JP2008081839A - Member made of aluminum alloy, method for producing the same, and fuel pump with the member made of aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a member made of an aluminum alloy in which a high quality alumite coating having a uniform thickness, a smooth surface, and excellent hardness, corrosion resistance, wear resistance or the like regardless of the material composition of a base layer is formed. <P>SOLUTION: The member is constituted of a base material 12 in which at least a portion of the surface of a base layer 10 composed of an aluminum alloy containing silicon is covered with an aluminum alloy having a silicon content lower than that of the base layer 10 or pure aluminum and an alumite layer 13 which is formed by the oxidation of a coating layer 11a covering the base layer 10 of the base material 12, that oxidation proceeds toward inside from the surface side, and has a hardness higher than the base material 12. At this time, an intermediate layer 11 may be formed between the base layer 10 and the alumite layer 13 by leaving a portion of the coating layer 11a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aluminum alloy member whose surface is subjected to alumite treatment for improving the corrosion resistance, wear resistance, and hardness of a substrate made of an aluminum alloy, a method for producing the same, and the aluminum alloy member It is related with the fuel pump provided with.

  Aluminum alloys such as aluminum castings and aluminum die-casting products are widely used as various vehicle members such as automobiles, industrial equipment members, electrical and electronic equipment members, and architectural members. In particular, when used as an automobile part, it contributes to vehicle weight reduction, fuel efficiency improvement, resource saving, pollution prevention, and the like, so it is preferably used as a member that replaces conventional iron-based materials.

  By the way, although aluminum alloy is lightweight, there is a drawback that it is soft and easily damaged. Therefore, for the purpose of improving corrosion resistance, wear resistance, hardness, etc., an anodizing treatment (anodizing treatment) for forming an oxide film on the surface is performed. Moreover, in general aluminum cast products and aluminum die cast products, an appropriate amount of silicon (Si) is often added to improve the castability, hardness, impact resistance, and the like. When silicon is added to aluminum, the fluidity of the molten aluminum alloy is improved and the solidification shrinkage is reduced. Moreover, the silicon crystallized in the substrate is hard.

In general, the alumite treatment is performed by applying a direct current between an object to be treated as an anode in an electrolytic bath and a cathode plate, thereby oxidizing the substrate surface as shown in FIG. This is a process for producing an aluminum oxide (Al ₂ O ₃ ) film having excellent wear resistance and hardness, and this aluminum oxide film is called an alumite (layer). Since the alumite layer grows by reaction of aluminum in the base material, the alumite layer grows (thickens) as the oxidation progresses, but the thickness of the base material decreases. Here, the silicon added for improving the castability and the like is crystallized as eutectic silicon in the base material as shown by an ellipse in FIG. In addition, the eutectic silicon crystallizes coarse enough to be observed with an optical microscope under cooling conditions in a general casting method. Since this eutectic silicon is not oxidized even by the alumite treatment, the eutectic silicon is gradually exposed to the surface of the base material as the base material is oxidized, and is deposited on the base material. When processing by direct current, the pores generated in the anodized layer grow linearly, so that an oxide film (alumite layer) is not formed on the eutectic silicon as shown in FIG. 6 (b). Even if it has only a very small thickness, the result is a rough anodized layer with a non-uniform thickness and a porous structure. Additives other than silicon also become an inhibiting factor for the formation of an alumite layer. Such an alumite layer does not fully exhibit hardness, corrosion resistance, wear resistance, and surface smoothness (surface roughness), and such pores may cause rust due to moisture intrusion. Therefore, the quality of the aluminum alloy member is deteriorated.

  In order to avoid this, it is conceivable to use an aluminum alloy having a low silicon content, for example, ADC6 (silicon content of 1.0% by mass or less) which is an aluminum die-cast product of JIS H5302, but in this case the silicon content is low. For this reason, it has excellent anodizing properties, but since it is inferior in castability, it tends to cause defects such as cast holes and hot water wrinkles, resulting in a problem of poor yield. In addition, aluminum alloys with a low silicon content are expensive.

  In order to deal with such problems, Patent Document 1 and Patent Document 2 have been proposed as inventions focusing on processing silicon in an aluminum alloy. In patent document 1, it consists of three components of nitric acid, ammonium hydrogen fluoride, and acetic acid as pretreatments, such as alumite treatment of the aluminum alloy containing silicon, nitric acid is 50 mass% or more, ammonium hydrogen fluoride is 10 mass% or more, and acetic acid Is pre-treated with a detergent solution composed of a mixed solution adjusted to have a concentration of 5 to 20 mass% or more, so that silicon in the substrate is selectively removed to achieve uniform formation of an alumite layer. In Patent Document 2, silicon in an aluminum alloy containing silicon is refined by remelting with high-density energy heat rays, and at the same time, silicon is diluted by dissolving an aluminum-based filler material having a low silicon content, and then anodized. We are processing. Further, in Patent Document 2, an alumite treatment is applied only to a piston ring groove that requires particularly high corrosion resistance and wear resistance in a piston for an internal combustion engine.

  On the other hand, Patent Document 3 discloses an invention in which an alumite treatment method is improved instead of treating an aluminum alloy. In Patent Document 3, the application of a positive voltage and the removal of electric charge are repeated instead of a conventional direct current, or an alumite treatment is performed using a power supply having an alternating current component. According to this, since the alumite layer is dense without orientation, and is grown so as to surround silicon, there is an advantage that it is not necessary to consider the composition of the aluminum alloy or perform pretreatment. Have.

