is calculated. The test results are as follows:

[0130] Table 4. Double shear test results

[0131]

[0132] As can be seen from Table 4 above: the residual oxide film on the surface, the corrosion pollution layer, and the hydrogen content on the surface will all cause the shear strength of the product to decrease.

[0133] Based on the above four tests, it can be concluded that in order to eliminate the oxide film, reduce the corrosion layer, reduce the hydrogen content, and obtain higher shear strength, the acid solution formula and pickling process of Example 6 are relatively preferred.

[0134] The above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the present application specification, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A pickling process for an α + β two-phase titanium alloy bolt, characterized by, The preparation steps include: (1) preparing the pickling solution: Mixing concentrated nitric acid with a concentration of 63%, 24% hydrofluoric acid, 36% hydrochloric acid and pure water uniformly to obtain the pickling solution. The ratio of the contents when used is as follows according to 1L volume solution: 63% concentrated nitric acid 300mL / L; 24% hydrofluoric acid 40mL / L; 36% hydrochloric acid 30~50mL / L; pure water the balance; (2) adding the auxiliary agent, which is potassium nitrate, ethanol, octadecyl dimethyl hydroxyethyl quaternary ammonium salt and sodium dodecyl sulfonate; (3) placing the titanium alloy bolt to be cleaned into a stainless steel material frame and immersing it into the pickling solution for a period of time; (4) placing the cleaned titanium alloy bolt into a water tank for rinsing and drying through a spin dryer before use; (5) placing the titanium alloy bolt into an oven for heat preservation for hydrogen removal treatment; (6) testing the performance of the product, including the oxidation film, the corrosion pollution layer and the hydrogen content; The temperature of the pickling solution in the above step (3) is 20~40℃, and the pickling time is 5~10min; The temperature for hydrogen removal in the above step (5) is 150~250℃, and the time is 2~10h.

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