JP4150700B2 - Manufacturing method of surface-treated titanium material excellent in oxidation resistance, engine exhaust pipe - Google Patents

Description

The present invention relates an exhaust pipe of an engine composed of surface-treated titanium material, a method for producing a surface-treated titanium material excellent in oxidation resistance of the exhaust pipe of the engine.

  Titanium alloys have a higher specific strength than common steel materials and are increasingly applied to the field of transportation equipment, particularly automobiles, which are strongly aimed at weight reduction. Among them, the exhaust pipe material around the engine is currently made of stainless steel, but the use of titanium in the exhaust pipe is being studied for the purpose of reducing the weight. However, since the temperature of the exhaust pipe becomes a high temperature of 500 ° C. or more depending on the part, the titanium alloy material that is not surface-treated has a problem in durability because the oxidation proceeds rapidly and the high-temperature oxidation resistance is inferior.

  For this reason, various surface treatments have been proposed in the past in order to improve the high temperature oxidation resistance (hereinafter also simply referred to as oxidation resistance) of the titanium material. For example, a material in which an Al plate is clad on the surface of a titanium alloy has been proposed (see Patent Document 1). In addition, a method of performing Al—Ti vapor deposition plating on the titanium alloy surface has been proposed (see Patent Document 2). Alternatively, a method of forming a TiCrAlN-based film on a titanium alloy surface by a PVD method has been proposed (see Patent Document 3).

  However, the cladding method is expensive. In addition, the vapor deposition method and the PVD method have problems such as high processing costs and difficulty in forming an oxidation resistant film on the inner surface of the tube when the titanium material has a tube shape such as the exhaust pipe. ing.

On the other hand, a method of forming an oxygen barrier film (oxidation-resistant film) for preventing the diffusion of oxygen into the material by attaching an inorganic binder and Al powder to the titanium alloy surface and firing it, or There has been proposed a treatment method in which sealing is performed with a sealing material based on chromic acid in order to fill voids generated between Al powders after firing (see Patent Document 4).
JP-A-10-99976 (Claims) JP-A-6-88208 (Claims) JP-A-9-256138 (Claims) Japanese Patent No. 3151713 (Claims, pages 1 to 3)

  The oxygen barrier film obtained by firing Al powder on the surface of the titanium alloy is effective as the oxidation-resistant film at the high temperature. However, voids are inevitably generated between the Al powders after firing. Therefore, in order to sufficiently function as an oxidation-resistant film, it is necessary to fill (seal) the generated voids with a sealer material based on chromic acid, as described in Patent Document 4.

  For this reason, a process using an inorganic binder for adhering Al powder onto a titanium substrate, and further a process using chromic acid to fill the voids formed between the Al powders after firing, are necessary. These processes are in two stages and are not efficient. Moreover, the chromic acid solution described only as an inorganic binder is extremely toxic, and there is a concern about its safety not only in the above treatment process but also in use as a member.

The present invention has been made in view of such circumstances, and its purpose is excellent in oxidation resistance, maintaining the oxidation resistance over a long period of time, and surface treatment itself is also inexpensive and safe. An object of the present invention is to provide an engine exhaust pipe made of a surface-treated titanium material and a method for producing a surface-treated titanium material having excellent oxidizability for an engine exhaust pipe .

To achieve the above object, the present onset Ming aspect is a surface treated titanium material of pure titanium or on a substrate made of titanium based alloys 5 [mu] m or more oxidation-resistant baked film is formed, the The fired coating layer is a surface obtained by applying Al alloy particles or pure Al particles containing 10 at% or less of Si and a solution containing a silicone resin on the base material and firing at a firing temperature of 200 to 400 ° C. The engine exhaust pipe is made of a treated titanium material .

In order to achieve the above object, the gist of the method for producing a surface-treated titanium material excellent in oxidation resistance for an exhaust pipe of the engine of the present invention is 10 at% or less on a substrate made of titanium or a titanium-based alloy. A solution containing Si alloy-containing Al alloy particles or pure Al particles and a silicone resin is applied and fired at a firing temperature of 200 to 400 ° C. to form an oxidation-resistant coating layer.

  Further, the gist of the engine exhaust pipe excellent in oxidation resistance according to the present invention for achieving the above object is that the exhaust pipe is composed of the surface-treated titanium material.

