Pickling process for alpha layer on surface of biphase titanium alloy forge piece

Abstract

The invention belongs to the technical field of surface treatment, and discloses an acid pickling process for an alpha layer on the surface of a biphase titanium alloy forge piece, and the used acid pickling solution comprises 100-130 g / L of HNO3 with the concentration of 65-68%, 35-55 g / L of HF with the concentration of 40%, and the balance of water. The pickling solution with the proportion shows a stable rate of removing the alpha layer of the forge piece under the constant temperature condition of 20-50 DEG C, and the rate is about 0.01 mm / min. In order to ensure that no alpha layer residue exists on the surface of the forge piece and avoid excessive pickling, the thickness of the oxygen-enriched alpha layer on the surface of the forge piece is detected through a metallographic method, the thickness is increased by 0.03 mm-0. 08mm on the basis of the detected maximum value of the thickness of the alpha layer and set as the pickling amount, the pickling time is calculated according to the pickling rate, and the oxygen-enriched alpha layer on the surface of the double-phase titanium alloy forge piece is accurately removed. The process can be realized by only one pickling solution, the pickling time is determined according to the pickling amount, the imagination of incomplete pickling or excessive pickling is avoided, the production process is effectively simplified, and the period is shortened.

Description

Technical Field

[0001] The invention belongs to the field of surface treatment of duplex titanium alloy forgings, and relates to a pickling process for an alpha layer on the surface of a duplex titanium alloy forging, and specifically relates to a pickling process that only requires one pickling solution and can remove the alpha layer on the surface of the titanium alloy at a stable rate. Background Art

[0002] Titanium alloys have excellent properties such as good heat resistance, corrosion resistance, high strength and low density, and are widely used in the aerospace and medical device industries. However, titanium alloys have a low elastic modulus, large springback during low-temperature processing, and are difficult to deform. Therefore, the forming and heat treatment of titanium alloy parts are usually carried out at medium and high temperatures. Due to the high activity of Ti, it is easy to adsorb oxygen in the air, forming an oxide film on the outermost layer, and the oxygen diffuses into the near-surface to form an oxygen-rich α layer. Oxygen is dissolved in the matrix, improving the strength and hardness of the matrix, but it has an adverse effect on the fatigue performance, impact, and fracture mode of the material. Due to the development of precision forging and net forming technology, there are many forged non-machined surfaces on aviation parts, so the oxygen-rich α layer must be completely removed.

[0003] The common method for removing the α layer of duplex titanium alloy is pickling. At present, the commonly used pickling process is mostly alkali pickling followed by pickling, or pickling with reducing acid first and then with oxidizing acid. The pickling process is relatively cumbersome, requiring the configuration of a variety of pickling solutions, and the pickling rate is not clear. The pickling time is difficult to grasp, resulting in incomplete removal of the α layer on the surface of the forging, dimensional deviation of the forging, and excessive hydrogen content. Summary of the invention

[0004] The purpose of the present invention is to provide a process for removing the α layer on the surface of titanium alloy forgings with a simplified process, requiring only one pickling solution and having a stable pickling rate, and being able to stably remove the surface oxygen-rich α layer at a constant rate. The pickling time is determined according to the pickling amount to achieve accurate removal of the oxygen-rich α layer on the surface of the dual-phase titanium alloy forging.

[0005] To solve this technical problem, the technical solution of the present invention is:

[0006] A process for removing the oxygen-rich α layer on the surface of a duplex titanium alloy forging, comprising the following steps:

[0007] (1) Sand blasting: Sand blasting removes the oxide scale on the surface of titanium alloy forgings;

[0008] (2) Determine the pickling amount and size measurement: Test the thickness of the α layer of the physical and chemical parts. Add 0.03 to 0.08 mm to the maximum thickness of the α layer as the pickling amount, and measure the dimensions of the typical positions of the forgings.

[0009] (3) Degreasing with cleaning agent: remove the oil stains on the forging surface for 5 to 10 minutes;

[0010] (4) Clean the residual detergent on the surface of the forging;

[0011] (5) Hanging: Use tooling to hold forgings, and forgings do not touch each other;

[0012] (6) Pickling: Mix the pickling solution, keep the pickling solution at a constant temperature of 20-50°C, immerse the titanium alloy forgings in the pickling solution, calculate the pickling time based on the thickness of the oxygen-rich α layer to be removed, and start the time when bubbles begin to appear on the surface of the forgings. During the pickling process, take the forgings out of the pickling solution every 10 minutes, turn them over, and immerse them in pickling again until the preset pickling time is reached.

