JP5141968B2 - Manufacturing method of metal parts - Google Patents

Description

The present invention relates to a manufacturing method for manufacturing a metal part in which at least a part of the surface of a substrate made of a high silicon-aluminum alloy is coated with an anodized film.

  For example, in an automobile, an oil pump is used to generate power for circulating oil in an engine or a hydraulic drive system. The oil pump is disposed in a shape having a working chamber, a suction passage and a discharge passage communicating with the working chamber, and a plurality of divided bodies, and is rotatably disposed around the shaft in the working chamber. And a rotor that sucks oil through the suction passage as it rotates and discharges the oil through the discharge passage.

A rear housing that faces the working chamber among the plurality of divided bodies constituting the casing and faces the shaft end of the rotor is formed of an aluminum alloy for reducing the weight of the oil pump, and at least the rotor of the rear housing In order to improve the wear resistance of the surface facing the shaft end of the metal, it has been proposed to coat the surface with an anodized film (see Patent Document 1).
JP 2007-132237 A

  Recently, as an aluminum (Al) alloy forming the rear housing, for example, silicon (Si) is used to increase the strength of the rear housing in order to prevent the rear housing from being distorted in response to the high pressure of the oil pump (for example, 8 MPa → 15 MPa). ) Is being studied to use a high silicon-aluminum alloy containing 1 to 25% by mass. However, in that case, in the conventional anodizing treatment, the surface smoothness of the anodized film formed on the surface of the rear housing is lowered, and the anodized film wears the opposite end of the shaft of the rotor or the like. There is a problem that it is easy to express.

The object of the present invention is to provide a surface of a base material made of a high silicon-aluminum alloy containing silicon at a ratio of 1 to 25% by mass as described above . An object of the present invention is to provide a manufacturing method for manufacturing a metal part having excellent characteristics by coating with an anodized film having no aggressiveness and excellent wear resistance.

When an inventor forms an anodic oxide film by the conventional anodic oxidation process on the surface of the base material which consists of a high silicon-aluminum alloy which contains the said silicon in the ratio of 1-25 mass% , the surface smoothness falls. As a result of examining the cause, the following facts were found. That is, since the high silicon-aluminum alloy has a high silicon concentration, solid phase separation of silicon proceeds during cooling, and a crystalline structure in which a silicon phase is precipitated in an aluminum phase or a continuous phase composed of an eutectic phase of aluminum and silicon, The surface of the substrate exhibits a state in which the silicon phase is exposed in an island shape in the continuous phase.

  However, the conductivity of the continuous phase containing aluminum is different from that of the silicon phase, and the silicon forming the silicon phase is hardly oxidized under conditions suitable for anodizing aluminum in the continuous phase, even if it is oxidized. Since the rate is remarkably small, the anodized film is selectively used in a region where the continuous phase on the surface of the substrate is exposed, particularly in the initial stage of the formation (sometimes abbreviated as “continuous phase region”). grow up.

  When the growth proceeds to some extent, a slight amount of an anodized film is formed even in a region where the silicon phase is exposed (sometimes abbreviated as “silicon phase region”), and the anodized film grown in the continuous phase region is formed in the silicon phase. Grows around the area. Therefore, the anodized film is finally free from large defects corresponding to the silicon phase region (as is well known, the anodized film of aluminum is composed of an active layer in contact with the surface of the substrate and a porous layer thereon. Thus, the porous layer is a continuous film (although it has a porous structure having very fine pores on the order of angstroms).

However, based on the difference in growth rate in the initial stage, the thickness of the anodic oxide film varies greatly between the two regions, resulting in a decrease in surface smoothness.
Therefore, the inventor uses the wrapping of the anodic oxide film from the continuous phase region to the silicon phase region of the surface of the substrate, and particularly the thickness of the anodic oxide film formed between the two regions in the initial stage. We considered making the difference as small as possible. As a result, the current density of the current applied between the ^two electrodes in the initial stage within a few minutes after the start of the anodic oxidation process is 0.35 A / dm ² or less per minute until the predetermined current density is reached from 0 A / dm ^2. It was found that it should be gradually increased at a rate of.

