JP2002060961A - Method for forming chemical film on sintered compact and rare earth metal magnet subjected to chemical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemically treating solution free from chromium harmful for the human body and also having adhesive properties and corrosion resistance equal to those of a chromium film. SOLUTION: In this method for forming a chemical film on a sintered compact by which a chemical film is formed on the surface or the outside surface of a sintered compact, the sintered compact is cleaned or not cleaned with an alkali solution, and then immersed into a chemically treating solution consisting of a zinc compound and an aqueous solution of phosphoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating a surface of a sintered magnet or the like containing a rare earth metal.

[0002]

2. Description of the Related Art Among rare earth metal magnets, in particular, Nd-Fe-
Since the B-based rare earth metal magnet is extremely rustable, a rust is prevented by forming a coating on its surface by plating or chemical conversion treatment. As a method of forming a film by chemical conversion treatment, as described in JP-A-60-63902, a chromate treatment (chromate treatment) is most commonly used from the viewpoint of production cost.

[0003]

In the above-mentioned chromate treatment, hexavalent chromium is contained in the treatment solution and the formed film. It is said that this hexavalent chromium penetrates into the body through the skin after prolonged contact with the human body and accumulates in the body without being excreted. ing. Therefore, the problem of disposal of a processing solution and the problem of disposal of a product subjected to chromate treatment are becoming more important.
Against this background, chromium regulations are set to be enforced in Europe from 2003. Prior to that, there have been many studies on chemical conversion treatments that do not use chromium, and some have already been put to practical use. However, such a case has not yet been found in rare earth metal magnets. With the demand for high performance magnets increasing, the need for rare earth metal magnets will further increase in the future. Accordingly, a first object of the present invention is to provide a chemical conversion treatment solution which does not contain chromium which is harmful to the human body and produces a film having adhesion and corrosion resistance comparable to a chromium film. A second object is to provide a method for applying the chemical conversion treatment liquid to a rare earth metal magnet.

[0004]

In the present invention, the above-mentioned problems are solved by adding zinc oxide, which is a zinc compound, to a phosphoric acid aqueous solution and using a chemical conversion treatment solution to which a trace amount of nitrate ion is added as a reaction accelerator. did. The reason for using this chemical conversion treatment liquid is described below. Phosphate conversion treatment has attracted attention as a non-chromium oxidation conversion treatment for steel materials. The best known of these is zinc phosphate treatment. In this case, excellent corrosion resistance is obtained by depositing a zinc phosphate coating (hopite) insoluble in water. In addition, the iron eluted from the substrate is taken into the coating as phosphophyllite, thereby improving the adhesion of the coating. Rare earth metal magnets such as neodymium-iron-boron magnets also contain iron as a component element like steel materials, and are expected to have excellent corrosion resistance and adhesion by zinc phosphate treatment. In the zinc phosphate treatment, phosphoric acid, zinc oxide,
Nitric acid is both inexpensive and suitable for mass production. For the above reasons, the inventors have applied the zinc phosphate chemical conversion solution to rare earth metal magnets.

Next, the details will be described. The present invention relates to a method for forming a chemical conversion film on a sintered body for forming a chemical conversion film on the surface or the outer surface of the sintered body, comprising washing a sintered body with an alkali solution, or without washing, comprising a zinc compound and a phosphoric acid aqueous solution. Characterized by being immersed in a chemical conversion solution,
Furthermore, the chemical conversion treatment liquid contains 0.05 to 0.20 (mol / l) zinc, and the molar ratio of phosphorus to zinc (P / Zn) is 2.4.
9.5, and a method for forming a chemical conversion coating on a sintered body, wherein the chemical conversion coating is formed on the surface or the outer surface of the sintered body, wherein the sintered body is formed of an acid except nitric acid. After washing with the liquid, the solution contains phosphorus of 0.49 to 1.22 (mol / l), and the molar ratio of phosphorus to zinc (P / Zn) is 2.4 to 1.2.
It is characterized by being immersed in a 5.9 chemical conversion treatment solution.

The present invention also relates to a rare earth metal magnet having a surface or an outer surface coated with a chemical conversion coating by a chemical conversion method, wherein the magnet is washed with an alkali solution or without washing in a chemical conversion solution comprising a zinc compound and an aqueous solution of phosphoric acid. The immersion chemical conversion coating is characterized by containing phosphorus and zinc as main elements.
0.2 (mol / l) of zinc, and the molar ratio of phosphorus to zinc (P / Zn) is 2.39 to 3.18. -T-B based sintered magnet (R is at least one kind of rare earth element including Y, and T is Fe or Fe and Co).