[0013] (7) Inspection: Inspect the dimensions of typical locations of forgings to ensure that the amount of pickling can completely remove the oxygen-rich α layer of the forgings;

[0014] (8) Washing with water;

[0015] (9) Drying: Dry in a hot air drying tank at a temperature of 90°C to 120°C for 3 to 5 minutes.

[0016] (10) Inspection: Metallographic examination is performed on the physical and chemical parts after pickling to ensure that there is no α layer remaining on the surface of the forging.

[0017] Wherein, the pickling solution in step (6) is made up of the following proportions:

[0018] HNO3 analytical pure (100-130) g / L with a concentration of 65%-68%;

[0019] The concentration is 40% HF analytical grade (35-55) g / L;

[0020] The rest is water.

[0021] The pickling time in step (6) is calculated by the following formula: pickling amount ÷ 0.01 mm / min. By measurement, the pickling solution is kept at a constant temperature of 20°C to 50°C, and the rate of removing the oxygen-rich α layer is about 0.01 mm / min. The pickling time is set according to the pickling amount, and the pickling time is determined as: (pickling amount ÷ 0.01 mm / min). The pickling time is counted from the time bubbles appear on the surface of the forging.

[0022] Step (5) Installation and hanging requirements: Ensure that the forging is completely immersed in the pickling solution during pickling, and the top of the forging is at least 20 cm away from the liquid surface and the bottom of the tank. During the pickling process, take it out of the pickling solution every 10 minutes, turn the forging position, and immerse it in pickling again until the preset pickling time is reached to ensure uniform removal of the α layer. The present invention only uses one pickling solution, and does not require pre-alkaline washing or pickling with a second pickling solution.

[0023] The typical positions in step (2) and step (7) refer to the inspection before and after pickling at the same position. Whether it is the inspection of the same position or the requirements for the installation during pickling, it is to remove the α layer uniformly.

[0024] Preferably, the pickling amount is set to increase the maximum thickness value of the detected α layer by 0.04 to 0.06 mm.

[0025] Preferably, the heating temperature for pickling is 30°C to 40°C.

[0026] Preferably, the HNO3 is analytically pure (110-120) g / L; the HF is analytically pure (40-50) g / L.

[0027] Preferably, the specific operation of step (4) is: flushing the surface of the forging with running clean water, and then flushing the surface of the forging with deionized water.

[0028] Preferably, the specific operation of step (8) is: immersing the pickled forging into a cold water tank, taking it out and rinsing the surface of the forging with deionized water.

[0029] The beneficial effects of the present invention are:

[0030] Compared with the prior art, the present invention has a significantly simplified process. The oxide scale on the surface of the forging after hot working is removed by sandblasting, and the surface oil is removed by a cleaning agent. Only one pickling solution is needed to remove the oxygen-rich α layer of the forging at a stable rate. No high-temperature alkali washing is required in advance to avoid premature aging strengthening of titanium alloy forgings. There is no need to configure two pickling solutions for pickling, which effectively simplifies the process steps and shortens the production cycle. In addition, the oxygen-rich α layer of the forging is unevenly distributed, and the thickness of the α layer of different titanium alloys varies greatly. Before pickling, the thickness of the oxygen-rich α layer of the physical and chemical parts is inspected, and the maximum thickness of the detected α layer is increased by 0.03mm to 0.08mm to set as the pickling amount, and the pickling time is determined according to the pickling amount, and the physical and chemical parts are inspected again after pickling to ensure that the α layer is completely removed without residue. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions implemented in the present invention, the following is a brief explanation of the drawings required to be used in the examples of the present invention. 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 work.

[0032] Figure 1 This is a photograph of the surface morphology detected before pickling in Example 1.

[0033] Figure 2 This is a photograph of the surface morphology detected after pickling in Example 1.

[0034] Figure 3 This is a photograph of the surface morphology detected before pickling in Example 2.

[0035] Figure 4 This is a photograph of the surface morphology detected after pickling in Example 2. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] The features of various aspects of the embodiments of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to fully understand the present invention. However, it is obvious to those skilled in the art that the present invention can also be implemented without these specific details. The following description of the embodiments is only for a better understanding of the present invention by illustrating examples of the present invention. The present invention is not limited to any specific settings and methods provided below, but covers all product structures, any improvements, replacements, etc. of methods covered without departing from the spirit of the present invention.