  As described above, the oxygen barrier film obtained by firing Al powder on the titanium alloy surface is effective as an oxidation-resistant film at a high temperature. However, as described above, since voids are inevitably generated between the Al powders after firing, in order to sufficiently function as an oxidation-resistant film, the generated voids are sealed with a sealing material (sealer material) or the like. Must be filled (sealed).

  In this respect, in the present invention, as the sealing material, as described above, the metal element M (wherein M is one or more of Ti, Zr, Cr, Si, Al) and C 2 and / or after firing, as described above. A compound consisting of O 2 is used. When the compound composed of the metal elements M and C and / or O is present between particles in a fired coating layer of a conventionally known pure Al-based or Al-Si alloy powder containing Si at 10 at% or less, The oxidation resistance of the fired coating at high temperatures is significantly improved.

In addition, the compound composed of the metal elements M and C and / or O 2 also serves as a binder for the Al powder, and improves the adhesion between the Al powders of the fired coating layer or between the fired coating layer and the titanium material surface. . Further, the coating on the titanium material surface of these compounds MonoHara fees, as the gist of the production method of the present invention a surface-treated titanium material, can simultaneously process a coating of Al powder, it is convenient. Moreover, these compounds do not have the toxicity like the above-mentioned conventional chromic acid, and are safe not only for the surface treatment process but also for use as a member.

  Hereinafter, embodiments of the present invention and reasons for limiting the requirements of the present invention will be specifically described.

(Al powder)
The pure Al powder of the present invention or the Al—Si alloy powder containing Si at 10 at% or less is a basic component for improving the oxidation resistance of the fired coating layer on the surface of the titanium material. The Al powder to be used may be pure Al (pure Al-based powder), Al-Si alloy powder containing Si at 10at% or less, or a mixture of these, and Al-Si alloy powder may be Al powder. And Si powder may be mixed.

  In the case of Al-Si alloy powder, since it contains Si, the oxidation resistance on the higher temperature side is improved. However, the effect of the Si content is saturated at about 10 at%, and when Si is contained at 10 at% or more, it is difficult to produce the powder itself. Accordingly, the Si content is 10 at% or less.

  The production of these Al powders is a known method such as direct atomization of molten metal, atomization method, molten metal stirring method, rotary disk dropping method, mechanical milling, stamp mill method, ball mill method, vibration mill method, attritor method, etc. The powder manufactured in can be applied. In these powder production methods, Al powder is produced with an average particle diameter of about 2 to 500 μm.

  However, although the particle diameter of these Al powders also depends on the thickness of the fired coating layer, an excessively large particle diameter is not preferable because more voids are formed between the particles. In this respect, in order to suppress the void formation between the particles as much as possible, it is preferable that the average particle diameter of the Al powder to be coated is 20 μm or less, and the Al powder having an average particle diameter of 20 μm or less is selected, selected and used. .

(Sealing material)
As the sealing material, a compound comprising metal element M (where M is one or more of Ti, Zr, Cr, Si, and Al) and C 2 and / or O 2 is used in the present invention between Al powder particles. It fills the gap and plays a role of improving the oxidation resistance of the fired coating layer. These compounds also serve as a binder for the Al powder, and improve the adhesion between the Al powders in the fired coating layer or between the fired coating layer and the titanium material surface.

In order to form a compound composed of a metal element M (where M is one or more of Ti, Zr, Cr, Si, and Al) and C 2 and / or O 2 between Al particles in the fired coating layer, An organometallic compound composed of element M (where M is one or more of Ti, Zr, Cr, Si, Al) and C 2, O 2, and H is applied in advance to the surface of the titanium material before firing.

These organometallic compounds that use a silicone resin. Silicone resins are easy to stable handling toxicity have low.

  As the metal element M 1, Si is particularly preferable from the viewpoint of improving the oxidation resistance at high temperature of the fired coating layer. Therefore, as the metal element M 1, other metal elements may be included, but those essentially including Si are particularly preferable. For example, when a silicone resin is selected as an organometallic compound composed of Si and C 2 and / or O 2, and a solution containing Al powder and silicone resin is applied to the titanium surface and baked, Si powder is bonded between the Al powder particles. A compound composed of -OC is formed and serves as a sealing material. Moreover, the role as a binder is also excellent.

Usually, the Si / O ratio in the silicone resin is approximately 1, but by selecting an appropriate firing temperature, the reaction between O and Si is promoted and the Si / O ratio is reduced. Thereby, the compound between particles becomes more stable and shows high oxidation resistance. This is thought to be due to the fact that by selecting the firing temperature, it approaches SiO2, which is the most stable oxide. Sintering temperatures for this shall be between 200 to 400 ° C.. However, since the binder portion is hardened by firing and cracking is likely to occur, it is recommended that firing be performed after the bending or the like. The amount of Si—O chemical bonds can be controlled by appropriately changing the firing temperature.

