A process method for hot-dip aluminizing on surface of TC4 titanium alloy

Abstract

The present application relates to a kind of process for the surface hot aluminum infiltration of TC4 titanium alloy, comprising the following steps: S1, cutting, TC4 titanium alloy plate material line cutting into multiple test pieces;S2, alkali washing, test piece is invaded mixed alkali solution;S3, pickling, test piece is invaded pickling mixed solution;S4, auxiliary plating, in water bath pot addition auxiliary plating agent;S5, aluminizing, test piece is aluminized at 760 DEG C temperature 15min;S6, air cooling, drying temperature is 120 DEG C, drying time is 30min, in air cooling;S7, cold rolling, make the deformation of test piece 5-15%;S8, annealing, annealing temperature is 700-900 DEG C, time is 3-10h.The technical problem that the surface treatment solves the titanium alloy aluminized layer easy to produce through crack, improve the surface property of titanium alloy, greatly improve the high temperature oxidation resistance and wear resistance of TC4 titanium alloy.

Description

Technical Field

[0001] This invention relates to the field of hot infiltration preparation technology, and in particular to a process method for hot infiltrating aluminum onto the surface of TC4 titanium alloy. Background Technology

[0002] TC4 titanium alloy possesses excellent properties, earning it the nicknames "space metal" and "marine metal," such as superior mechanical properties and weldability, good high- and low-temperature resistance, excellent corrosion resistance, and good hot deformability. TC4 titanium alloy is an α+β type alloy, where the α and β phases undergo interconversion during temperature increases and decreases. Al and V, as alloying elements in TC4, dissolve in the alloy as substitutional solutes; therefore, all TC4 alloys are substitutional solid solutions. The majority of Al is present in α-type Ti, forming an α solid solution, which also increases the β transformation temperature. A small amount of Al also dissolves in β-type titanium, forming a β solid solution. Al increases the alloy's strength but has little effect on its plasticity, while V, as a stabilizing element of the β phase, lowers the β phase transformation temperature. V can be dissolved in β-type Ti without limitation, but its solubility in α-type Ti is limited. V can also strengthen TC4 titanium alloy through solid solution treatment, increasing strength while maintaining almost no change in plasticity. The addition of other trace interstitial elements increases the β-transformation temperature. It consists of α and β phases, with Widmanstätten α+β and equiaxed α+β structures, the latter being the most widely used. Titanium alloys possess excellent properties such as low density, good toughness, high strength, high temperature resistance, and good corrosion resistance, leading to their widespread application. These characteristics make titanium alloys crucial in various fields.

[0003] In recent years, with the rapid development of various fields in my country, such as aviation, aerospace, and marine engineering, the application requirements for titanium alloys have been increasing, especially in terms of mechanical properties. Titanium alloy is an important lightweight material with outstanding comprehensive mechanical properties, such as high strength, excellent plasticity and toughness, and good corrosion resistance. Most titanium alloys can operate under high temperature conditions, and are the main materials for aircraft engine exhaust pipes, engine compressors, and impact-resistant components. However, TC4 titanium alloy has high chemical reactivity. Titanium is not only easily oxidized but also readily reacts with elements such as nitrogen and hydrogen in the air. When the temperature reaches above 500°C, titanium reacts strongly with oxygen to form a hardened layer. When the temperature reaches 600°C, it can form a hardened layer with nitrogen. As the temperature increases, the diffusion rate of oxygen inside the titanium alloy matrix accelerates. After 700°C, the diffusion rate of oxygen inside the titanium alloy matrix increases significantly. At this point, oxygen reacts chemically with the surface of the titanium alloy matrix to form a porous and loose oxide film. The structure of this oxide film differs from that of the oxide film on the surface of titanium alloys at low temperatures. Its composition is much more complex, typically containing TiO2 and a small amount of Al2O3. At this point, the porous and loose oxide film on the surface of the titanium alloy cannot prevent oxygen from entering the interior of the titanium alloy. This makes the surface of the titanium alloy more brittle, and reduces its plasticity and toughness, seriously affecting the hot working process of titanium alloys at high temperatures. As a result, the application of titanium alloys in industrial manufacturing is limited to a certain extent. At present, titanium alloys still have many shortcomings, and it is these defects that limit their application range to a certain extent. Its main disadvantage is that it is prone to abrasion during use. Because the oxide film generated by its own oxidation has a weak bond with the substrate, it is easy to fall off and cannot play a good protective role, resulting in poor comprehensive mechanical properties at higher temperatures and poor resistance to high-temperature oxidation.