If P / Zn is less than 2.3, zinc oxide cannot be completely dissolved and remains undissolved. Conversely, if it is larger than 3.2, a foaming phenomenon is observed during the treatment, which is considered to be due to the elution of the base material, which lowers the magnetic force and is unsuitable for application to magnets. The higher the phosphoric acid concentration, the better the adhesion of the coating, but the pH of the treatment liquid is 1.0 to 2.0.
An acidity of 0 is preferred. Particularly preferably, it is 1.3 to 1.8.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One example of the chemical conversion treatment process of the present invention will be described below. First, the object to be treated of the rare earth metal magnet was subjected to an alkali degreasing treatment or an acid treatment to clean the surface of the object to be treated and then sufficiently washed with water. As the acid treatment, dilute sulfuric acid or its salt, dilute hydrochloric acid or its salt, or dilute nitric acid or its salt can be used alone or in combination. In the present invention, dilute sulfuric acid solution alone or a combination of dilute sulfuric acid and nitrate was used. For alkaline degreasing,
An aqueous solution containing sodium hydroxide and sodium carbonate as main components was used. After sufficient water washing after the pretreatment, the coating was immersed in a zinc phosphate chemical conversion treatment solution to form a chemical conversion coating. After the treatment, it was sufficiently washed with water and dried at room temperature.

Table 1 shows that the main component composition is Nd: 26.2,
Pr: 5.0, Dy: 0.8, B: 0.97, Co:
3.0, Al: 0.1, Ga: 0.1, Cu: 0.1,
The results of a test on the corrosion resistance of a coating formed on a R-T-B based sintered magnet body of Fe: bal (all wt%) by chemical conversion treatment, and the composition, properties, treatment conditions, etc. of the chemical conversion treatment solution used are as follows. It is shown.

[0010]

[Table 1]

[0011] Of the tests shown in Table 1, those of groups A and B were all pretreated with a 1 vol% sulfuric acid aqueous solution.
Group C was pretreated with a 0.5 wt% aqueous sulfuric acid solution added with sodium nitrate. Group D was 50 g of sodium hydroxide and 50 g of sodium carbonate.
Pre-treated with a solution of
In the group, the pretreatment is omitted, and in the present invention, it is referred to as no cleaning. However, although it is referred to as no cleaning, it includes ultrasonic cleaning with water to the extent that it removes deposits after processing. The corrosion resistance is constant temperature and humidity test (60 ° C, RH 90%, 20
0 hr).

The group A in the table shows the corrosion resistance of the coating film when the concentration of zinc in the chemical conversion treatment solution was fixed at 0.2 (mol / l) and the concentration of phosphorus was changed. The results showed generally good corrosion resistance except for the test No. 1. However, the test No. 2 was best when the phosphorus concentration was 0.49 (mol / l) and the Zn / P molar ratio was 2.39. It showed corrosion resistance. Group B to Group E include the composition of the chemical conversion treatment solution of Test No. 2 which showed the best corrosion resistance in Group A, and set the phosphorus concentration of the chemical conversion treatment solution to 0.4.
This is a test in which the coating was fixed at 9 (mol / l) and the corrosion resistance of the coating when the zinc concentration was changed was tested. In the case of the group C, the corrosion resistance was poor, and red rust was generated in the case of the chemical conversion treatment solutions having all compositions.

D-grooves, that is, those subjected to a pretreatment with an alkaline solution, exhibited good corrosion resistance in all cases, but especially in Test Nos. 14 and 15, ie, when the phosphorus concentration was 0.49.
(Mol / l) and the zinc concentration is 0.15 to 0.20 (mol / l).
1) showed the best corrosion resistance. In the E group, that is, in the case of no washing, the same good corrosion resistance as in the D group was exhibited in all cases.
The one with 0.20 (mol / l) showed the best corrosion resistance.

As a result of EDX analysis of the surface of the object to be treated, phosphorus and zinc as components of the treatment solution were detected in addition to the base components such as neodymium and iron. FIG. 1 corresponds to the group A in Table 1 and shows the change in the amount of EDX of phosphorus and zinc detected on the surface of the chemical conversion coating when the zinc concentration is fixed and the phosphorus concentration is changed. The pretreatment was performed at 40 ° C. for 10 minutes using a 1 vol% sulfuric acid aqueous solution. The amount of detected phosphorus tends to increase as the concentration of phosphoric acid in the processing solution increases. The detected amount of zinc is minimum when the phosphoric acid concentration is 0.98 mol / l. The inconsistent ratio of zinc and phosphorus detection means that not all phosphorus is bound equally to zinc,
This indicates that phosphophyllite was deposited.
Therefore, it is considered that the adhesion of the film is improved as the phosphoric acid concentration is increased. The detected amount of the background component should always take a constant value, but as the phosphoric acid concentration increases, iron decreases and neodymium increases. this is,
This indicates that iron is more soluble in phosphoric acid than neodymium.

FIGS. 2, 3, 4 and 5 show B, C,
This corresponds to groups D and E, and shows the results of EDX analysis of phosphorus and zinc on the surface of the chemical conversion coating when the zinc concentration is changed while the concentration of phosphorus in the treatment liquid is kept constant. The processing conditions are 60 ° C. for 3 minutes. When pickling is performed as a pretreatment, the amounts of detected phosphorus and zinc increase with the zinc concentration. However, the zinc concentration was 0.102 mol / l, which was the maximum, in the cases without alkali degreasing and pretreatment.