  That is, when the current density is gradually increased at the above rate, in the initial stage, while suppressing the rapid growth of the anodic oxide film in the continuous phase region, the anodic oxide film is also circulated into the silicon phase region, thereby The difference in the thickness of the anodized film formed between the regions can be made smaller than before. Therefore, after the surface of the silicon phase is covered with an anodic oxide film, the entire surface of the substrate is almost uniform in thickness and surface smoothness by continuing the anodizing treatment at a constant current density by normal constant current control. It becomes possible to coat with an excellent anodic oxide film.

Therefore, the present invention provides a metal part in which at least a part of the surface of a base material made of a high silicon-aluminum alloy containing silicon at a ratio of 1 to 25% by mass is anodized and the surface is coated with an anodized film. In the state where the base material is used as an anode and immersed in an electrolytic solution together with a cathode,
(1) a first step of increasing the current density of the current applied between the ^two electrodes from 0 A / dm ^{2 at} a rate of 0.35 A / dm ² or less per minute;
(2) a second step of continuing the anodizing process while maintaining the predetermined current density after the current density reaches a predetermined value;
Then, the surface is coated with an anodized film (claim 1).

  According to the present invention, as the ratio of increasing the current density in the first step is reduced, the thickness of the anodized film formed through the first and second steps can be made uniform and the surface thereof can be smoothed. However, the smaller the rate of increasing the current density in the first step, the longer the treatment required to form the anodic oxide film having a predetermined thickness, and the lower the productivity of metal parts having the anodic oxide film. Tend to.

Therefore, considering the production of a metal part having an anodized film excellent in surface smoothness and the like described above while maintaining the productivity of the metal part, the ratio of increasing the current density in the first step is Even within the range, it is preferably 0.15 A / dm ² or more per minute (Claim 2).
In the second step a current density of 0.8 A / dm ² or more, preferably maintained at a predetermined value of 1.2A / dm ² or less (claim 3). If the current density is less than the above range, it takes a long time to form an anodic oxide film having a predetermined thickness, which may reduce the productivity of metal parts having the anodic oxide film. On the other hand, when the above range is exceeded, the surface roughness of the anodized film becomes large, which may reduce the wear resistance and the performance of the oil pump.

  As a metal part manufactured in the manufacturing method of the present invention, for example, the rear housing (1) of the oil pump (2) described above can be cited, facing the working chamber (6) of the rear housing, and the rotor (3). The surface (25) opposite to the shaft end of the substrate is covered with an anodized film through the first and second steps (claim 4). The alphanumeric characters in parentheses represent corresponding components in the embodiments described later.

FIG. 1 is a cross-sectional view showing a cross section along the direction of the axis 5 of the shaft 4 of a rotor 3 of an oil pump 2 including a rear housing 1 as an example of a metal part manufactured by the manufacturing method of the present invention. FIG. 3 is a side view showing a state where a rear housing 1 is removed from the oil pump 2.
With reference to FIG. 1, an oil pump 2 of this example includes a housing 9 having a working chamber 6, an oil suction passage 7 and a discharge passage 8 communicating with the working chamber 6, and the working chamber 6. A rotor 3 is disposed so as to be rotatable about an axis 5 and sucks oil through the suction passage 7 and discharges it through the discharge passage 8 as the shaft 4 rotates.

The housing 9 is constituted by a plurality of divided bodies in a shape having the above-described parts. That is, the housing 9 includes a front housing (divided body) 11 and a rear housing (divided body) 1 that can be divided by the dividing surface 10. The front housing 11 has a working chamber 6 by recessed from split surface 10. The front housing 11 and the rear housing 1 are sealed by a seal 12 provided on the dividing surface 10. The front housing 11 and the rear housing 1 are fixed to each other by screwing a bolt 15 into a screw hole 13 provided in the front housing 11 through a through hole 14 provided in the rear housing 1.