[0004] Currently, a Ti-Al diffusion layer can be prepared on the surface of Ti6Al4V titanium alloy using hot-dip aluminizing, followed by diffusion annealing at 1100℃ for 6 hours. Research results show that with prolonged diffusion annealing time, interatomic diffusion becomes more complete, the content of Ti-Al intermetallic compounds increases, and the thickness of both the inner and outer diffusion layers significantly increases, resulting in excellent surface treatment. Studies indicate that diffusion annealing can accelerate interatomic interdiffusion, thereby significantly improving the bonding strength of the titanium / aluminum bimetallic alloy. As the diffusion temperature increases, the activity of the Ti-Al binary diffusion system also increases, with the most favorable temperature for mutual diffusion being 650℃ (slightly below the melting point of aluminum). However, it should be noted that although increasing the diffusion annealing temperature helps the two to diffuse into each other, it also promotes the growth of intermetallic compounds. When there are a large number of intermetallic compounds at the titanium / aluminum composite interface, the interfacial bonding strength will also decrease significantly. Hot-dip aluminizing improves the high-temperature oxidation resistance of TC4 titanium alloy, but due to the presence of through cracks, it becomes a channel for oxygen to contact the titanium alloy matrix under high temperature conditions, which leads to the loss of the protective effect of the aluminized layer and results in severe local oxidation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a new process method for hot-dip aluminizing, rolling and annealing of TC4 titanium alloy, which solves the problem of through cracks in the aluminized layer, greatly improves the high temperature oxidation resistance and wear resistance of TC4 titanium alloy, and solves the technical problem of through cracks easily generated in the aluminized layer of titanium alloy.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A process for hot-dip aluminum infiltration onto the surface of TC4 titanium alloy includes the following steps:

[0008] S1. Cutting: The TC4 titanium alloy sheet is wire-cut into multiple sample pieces, and the sample pieces are mechanically polished.

[0009] S2. Alkali washing: Immerse the sample in the mixed alkaline solution and clean it in an ultrasonic cleaner for 5 minutes. Remove the sample and wash it with warm water. The mixed alkaline solution consists of NaOH (80 g / L), Na2CO3 (30 g / L), Na3PO4 (30 g / L) and Na2SiO3 (8 g / L).

[0010] S3. Pickling: Immerse the sample in the pickling mixture and clean it in an ultrasonic cleaner for 5 minutes. Remove the sample and clean it with warm water. The mixture consists of HCl (15%) and hexamethylenetetramine (2-3%).

[0011] S4. Plating flux: Add plating flux to a warm water bath. Immerse the sample in the flux for 5 minutes, then remove it, blot dry with filter paper, and dry with a hair dryer. The constant temperature in the warm water bath is 60-95℃. The plating flux is a supersaturated aqueous solution of K2ZrF6.

[0012] S5, Aluminizing: At a temperature of 760℃, the sample after fluxing is immersed in molten aluminum for aluminizing for 15 minutes, and then air-cooled.

[0013] S6. Cold rolling: The sample is cold rolled to reduce the deformation of the sample to 5-15%.

[0014] S7. Annealing: Anneal the TC4 aluminized sample after rolling deformation treatment at a temperature of 700-900℃ for 3-10 hours.