Japanese Patent Laid-Open No. 11-264088 JP-A-5-17899 JP 2006-83467 A

  In Patent Document 1, by selectively removing silicon to prevent the formation of an alumite layer, and by adjusting the concentration ratio of ammonium hydrogen fluoride to nitric acid appropriately, large pores are removed around the removed silicon. Is also prevented from forming. However, since the pores in the portion where the silicon is selectively removed are generated, the surface of the substrate becomes rough, which makes the thickness of the alumite layer non-uniform and the surface rough, which makes it difficult to apply to precision parts and sliding members. . The higher the silicon content, the greater the surface roughness. In Patent Document 2, although the adverse effect on the alumite layer is made as small as possible by diminishing and diluting silicon, the silicon still remains and the essential problem is solved. Not in.

  On the other hand, in Patent Document 3, a dense alumite layer having a uniform film thickness can be formed without being affected by additives such as silicon and impurities in the aluminum alloy. However, as will be described in detail later, the alumite layer here is formed so as to surround silicon due to the difference in film formation characteristics, for example, by repeatedly supplying and removing charges. In order to improve the degree, it is necessary to form an alumite layer having sufficient thickness by reliably surrounding silicon. Therefore, when such an aluminum alloy member is used in a portion requiring particularly good surface roughness, it is necessary to lengthen the alumite treatment time. In addition, for example, when it is desired to form an intermediate layer between the base material and the alumite layer, the thickness of the intermediate layer becomes small so that the function cannot be sufficiently exhibited, or in the worst case, the intermediate layer cannot be formed. . In the first place, when an aluminum alloy containing a large amount of silicon is alumite-treated as it is, there are problems as described above, and there is a limit in improving the surface roughness.

  Accordingly, an object of the present invention is to provide an aluminum alloy in which a high-quality alumite film excellent in hardness, corrosion resistance, wear resistance, and the like is formed regardless of the material composition of the base layer. An object of the present invention is to provide a member and a manufacturing method thereof, and a fuel pump including the member made of aluminum alloy.

  In order to achieve the object of solving the above-mentioned problems, according to the present invention, at least part of the surface of a base layer made of an aluminum alloy containing silicon has a lower silicon content than the base layer. Formed by oxidation of a base material coated with an aluminum alloy or pure aluminum and an aluminum alloy or pure aluminum covering the base layer of the base material from the surface side toward the inside. It is a member made from an aluminum alloy characterized by comprising an alumite layer having a high thickness.

The alumite layer here means a coating layer made of aluminum oxide (Al ₂ O ₃ ) produced by alumite treatment of an aluminum alloy or pure aluminum. The alumite treatment is also referred to as an anodic oxidation treatment. In the aluminum alloy member according to claim 1, the entire aluminum alloy film or pure aluminum film covering the base layer may be oxidized, or the aluminum alloy film or pure aluminum film covering the base layer is in the thickness direction. It may be partially oxidized and a part of the aluminum alloy film or the pure aluminum film may remain. The case where a part of the aluminum alloy film or the pure aluminum film remains corresponds to the present invention according to claim 4.

  The present invention according to claim 2 is a substrate in which at least a part of the surface of a base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content than the base layer; An alumite layer formed by oxidation progressing from the entire surface of the base material including the base layer and an aluminum alloy or pure aluminum covering the base layer, and having a hardness higher than that of the base material; It is the member made from aluminum alloy characterized by comprising.

  A third aspect of the present invention is the aluminum alloy member according to the first or second aspect, wherein the anodized layer grows so as to surround silicon in the substrate and has an orientation. It is characterized by not. The alumite layer has no orientation because of the growth of the alumite layer in a random direction.

  A fourth aspect of the present invention is the aluminum alloy member according to any one of the first to third aspects, wherein an aluminum alloy or pure aluminum that covers and oxidizes the base layer comprises: It is characterized by remaining as an intermediate layer between the alumite layer.

  A fifth aspect of the present invention is the aluminum alloy member according to the fourth aspect, wherein the intermediate layer has a lower pitting corrosion potential than the base layer. A low pitting potential means that the ionization tendency is base, that is, it is easily oxidized.

  According to the sixth aspect of the present invention, at least a part of the surface of a base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content than the base layer to form a coating layer. An aluminum alloy member manufacturing method comprising forming and subjecting the coating layer to an alumite treatment.

  According to the seventh aspect of the present invention, a coating layer is formed by coating at least part of the surface of a base layer made of an aluminum alloy containing silicon with an aluminum alloy or pure aluminum having a lower silicon content than the base layer. A method for producing an aluminum alloy member comprising: forming and repeating a positive voltage application and charge removal over the entire base layer and coating layer, or performing alumite treatment using a power source having an AC component It is.

  The aluminum alloy member according to the present invention as set forth in claims 1 to 5 and the method for producing the aluminum alloy member according to the present invention as set forth in claims 6 and 7 are used for various vehicle members such as automobiles. The present invention can be widely applied without limitation to fields such as electronic device members such as computer-related members, building members such as building panels, and household appliance members. Among them, it can be suitably used as a member having a sliding surface that requires high hardness, corrosion resistance, wear resistance, and good surface roughness.

  In addition, the present invention according to claim 8 is the aluminum alloy member according to any one of claims 1 to 5, comprising: a cover member and a pump body that are installed opposite to each other with an impeller arranged rotatably. The fuel pump is characterized in that an aluminum alloy or pure aluminum covering the base layer of the base material is formed on at least a sliding surface of the cover member and the impeller in the pump body.