(Firing coating layer)
The compound of the metal elements M and C and / or O is preferably contained in the fired coating layer in an amount of about 5 to 50 vol% in order to fulfill the function of the binder and the function of the sealing material. For example, even when spherical Al powder particles having the same size are ideally filled, about 26% of the volume ratio in the fired coating layer becomes voids, which need to be filled. That is, in the closest packing of the compound, the volume ratio of the compound in the fired coating layer is 74 vol%. On the other hand, when Al powder particles having different sizes are mixed, the volume ratio in the fired coating layer of the voids is further increased, and the degree of filling of the compound is increased, so that the volume ratio is about 5 to 50 vol%. To do.

(Firing coating layer thickness)
The thickness of the fired coating layer shall be 5 μm or more. If it is less than 5 μm, it is too thin to eliminate the oxygen barrier effect of the fired coating layer itself. On the other hand, since the oxygen barrier effect is saturated even if it exceeds 200 μm, the upper limit of the preferable thickness is set to 200 μm.

  The ratio of Al / Si in the fired coating layer when using a silicone resin or the like can be measured by a normal surface element analysis method such as EDX. In addition, the method for confirming the presence of a compound consisting of M / CO 2 between the Al particles of the fired coating layer is to confirm the presence of the element by conducting elemental analysis of the cross section (cut surface or fracture surface) of the fired coating layer. be able to. Further, when measured by XPS, the bonding of M—O and M—C in the fired coating layer can be detected. Analysis of chemical bonds such as M-O, eg, Si-O, between the metal elements M and O can be measured by XPS or FTIR.

(Titanium oxide layer)
Before forming the fired coating layer, the surface of the substrate made of pure titanium or titanium-based alloy is oxidized, and an oxide film is formed in advance, thereby improving the adhesion between the fired coating layer and the substrate, and higher oxidation resistance. Sex can be obtained. In this case, the surface-treated titanium material has a titanium oxide layer between the fired coating layer and the base material.

  The sealing material (compounds of metal elements M, C and O) present on the surface of the Al powder particles may have insufficient adhesion to the substrate surface depending on the application. In such a case, in Patent Document 4 and the like, surface roughening treatment such as shot blasting is performed, and the adhesion is improved by the anchor effect. However, depending on the application, the roughening treatment of the substrate may not be performed. On the other hand, when a titanium oxide film is formed on the surface of the base material in advance by oxidation treatment, the sealing material is remarkably excellent in adhesion to the formed titanium oxide film.

  This oxidation treatment may be performed by a wet method such as heating in the atmosphere (recommended temperature: 300 to 500 ° C.) or anodizing. If the thickness of the oxide layer is between 0.1 μm and 5 μm, the effect will not change. The oxide layer can be observed and measured with a TEM when the cross section is SEM or thin.

(Molten aluminum plating layer)
Before forming the fired coating layer, the corrosion resistance of the substrate can be further improved by previously forming a molten aluminum plating layer on the surface of the substrate made of pure titanium or a titanium-based alloy. In this case, the surface-treated titanium material has a molten aluminum plating layer between the fired coating layer and the base material. The molten aluminum plating itself has oxidation resistance, but the corrosion resistance of the base material can be further improved by laminating the fired coating layer of the present invention thereon, and the appearance of the molten aluminum plating The sex is also improved.

(Method for producing surface-treated titanium material)
As described above, the method for producing a surface-treated titanium material in the present invention comprises a Al alloy particle or pure Al particle containing 10 at% or less of Si and a solution containing a silicone resin on a substrate made of titanium or a titanium-based alloy. It is applied and fired to form an oxidation resistant coating layer.

(Coating solution)
At this time, regarding the solution applied to the substrate surface, any kind of aqueous solution or solvent may be used as long as each compound can be uniformly dispersed or dissolved. Further, in the solid content ratio of the metal particles (Al / Si and / or metal element M) and C / O in the coating solution, at least 5 wt% or more of these metal particles are contained in the C / O compound. It is preferable. When these metal particles are less than 5 wt%, the metal particles (Al / Si and / or metal element M) in the fired coating layer are insufficient, and a sufficient effect on oxidation resistance and adhesion can be obtained. There is no possibility. On the other hand, if these metal particles are contained in an amount exceeding 80 wt% with respect to the C / O compound, the ability to form a coating film that retains the particles will decrease, so the adhesion and durability of the fired coating layer will be reduced. May cause problems. Therefore, it is preferably in the range of 5 to 80 wt%.