[0038] In the various drawings and the following description, well-known structures and techniques are not shown to avoid unnecessarily obscuring the present invention.

[0039] Embodiment 1

[0040] This embodiment provides a pickling process for removing the α layer on the surface of TC6 titanium alloy forgings. The pickling solution is composed of: 105 g / L of HNO3 with a concentration of 65-68%, 45 g / L of HF with a concentration of 40%, and the rest is water. The specific pickling process is as follows:

[0041] (1) Sand blasting: remove the oxide scale on the surface of titanium alloy forgings by sand blasting;

[0042] (2) Determine the pickling amount and forging size measurement: The maximum thickness of the α layer of the physical and chemical parts inspection of this batch of forgings is 0.32mm, and the pickling amount is set to 0.35-0.40mm. The size of the typical position of the forging is measured to be 120.80mm;

[0043] (3) Degreasing with detergent: Immerse the forging in a 5% detergent for 5 minutes to remove oil stains on the forging surface;

[0044] (4) Cleaning detergent: Take out the forging, rinse the surface of the forging with running water to remove the detergent attached to the surface of the forging until no more foam appears on the surface of the forging, and then rinse the surface of the forging with deionized water;

[0045] (5) Installation: Use special tooling to hold the forgings, and the forgings do not touch each other;

[0046] (6) Pickling: Keep the pickling solution at a constant temperature of 25°C. Calculate the pickling time based on the pickling amount to be 35 to 40 minutes. The pickling time starts from the time bubbles appear on the surface of the forging. Immerse the forging to be pickled in the pickling solution, and keep the top of the forging at least 20 cm away from the liquid surface and the bottom of the tank. Every 10 minutes, turn the forging over and put it back into the tooling, and immerse it in pickling again. Take out the forging when the pickling time is 36 minutes.

[0047] (7) Inspection: The typical size of the forgings to be inspected is 120.08 mm, and the pickling amount on one side is 0.36 mm, which meets the preset pickling amount requirements.

[0048] (8) Water washing: Immerse the pickled forgings in a cold water tank, take them out and rinse the forging surface with deionized water;

[0049] (9) Drying: Dry in a hot air drying tank at a temperature of 100°C for 3 minutes.

[0050] (10) Inspection: Metallographic examination of physical and chemical parts was performed, and no α layer remained on the surface of the forgings.

[0051] Comparison of forgings before and after the pickling process of the present invention Figure 1 , Figure 2 As shown in the figure, it can be seen that the metallographic structure of the surface of TC6 titanium alloy before pickling is as follows: Figure 1 As shown in the figure, there is a significant difference between the core and surface structures. There is a high-density bright α layer on the surface. As the distance from the surface increases, the proportion of α phase decreases. Using GB / T23603 "Detection Method for Surface Contamination Layer of Titanium and Titanium Alloys", the maximum thickness of the oxygen-rich α layer was detected to be 318.3 microns. The metallographic structure of the titanium alloy surface after pickling is as follows Figure 2 As shown, the surface tissue has no shiny α layer and is no different from the core tissue, indicating that the oxygen-rich α layer is completely removed.

[0052] Embodiment 2

[0053] This embodiment provides a pickling process for removing the α layer on the surface of a TC4 titanium alloy forging. The pickling solution is composed of the following mass percentages: 115 g / L of HNO3 analytically pure with a concentration of 65-68%, 48 g / L of HF analytically pure with a concentration of 40%, and the rest is water. The specific pickling process is as follows:

[0054] (1) Sand blasting: Remove the oxide scale on the surface of titanium alloy forgings by sand blasting;

[0055] (2) Determine the pickling amount and forging size measurement: The maximum thickness of the α layer of the physical and chemical parts inspection of this batch of forgings is 0.06mm, and the pickling amount is set to 0.09-0.14mm. The size of the typical position of the forging is 53.20mm;

[0056] (3) Degreasing with detergent: Immerse the forging in a detergent with a concentration of 5% for 3 minutes to remove the oil stains on the forging surface;

[0057] (4) Cleaning detergent: Take out the forging, rinse the surface of the forging with running water to remove the detergent attached to the surface of the forging until no more foam appears on the surface of the forging, and then rinse the surface of the forging with deionized water;

[0058] (5) Installation: Use special tooling to hold the forgings, and the forgings do not touch each other;

[0059] (6) Pickling: Keep the mixed pickling solution at a constant temperature of 30°C. Calculate the pickling time to be 9-14 minutes based on the set pickling amount. Immerse the forging to be pickled in the pickling solution. The pickling time starts from the time bubbles appear on the surface of the forging. Take out the forging when the pickling time is 11 minutes.