  According to the present invention, as a pre-stage of the alumite treatment, a base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content. Furthermore, since the aluminum alloy film having a low silicon content or the pure aluminum film not containing silicon is oxidized, even if the aluminum is oxidized and the thickness is reduced, the silicon is hardly exposed, and the surface Oxidation proceeds with a smooth surface. Therefore, the alumite layer produced without being inhibited by silicon can form a high-quality alumite layer that has a uniform film thickness, becomes dense and has a smooth surface, and is excellent in hardness, corrosion resistance, wear resistance, and the like. Therefore, it can be suitably used as a member for which good surface smoothness (surface roughness), wear resistance, and the like are desired. Moreover, since the alumite layer is formed from an aluminum alloy or pure aluminum having a lower silicon content than the base layer, it is not necessary to lengthen the alumite treatment time in order to ensure good surface smoothness.

  At this time, if an alumite layer is formed on the surface of the base layer in addition to the film made of an aluminum alloy or pure aluminum, a portion that requires good surface smoothness (surface roughness), wear resistance, etc. In addition, since a certain hardness and corrosion resistance can be imparted, the quality of the aluminum alloy member can be further improved.

  If the alumite layer grows so as to surround the silicon in the base material, a high-quality alumite layer can be formed even with a base layer having a relatively high silicon content. In addition, if the alumite layer does not have orientation, that is, grows in a random direction, the pores that become the infiltration paths of moisture and the like are branched, so that the corrosion resistance can be further improved.

  Since the aluminum alloy or pure aluminum covering the base layer has a lower silicon content than the aluminum alloy constituting the base layer, the aluminum alloy or pure aluminum covering the base layer is generally The hardness is lower than that of the aluminum alloy constituting the base layer. If the aluminum alloy or pure aluminum that covers and oxidizes the base layer remains as an intermediate layer between the base layer and the anodized layer, the intermediate layer between the high-hardness anodized layer and the moderately hard base layer is used. In addition, a three-layer structure in which an intermediate layer having a slightly low hardness is formed. As a result, the intermediate layer functions as an impact absorbing layer (damper layer), and is particularly suitable for a member that requires high impact resistance against cavitation and the like. Cavitation is a reduction in which a low pressure portion is vaporized in a fluid such as water flowing at high speed to form a vapor cavity, and the cavity collapses and disappears in a very short time. It is said that the impact force due to the collapse of the cavity ranges from several MPa to several GPa.

  If the intermediate layer has a lower pitting potential than the base layer, that is, a base composition with a tendency to ionize, holes (pinholes) are generated in the anodized layer due to external impacts, etc., and the substrate is corroded from there. Even in such a case, the base layer can be effectively protected because the intermediate layer is so-called sacrificial corrosion that is preferentially corroded over the base layer as in the anode type plating.

  Repeated application of positive voltage and charge removal, or alumite treatment using a power supply having an alternating current component, grows so as to surround silicon in the substrate and forms an alumite layer having no orientation. Therefore, a good quality alumite layer can be formed on the base layer having a certain silicon content.

  The aluminum alloy member according to the present invention is used as a cover member and a pump body that are installed opposite to each other with an impeller arranged rotatably in a fuel pump, and has high hardness, corrosion resistance, wear resistance, and impact resistance. If an aluminum alloy or pure aluminum with a low silicon content that covers the base layer is formed on the sliding surface with the impeller, which requires high performance and good surface roughness, the alumite layer formed from this will be the base Since each of the above properties is superior to an alumite layer formed from a layer, it is possible to obtain a fuel pump with high performance in which deterioration over time is suppressed. In other words, the cover member and pump body of the fuel pump are members that are directly affected by friction due to the rotation of the impeller and cavitation when pumping up the fuel, but the part is formed from an aluminum alloy or pure aluminum with a low silicon content. If the alumite layer is provided, it can sufficiently withstand the friction with the impeller and the impact of cavitation. At this time, a minimum high impact resistance is required by forming an aluminum alloy or pure aluminum having a lower silicon content than the base layer on at least the sliding surface of the cover member and the impeller of the pump body. Since only the surface is efficiently protected, the production cost can be reduced.

(First embodiment)
Embodiments of an aluminum alloy member and a method for manufacturing the same according to the present invention will be described below with reference to the drawings. FIG. 1 is a process diagram showing a manufacturing process of an aluminum alloy member according to the first embodiment of the present invention. FIG. 2 is an explanatory view showing a state in which the intermediate layer is sacrificially corroded.

  The aluminum alloy member 1 according to the first embodiment covers a base layer 10 made of an aluminum alloy containing silicon and at least a part of the surface of the base layer 10, and has a lower silicon content than the base layer 10. From the base material 12 of the structure in which the intermediate | middle layer 11 which consists of aluminum alloy or a pure aluminum was formed as needed, and the alumite layer 13 formed by oxidizing the membrane | film | coat layer 11a which coat | covers the base layer 10 of the base material 12 (See FIG. 1C). The intermediate layer 11 is formed if necessary. The intermediate layer 11 is a layer that remains in the coating layer 11a without being oxidized, and the intermediate layer 11 is not formed by oxidizing all of the coating layer 11a. This is because there are cases.

[Base layer 10]
The aluminum alloy containing silicon that constitutes the base layer 10 is not particularly limited, and preferred examples include aluminum cast products and aluminum die cast products that are standardized by JIS standards. Aluminum alloys other than JIS standards can also be used. However, since the castability is poor when the silicon content is low, an aluminum alloy having a certain silicon content is desired in consideration of ensuring good castability and increasing productivity. The silicon content is 4.0 to 25% by mass, preferably 7.5 to 18% by mass, more preferably 9.0 to 12.0% by mass. Examples of such aluminum alloys include aluminum cast products (JIS H5202) such as AC2A, AC2B, AC3A, AC4A, AC4B, AC4C, AC4D, AC8A, AC8B, AC8C, AC9A, AC9B, and aluminum die cast products (JIS H5302). ADC1, ADC3, ADC10, ADC12, ADC14, AlSi9, AlSi12 (Fe), AlSi10MG (Fe), AlSi8Cu3, AlSi9Cu3 (Fe), AlSi9Cu3 (Fe) (Zn), AlSi11Cu2 (Fe), AlSi11Cu3 (Fe), AlSi12Cu1 (Fe), AlSi17Cu4Mg, and the like. Among these, ADC12 which is a general-purpose aluminum die-cast product having excellent castability and low material cost is most preferable.