(Baking)
In firing, the coated silicone resin is oxidized, and consists of metal element M (where M is one or more of Ti, Zr, Cr, Si, Al) and C 2 and / or O 2 between Al particles. A fired coating layer filled with the compound is formed to improve the oxidation resistance, adhesion and durability of the fired coating layer.

The firing temperature for this is selected appropriately for each organometallic compound and according to other coating raw material conditions. In the case of the silicone resin , the firing compound has high oxidation resistance. the calcination temperature for obtaining a chemical bond amount of MO indicating to select. For the silicone resin sintering temperature Ru der between 200 to 400 ° C.. Further, the firing time is set to a necessary time for producing the firing effect, depending on the selected temperature.

  Note that the firing atmosphere may be an oxidizing atmosphere as in a normal firing atmosphere, and air, an oxygen-containing atmosphere, or the like is appropriately selected.

(Post-processing)
After the formation of these oxidation-resistant fired coating layers, when higher oxidation resistance is required, after forming the fired coating layer, as a post-treatment, voids between Al particles slightly remaining on the surface of the fired coating layer are formed. Can disappear. This post-treatment is preferably a blast treatment with hard particles such as shot blasting, and the blast treatment can give an impact to the surface of the fired coating layer and eliminate the slight gap between the Al particles.

  In addition, according to such blasting treatment, an Al oxide film or metal element M (where M is one or more of Ti, Zr, Cr, Si, Al) and C 2 formed on the surface during firing. A beautiful surface having a metallic luster can also be obtained by removing only the surface of the compound consisting of /.

(Applicable titanium material)
The titanium substrate referred to in the present invention refers to a titanium material such as pure titanium or a titanium-based alloy that has been formed into various shapes by plastic working such as rolling. In the present invention, the titanium material to be surface-treated is not specified, and any of an α alloy, an α-β alloy, and a β alloy may be used depending on the required characteristics (mechanical properties, etc.) of the application. For example, pure titanium (JIS type 2), Ti-1.5Al, Ti-0.5Al-0.45Si-0.2Nb, Ti-6Al-4V, Ti-3Al-2.5V, Ti-15V-3Al-3Sn-3Cr, etc. Can be used.

  In particular, when used for exhaust pipe applications, it is preferable to use a titanium alloy described in Japanese Patent Application No. 2004-071275 filed earlier by the inventors. That is, it is a titanium alloy material containing Al: 0.30 to 1.5% and Si: 0.10 to 1.0% by mass%, preferably Si / Al is 1/3 in mass ratio, and further selectively Nb. : The thing containing 0.1 to 0.5% is preferable. Al is contained in an amount of 0.30% or more for improving heat resistance and high-temperature oxidation resistance, and is contained in an amount of 1.5% or less for preventing deterioration of ductility and corrosion resistance. Si, combined with Al, improves high-temperature strength and minimizes deterioration in corrosion resistance while improving high-temperature oxidation resistance, particularly scale loss resistance and oxygen diffusion layer formation. Further, fatigue characteristics and brittleness are improved by suppressing the growth of crystal grains. For this reason, Si is contained at 0.10% or more, and is contained at 1.0% or less for preventing deterioration of moldability and corrosion resistance. Further, when Nb is selectively contained in an amount of 0.1% or more, high temperature oxidation resistance, in particular, scale loss resistance and oxygen diffusion layer forming property is improved while minimizing the decrease in corrosion resistance. On the other hand, Nb is contained in an amount of 0.5% or less in order to prevent moldability deterioration.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention is not limited to the following examples. Of course, it is also possible to implement them, and they are all included in the technical scope of the present invention.

  On the surface of the titanium base material, a solution in which Al powder and silicone are mixed under the coating conditions shown in Table 1 is applied and baked, and the compounds (metal elements M 1 and C 2 and / or 3) between the Al particles shown in Table 1 are baked. As oxidation compounds, oxidation-resistant fired coating layers having various Si / O ratios were formed. These test materials were subjected to a high-temperature oxidation test, and the oxidation resistance was evaluated from the weight increase after the oxidation test. Table 1 shows the evaluation results.