  A first side plate (divided body) 17 is fitted into the working chamber 6 via a seal 16. The rear housing 1 also functions as a member that sandwiches the rotor 3 from both sides together with the first side plate 17 and is also called a second side plate. A through-hole 18 through which the shaft 4 is inserted from the bottom in the direction of the axis 5 perpendicular to the dividing surface 10 is formed in the center of the front housing 11 in the surface direction of the bottom of the working chamber 6.

  The first side plate 17 includes a surface facing the rotor 3 accommodated in the working chamber 6 and a surface facing the bottom of the working chamber 6 in a state of being fitted in the working chamber 6. A through hole 19 is formed through which the shaft 4 is inserted in communication with the through hole 18. Discharge ports 20 penetrating between the both surfaces are formed in parallel with the through hole 19 at two positions around the through hole 19 and symmetrically across the axis 5.

  An annular discharge recess 21 connected to the discharge port 20 is provided around the through hole 18 at the bottom of the working chamber 6. The discharge port 20 and the discharge recess 21, and a passage 22 formed in the front housing 11 Are connected to form a discharge passage 8. A cylindrical metal bearing 23 that rotatably supports the shaft 4 is disposed in the through hole 18. A seal 24 that seals between the shaft 4 and the front housing 11 is disposed at the opening of the through hole 18 on the opposite side of the working chamber 6.

  A concave surface 26 into which the tip of the shaft 4 is inserted is provided on the facing surface 25 of the rear housing 1 facing the rotor 3. A cylindrical metal bearing 27 that rotatably supports the shaft 4 is disposed in the recess 26. In the rear housing 1, a passage 28 (indicated by a broken line in the drawing) constituting the suction passage 7 is provided. Suction ports 29 (also indicated by broken lines in the figure) for connecting the passage 28 and the working chamber 6 are provided at two symmetrical positions on the opposite surface 25 around the recess 26 with respect to the axis 5. .

The front housing 11 forms the suction passage 7 together with the passage 28 and the suction port 29, and when the oil flowing through the discharge passage 8 is excessive, part of the oil is returned to the suction passage 7 through the bypass passage 30. Passage members 31 and 32 constituting a flow control valve are provided, and a suction cylinder 33 that is an oil inlet is connected to the passage member 32.
Referring to FIGS. 1 and 2, a cylindrical cam ring 34 surrounding the rotor 3 is fitted in the working chamber 6 so as to be sandwiched between the first side plate 17 and the rear housing 1. The inner peripheral surface of the cylinder of the cam ring 34 is a cam surface 35 whose shape in a direction orthogonal to the direction of the axis 5 is an ellipse.

The rotor 3 is fitted into a rotor main body 36 integrally attached to the shaft 4 and a plurality of grooves 37 provided radially from the outer peripheral surface of the rotor main body 36 toward the axis 5 so as to be outside the outer peripheral surface. And a plurality of vanes 38 arranged radially. Each vane 38 is provided so as to be able to be inserted and removed from the groove 37 and is urged radially outward by a hydraulic pressure applied to the vane.
When the shaft 4 is rotated, the vane 38 is urged radially outward by hydraulic pressure, and rotates together with the rotor body 36 while maintaining the state where the tip is in contact with the cam surface 35 of the cam ring 34. The suction ports 29 are provided at two locations corresponding to the chambers 39 and 40 partitioned by the adjacent vanes 38 in the state of FIG. 2 on the facing surface 25 of the rear housing 1. Further, the discharge port 20 is provided at two locations corresponding to the chambers 41 and 42 partitioned by the adjacent vanes 38 in the state of FIG. 2 in the first side plate 17.

  When the shaft 4 is rotated in the direction indicated by the solid arrow in FIG. 2, each chamber 39 partitioned by the vane 38 itself rotates from the suction port 29 toward the discharge port 20, thereby sucking in oil. It can be sucked through the passage 7 and discharged through the discharge passage 8. Further, at this time, the following suction force and discharge force are generated in the respective chambers 39 along with the rotation, thereby preventing the back flow of oil.