[0015] In step S1, the sample is cut into a large-size sample and a small-size sample. The large-size sample has dimensions of 15mm × 80mm × 3mm, and the small-size sample has dimensions of 15mm × 15mm × 3mm. A 2mm diameter circular hole is drilled on one corner of each sample. The surface hard oxide layer is removed by polishing with 180#, 400# and 800# metallographic sandpaper.

[0016] In step S5, a covering agent is added to the upper surface of the molten aluminum liquid in the aluminizing process. The covering agent is a solid mixed salt of KCl (50%) and NaCl (50%).

[0017] The temperature range of the warm water is 50-90℃.

[0018] The beneficial effects of this invention are:

[0019] 1. By immersing the titanium alloy workpiece in molten aluminum, where the temperature of the molten aluminum is higher than the melting point of pure aluminum but lower than that of titanium alloy, the titanium alloy is prevented from melting. Under high temperature conditions, a series of thermochemical reactions form a thin protective film on the surface of the titanium alloy matrix. At a certain temperature, diffusion annealing can form a stable TixAly type intermetallic compound on the surface. TixAly alloy has high hardness and good corrosion resistance, and it is easy to form a dense Al2O3 on the outer layer of the matrix, thus avoiding oxidation of the matrix structure at high temperatures. This effectively improves the alloy's hardness, high-temperature oxidation resistance, and wear resistance.

[0020] 2. Remove residual alkali and acid solutions from the sample by washing with water.

[0021] 3. The fluxing process is a crucial step in the hot-dip aluminizing process because there is interphase tension between the molten aluminum and the TC4 substrate. The role of the flux in the hot-dip aluminizing process is to reduce this interphase tension. Reducing the interphase tension can increase the wettability of the molten aluminum to the titanium alloy substrate. However, the sample after pickling must be placed in the fluxing solution in time (within 3 seconds) to complete the fluxing. If the fluxing is not done in time, the surface of the treated sample will be exposed to the air and will easily react with oxygen in the air, thus forming an oxide film on the surface of the sample. Alternatively, the sample may be easily oxidized in the high-temperature atmosphere above the molten aluminum to form a loose and porous oxide film. This oxide film will reduce the wettability between the molten aluminum and the sample surface, preventing the molten aluminum from contacting the sample well. This will cause phenomena such as leakage, uneven diffusion layer, and pores in the sample.

[0022] 4. During the plating process, a protective film can be formed on the surface of the titanium alloy substrate. This protective film must be dense and free of pinholes. During hot-dip aluminum infiltration, the addition of the plating flux can significantly improve the wettability of the titanium alloy substrate during contact with it. It will not adhere to the surface of the titanium alloy and will not affect the contact between the aluminum solution and the titanium alloy substrate. It will not cause pollution to the plating solution.

[0023] 5. The sample was heated and kept warm in a water bath at 95°C to ensure that K2ZrF6 could be completely dissolved. The sample was immersed in the flux for 5 minutes to achieve the formation of a continuous and dense oxide film on the surface.

[0024] 6. During hot-dip aluminizing, if the molten aluminum is exposed to air, an oxidation reaction will occur upon contact with the air. This will result in an uneven surface on the sample after aluminizing, or even leakage. To prevent this, a covering agent needs to be added to the surface of the molten aluminum. The covering agent adsorbs and dissolves the Al2O3 film formed on the surface of the molten aluminum and prevents the formation of other oxide inclusions. The covering agent can significantly improve the effect of hot-dip aluminizing on the sample.

[0025] 7. After the surface of TC4 titanium alloy is treated by hot-dip aluminizing (R) + rolling (Z) + annealing (T), the technical problem of through cracks easily generated in the aluminized layer of titanium alloy can be effectively solved. The key technology is that rolling is introduced on the basis of traditional aluminizing technology to obtain an appropriate amount of plastic deformation and accumulate a certain degree of distortion energy. In the subsequent annealing treatment, the diffusion rate difference between Ti atoms and Al atoms can be reduced, so that Al atoms and Ti atoms can diffuse evenly. At the same time, the stress concentration caused by the formation of TiAl3 is reduced, thus avoiding the generation of through cracks. Attached Figure Description

[0026] Figure 1This is the microstructure of the TC4 titanium alloy impregnated with aluminum and the diffusion annealed layer in this invention.