FIGS. 6 to 10 show EDX analysis results of iron and neodymium in the vicinity of the chemical conversion coating corresponding to FIGS. 1 to 5, respectively. As for the detection amounts of the base iron and neodymium, the iron detection amount decreases and the neodymium detection amount increases as the zinc concentration increases, as in the case where the phosphorus concentration increases. Also, looking at the ratio of the detected amount of iron and neodymium at the same concentration, the detected amount of neodymium when pickling was lower. Therefore, it can be seen that neodymium is more soluble in sulfuric acid.

From the above results, from the viewpoint of the corrosion resistance of the coating film, the most preferred chemical conversion treatment composition has a phosphorus concentration of 0.49 (mol / l), a zinc concentration of 0.154 (mol / l), Is 1.46, which means that the pretreatment may be other than an acidic aqueous solution containing nitric acid. The processing temperature is preferably 60 ° C. Even if this temperature fluctuates somewhat, the properties of the film are not affected, but if the liquid temperature is low, the film formation rate is slowed, and there is a risk of oxidation. In addition, when the temperature increases, the liquid evaporates violently, making it difficult to manage the liquid. Considering the time suitable for mass production, the processing time is most preferably about 3 minutes.

Table 2 shows the RTs used in the tests shown in Table 1.
FIG. 2 shows the results of tests of the demagnetization rate and the thermal demagnetization rate after each pretreatment of a -B rare earth magnet. The materials in Table 2 indicate those that have not been subjected to pre-treatment or chemical conversion treatment. The pre-treatment includes a 1 vol% sulfuric acid aqueous solution, a 0.5 wt% sulfuric acid aqueous solution containing sodium nitrate, and sodium hydroxide 5
Washing was performed using an aqueous solution in which 0 g and 50 g of sodium carbonate were dissolved in 1000 ml of water. Hereinafter, these are referred to as pre-processing, pre-processing, and pre-processing in order for convenience. The demagnetization rate in Table 2 indicates the flux reduction rate of the sample after each treatment with respect to the sample not subjected to the pretreatment and the chemical conversion treatment (corresponding to the material in Table 2), and the thermal demagnetization rate indicates the sample immediately after the pretreatment. 3 shows the flux reduction rate of the sample after heat treatment (85 ° C., 2 hours).

[0019]

[Table 2]

Table 3 shows the RTs used in the tests shown in Table 1.
FIG. 2 shows the results of tests of the demagnetization rate and the thermal demagnetization rate of each of the -B rare earth magnets after each chemical conversion treatment. In the chemical conversion treatment solution, the phosphorus concentration in the test shown in Table 1 was fixed at 0.49 (mol / l), and the zinc concentrations were 0.20 and 0.1, respectively.
5, 0.05 were used, and nitric acid was added as a reaction accelerator. Hereinafter, these are referred to as chemical conversion treatment I and chemical conversion treatment II for convenience. The chemical conversion solution used for the chemical conversion treatment II is actually a solution obtained by dissolving 10 ml of phosphoric acid, 3.75 g of zinc oxide, and 3 ml of nitric acid in 287 ml of water.

[0021]

[Table 3]

The rare earth metal magnet used in this test was RT
The reason for limiting the composition in the case of a -B based sintered magnet body (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co) will be described below. Hereinafter, what is simply described as% means% by weight. R-T-B based sintered magnet body, with the total of R, B and T of the main components as 100%,
R: 27-34%, B: 0.5-2%, and the balance T, R ₂ T
_The primary phase is a _14B type intermetallic compound. When the total weight of the RTB-based sintered magnet body is 100%, the content of oxygen of 0.6% or less, more preferably 0.3% or less, particularly preferably less than 0.2% as an inevitable impurity component is allowable. Not more than 0.2%, more preferably not more than 0.1% of carbon, not more than 0.08% of nitrogen, not more than 0.02% of hydrogen, not more than 0.2%,
More preferably, Ca content of 0.05% or less, particularly preferably 0.02% or less is allowed. R is (Nd, Dy) or Dy or Pr or (Dy, Pr) or (Nd, Dy,
Pr) is practically selected. The R amount is preferably from 27 to 34%. When R is less than 27%, the intrinsic coercive force iHc is greatly reduced, and 3
If it exceeds 4%, the residual magnetic flux density Br is greatly reduced. B content is preferably 0.5 to 2%. If the B content is less than 0.5%, iHc that can be used practically cannot be obtained, and if it exceeds 2%, Br is greatly reduced.
A more preferred B amount is 0.8 to 1.5%.