Suction force: the suction of sucking oil into the chambers 39, 40 through the suction passage 7 and the suction port 29 by increasing the volume of the chambers 39, 40 to be separated from the suction port 29 based on the shape of the cam surface 35. Force is generated.
Discharge force: Discharge that causes oil to be discharged from the chambers 41 and 42 through the discharge port 20 and the discharge passage 8 by reducing the volume of the chambers 41 and 42 that approach the discharge port 20 based on the shape of the cam surface 35. Force is generated.

The first side plate 17, the cam ring 34, the rotor body 36, and the vane 38 are made of, for example, an iron-nickel-molybdenum-carbon based sintered alloy, particularly an iron-nickel-copper-molybdenum-carbon based sintered body. density was formed by high-density warm die lubrication to increase the strength and wear resistance ρ = 7.25g / cm ³ or more, in particular high-density sintered body of 7.25~7.5g / cm ^3, more The high-density sintered body is formed by a sintered body or the like that has been subjected to carburizing and quenching treatment, that is, vacuum carburizing treatment and subsequent quenching treatment.

The rear housing 1 is manufactured by the metal component manufacturing method of the present invention. That is, the rear housing 1 and the front housing 11, together with the weight of the oil pump 2, in particular for increasing the strength in order to prevent distortion in response to the high pressure of the oil pump (e.g. 8 MPa → 15 MPa), a divorced It is formed of a high silicon-aluminum alloy containing 1 to 25% by mass, preferably about 10 to 20% by mass. Further, the opposed surface 25 of the rear housing 1 facing the shaft end of the rotor 3, that is, the side surface of the rotor main body 36 and the side edge of the vane 38 and in which the both portions are slidably contacted is not shown in order to improve the wear resistance. It is covered with an anodized film.

However, when the rear housing 1 made of the high silicon-aluminum alloy is used as a base material and anodized under normal conditions, the surface smoothness of the anodized film is lowered as described above, and the rotor body 36 And the problem of developing aggressiveness against the vane 38 occurs.
On the other hand, in the present invention, the rear housing 1 as a base is used as an anode, and is immersed in an electrolyte together with a cathode.
(1) a first step of increasing the current density of the current applied between the ^two electrodes from 0 A / dm ^{2 at} a rate of 0.35 A / dm ² or less per minute;
(2) a second step of continuing the anodizing process while maintaining the predetermined current density after the current density reaches a predetermined value;
Then, the surface smoothness of the anodized film can be improved by coating the facing surface 25 with the anodized film.

Therefore, according to the present invention, it is possible to manufacture the rear housing 1 in which the facing surface 25 covered with the anodized film does not have an aggressiveness against the rotor body 36 and the vane 38 and also has excellent wear resistance. .
The smaller the rate of increasing the current density in the first step, the more uniform the thickness of the anodized film formed through the first and second steps, and the smoother the surface. However, the smaller the rate of increasing the current density in the first step, the longer the treatment required to form the anodic oxide film having a predetermined thickness, and the lower the productivity of metal parts having the anodic oxide film. Tend to.

Therefore, considering that the rear housing 1 having an anodized film having excellent surface smoothness and the like is manufactured while maintaining good productivity, the ratio of increasing the current density in the first step is within the above range. It is preferably 0.15 A / dm ² or more per minute, particularly 0.16 to 0.34 A / dm ² per minute. The current density may be unilaterally increased from 0 A / dm ² to a predetermined value, or may be increased stepwise.

Maintaining the current density in the second step, the constant current control by 0.8 A / dm ² or more, 1.2A / dm ² or less, in particular 0.9 A / dm ² or more, the predetermined value of 1.1A / dm ² or less It is preferable to do this. If the current density is less than the above range, it takes a long time to form an anodic oxide film having a predetermined thickness, which may reduce the productivity of metal parts having the anodic oxide film. On the other hand, when the above range is exceeded, the surface roughness of the anodized film becomes large, which may reduce the wear resistance and the performance of the oil pump.