[0027] Figure 2 This is a scan of the diffusion annealing layer after aluminizing in this invention;

[0028] Figure 3 This is a kinetic curve of the sample after aluminizing and diffusion annealing at different temperatures for 100 hours of cyclic oxidation in this invention;

[0029] Figure 4 This is a photograph of the microstructure of the hot-dip aluminized layer in the cold-rolled and diffusion-annealed state in this invention;

[0030] Figure 5 This is a scanned image of the diffusion layer after cold rolling annealing and high-temperature oxidation with a 15% deformation amount in this invention;

[0031] Figure 6 This is a kinetic curve of cold-rolled specimens with different deformation amounts after 100 hours of cyclic oxidation at different temperatures in this invention; Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments. Example

[0033] A process for hot-dip aluminum infiltration onto the surface of TC4 titanium alloy includes the following steps:

[0034] S1. Cutting: The TC4 titanium alloy sheet is wire-cut into multiple sample pieces, and the sample pieces are mechanically polished.

[0035] S2. Alkali washing: Immerse the sample in the mixed alkaline solution and clean it in an ultrasonic cleaner for 5 minutes. Remove the sample and wash it with warm water. The mixed alkaline solution consists of NaOH (80 g / L), Na2CO3 (30 g / L), Na3PO4 (30 g / L) and Na2SiO3 (8 g / L).

[0036] S3. Pickling: Immerse the sample in the pickling mixture and clean it in an ultrasonic cleaner for 5 minutes. Remove the sample and clean it with warm water. The mixture consists of HCl (15%) and hexamethylenetetramine (2-3%).

[0037] S4. Plating flux: Add plating flux to a warm water bath. Immerse the sample in the flux for 5 minutes, then remove it, blot dry with filter paper, and dry with a hair dryer. The constant temperature in the warm water bath is 60-95℃. The plating flux is a supersaturated aqueous solution of K2ZrF6 (98%).

[0038] S5, Aluminizing: At a temperature of 760℃, the sample after fluxing is immersed in molten aluminum for aluminizing for 15 minutes, and then air-cooled.

[0039] S6. Cold rolling: The sample is cold rolled to reduce the deformation of the sample to 5-15%.

[0040] S7. Annealing: Anneal the TC4 aluminized sample after rolling deformation treatment at a temperature of 700-900℃ for 3-10 hours.

[0041] In step S1, the sample is cut into a large-size sample and a small-size sample. The large-size sample has dimensions of 15mm × 80mm × 3mm, and the small-size sample has dimensions of 15mm × 15mm × 3mm. A 2mm diameter circular hole is drilled on one corner of each sample. The surface hard oxide layer is removed by polishing with 180#, 400# and 800# metallographic sandpaper.

[0042] In step S5, a covering agent is added to the upper surface of the molten aluminum liquid in the aluminizing process. The covering agent is a solid mixed salt of KCl (50%) and NaCl (50%).

[0043] The temperature range of the warm water is 50-90℃.

[0044] By immersing the titanium alloy workpiece in molten aluminum at a temperature higher than the melting point of pure aluminum but lower than that of titanium alloy, the titanium alloy is prevented from melting. Under high temperature conditions, a series of thermochemical reactions form a thin protective film on the surface of the titanium alloy matrix. At a certain temperature, diffusion annealing can form a stable TixAly type intermetallic compound on the surface. TixAly alloy has high hardness and good corrosion resistance, and it is easy to form a dense Al2O3 on the outer layer of the matrix, thus avoiding oxidation of the matrix structure at high temperatures. This effectively improves the alloy's hardness, high-temperature oxidation resistance, and wear resistance.

[0045] The residual alkali and acid solutions on the sample are removed by washing with water.