In order to improve magnetic characteristics, Nb, Al,
It is preferable to contain an appropriate amount of at least one of Co, Ga and Cu. The content of Nb is set to 0.1 to 2%. N
By the addition of b, a boride of Nb is generated during the sintering process, and abnormal grain growth of crystal grains is suppressed. If the Nb content is less than 0.1%, the effect of addition cannot be obtained. If the Nb content is more than 2%, the amount of Nb boride produced increases and Br is greatly reduced. The content of Al is set to 0.02 to 2%. If the Al content is less than 0.02%, the effect of addition cannot be obtained, and if it exceeds 2%, the Br sharply decreases. C
The o content is 0.3 to 5%. If the Co content is less than 0.3%, the effect of improving the Curie point and corrosion resistance cannot be obtained,
If it exceeds 5%, Br and iHc are greatly reduced. Ga content is
It is 0.01 to 0.5%. If the Ga content is less than 0.01%, iHc
Cannot be obtained, and if it exceeds 0.5%, the reduction of Br becomes remarkable. The Cu content is 0.01 to 1%. Addition of a small amount of Cu improves iHc, but the addition effect is saturated when the Cu content exceeds 1%, and the addition effect cannot be obtained when the Cu content is less than 0.01%. In addition, as a sample of this test, length 5mm
× R of 5 mm width × 1 mm thickness (magnetization direction)
-A T-B based sintered magnet body was used.

In Table 2, the demagnetization rate after the pre-treatment was large in the pre-treatment with a high PH of test No.
In the pretreatment with a low PH, the value is smaller than that, and in the pretreatment with the alkali liquid of Test No. 4, the value is as good as 0%. Therefore, it is considered that the largest factor of the magnitude of the demagnetization rate is the elution of the base material in the pretreatment. Elution of the substrate is an important issue in the surface treatment of magnets,
It is desirable to suppress this. From this viewpoint, pretreatment with an acid is not preferable.

In Table 3, tests No. 1, No. 2, No.
The chemical conversion treatment I and the chemical conversion treatment II of No. 3 have a demagnetization rate of about 1% and a thermal demagnetization rate that is smaller than that of the material of Test No. 1 in Table 2, so that the function as a coating is sufficiently fulfilled. This is comparable to the chromate treatment conventionally performed. However, when the chemical conversion treatment liquid shown in Table 1 shows a foaming phenomenon, as in Test No. 4 chemical conversion treatment III, the thermal demagnetization rate becomes inferior to that of the material, which is not suitable for application to a magnet body. .

[0026]

When the zinc phosphate chemical conversion treatment solution of the present invention is used for a rare earth magnet, a chemical conversion coating film having a certain level of corrosion resistance can be obtained without using chromium which is harmful to the human body and the environment.

[Brief description of the drawings]

FIG. 1 is a diagram showing changes in zinc and phosphorus in a formed film with respect to a concentration of phosphorus in a method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 2 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 3 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 4 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 5 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 6 is a graph showing changes in iron and neodymium in the formed film with respect to the concentration of phosphorus in the method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 7 is a diagram showing changes in iron and neodymium in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 8 is a diagram showing changes in iron and neodymium in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 9 is a graph showing changes in iron and neodymium in the formed film with respect to the concentration of zinc in the method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 10 is a graph showing changes in iron and neodymium in the formed film with respect to the concentration of zinc in the method for forming a chemical conversion film on a sintered body of the present invention.

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[Procedure amendment]

[Submission date] October 5, 2001 (2001.10.
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Method for forming a chemical conversion coating on a sintered body and rare earth metal magnet provided with a chemical conversion coating

[Claims]

5. A rare-earth metal magnet having a surface provided with a chemical conversion coating by a chemical conversion treatment method, wherein the chemical conversion coating contains phosphorus and zinc as main elements.

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a chemical conversion film such as a sintered magnet containing a rare earth metal and a rare earth metal magnet provided with a chemical conversion film.

[0002]

2. Description of the Related Art Among rare earth metal magnets, in particular, Nd-Fe-
Since the B-based rare earth metal magnet is extremely rustable, a rust is prevented by forming a coating on its surface by plating or chemical conversion treatment. As a method of forming a film by chemical conversion treatment, as described in JP-A-60-63902, a chromate treatment (chromate treatment) is most commonly used from the viewpoint of production cost.

[0003]

In the above-mentioned chromate treatment, hexavalent chromium is contained in the treatment solution and the formed film. It is said that this hexavalent chromium penetrates into the body through the skin after prolonged contact with the human body and accumulates in the body without being excreted. ing. Therefore, the problem of disposal of a processing solution and the problem of disposal of a product subjected to chromate treatment are becoming more important.
Against this background, chromium regulations are set to be enforced in Europe from 2003. Prior to that, there have been many studies on chemical conversion treatments that do not use chromium, and some have already been put to practical use. However, such a case has not yet been found in rare earth metal magnets. With the demand for high performance magnets increasing, the need for rare earth metal magnets will further increase in the future. Accordingly, a first object of the present invention is to provide a method for forming a chemical conversion coating which does not contain chromium which is harmful to the human body and has an adhesion and corrosion resistance comparable to a chromium coating on a sintered body. A second object is to provide a method for applying the chemical conversion treatment liquid to a rare earth metal magnet.