[Intermediate layer 11]
In addition to pure aluminum, an aluminum alloy can also be used for the intermediate layer 11 that covers the base layer 10. The aluminum alloy constituting the intermediate layer 11 is not particularly limited as long as the silicon content is lower than that of the base layer 10, and is not limited to non-silicon type such as Al—Mg type or Al—Mg—Mn type. An aluminum alloy, an aluminum plate or a laminated plate specified in JIS H4000, an aluminum die-cast product having a low silicon content, or an aluminum cast product can be used. In particular, in order to suppress the influence of silicon as much as possible, an aluminum die-cast product or an aluminum cast product has a silicon content of 1.0% by mass or less, preferably 0.75% by mass or less, more preferably 0.6% by mass or less. To do. This is because if the silicon content exceeds 1.0% by mass, the alumite layer has a porous structure and the hardness is rapidly lowered. The lower limit of the silicon content is 0% by mass. Examples of aluminum die cast products having a silicon content of 1.0% by mass or less include ADC5 and ADC6, and examples of aluminum cast products having a silicon content of 1.0% by mass or less include AC1B, AC5A, and AC7A. it can. Of course, you may use the aluminum alloy outside a JIS specification by which silicon content was adjusted to said range. Such an aluminum alloy or pure aluminum generally has a lower hardness than an aluminum alloy for the base layer 10 because of its low silicon content.

The aluminum alloy also contains copper (Cu). This copper is also present in the aluminum alloy as an intermetallic compound of copper and aluminum (CuAl ₂ ), and can be a factor that inhibits alumite together with eutectic silicon. Therefore, in order to further improve the alumite property, it is preferable to adjust the copper content at the same time as the silicon content of the intermediate layer 11, specifically 2.0 mass% or less, preferably 1.5 mass%. The following. The lower limit of the copper content is also 0% by mass. Examples of aluminum die cast products having a silicon content of 1.0% by mass or less and a copper content of 2.0% by mass or less include ADC5 and ADC6, and examples of aluminum cast products include AC7A. Can do. Of course, also in this case, you may use the aluminum alloy outside a JIS specification by which silicon content and copper content were adjusted to said range.

  Further, as shown in FIG. 2A, when a pinhole or the like is generated in the alumite layer 13 due to an external impact or the like and the base material 12 is corroded from the pinhole, the anode type as shown in FIG. The intermediate layer 11 has a lower ionization tendency than the base layer 10, that is, has a lower pitting potential so that the intermediate layer 11 can take the form of sacrificial corrosion that preferentially corrodes the base layer 10 like plating. A composition is preferred.

  As described above, various materials that can be applied to the base layer 10 and the intermediate layer 11 constituting the base material 12 in the present embodiment are listed. Of these, what is the combination of the base layer 10 and the intermediate layer 11? It may be a combination.

[Production method]
Next, the manufacturing method of the aluminum alloy member of the first embodiment and the state of each layer in each step will be described with reference to FIG. The shape of the aluminum alloy member shown in FIG. 1 is a conceptual illustration of the aluminum alloy member and the manufacturing method thereof in the present invention, and is not limited to this. The actual shape depends on the member to be applied. Needless to say, it is different in various ways.

  First, an aluminum alloy constituting the base layer 10 of the substrate 12 is formed into a predetermined shape by a known method such as casting or high pressure casting. At this time, as shown in FIG. 1A, the base layer 10 is in a state in which eutectic silicon 16 and sometimes an intermetallic compound of copper and aluminum are scattered in the primary crystal aluminum 15.

  Next, as shown in FIG. 1B, an aluminum alloy or pure aluminum with a low silicon content is applied to the surface of the base layer 10 by physical vapor deposition (PVD) such as vacuum vapor deposition, sputtering, ion plating, thermal spraying, wet plating, etc. The coating is performed by a known method. At this time, the entire surface of the base layer 10 may be covered, or only a part of the surface limited to a portion where particularly high hardness is required, but in consideration of production cost, the portion to be covered is covered only in a necessary portion. It is preferable. In FIG. 1, only the upper surface of the base layer 10 is covered. The thickness of the coating layer 11a covering the base layer 10 is preferably 1 to 100 μm, more preferably 3 to 50 μm, and still more preferably 5 to 20 μm. A portion of the coating layer 11 a that covers the base layer 10 that remains without being oxidized becomes the subsequent intermediate layer 11. If the thickness of the coating layer 11a is less than 1 μm, the thickness of the alumite layer 13 is also reduced, so that the oxide coating effect cannot be expressed effectively. Even when the coating layer 11a is left as the intermediate layer 11, the thickness is reduced. The damper effect cannot be effectively secured. If the thickness of the coating layer 11a is greater than 100 μm, an excessive oxide film effect due to the alumite layer 13 and a damper effect due to the intermediate layer 11 will result in wasted cost.