[0060] (7) Inspection: The typical size of the forgings to be inspected is 52.98 mm, and the pickling amount on one side is 0.11 mm, which meets the requirement of completely removing the α layer.

[0061] (8) Water washing: Immerse the pickled forgings in a cold water tank, take them out and rinse the forging surface with deionized water;

[0062] (9) Drying: Dry in a hot air drying tank at a temperature of 100°C for 3 minutes.

[0063] (10) Inspection: Metallographic examination of physical and chemical parts was performed, and no α layer remained on the forgings.

[0064] The forgings of this embodiment are as follows before and after the pickling process of the present invention. Figure 3 , Figure 4 As shown in the figure, it can be seen that the metallographic structure of the surface of TC4 titanium alloy before pickling is as follows: Figure 3 As shown in the figure, there is a bright α layer on the surface, which is obviously different from the matrix structure. According to GB / T23603 "Detection Method of Surface Contamination Layer of Titanium and Titanium Alloys", the maximum thickness of the oxygen-rich α layer is 61 microns. Figure 4 As shown, the surface tissue has no bright α layer, and the oxygen-rich α layer is completely removed.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A pickling process for the α layer on the surface of a duplex titanium alloy forging, characterized in that: The steps include: (1) Sand blasting: Sand blasting removes the oxide scale on the surface of titanium alloy forgings; (2) Determine the pickling amount and size measurement: Test the thickness of the α layer of the physical and chemical parts. Add 0.03 to 0.08 mm to the maximum thickness of the α layer as the pickling amount, and measure the dimensions of the typical positions of the forgings. (3) Degreasing with cleaning agent: remove the oil stains on the forging surface for 5 to 10 minutes; (4) Clean the residual detergent on the surface of the forging; (5) Hanging: Use tooling to hold forgings, and forgings do not touch each other; (6) Pickling: Mix the pickling solution, keep the pickling solution at a constant temperature of 20-50°C, immerse the titanium alloy forgings in the pickling solution, calculate the pickling time based on the thickness of the oxygen-rich α layer to be removed, and start the time when bubbles begin to appear on the surface of the forgings. During the pickling process, take the forgings out of the pickling solution every 10 minutes, turn them over, and immerse them in pickling again until the preset pickling time is reached. (7) Inspection: Inspect the dimensions of typical locations of forgings to ensure that the amount of pickling can completely remove the oxygen-rich α layer of the forgings; (8) Washing with water; (9) Drying: Dry in a hot air drying tank at a temperature of 90°C to 120°C for 3 to 5 minutes. (10) Inspection: Metallographic examination is performed on the physical and chemical parts after pickling to ensure that there is no α layer remaining on the surface of the forging.

2. The process according to claim 1, characterized in that: The pickling solution in step (6) is made up of the following proportions: HNO3 analytical pure (100-130) g / L with a concentration of 65%-68%; The concentration is 40% HF analytical grade (35-55) g / L; The rest is water.

3. The process according to claim 1, characterized in that: Pickling time in step (6): pickling amount ÷ 0.01 mm / min.

4. The process according to claim 1, characterized in that: Step (5) Installation requirements: Ensure that the forging is completely immersed in the pickling solution during pickling, and the top of the forging is at least 20 cm away from the liquid surface and the bottom of the tank.

5. The process according to claim 1, characterized in that: The typical positions in step (2) and step (7) refer to the inspection before and after pickling at the same position.

6. The process according to claim 1, characterized in that: The pickling amount is set to increase the maximum thickness value of the detected α layer by 0.04 to 0.06 mm.

7. The process according to claim 1, characterized in that: The heating temperature for pickling is 30°C to 40°C.

8. The process according to claim 1, characterized in that: The HNO3 is analytically pure (110-120) g / L; the HF is analytically pure (40-50) g / L.

9. The process according to claim 1, characterized in that: The specific operation of step (4) is: rinse the surface of the forging with running clean water, and then rinse the surface of the forging with deionized water.

10. The process according to claim 1, characterized in that: The specific operation of step (8) is: immerse the pickled forging into a cold water tank, take it out and rinse the surface of the forging with deionized water.

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