[0046] The fluxing process is a crucial step in the hot-dip aluminizing process because there is interphase tension between the molten aluminum and the TC4 substrate. The role of the flux in hot-dip aluminizing is to reduce this interphase tension, which increases the wettability of the molten aluminum to the titanium alloy substrate. However, the sample after pickling must be placed in the fluxing solution in time (within 3 seconds) to complete the fluxing process. If the fluxing is not done in time, the surface of the treated sample will be exposed to the air and easily react with oxygen in the air, thus forming an oxide film on the surface of the sample. Alternatively, the sample may be easily oxidized in the high-temperature atmosphere above the molten aluminum to form a loose and porous oxide film. This oxide film will reduce the wettability between the molten aluminum and the sample surface, preventing the molten aluminum from making good contact with the sample. This will cause phenomena such as leakage, uneven diffusion layer, and pores in the sample.

[0047] During the plating process, a protective film can be formed on the surface of the titanium alloy substrate. This protective film must be dense and free of pinholes. During hot-dip aluminum infiltration, the addition of the plating flux can significantly improve the wettability of the titanium alloy substrate during contact with it. It will not adhere to the surface of the titanium alloy and will not affect the contact between the aluminum solution and the titanium alloy substrate. It will not cause pollution to the plating solution.

[0048] The sample was heated and kept warm in a water bath at 95°C to ensure that K2ZrF6 could be completely dissolved. The sample was immersed in the flux for 5 minutes to achieve the formation of a continuous and dense oxide film on the surface.

[0049] If molten aluminum is exposed to air during hot-dip aluminizing, an oxidation reaction will occur upon contact with the air, resulting in an uneven surface or even leakage of the aluminized sample. To prevent this, a covering agent needs to be added to the surface of the molten aluminum. The covering agent adsorbs and dissolves the Al2O3 film formed on the surface of the molten aluminum and prevents the formation of other oxide inclusions. The covering agent can significantly improve the effect of hot-dip aluminizing on the sample.

[0050] After the surface of TC4 titanium alloy is treated by hot-dip aluminizing (R) + rolling (Z) + annealing (T), the technical problem of through cracks easily generated in the aluminized layer of titanium alloy can be effectively solved. The key technology lies in the introduction of rolling method on the basis of traditional aluminizing technology to obtain an appropriate amount of plastic deformation and accumulate a certain degree of distortion energy. In the subsequent annealing treatment, the diffusion rate difference between Ti atoms and Al atoms can be reduced, so that Al atoms and Ti atoms can diffuse evenly. At the same time, the stress concentration caused by the formation of TiAl3 is reduced, thus avoiding the generation of through cracks.

[0051] After hot-dip aluminum infiltration is completed on the surface of TC4 titanium alloy, the cold rolling process for the sample is as follows:

[0052] A1. Raw materials: The hot-dip aluminized sample is used as the raw material for cold rolling;

[0053] A2. Pickling: Using hydrochloric acid to remove oxides from the surface of the sample after hot-dip aluminizing;

[0054] A3. Cold rolling: Multiple specimens are cold rolled with deformation amounts of 5%, 10% and 15% respectively, and titanium alloy specimens with different deformation amounts are obtained through rolling.

[0055] A4. Heat treatment: Anneal the cold-rolled sample to obtain better performance. The annealing temperature is 700-900℃ and the time is 3-10h.

[0056] The cross-sectional morphology before and after diffusion is shown below:

[0057] like Figure 1 The image shows the microstructure of the aluminized layer of TC4 titanium alloy after hot-dip aluminizing at 760℃ for 15 min followed by diffusion annealing at 700℃ for 3 h. Figure 1 (a) Before diffusion, a uniform aluminized layer was obtained after aluminizing, with a straight interface. The thickness of this layer increased significantly after diffusion annealing, from 5 μm to 45 μm. Notably, obvious through cracks appeared in the aluminized layer after diffusion annealing. Figure 1 (b) shows the elliptical region after diffusion; this is because the main phase composition of the aluminized layer is TiAl3 intermetallic compound, which is hard and brittle, and its thermal expansion coefficient differs greatly from that of the matrix. As the thickness of the aluminized layer increases, the thermal stress between the matrix and the aluminized layer also increases. When the thickness of the aluminized layer reaches a certain value, the thermal stress exceeds the strength of the aluminized layer and through cracks will appear. This is also a common defect in hot-dip aluminized aluminized layers. The presence of through cracks will significantly reduce the high-temperature oxidation resistance of the material and is prone to peeling.