  Next, the coating layer 11a is anodized by a known direct current electrolysis method. At this time, the base layer 10 may also be anodized, but when the base layer 10 is not anodized, a sealing material may be disposed on the surface of the base layer 10. As shown in FIG. 1C, the coating layer 11a is oxidized and gradually becomes a thin film by the alumite treatment, and at the same time, the alumite layer 13 made of aluminum oxide is generated on the surface of the substrate 12. At this time, since the coating layer 11a contains almost no silicon or copper that inhibits the formation of the anodized layer 13, the high-quality anodized layer 13 having a uniform film thickness, a dense (non-porous) surface and a smooth surface can be formed. It is possible to obtain an aluminum alloy member that is excellent in hardness, corrosion resistance, wear resistance, and the like. When the film thickness of the coating layer 11a decreases by 1 μm, an alumite layer 13 having a film thickness of 2 μm is generated. That is, the relationship of the film thickness over time between the coating layer 11a and the alumite layer 13 during the alumite treatment has a relationship of −1: 2. Based on this relationship, the thickness of the coating layer 11a, the alumite treatment time, the thickness of the intermediate layer 11 and the alumite layer 13 and the like may be appropriately adjusted while considering the hardness and corrosion resistance required by the member to be applied. The alumite treatment may oxidize the entire coating layer 11a, or may be stopped in a state where the coating layer 11a remains at a predetermined thickness, and this may be used as the intermediate layer 11.

  By comprising as mentioned above, since an alumite layer is precise | minute, a film thickness is uniform and the surface is smooth, the member made from aluminum alloy excellent in hardness, corrosion resistance, and abrasion resistance can be obtained. Further, since the intermediate layer 11 has a lower silicon content than the base layer 10, the intermediate layer 11 has lower hardness and pitting potential than the base layer 10. Therefore, since the intermediate layer 11 exhibits a damper effect, it has excellent impact resistance, and even if pinholes or the like are generated in the anodized layer 13 as shown in FIG. 2A, the intermediate layer is shown in FIG. 2B. The base layer 10 can be reliably protected by the sacrificial corrosion of 11.

(Hardness, corrosion resistance, surface roughness measurement test)
The hardness, corrosion resistance, and surface roughness in each of Examples 1 to 4 and Comparative Example 1 manufactured according to the first embodiment of the present invention were measured and compared. In Examples 1 to 4, a plate-like base layer of 60 × 80 × 1 mm was produced by high pressure casting with ADC 12, and an aluminum alloy or the like shown in Table 1 was coated to a thickness of 10 μm by ion plating. Produced. The contents of Si and Cu in Table 1 are reference values in each aluminum alloy and the like constituting the coating layer. By subjecting this base material to oxalic acid alumite treatment by direct current electrolysis, the coating layer was oxidized to form an alumite layer, and each property of the alumite layer was measured. The thickness of the intermediate layer (coating layer) at this time was 5 μm, and the thickness of the alumite layer was 10 μm. Moreover, the comparative example measured the property at the time of forming a 10-micrometer-thick alumite layer without anodizing, without coat | covering with a membrane | film | coat layer. The measurement results are shown in Table 2. The hardness was evaluated by Vickers hardness, the corrosion resistance was measured by a salt spray test specified in JIS Z2371, and the surface roughness was measured by a ten-point average roughness specified in JIS B0601.

  As is apparent from Table 2, the alumite layer (Example 1 to Example 4) made of an aluminum alloy or the like having a low silicon content and copper content is an alumite layer made of an aluminum alloy having a silicon content of about 11% by mass (comparison). It can be seen that the hardness and corrosion resistance are dramatically improved as compared with Example 1), and the surface roughness of each example is better. Comparing each example, pure aluminum not containing silicon or the like (Example 2) was slightly inferior in hardness to the other examples. Therefore, it is understood that it is preferable to appropriately contain other metals as long as the corrosion resistance and the surface roughness are not affected.

(Hardness change measurement test by Si content)
Next, it was measured how the difference in the silicon content in the aluminum alloy affects the hardness of the anodized layer. The test piece used at this time was the same base layer as in Examples 1 to 4 above, but the aluminum content was changed stepwise while keeping the content of copper, magnesium, etc. consistent with the ADC6 standard. The Vickers hardness of an alumite layer having a thickness of 10 μm when this was coated with an alloy and anodized was measured. The result is shown in FIG. In FIG. 3, the silicon content shown on the horizontal axis is mass%.

  FIG. 3 shows that the Vickers hardness of the anodized layer tends to decrease with increasing silicon content. If it sees in detail, if silicon content is 0.6 mass% or less, the hardness of an alumite layer will be substantially constant. When the silicon content exceeds 0.6% by mass and reaches 0.75% by mass, the hardness reduction of the alumite layer is almost negligible. When the silicon content exceeds 0.75 mass% and reaches 1.0 mass%, the hardness of the anodized layer gradually decreases, and when the silicon content exceeds 1.0 mass%, the hardness of the anodized layer decreases rapidly. ing. This is because as the silicon content increases, the exposed surface area of the eutectic silicon substrate due to the progress of oxidation increases, and the alumite layer becomes a porous structure and its hardness decreases. The larger the exposed surface area of the eutectic silicon substrate, the greater the influence on the formation of the anodized layer. In particular, when the silicon content is 1.0% by mass or more, the hardness of the anodized layer decreases in a quadratic curve. Will go. Further, it has been empirically found that a member requiring high impact resistance due to cavitation or the like has no practical problem if the Vickers hardness is at least 420 or more. In view of the above points, it was found that the silicon content of the coating layer should be at least 1.0% by mass or less.

(Pitting corrosion potential measurement test)
Next, the pitting corrosion potential of other aluminum alloys that can be used as the intermediate layer in addition to the intermediate layer used for the base layers used in Examples 1 to 4 was measured. The pitting corrosion potential was measured by an electrochemical measurement method specified in JIS G0577. The results are shown in Table 3. The reason why the pitting corrosion potential of one aluminum alloy has a width is that the pitting corrosion potential changes depending on the processing temperature.