[0004]

In the present invention, the above-mentioned problems are solved by adding zinc oxide, which is a zinc compound, to a phosphoric acid aqueous solution and using a chemical conversion treatment solution to which a trace amount of nitrate ion is added as a reaction accelerator. did. The reason for using this chemical conversion treatment liquid is described below. Phosphate conversion treatment has attracted attention as a non-chromium oxidation conversion treatment for steel materials. The best known of these is zinc phosphate treatment. In this case, excellent corrosion resistance is obtained by depositing a zinc phosphate coating (hopite) insoluble in water. In addition, the iron eluted from the substrate is taken into the coating as phosphophyllite, thereby improving the adhesion of the coating. Rare earth metal magnets such as neodymium-iron-boron magnets also contain iron as a component element like steel materials, and are expected to have excellent corrosion resistance and adhesion by zinc phosphate treatment. In the zinc phosphate treatment, phosphoric acid, zinc oxide,
Nitric acid is both inexpensive and suitable for mass production. For the above reasons, the inventors have applied the zinc phosphate chemical conversion solution to rare earth metal magnets.

Next, the details will be described. The present invention relates to a method for forming a chemical conversion film on a sintered body for forming a chemical conversion film on the surface or the outer surface of the sintered body, comprising washing a sintered body with an alkali solution, or without washing, comprising a zinc compound and a phosphoric acid aqueous solution. Characterized by being immersed in a chemical conversion solution,
Further, the chemical conversion treatment solution contains 0.05 to 0.20 (mol / l) of zinc, and the molar ratio of phosphorus to zinc (P / Zn) is 2.3.
９9.55. Also,
In the case where the sintered body is washed with an acidic liquid except for nitric acid, the cleaning is performed in a range of 0.
It is preferable to be immersed in a chemical conversion treatment liquid containing more than 24 to 1.22 (mol / l) of phosphorus and having a molar ratio of phosphorus to zinc (P / Zn) of 2.4 to 5.9.

The present invention also relates to a rare-earth metal magnet having a surface provided with a chemical conversion coating by a chemical conversion treatment method, which is immersed in a chemical conversion treatment solution comprising a zinc compound and a phosphoric acid aqueous solution after washing with an alkali solution or without washing. And the main element of the chemical conversion coating as a sintered body contains phosphorus and zinc. Furthermore, the chemical conversion treatment solution is 0.15 to
It preferably contains 0.2 (mol / l) zinc, and the molar ratio of phosphorus to zinc (P / Zn) is preferably 2.39 to 3.18. The rare earth metal magnet is an RTB based sintered magnet (R
Is at least one kind of rare earth element including Y, and T is F
e or Fe and Co).

If P / Zn is less than 2.3, zinc oxide cannot be completely dissolved and remains undissolved. Conversely, if it is larger than 9.55, a foaming phenomenon may be observed during the treatment, and at this time, it is considered that the base component is eluted and the magnetic force is reduced, so that it is not suitable for application to a magnet. .
When it is 3.2 or less, the occurrence of fine foaming can be reduced as much as possible, which is preferable. The higher the phosphoric acid concentration, the better the adhesion of the coating,
The pH of the treatment liquid is preferably 1.0 to 2.0 acidic. Particularly preferably, it is 1.3 to 1.8.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the process for forming a chemical conversion film of the present invention will be described below. First, the object to be treated of the rare earth metal magnet was subjected to an alkali degreasing treatment or an acid treatment to clean the surface of the object to be treated and then sufficiently washed with water. As the acid treatment, dilute sulfuric acid or a salt thereof, dilute hydrochloric acid or a salt thereof can be used alone or in combination. In this example, only a dilute sulfuric acid solution was used, and in a comparative example, a combination of dilute sulfuric acid and nitrate was used. In another example, an aqueous solution containing sodium hydroxide and sodium carbonate as main components was used as the one using the alkali degreasing treatment.
In another example, a non-washed one was used. After sufficient water washing after the pretreatment, the coating was immersed in a zinc phosphate chemical conversion treatment solution to form a chemical conversion coating. After the treatment, it was sufficiently washed with water and dried at room temperature.

Table 1 shows that the main component composition is Nd: 26.2,
Pr: 5.0, Dy: 0.8, B: 0.97, Co:
3.0, Al: 0.1, Ga: 0.1, Cu: 0.1,
A test result of corrosion resistance of a chemical conversion film formed by a chemical conversion treatment under the following conditions on an RTB-based sintered magnet body of Fe: bal (all wt%), and the composition and properties of the chemical conversion treatment solution used , Processing conditions and the like.