The anodizing treatment can be performed in the same manner as in the prior art except that the current density is controlled through the steps (1) and (2). For example, the rear housing 1 as a base material is preferably subjected to pretreatment such as degreasing prior to being immersed in the electrolytic solution.
The anodic oxide coating only needs to cover at least the opposing surface 25 of the rear housing 1. To selectively cover only the opposing surface 25 with the anodic oxide coating, the other surface of the rear housing 1 must be masked. That's fine. However, in consideration of saving troubles such as masking and improving the wear resistance of the entire surface of the rear housing 1, it is preferable to cover the entire surface of the rear housing 1 including the facing surface 25 with an anodized film.

Lead (Pb), carbon (C) or the like is used as the cathode.
Examples of the electrolytic solution include a sulfuric acid bath, an oxalic acid bath, a chromic acid bath, a phosphoric acid bath, an alkaline bath, and the like, and a sulfuric acid bath is particularly preferable. The liquid temperature of the electrolyte solution is controlled to a certain extent while forming a dense anodic oxide film with as high a hardness as possible and suppressing the selective and rapid growth of the anodic oxide film in the continuous phase region, particularly in the initial stage of formation. In consideration of maintaining the growth rate of the rear housing 1 and maintaining the productivity of the rear housing 1, the temperature is preferably 10 to 40 ° C, particularly preferably 10 to 20 ° C.

The anodic oxide film formed by the anodic oxidation treatment includes an active layer in contact with the surface of the base material, that is, the facing surface 25 of the rear housing 1 and a porous layer thereon, as in the prior art, and the porous layer is angstrom. It has a porous structure with very fine pores of the order.
For this reason, it is expected that oil is held in the through holes of the porous layer to give good lubricity to the rotor body 36 and the vane 38. For example, when the oil pump 2 is used in a high temperature environment such as around the engine of an automobile, in order to prevent seizure between the rear housing 1 and the rotor main body 36 and the vane 38, the through hole is provided with, for example, disulfide. A solid lubricant such as molybdenum (MoS ₂ ) may be impregnated.

In order to improve the surface smoothness, corrosion resistance, etc., the formed anodic oxide film is preferably subjected to sealing treatment such as immersing in water and boiling.
As described above, the surface of the anodized film is required to be as smooth as possible in order to suppress the aggressiveness to the rotor body 36 and the vane 38. Specifically, the ten-point average roughness R defined in Appendix 1 of Japanese Industrial Standard JIS B0601: 2001 “Product Geometrical Specification (GPS) —Surface Properties: Contour Curve Method—Terms, Definitions, and Surface Property Parameters” _{It is preferable} that the ten-point average roughness R _{ZJIS94 of the} anodized film coated on the facing surface 25 finished with _ZJIS94 to 1 μm through the steps (1) and (2) is 3 μm or less. The lower limit of the ten-point average roughness is ideally 0 μm, that is, it is ideal that the surface is completely smooth, but practically it is preferably about 2 μm.

The thickness of the anodized film is 6 to 15 μm, particularly 8 to 10 μm in consideration of imparting good wear resistance to the facing surface 25 of the rear housing 1 while maintaining the productivity of the rear housing 1. Is preferred.
The hardness of the anodic oxide film, considering that sufficient wear resistance is imparted to the facing surface 25 of the rear housing 1, has an internal hardness (hardness at a depth of 1 mm from the surface) of Japanese Industrial Standard JIS. Z2244: 2003 facing surface made of high silicon-aluminum, expressed as Vickers hardness HV0.01 at a test force of 0.09807N, 150, measured by the measurement method defined in “Vickers hardness test—test method” 25, it is preferable that the same Vickers hardness HV0.01 of the surface of the anodized film coated through the steps (1) and (2) is about 200 to 300.