  As is clear from Table 3, the pitting corrosion potential of the intermediate layer was lower than that of the base layer. From these results, if these aluminum alloys are used as an intermediate layer, even if pinholes or the like are generated in the anodized layer, the intermediate layer is sacrificed to be corroded in preference to the base layer. Protection can be achieved.

  Next, referring to FIG. 4 and FIG. 5, the aluminum alloy member described above is a fuel pump member that is mainly installed in the fuel supply path of the automobile, and is installed in an opposing manner with the impeller 32 interposed therebetween. An embodiment applied to the cover member 31 and the pump body 33 that have been made will be described. However, it is not limited to this, The aluminum alloy member which concerns on this invention can also be applied as another member. FIG. 4 is a partially cutaway side view of a fuel pump provided with an aluminum alloy member according to the present invention. FIG. 5 is a perspective view of the cover member 31, the impeller 32, and the pump body 33, illustrating the relative positional relationship between the cover member 31, the impeller 32, and the pump body 33.

  In FIG. 4, the fuel pump 20 is made of a metal pump housing 21 having a substantially cylindrical shape, an electric motor portion 22 disposed on the upper portion of the pump housing 21, and an aluminum die cast attached to the lower end portion of the pump housing 21. The pump unit 23 is disposed via a cover member 31. The fuel pump 20 is installed substantially vertically in the interior space of the fuel tank of the automobile.

  The drive shaft 25 of the rotor 24 in the electric motor unit 22 is rotatably supported by the cover member 31 via a bearing 26. A synthetic resin impeller 32 is engaged with the lower end of the drive shaft 25. The impeller 32 has a substantially disk shape and has a plurality of blade grooves 40 (see FIG. 5) on the outer peripheral edge thereof.

  A pump body 33 made of aluminum die casting is fixed to the lower end portion of the pump housing 21 together with the cover member 31 by caulking the lower end edge of the pump housing 21. An impeller 32 is rotatably accommodated between the cover member 31 and the pump body 33.

  The cover member 31 and the pump body 33 are formed with a groove 41 that forms a substantially C-shaped pump chamber 35 along the outer periphery of the impeller 32 (see FIG. 5). Although not shown in the cross section in FIG. 4, the pump chamber 35 communicates with an inlet port 36 formed in the pump body 33. A filter (not shown) is provided below the inlet port 36. The filter is brought into contact with the bottom of the fuel tank, and the fuel pump 20 is attached to the fuel tank in the state shown in FIG. The pump chamber 35 communicates with the internal space 21 a of the pump housing 21 through an outlet port (not shown) formed in the cover member 31.

  As the electric motor unit 22 is driven, the impeller 32 rotates together with the drive shaft 25. Then, a pressure increasing action is generated in the pump chamber 35, whereby the fuel in the fuel tank is sucked into the pump chamber 35 from the inlet port 36. The fuel is pressurized while flowing through the pump chamber 35, and then pumped from the outlet port to the internal space 21 a of the pump housing 21.

  And in 1st Embodiment, as FIG.4 and FIG.5 shows well, the whole facing surface side with respect to the impeller 32 in the cover member 31 and pump body 33 made from aluminum die-casting, ie, the sliding surface of the impeller 32, The coating layer 11a is coated on the surface of the groove 41 or the central recess 42 formed on the sliding surface, and anodizing is performed so that a part of the coating layer 11a remains as the intermediate layer 11. Layer 13 is formed. Therefore, the cover member 31 and the pump body 33 can be made more resistant to wear due to sliding of the impeller 32 and to the impact caused by cavitation generated in the fuel in combination with the damper function of the intermediate layer 11. A fuel pump with few failures can be obtained. Moreover, since the alumite layer 13 produced | generated from the film layer 11a which consists of aluminum alloy or pure aluminum with less silicon content than the base layer 10 has favorable surface smoothness, the danger that vapor lock will arise is also reduced. .

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the previous first embodiment, only the coating layer 11a covering the base layer 10 is subjected to the alumite treatment by the conventional method, whereas in the second embodiment, the base layer 10 and the coating layer 11a are included. Alumite treatment is applied to the entire surface of the substrate 12, and the alumite treatment is not a direct current method as in the prior art. Specifically, a positive voltage is applied and charge removal is repeated, or a power source having an alternating current component is used. Attention is paid to what is going on. Others are the same as those in the first embodiment, and the following description will focus on the characteristic points of the second embodiment.

[Anodizing method]
The alumite treatment in the second embodiment is similar to the conventional general method in that the treatment is performed by an alumite treatment apparatus including an electrolytic bath and a power source, but the application of a positive voltage and the removal of charges are repeated. Or the point which uses the power supply which has an alternating current component differs from the conventional general method. 7 and 8 show an example of the alumite processing apparatus 50. FIG. An alumite treatment apparatus 50 shown in FIGS. 7 and 8 includes an electrolytic bath 51 made of a known treatment solution such as sulfuric acid, oxalic acid, and phosphoric acid, and a power source that repeats the application of positive voltage and the removal of charges, or has an AC component. And a pair of left and right cathode plates 53 arranged in an opposing manner in the electrolytic bath 51, an anode wire 54 connecting the cathode side of the power source and the cathode plate 53, and a pair of left and right cathode plates 53, and an oxidation treatment. And the anode electric wire 55 that connects the anode side of the power source and the substrate 12. The base member 12 which is a member to be treated is attached as an anode in the electrolytic bath 51, and this is anodized, whereby the aluminum alloy member 1 of the present invention having the alumite layer 13 formed on the surface thereof is obtained.