[0010]

[Table 1]

[0011] Of the tests shown in Table 1, the samples in groups A and B were all pretreated with a 1.8 wt% aqueous sulfuric acid solution, and those in group C were prepared by adding sodium nitrate to a 0.5 wt% aqueous sulfuric acid solution. Pre-treated with the mixture, those of group D were 50 g of sodium hydroxide and 5 g of sodium carbonate.
0 g was dissolved in 1000 ml of water and pre-treated, and those of Group E were those without the pre-treatment, and are referred to as no washing in the present invention. However, although it is referred to as no cleaning, it includes ultrasonic cleaning with water to the extent that it removes deposits after processing. Corrosion resistance is constant temperature and humidity test (60 ° C, RH90%,
200 hr). ／/ × in the table indicates whether or not red rust was generated on the surface of the sintered body. In addition, “+” attached to the right shoulder of ○ indicates the frequency of liquid foaming relatively.

The group A in the table shows the corrosion resistance of the coating film when the concentration of zinc in the chemical conversion treatment solution was fixed at 0.2 (mol / l) and the concentration of phosphorus was changed. The results showed generally good corrosion resistance except for the test No. 1. However, the test No. 2 was best when the phosphorus concentration was 0.49 (mol / l) and the Zn / P molar ratio was 2.39. It showed corrosion resistance. Group B to Group E include the composition of the chemical conversion treatment solution of Test No. 2 which showed the best corrosion resistance in Group A, and set the phosphorus concentration of the chemical conversion treatment solution to 0.4.
This is a test in which the coating was fixed at 9 (mol / l) and the corrosion resistance of the coating when the zinc concentration was changed was tested. Those treated with sodium nitrate of Group C had poor corrosion resistance, and red rust was generated in the chemical conversion treatment liquids of all compositions.

D-grooves, that is, those subjected to a pretreatment with an alkaline solution, exhibited good corrosion resistance in all cases, but especially in Test Nos. 14 and 15, ie, when the phosphorus concentration was 0.49.
(Mol / l) and the zinc concentration is 0.15 to 0.20 (mol / l).
1) showed the best corrosion resistance. In the E group, that is, in the case of no washing, the same good corrosion resistance as in the D group was exhibited in all cases.
The one with 0.20 (mol / l) showed the best corrosion resistance.

As a result of EDX analysis of the surface of the object to be treated, phosphorus and zinc as components of the treatment solution were detected in addition to the base components such as neodymium and iron. FIG. 1 corresponds to the group A in Table 1 and shows the change in the amount of EDX of phosphorus and zinc detected on the surface of the chemical conversion coating when the zinc concentration is fixed and the phosphorus concentration is changed. The pretreatment is performed at 40 ° C. for 10 minutes using a 1.8 wt% sulfuric acid aqueous solution. The amount of detected phosphorus tends to increase as the concentration of phosphoric acid in the processing solution increases. The detected amount of zinc is minimum when the phosphoric acid concentration is 0.98 mol / l. The non-constant ratio of zinc and phosphorus detection suggests that not all phosphorus is bound equally to zinc and that phosphophyllite has precipitated. Therefore, it is considered that the adhesion of the film is improved as the phosphoric acid concentration is increased. The detected amount of the background component should always take a constant value, but as the phosphoric acid concentration increases, iron decreases and neodymium increases. This indicates that iron is more soluble in phosphoric acid than neodymium.

FIGS. 2, 3, 4 and 5 show B, C,
This corresponds to groups D and E, and shows the results of EDX analysis of phosphorus and zinc on the surface of the chemical conversion coating when the zinc concentration is changed while the concentration of phosphorus in the treatment liquid is kept constant. The processing conditions are 60 ° C. for 3 minutes.

FIGS. 6 to 10 show EDX analysis results of iron and neodymium in the vicinity of the chemical conversion coating corresponding to FIGS. 1 to 5, respectively. As for the detection amounts of the base iron and neodymium, the iron detection amount decreases and the neodymium detection amount increases as the zinc concentration increases, as in the case where the phosphorus concentration increases. Also, looking at the ratio of the detected amount of iron and neodymium at the same concentration, the detected amount of neodymium when pickling was lower. Therefore, it can be seen that neodymium is more soluble in sulfuric acid.

From the above results, from the viewpoint of the corrosion resistance of the coating film, the most preferred chemical conversion treatment composition has a phosphorus concentration of 0.49 (mol / l), a zinc concentration of 0.15 (mol / l), Is 1.46, which means that the pretreatment may be other than an acidic aqueous solution containing nitric acid. Processing temperature is 6
0 ° C. is preferred. Even if this temperature fluctuates somewhat, the properties of the film are not affected, but if the liquid temperature is low, the film formation rate is slowed, and there is a risk of oxidation. In addition, when the temperature increases, the liquid evaporates violently, making it difficult to manage the liquid. Considering the time suitable for mass production, the processing time is most preferably about 3 minutes.