  As a titanium base material, a pure titanium rolled plate (JIS type 3, thickness 1 mm) was used. The coating solution may be pure Al particles having an average particle size of 5 μm (described as Al in the table) or Al alloy particles having different Si contents (described as Al-Si in the table) in an organic solvent such as ethanol or isopropanol. A solution mixed with silicone was prepared.

  The coating was carried out by dipping (dip), dried at 120 ° C. for 0.5 hour, and then baked at 250 ° C. for 0.5 hour to form an oxidation resistant coating layer having a film thickness of about 30 μm in common with each example.

  In addition, in order to confirm the influence of the titanium oxide layer (preliminary oxide layer) on the surface, the base material formed by previously oxidizing the titanium base material in the range of 500 to 700 ° C. and changing the thickness of the oxide layer, The oxidation-resistant fired coating layer was formed (numbers 9 to 12 in Table 1). The thickness of this oxide layer is also listed in Table 1.

  In the high-temperature oxidation test, the resistance to high-temperature oxidation was evaluated by measuring the weight increase after the oxidation test when these specimens were exposed to high-temperature air at 800 ° C. for 100 hours.

Invention Examples 3 to 12 in Table 1 (7 and 8 are reference examples) are about 2.5 mg / cm ² even if the weight increase after the oxidation test is large. On the other hand, Comparative Example 1 does not perform surface treatment of the equipment, and does not have an oxidation-resistant fired coating layer itself. For this reason, the weight increase after a high temperature oxidation test is as large as 12 mg / cm ² . In Comparative Example 2, the oxidation-resistant fired coating layer is only Al particles, and there is no compound (compound composed of metal elements M and C and / or O) between the Al particles. For this reason, the weight increase after a high temperature oxidation test is as large as 8.9 mg / cm ² . Therefore, it can be seen that Invention Examples 3 to 12 are remarkably superior in high-temperature oxidation resistance as compared to Comparative Examples 1 and 2.

  Further, among Invention Examples, Invention Examples 9 to 12 in which a titanium oxide layer (preliminary oxidation layer) is provided on a substrate are generally high-temperature oxidation resistant compared to Invention Examples 3 to 8 in which a titanium oxide layer is not provided. Is relatively good.

  In Reference Examples 7 and 8, although the high-temperature oxidation resistance is excellent, the Si content in Al exceeds 10 at%. Therefore, since it became difficult to produce Al powder itself and it was industrially unsuitable, it was used as a reference example.

  On the surface of the titanium base material, a solution in which Al powder and various organometallic compounds (chemical formulas other than silicone are described) are applied and fired under the same coating conditions as in Example 1 under the coating conditions shown in Table 2. As shown in Table 2, an oxidation-resistant fired coating layer made of a compound (compound composed of metal elements M and C and / or O) between Al particles was formed. For these specimens, a high-temperature oxidation test was conducted in the same manner as in Example 1, and the oxidation resistance was evaluated from the weight increase after the oxidation test. Table 2 shows the evaluation results.

  Specific conditions for the titanium substrate, coating solution, Al particles, coating-firing, and high-temperature oxidation test were the same as in Example 1 except for the type of organometallic compound.

Invention Examples 13 to 18 in Table 2 are about 2.4 mg / cm ² regardless of whether an organometallic compound other than silicone is used or the weight increase after the oxidation test is large. However, Invention Examples 13 and 18 using silicone are relatively superior in high-temperature oxidation resistance to Invention Examples 14 to 17 using organometallic compounds other than silicone. In this respect, as the metal element M 1, it is understood that Si is particularly preferable from the viewpoint of the effect of improving the oxidation resistance of the fired coating layer at a high temperature. Inventive Examples 14 to 17 using these organometallic compounds other than silicone are reference examples outside the scope of the present invention.

  Comparative Examples 1 and 2 are the same as Comparative Examples 1 and 2 of Example 1 (Table 1). Therefore, it can be seen that Invention Examples 13 to 18 are remarkably superior in high-temperature oxidation resistance as compared with Comparative Examples 1 and 2.

  Preferred titanium alloy material as described above, which contains, as a titanium base material, Al: 1.0% and Si: 0.33% in mass%, Si / Al is 1/3 in mass ratio, and selectively contains Nb: 0.2%. Was subjected to the surface treatment of the present invention. That is, on the surface of the titanium alloy material, a mixed solution of Al powder and silicone was applied under the same coating conditions as in Example 1 under the coating conditions shown in Table 3. An oxidation-resistant fired coating layer made of a compound (compound consisting of metal elements M and C and / or O) between the particles was formed. For these specimens, a high-temperature oxidation test was conducted in the same manner as in Example 1, and the oxidation resistance was evaluated from the weight increase after the oxidation test. Table 3 shows the evaluation results.