  The alumite treatment apparatus 50 shown in FIG. 7 uses a power supply having an AC component, and uses an AC / DC superimposed power supply 57 that performs AC / DC superimposed electrolysis processing in which an AC power supply 57a and a DC power supply 57b are connected in series. The AC / DC superimposed power source 57 supplies positive charges to the substrate 12 and performs anodization in a very short time, while releasing the charges accumulated at the interface of the alumite layer 13 formed during the alumite treatment in a very short time. Can do. Further, the alumite treatment apparatus 50 shown in FIG. 8 uses a power source that repeatedly applies a positive voltage and removes a charge, and an anodizing DC power source 58a, a charge discharging DC power source 58b, and an anodizing DC power source 58a. And a DC power source 58b for charge discharge. The power source 58 includes a switch 58c that switches between the DC power supply 58b and the charge discharge. The switch 58c can switch between plus voltage application and charge removal. When applying a positive voltage and a negative voltage using an AC power supply or an AC / DC superimposed power supply, the energizing time for one positive voltage application is in a range of 25 μs to 100 μs, a frequency of 5 kHz to 20 kHz, and a duty ratio of 40 to 60%. What is necessary is just to adjust suitably. Note that the duty ratio is a ratio of a time during which a current is passed per cycle.

[Formation of anodized layer]
Next, the mechanism by which an alumite layer is formed when the application of a positive voltage and the removal of electric charge are repeated, or when an alumite treatment is performed using a power supply having an AC component will be described with reference to FIG. Since the case where the alumite layer 13 is formed on the surface of the base layer 10 having a high silicon content will be described as an example, FIG. 9 shows a coating layer 11a made of an aluminum alloy or pure aluminum covering the base layer 10. Omitted. Fig.9 (a) shows the state of the base material 12 before anodizing. As described above, the eutectic silicon 16 and the like are interspersed in the primary crystal aluminum 15 in the base layer 10.

  When a positive application is applied to the base material 12 from the state shown in FIG. 9A, the aluminum 15 of the base layer 10 is dissolved from the surface side, and the dissolved aluminum 15 is combined with oxygen in the electrolytic solution, As shown in FIG. 9B, an alumite layer 13 a made of an oxide film is generated on the surface of the aluminum 15. This anodized layer 13a is an insulator. Simultaneously with the generation of the alumite layer 13a, electric charges are stored at the interface between the aluminum 15 as a conductor and the alumite layer 13a as an insulator. As described above, the accumulation of electric charges at the interface between the alumite layer 13a and the base layer 10 makes it easier for aluminum to be dissolved and oxidized by electrolysis, and the thickness of the alumite layer 13a is first increased at a portion where it is likely to be generated. Become thicker. In places where silicon is present and the anodized layer 13a is difficult to be generated, the opportunity for dissolution of aluminum by electrolysis is lost, the growth of the anodized layer 13a is slow, and the film thickness becomes thin. Therefore, at this stage, the thickness of the alumite layer 13a partially varies.

  Next, once the positive application is stopped and a short circuit of the pole or a negative voltage is applied, the charges accumulated at the interface between the alumite layer 13a and the base layer 10 are removed. In this state, when positive application is performed again for a short time, the thick portion of the alumite layer 13a generated earlier is an insulator, and once the charge is removed, Electrolysis is difficult to proceed. On the other hand, in the portion of the anodized layer 13a that is thin due to the presence of silicon, charges are quickly accumulated, so that the formation of a new anodized layer 13b proceeds more easily than the thick portion. Therefore, as shown in FIG. 9C, a new alumite layer 13b is generated so as to fill the unevenness of the surface of the previously formed alumite layer 13a and to surround silicon. When the positive application is once stopped and the positive application is performed again after short-circuiting the poles in this way, a phenomenon occurs in which the growth direction of the alumite layer 13 changes or branches. When this phenomenon is repeated again, as shown in FIG. 9 (d), a new anodized layer 13c is generated so as to further surround silicon, and new anodized layers are sequentially generated by repeating this phenomenon. Therefore, the alumite treatment may be finished when the desired film thickness is reached. Ultimately, the dense and uniform alumite layer 13 is formed so as to surround silicon. That is, the growth of the alumite layer 13 is not inhibited by the presence of silicon.

  9 illustrates the case where the alumite layer 13 is generated on the surface of the base layer 10 in which a relatively large amount of eutectic silicon 16 and the like are dispersed in the primary crystal aluminum 15, but the silicon content is small. Even on the surface of the coating layer 11a made of pure aluminum containing no aluminum alloy or silicon, the alumite layer 13 is generated by the same mechanism. However, in this case, the surface of the anodized layer 13 is generated in a smooth state from the beginning because the presence of silicon is small, the film thickness of the anodized layer 13 is more uniform, and the surface smoothness is better. Moreover, since there is little silicon content, it is not necessary to carry out an alumite process until the alumite layer 13 surrounds silicon reliably, and can shorten processing time. This is also convenient when it is desired to leave the coating layer 11a as the intermediate layer 11.

  Thus, the alumite layer 13 formed by repeatedly applying a positive voltage and removing a charge or using a power source having an alternating current component grows in a random direction with respect to the surface of the substrate 12 and is oriented. Does not have sex. Therefore, even the anodized layer 13 generated from the base layer 10 can be expected to have the following effects. That is, by growing in a random direction, resistance to moisture that has entered the portion where the direction changes (where bending occurs) can be prevented, and moisture can be prevented from proceeding to the substrate 12. In addition, the depth (length) of the pores becomes greater than the thickness of the alumite layer 13 due to the complicated path, so that the time for moisture to penetrate into the substrate 12 can be delayed. Furthermore, if the pores are also oriented in a random direction, it is possible to prevent a large amount of water from entering the pores once by the pressure in one direction. Therefore, rust prevention treatment such as sealing treatment is not always necessary.