Table 2 shows the RTs used in the tests shown in Table 1.
FIG. 2 shows the results of tests of the demagnetization rate and the thermal demagnetization rate after each pretreatment of a -B rare earth magnet. The materials in Table 2 indicate those that have not been subjected to pre-treatment or chemical conversion treatment. The pre-treatment includes a 1.8 wt% sulfuric acid aqueous solution, a 0.5 wt% sulfuric acid aqueous solution containing sodium nitrate, 50 g of sodium hydroxide and carbonic acid. Washing was performed using an aqueous solution in which 50 g of sodium was dissolved in 1000 ml of water. Hereinafter, for convenience, these are referred to as preprocessing (example), preprocessing (comparative example), and preprocessing (example), respectively. Table 2 during pre-chemical treatment and the demagnetizing factor of the post-processing for the total magnetic flux amount [Phi ₁₁ of the R-T-B rare earth magnet (pre-treatment prior before when processing performed) R-T-
B system shows the total magnetic flux amount [Phi ₁₂ reduction ratio of the rare earth magnet material,
It was determined by the following equation. Demagnetization rate = [(Φ ₁₁ −Φ ₁₂ ) / Φ ₁₁ ] × 100
(%) The thermal demagnetization rate indicates the demagnetization rate due to the thermal history of the obtained chemical conversion film-coated RTB-based rare earth magnet. The total amount of magnetic flux Φ ₂₁ when magnetized and the conversion coating RTB
The total amount of magnetic flux Φ when the rare earth magnet is heated at 85 ° C. in the air for 2 hours, cooled to room temperature, and then magnetized under the saturation condition.
₂₂ and was determined by the following equation. Thermal demagnetization rate = [(Φ ₂₁ −Φ ₂₂ ) / Φ ₂₁ ] × 100
(%)

[0019]

[Table 2]

Table 3 shows the RTs used in the tests shown in Table 1.
FIG. 2 shows the results of tests of the demagnetization rate and the thermal demagnetization rate of each of the -B rare earth magnets after each chemical conversion treatment. In the chemical conversion treatment solution, the phosphorus concentration in the test shown in Table 1 was fixed at 0.49 (mol / l), and the zinc concentrations were 0.20 and 0.1, respectively.
5, 0.05 were used, and nitric acid was added as a reaction accelerator. Hereinafter, these are referred to as chemical conversion treatment I and chemical conversion treatment II for convenience. The chemical conversion solution used for the chemical conversion treatment II is actually a solution obtained by dissolving 10 ml of phosphoric acid, 3.75 g of zinc oxide, and 3 ml of nitric acid in 287 ml of water.

[0021]

[Table 3]

The rare earth metal magnet used in this test was RT
The reason for limiting the composition in the case of a -B based sintered magnet body (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co) will be described below. Hereinafter, what is simply described as% means% by weight. The RTB-based sintered magnet body is composed of R: 27 to 34%, B: 0.5 to 2%, and the balance T, with the total weight of the main components R, B, and T being 100%.
_The main phase is a ₂ T ₁₄ B type intermetallic compound.
When the total weight of the RTB-based sintered magnet body is 100%, the content of oxygen of 0.6% or less, more preferably 0.3% or less, particularly preferably less than 0.2% as an inevitable impurity component is allowable. A content of carbon of 0.2% or less, more preferably 0.1% or less, a nitrogen content of 0.08% or less is allowed, a hydrogen content of 0.02% or less is allowed, and 0.2% or less, more preferably 0.05% or less. % Or less, particularly preferably 0.02%
The following Ca is allowed to be contained. As R, (Nd, D
y) or Dy or Pr or (Dy, Pr) or (Nd,
Dy, Pr) is practically selected. The R amount is preferably from 27 to 34%. If R is less than 27%, the intrinsic coercive force iHc greatly decreases, and if it exceeds 34%, the residual magnetic flux density Br greatly decreases.
B content is preferably 0.5 to 2%. If the B content is less than 0.5%, iHc that can be used practically cannot be obtained, and if it exceeds 2%, Br is greatly reduced. A more preferred B amount is 0.8 to 1.5%.

In order to improve magnetic characteristics, Nb, Al,
It is preferable to contain an appropriate amount of at least one of Co, Ga and Cu. The content of Nb is set to 0.1 to 2%. N
By the addition of b, a boride of Nb is generated during the sintering process, and abnormal grain growth of crystal grains is suppressed. If the Nb content is less than 0.1%, the effect of addition cannot be obtained. If the Nb content is more than 2%, the amount of Nb boride produced increases and Br is greatly reduced. The content of Al is set to 0.02 to 2%. If the Al content is less than 0.02%, the effect of addition cannot be obtained, and if it exceeds 2%, the Br sharply decreases. C
The o content is 0.3 to 5%. If the Co content is less than 0.3%, the effect of improving the Curie point and corrosion resistance cannot be obtained,
If it exceeds 5%, Br and iHc are greatly reduced. Ga content is
It is 0.01 to 0.5%. If the Ga content is less than 0.01%, iHc
Cannot be obtained, and if it exceeds 0.5%, the reduction of Br becomes remarkable. The Cu content is 0.01 to 1%. Addition of a small amount of Cu improves iHc, but the addition effect is saturated when the Cu content exceeds 1%, and the addition effect cannot be obtained when the Cu content is less than 0.01%. In addition, as a sample of this test, length 5mm
× R of 5 mm width × 1 mm thickness (magnetization direction)
-A T-B based sintered magnet body was used.