[0058] The phase composition analysis after diffusion annealing is as follows:

[0059] The compositional distribution of the diffusion-annealed layer is as follows:

[0060] like Figure 2 As shown, from the interior of the matrix to the surface of the infiltrated layer, Figure 2 (a) is a backscattered electron scan image, in Figure 2 In (a), the concentration of Al atoms increases in a gradient; Figure 2In (b), the concentration of Ti atoms decreases gradually; this indicates that Al atoms diffuse from the surface inwards, while Ti atoms diffuse from the inside out. The concentration fluctuations of Si and Fe in the diffusion layer are relatively small, while the content of V in the matrix is ​​higher than that in the diffusion layer, and it is more stable in the diffusion layer. There is a plateau in the Ti and Al elements in the intermetallic compound layer, indicating that the composition is relatively uniform. Similarly, the composition in the matrix and the pure aluminum layer is also relatively uniform. The Ti element shows a sharp drop at 112 μm, and the diffusion layer thickness is about 45 μm. Therefore, it is preliminarily determined that the outer layer of TC4 hot-dip aluminized aluminum is a pure aluminum layer, and the inner layer is a Ti-Al intermetallic compound.

[0061] A comparison of the high-temperature oxidation resistance of aluminized parts and aluminized diffusion-annealed parts is as follows:

[0062] Figure 3 The oxidation kinetic curves are shown for the sample pieces after cyclic oxidation at 700℃ and 800℃ for 100h, respectively. Figure 3 (a) At 700℃, the oxidation resistance of the annealed specimen after aluminizing is better than that of the specimen after aluminizing. When the oxidation time exceeds 60h, the curves of the aluminized specimen and the specimen after diffusion annealing after aluminizing gradually become flat and the oxidation rate decreases. Figure 3 (b) The high-temperature oxidation resistance of the sample after diffusion annealing after aluminizing is better than that of the sample after aluminizing at 800°C.

[0063] The microstructure of the interface before and after annealing after rolling is shown below:

[0064] like Figure 4 As shown, (a) and (b) represent the microstructure at the interface with a deformation of 15%. It can be seen that cold rolling with a deformation of 15% results in a finer, more fragmented microstructure; after high-temperature annealing, the diffusion layer microstructure is dense and free of through cracks. Cold rolling with a deformation of 20% results in severe microstructure fragmentation; after high-temperature annealing, the diffusion layer microstructure is loose and free of through cracks. Therefore, the deformation should not exceed 20%.

[0065] like Figure 5As shown in Figure 5, where Figure 5(a) is an electron scanning image, Figure 5(b) is an Al elemental distribution map, Figure 5(c) is a Ti elemental distribution map, and Figure 5(d) is an O elemental distribution map; Figure 5(a) divides the entire diffusion layer into three layers: the matrix, the inner diffusion layer, and the outer diffusion layer, with O, Ti, and Al as the main elements. Inside the matrix, Ti is the main element, while the concentrations of O and Al are relatively low. In the inner diffusion layer, the Ti content decreases sharply, the Al content increases sharply, and the O content is relatively low. In the outer diffusion layer, the O content increases sharply and shows several peaks; the Al content does not increase significantly compared to the inner diffusion layer but shows several peaks; the Ti content gradually decreases and also shows several small peaks. In the outer diffusion layer, from the surface inwards, diffusion layers of Al2O3, TiO2, TiAl3 and oxygen are generated, as shown in Figures 5(b), 5(c) and 5(d), indicating that Al2O3 can effectively block further diffusion of oxygen, and there are no through cracks in the entire diffusion layer.