The method for producing a metal part of the present invention is not limited to the production of the rear housing 1 of the oil pump 2 in the example of the drawings described above, but is a high silicon-aluminum alloy containing silicon in a proportion of 1 to 25% by mass . The present invention can be applied to various metal parts manufacturing methods in which at least a part of the surface is coated with an anodized film. At that time, the ten-point average roughness, thickness, hardness, etc. of the surface of the anodized film can be set within a suitable range required for the metal part. In addition, various changes can be made without departing from the scope of the present invention.

Example 1
A flat plate material (length 25 mm × width 25 mm × thickness 5 mm) made of a high silicon-aluminum alloy having a silicon content of 14% by mass was prepared as a base material. The Vickers hardness HV0.01 at a depth of 1 mm from the surface of the high silicon-aluminum alloy forming the plate material was 150. The ten-point average roughness _RZJIS94 of the surface of the plate material was finished to 1 μm.

The plate material is degreased in advance and then connected to the anode of the power supply device and immersed in a sulfuric acid bath together with the lead cathode. First, the current density applied between the electrodes in the first step is changed from 0 A / dm ² to 0. Increased to 1 A / dm ² over 3 minutes at a rate of 333 A / dm ² .
Subsequently, after the current density reaches the predetermined value, the anodization treatment is further performed for a further 37 minutes while maintaining the current density by constant current control, and then the substrate is taken out from the sulfuric acid bath and washed with water. Further, a metal part having a surface coated with an anodized film was manufactured by boiling in water and sealing.

(Example 2)
In the first step, the current density of the current applied between the ^two electrodes is increased from 0 A / dm ² to 1 A / dm ² over 6 minutes at a rate of 0.167 A / dm ² per minute, and then the current density is controlled by constant current control. A metal part whose surface was coated with an anodized film was produced in the same manner as in Example 1 except that the anodizing treatment was further performed for 34 minutes for a total of 40 minutes while maintaining the above.

(Comparative Example 1)
After increasing the current density of the current applied between the electrodes to 1A / dm ² over a period of 1 minute per minute 1A / dm ² from 0A / dm ² in a first step, maintaining the current density by the constant current control However, a metal part having a surface coated with an anodized film was produced in the same manner as in Example 1 except that the anodizing treatment was further performed for 39 minutes for a total of 40 minutes.

(Surface roughness measurement)
The ten-point average roughness _RZJIS94 of the surface of the anodized film of the metal parts produced in Examples 1 and 2 and Comparative Example 1 was measured using a surface roughness meter. The measurement conditions were 6 sections, cut-off value λ _C = 0.8 mm, λ _S = 0.0025 mm, measurement speed: 0.5 mm / sec, and a 10-point average roughness R by applying a Gaussian filter to the measurement results. _ZJIS94 was determined.

(Thickness measurement)
The metal parts manufactured in Examples 1 and 2 and Comparative Example 1 were cut in the thickness direction of the anodic oxide film, and the cut surface was polished by embedding the resin, and then a microphotograph of 400 times was taken. The average value of the measured thickness was determined and used as the thickness of the anodized film. Further, the difference between the maximum value and the minimum value of the ten measured values was determined to evaluate the thickness variation.

(Hardness measurement)
After lapping the surface of the anodized film of the metal parts produced in Examples 1 and 2 and Comparative Example 1, the Vickers hardness HV0.01 was measured.
(Ball-on-plate friction test)
A ball made of bearing steel (SUJ2) having a diameter of 4.76 mm was always brought into contact with the surface of the anodized film of the metal part (plate) manufactured in Example 1 and Comparative Example 1 at one point on the spherical surface. In the state, it was slid so as to draw a circle having a diameter of 20 mm while applying a load of 10 N in the thickness direction of the anodized film. The sliding speed was 0.08 m / s and the sliding distance was 432 m. The sliding was performed in a state where the metal parts and the balls were immersed in PS oil (manufactured by JTEKT Corporation, oil temperature 100 ° C.).