  The titanium base material was previously provided with a molten aluminum plating layer having a thickness shown in Table 3. Inventive Examples 19 and 21 in Table 3 do not contain Nb in the above-mentioned titanium alloy material. Inventive Examples 20, 22, and 23 in Table 3 do not contain Nb in the above-mentioned titanium alloy material. What was contained was used.

Further, the titanium base materials of Invention Examples 20 and 22 in Table 3 were subjected to blasting treatment with hard alumina particles (average particle size 50 μm) on a fired coating layer formed using a commercially available shot blasting machine (gas pressure: 3 kg). / cm ² ) was applied for 10 seconds.

  Other specific conditions such as titanium substrate, coating solution, Al particles, coating-firing, high-temperature oxidation test were the same as those in Example 1.

  In Table 3, the surface-treated titanium material of Invention Examples 20 to 23, in which a molten aluminum plating layer was previously provided on a titanium base material, was significantly more resistant to high temperature oxidation than Comparative Examples 1 and 2 as in Example 1. Is excellent. Also, in Table 3, compared with Invention Example 19 in which a molten aluminum plating layer is not provided and Invention Example 21 in which the thickness of the molten aluminum plating layer is thin, a molten aluminum plating layer provided or a thicker molten aluminum plating layer is used. Invention Example 20 and Invention Examples 22 and 23 are superior in resistance to high-temperature oxidation. Shot blasting also contributes to the improvement of the high temperature oxidation resistance of Invention Examples 20 and 22.

  From the results of these examples, the critical significance of the requirements of the present invention and the significance of the preferred requirements regarding the improvement of the high temperature oxidation resistance of the titanium material are supported. Further, according to the present invention, it can be seen that the surface-treated titanium material is excellent in oxidation resistance, maintains its oxidation resistance over a long period of time, and the surface treatment itself is inexpensive and safe.

According to the present invention, a surface-treated titanium material and a method for producing the same that are excellent in oxidation resistance, maintained for a long period of time, and inexpensive and safe in surface treatment itself, and further, the engine exhaust thereof. Can provide a tube.

Claims (9)

A surface-treated titanium material in which an oxidation-resistant fired coating layer of 5 μm or more is formed on a substrate made of pure titanium or a titanium-based alloy, and the fired coating layer is 10 at% or less on the substrate. An engine exhaust pipe composed of a surface-treated titanium material that is obtained by applying a solution containing Al alloy particles or pure Al particles containing Si and a silicone resin , and firing at a firing temperature of 200 to 400 ° C. The engine exhaust pipe according to claim 1, wherein the Al alloy particles in the fired coating layer of the surface-treated titanium material are an Al alloy containing 2 to 10 at% of Si . 3. The engine exhaust pipe according to claim 1 , wherein a Si—O chemical bond is present in the fired coating layer of the surface-treated titanium material, and the Si / O ratio is 0.4 ≦ Si / O ≦ 2. . The engine exhaust pipe according to any one of claims 1 to 3, further comprising a titanium oxide layer between the fired coating layer of the surface-treated titanium material and the base material . The molten aluminum plating layer is previously provided on the base material of the surface-treated titanium material, and the oxidation-resistant fired coating layer is formed on the molten aluminum plating layer. engine exhaust pipe. The engine exhaust according to any one of claims 1 to 5, wherein the substrate of the surface-treated titanium material is a titanium alloy material containing Al: 0.30 to 1.5% and Si: 0.10 to 1.0% by mass%. tube. Apply a solution containing Al alloy particles or pure Al particles containing 10 at% or less of Si and a silicone resin on a substrate made of titanium or a titanium-based alloy, and firing at a firing temperature of 200 to 400 ° C. A method for producing a surface-treated titanium material excellent in oxidation resistance for an engine exhaust pipe , characterized by forming a conductive coating layer. The method for producing a surface-treated titanium material according to claim 7, wherein the fired coating layer is subjected to blasting with hard particles . The method for producing a surface-treated titanium material according to claim 7 or 8, wherein the base material of the surface-treated titanium material is a titanium alloy material containing Al: 0.30 to 1.5% and Si: 0.10 to 1.0% by mass%. .