In Table 2, the demagnetization rate after the pre-treatment was large in the pre-treatment with a high PH of test No.
In the pretreatment with a low PH, the value is smaller than that, and in the pretreatment with the alkali liquid of Test No. 4, the value is as good as 0%. Therefore, it is considered that the largest factor of the magnitude of the demagnetization rate is the elution of the base material in the pretreatment. Elution of the substrate is an important issue in the surface treatment of magnets,
It is desirable to suppress this. From this viewpoint, pretreatment with an alkali solution is more preferable than acid.

In Table 3, tests No. 1, No. 2, No.
The chemical conversion treatment I and the chemical conversion treatment II of No. 3 have a demagnetization rate of about 1% and a thermal demagnetization rate that is smaller than that of the material of Test No. 1 in Table 2, so that the function as a coating is sufficiently fulfilled. This is comparable to the chromate treatment conventionally performed. However, since the foaming phenomenon of the chemical conversion treatment liquid shown in Table 1 is observed as in the chemical conversion treatment III of Test No. 4, the thermal demagnetization rate is inferior to that of the material. Therefore, the Zn content is preferably more than 1.0.

[0026]

When the zinc phosphate chemical conversion treatment solution of the present invention is used for a rare earth magnet, a chemical conversion coating film having a certain level of corrosion resistance can be obtained without using chromium which is harmful to the human body and the environment.

[Brief description of the drawings]

FIG. 1 is a diagram showing changes in zinc and phosphorus in a formed film with respect to a concentration of phosphorus in a method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 2 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 3 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 4 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 5 is a graph showing changes in zinc and phosphorus in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 6 is a graph showing changes in iron and neodymium in the formed film with respect to the concentration of phosphorus in the method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 7 is a diagram showing changes in iron and neodymium in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 8 is a diagram showing changes in iron and neodymium in a formed film with respect to a concentration of zinc in a method for forming a chemical conversion film on a sintered body according to the present invention.

FIG. 9 is a graph showing changes in iron and neodymium in the formed film with respect to the concentration of zinc in the method for forming a chemical conversion film on a sintered body of the present invention.

FIG. 10 is a graph showing changes in iron and neodymium in the formed film with respect to the concentration of zinc in the method for forming a chemical conversion film on a sintered body of the present invention.

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Claims (6)

[Claims] 1. A method for forming a chemical conversion coating on a sintered body, wherein the chemical conversion coating is formed on the surface or outer surface of the sintered body, wherein the zinc oxide and a phosphoric acid aqueous solution are washed with an alkali solution or without washing. A method of forming a chemical conversion coating on a sintered body, characterized by immersing the film in a chemical conversion treatment solution comprising: 2. The chemical conversion treatment solution contains 0.05 to 0.20 (mol / l) of zinc, and has a molar ratio of phosphorus to zinc (P / Zn).
Is from 2.4 to 9.5, the method for forming a chemical conversion coating on a sintered body according to claim 1, wherein 3. A method for forming a chemical conversion coating on a sintered body, wherein the chemical conversion coating is formed on a surface or an outer surface of the sintered body, wherein the sintered body is washed with an acidic solution excluding nitric acid, and then subjected to 0.49 to 1.22.
(Mol / l) of phosphorus and the molar ratio of phosphorus to zinc (P /
A method for forming a chemical conversion coating on a sintered body, characterized by immersing the composition in a chemical conversion treatment solution having a Zn content of 2.4 to 5.9. 4. A rare earth metal magnet having a surface or an outer surface provided with a chemical conversion coating by a chemical conversion treatment method, which is immersed in a chemical conversion treatment solution comprising a zinc compound and a phosphoric acid aqueous solution after washing with an alkali solution or without washing. A rare earth metal magnet provided with a chemical conversion coating, wherein the conversion coating contains phosphorus and zinc as main elements. 5. A chemical conversion treatment solution containing 0.15 to 0.2 (mol / mol).
The rare-earth metal magnet provided with a chemical conversion coating according to claim 4, wherein 1) zinc is contained, and the molar ratio of phosphorus to zinc (P / Zn) is 2.39 to 3.18. 6. The rare earth metal magnet is an RTB based sintered magnet (R is at least one kind of rare earth element including Y;
The rare earth metal magnet provided with the chemical conversion coating according to claim 4, wherein the magnet is Fe or Fe and Co).