  Therefore, if the aluminum alloy member 1 in the second embodiment is used as the cover member 31 and the pump body 33 of the fuel pump as in the first embodiment, a higher quality fuel pump can be obtained. Can do. Specifically, on the entire surface of the cover member 31 and the pump body 33 facing the impeller 32, that is, on the surface of the sliding surface of the impeller 32 and the concave groove 41 or the central concave portion 42 formed on the sliding surface. The cover member 31 and the pump body 33 are coated so that the coating layer 11a made of an aluminum alloy or pure aluminum having a lower silicon content than the base layer 10 is coated and a part of the coating layer 11a remains as the intermediate layer 11. Alumite treatment is applied to the entire surface. As a result, the surface facing the impeller 32 that requires high surface smoothness, wear resistance and the like is formed from the coating layer 11a having a low silicon content, and is excellent in hardness, corrosion resistance, wear resistance, surface roughness, and the like. The alumite layer 13 having a uniform and dense film thickness is formed, and the alumite layer 13 having a certain hardness and corrosion resistance is also formed on the surface other than the surface facing the impeller 32. And a fuel pump with few failures. The other parts are the same as those in the first embodiment, and the same members are denoted by the same reference numerals and the description thereof is omitted.

(Corrosion resistance, surface roughness measurement test)
The corrosion resistance and surface roughness of Example 5 manufactured according to the second embodiment of the present invention and Comparative Example 2 which is a DC electrolytic product were measured and compared. In Example 5, a base material in which a flat base layer of 60 × 80 × 1 mm was fabricated by high pressure casting with ADC12 was fabricated. That is, the film layer is not formed in Example 5. The base material was anodized with a sulfuric acid bath having a concentration of 300 g / l by high frequency to oxidize the entire surface of the base material to form an alumite layer having a thickness of 10 μm, and each property of the anodized layer was measured. The high frequency at this time was set to a frequency of 5 kHz, an average current density of 2 A / dm ² , and a duty ratio of 50%. On the other hand, Comparative Example 2 was anodized under the same conditions as in Example 5 except that the same base material as in Example 5 was used and a direct current was used. The measurement results are shown in Table 4. The corrosion resistance was measured by the salt spray test specified in JIS Z2371, and the surface roughness was measured by the arithmetic average roughness specified in JIS B0601.

  As is clear from Table 4, the anodized layer (Example 5) by high frequency electrolysis is better in both corrosion resistance and surface roughness than the anodized layer by DC electrolysis (Comparative Example 2). Therefore, it can be seen that the quality of the aluminum alloy member can be further improved by forming an alumite layer on the surface of the base layer other than the portion where high surface smoothness and corrosion resistance are required by high frequency electrolysis.

It is process drawing which shows the manufacturing process of the member made from aluminum alloy in 1st Embodiment. It is explanatory drawing which shows the corrosion mechanism of a base material. It is a graph which shows the hardness change of an alumite layer with respect to silicon content. It is a partially broken side view of the fuel pump provided with the member made from aluminum alloy in a 1st embodiment. It is a perspective view of the cover member 31, the impeller 32, and the pump body 33 in 1st Embodiment. It is explanatory drawing which shows the reaction mechanism of the alumite process in 1st Embodiment. It is the schematic which shows the alumite processing apparatus in 2nd Embodiment. It is the schematic which shows another alumite processing apparatus in 2nd Embodiment. It is the schematic explaining the production | generation mechanism of the alumite layer in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum alloy member 10 Base layer 11 Intermediate layer 11a Coating layer 12 Base material 13 Anodized layer 20 Fuel pump 21 Pump housing 22 Electric motor part 23 Pump part 24 Rotor 25 Drive shaft 26 Bearing 31 Cover member 32 Impeller 33 Pump body 36 Inlet port 41 Groove 42 Central recess 50 Anodized processing device 51 Electrolytic bath 53 Cathode plates 57 and 58 Power supply

Claims (8)

A base material in which at least a part of the surface of a base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content than the base layer;
The aluminum is formed by an aluminum alloy or pure aluminum covering the base layer of the base material, which is formed by oxidation progressing from the surface side toward the inside, and is composed of an alumite layer having a hardness higher than that of the base material. Alloy member. A base material in which at least a part of the surface of a base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content than the base layer;
From the alumite layer formed by oxidation progressing from the whole surface of the base material including the base layer and the aluminum alloy or pure aluminum covering the base layer toward the inside, and having a higher hardness than the base material An aluminum alloy member characterized by comprising: The aluminum alloy member according to claim 1 or 2,
The aluminum alloy member is characterized in that the alumite layer grows so as to surround silicon in the substrate and has no orientation. An aluminum alloy member according to any one of claims 1 to 3,
An aluminum alloy member characterized in that an aluminum alloy or pure aluminum which covers and oxidizes the base layer remains as an intermediate layer between the base layer and the alumite layer. The aluminum alloy member according to claim 4,
The aluminum alloy member, wherein the intermediate layer has a lower pitting corrosion potential than the base layer. At least a part of the surface of the base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content than the base layer to form a coating layer,
A method for producing an aluminum alloy member, comprising subjecting the coating layer to an alumite treatment. At least a part of the surface of the base layer made of an aluminum alloy containing silicon is coated with an aluminum alloy or pure aluminum having a lower silicon content than the base layer to form a coating layer,
A method for producing an aluminum alloy member, characterized in that a positive voltage is applied and charge removal is repeated on the entire base layer and coating layer, or an alumite treatment is performed using a power source having an AC component. The aluminum alloy member according to any one of claims 1 to 5, comprising a cover member and a pump body that are installed facing each other with an impeller arranged rotatably.
A fuel pump, wherein an aluminum alloy or pure aluminum covering the base layer of the base material is formed on at least a sliding surface of the cover member and an impeller in the pump body.

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