  The surface of the ball after sliding is observed with a stereomicroscope to measure the wear scar radius a (mm). From the wear scar radius a and the ball radius r (= 2.38 mm), the formula (A):

Was used to determine the wear scar depth h (mm).
Next, from the wear mark depth h and the wear mark radius a, the formula (B):

The amount of wear (mm ³ ) is obtained by the above equation, and from the amount of wear, the load (= 10 N), and the sliding distance (= 432 m), the formula (C):

Thus, the specific wear amount (mm ³ / N · m) of the ball serving as an index of the aggressiveness of the anodized film against the mating member was determined. It is shown that the smaller the specific wear amount, the smaller the anodic oxide film is attacking the mating member.
Also, the surface of the plate before and after sliding was compared with the roughness curves measured using a surface roughness meter, and the width b (mm) of the wear mark formed by sliding the ball on the surface of the plate. ) And depth d (mm), and from the above two values, formula (D):

The virtual radius R (mm) of the cross section of the wear scar is obtained by the above equation, and the formula (E):

Was used to determine the angle φ (°) of the virtual fan shape of the wear scar.
Next, from the virtual radius R, the angle φ, the width b, and the depth d, the formula (F):

The amount of wear (mm ³ ) is obtained from the above, and from the amount of wear, the load (= 10 N), and the sliding distance (= 432 m), the plate serving as an index of the wear resistance of the anodized film according to the above equation (C) The specific wear amount (mm ³ / N · m) was determined. It shows that the smaller the specific wear amount, the better the anodized film has its own wear resistance.
The results are shown in Table 1.

From the table, the metal parts of Examples 1 and 2 in which the current density was increased at a rate of 0.35 A / dm ² or less per minute in the first step of the anodizing treatment increased the current density beyond the above range. It was confirmed that the variation in thickness of the anodized film was smaller than that of Comparative Example 1, the surface smoothness was excellent, the aggression against the mating member was not exhibited, and the wear resistance itself was excellent. Further, when Examples 1 and 2 are compared with each other, Example 2 has a tendency that the thickness of the anodized film is lower than that of Example 1, so that the current density in the first step is a ratio of 0.15 A / dm ² or more. It has been confirmed that the increase in the thickness is preferable in that the productivity of metal parts can be improved by forming an anodic oxide film having a sufficient thickness in as short a time as possible.

It is sectional drawing which shows the cross section along the direction of the axis of the axis | shaft of a rotor of the oil pump containing the rear housing as an example of the metal component manufactured by the manufacturing method of this invention. It is a side view which shows the state which removed the rear housing from the oil pump of FIG.

Explanation of symbols

  1: rear housing, 2: oil pump, 3: rotor, 6: working chamber, 25: facing surface.

Claims (4)

For producing a metal part in which at least a part of the surface of a base material made of a high silicon-aluminum alloy containing silicon in a proportion of 1 to 25% by mass is anodized, and the surface is coated with an anodized film In the production method, the substrate as an anode, immersed in an electrolyte together with a cathode,
(1) a first step of increasing the current density of the current applied between the ^two electrodes from 0 A / dm ^{2 at} a rate of 0.35 A / dm ² or less per minute;
(2) a second step of continuing the anodizing process while maintaining the predetermined current density after the current density reaches a predetermined value;
Then, the surface is coated with an anodized film, and the method for producing a metal part is characterized in that: The method of manufacturing a metal part according to claim 1, wherein in the first step, the current density is increased at a rate of 0.15 A / dm ² or more per minute. In the second step, current density 0.8 A / dm ² or more, a manufacturing method of a metal part according to claim 1 or 2 is maintained at a predetermined value of 1.2A / dm ² or less.   A metal part is disposed in a shape having a working chamber, a suction passage and a discharge passage communicating with the working chamber, and a plurality of divided bodies, and is rotatably disposed around the shaft in the working chamber. The rear housing of the oil pump having a rotor that sucks oil through the suction passage and rotates through the discharge passage as it rotates, facing the working chamber in the divided body constituting the housing and facing the shaft end of the rotor The method of manufacturing a metal part according to any one of claims 1 to 3, wherein at least a surface of the rear housing facing the shaft end of the rotor is covered with an anodized film.

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