[0066] Figure 6 The figures show the oxidation kinetic curves of the samples after aluminizing, cold rolling, and diffusion annealing, after cyclic oxidation at 700℃, 800℃, and 900℃ for 100 hours. As can be seen from the figures, at different temperatures, the sample with a deformation of 15% has the least oxidation weight gain and the best high-temperature oxidation resistance, while the sample with a deformation of 10% has the most oxidation weight gain and the worst high-temperature oxidation resistance.

[0067] This invention utilizes surface metallurgy technology to perform a composite treatment of aluminizing, cold rolling, and diffusion annealing on TC4 alloy, resulting in an aluminized layer on the alloy surface. The aluminized layer was detected and analyzed using SEM, EDS, XRD, cold rolling tests, and high-temperature oxidation tests.

[0068] (1) After hot-dip aluminizing and diffusion annealing, the thickness of the aluminized layer on the surface of the titanium alloy increases significantly, forming a relatively dense aluminized layer, but there are through cracks on the aluminized layer.

[0069] (2) After aluminizing and aluminizing + diffusion annealing, the aluminized layer is mainly composed of pure aluminum phase, Al3Ti and a small amount of Al2O3, TiAl and TiO2 before high temperature oxidation. After high temperature oxidation at 800℃ and 900℃ for 100h, the aluminized layer is mainly composed of Al3Ti and Al2O3, of which TiAl3 is the main anti-high temperature oxidation layer.

[0070] (3) The deformation of the specimens after aluminizing + cold rolling + diffusion annealing will significantly affect their high-temperature oxidation resistance. The specimens with a deformation of 15% have the best high-temperature oxidation resistance.

[0071] By immersing the titanium alloy workpiece in molten aluminum at a temperature higher than the melting point of pure aluminum but lower than that of titanium alloy, the titanium alloy is prevented from melting. Under high temperature conditions, a series of thermochemical reactions form a thin protective film on the surface of the titanium alloy matrix. At a certain temperature, diffusion annealing can refine the microstructure, resulting in the formation of a stable TixAly type intermetallic compound on the surface. TixAly alloy has high hardness and good corrosion resistance, and it readily forms a dense Al2O3 layer on the outer layer of the matrix, thus preventing oxidation of the matrix structure at high temperatures. This effectively improves the alloy's hardness, high-temperature oxidation resistance, and wear resistance, preventing cracking of TC4 titanium alloy during cold rolling.

[0072] The residual alkali and acid solutions on the sample are removed by washing with water.

[0073] The fluxing process is a crucial step in the hot-dip aluminizing process because there is interphase tension between the molten aluminum and the TC4 substrate. The role of the flux in hot-dip aluminizing is to reduce this interphase tension, which increases the wettability of the molten aluminum to the titanium alloy substrate. However, the sample after pickling must be placed in the fluxing solution in time to complete the fluxing process. If the fluxing is not done in time, the surface of the treated sample will be exposed to the air and will easily react with oxygen in the air, forming an oxide film on the surface of the sample. Alternatively, the sample may be easily oxidized in the high-temperature atmosphere above the molten aluminum to form a loose and porous oxide film. This oxide film will reduce the wettability between the molten aluminum and the sample surface, preventing the molten aluminum from making good contact with the sample. This will cause phenomena such as leakage, uneven diffusion layer, and pores in the sample.

[0074] During the plating process, a protective film can be formed on the surface of the titanium alloy substrate. This protective film must be dense and free of pinholes. During hot-dip aluminum infiltration, the addition of the plating flux can significantly improve the wettability of the titanium alloy substrate during contact with it. It will not adhere to the surface of the titanium alloy and will not affect the contact between the aluminum solution and the titanium alloy substrate. It will not cause pollution to the plating solution.

[0075] The sample was heated and kept warm in a water bath at 95°C to ensure that K2ZrF6 could be completely dissolved. The sample was immersed in the flux for 5 minutes to achieve the formation of a continuous and dense oxide film on the surface.

[0076] If molten aluminum is exposed to air during hot-dip aluminizing, an oxidation reaction will occur upon contact with the air, resulting in an uneven surface or even leakage of the aluminized sample. To prevent this, a covering agent needs to be added to the surface of the molten aluminum. The covering agent adsorbs and dissolves the Al2O3 film formed on the surface of the molten aluminum and prevents the formation of other oxide inclusions. The covering agent can significantly improve the effect of hot-dip aluminizing on the sample.

[0077] In step S1, after the grinding is completed, the sample is electropolished using an electrolyte. The electropolishing current is 1A, with the sample as the anode and titanium as the cathode. A mixture of 30ml perchloric acid, 90ml n-butanol, and 180ml methanol is used, and liquid nitrogen is added to bring the temperature to about 0°C for 40 seconds. After electropolishing is completed, the sample is removed and rinsed with water. Finally, it is etched with an etching solution prepared with HF:HNO3:H2O=2:4:94.

[0078] The ultrasonic cleaner is model YM-010S and is manufactured by Taizhou CNC Machine Tool Manufacturing Co., Ltd.

[0079] The equipment used for polishing is a metallographic sample polishing machine, model P-2T, manufactured by Laizhou Medical Instrument Manufacturing Co., Ltd.

[0080] The electronic balance is model FA2204 and is manufactured by Shanghai Jingqi Instrument Co., Ltd.

[0081] The blower dryer is model number 9030A and is manufactured by Zhejiang Hengyue Instrument Co., Ltd.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for hot-dip aluminum infiltration onto the surface of TC4 titanium alloy, characterized in that; Includes the following steps: S1. Cutting: The TC4 titanium alloy sheet is wire-cut into multiple sample pieces, and the sample pieces are mechanically polished. S2. Alkali washing: Immerse the sample in the mixed alkaline solution and clean it in an ultrasonic cleaner for 5 minutes. Remove the sample and wash it with warm water. The mixed alkaline solution consists of 80 g / L NaOH, 30 g / L Na2CO3, 30 g / L Na3PO4 and 8 g / L Na2SiO3. S3. Pickling: Immerse the sample in the pickling mixture and clean it in an ultrasonic cleaner for 5 minutes. Remove the sample and clean it with warm water. The mixture consists of HCl and hexamethylenetetramine. S4. Plating flux: Add plating flux to a warm water bath. Immerse the sample in the flux for 5 minutes, then remove it, blot dry with filter paper, and dry with a hair dryer. The constant temperature in the warm water bath is 60-95℃. The plating flux is a supersaturated aqueous solution of K2ZrF6. S5, Aluminizing: At a temperature of 760℃, the sample after fluxing is immersed in molten aluminum for aluminizing for 15 minutes, and then air-cooled. S6. Cold rolling: The sample is cold rolled to reduce the deformation of the sample to 5-15%. S7. Annealing: Anneal the TC4 aluminized sample after rolling deformation treatment at a temperature of 700-900℃ for 3-10 hours.

2. The process for hot-dip aluminum infiltration onto the surface of TC4 titanium alloy as described in claim 1, characterized in that: In step S1, the sample is cut into a large-size sample and a small-size sample. The large-size sample has dimensions of 15mm × 80mm × 3mm, and the small-size sample has dimensions of 15mm × 15mm × 3mm. A 2mm diameter circular hole is drilled on one corner of each sample. The surface hard oxide layer is removed by polishing with 180#, 400# and 800# metallographic sandpaper.

3. The process method for hot-dip aluminum infiltration onto the surface of TC4 titanium alloy as described in claim 1, characterized in that: In step S5, a covering agent is added to the upper surface of the molten aluminum liquid in the aluminizing process. The covering agent is a solid mixed salt of KCl and NaCl.

4. The process method for hot-dip aluminum infiltration onto the surface of TC4 titanium alloy as described in claim 1, characterized in that: The temperature range of the warm water is 50-90℃.

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