JPH0533154A - Chemical conversion treatment - Google Patents

Abstract

PURPOSE:To chemically covert steel and aluminum at the same time by uniformly depositing a crystal excellent in adhesion and corrosion resistance on the surface, ground part and edge of the aluminum under the conditions where the steel and aluminum are mixed almost in the same amt. as on the steel. CONSTITUTION:Test pieces 10a and 10b formed respectively from a steel sheet and aluminum sheet are suspended from a supporting rod 16 and dipped in a liq. tank 20 storing a zinc phosphate soln. 18 contg. fluorine for simultaneous chemical conversion treatment. The test pieces 10a and 10b are dipped in the soln., ordinary chemical conversion treatment is carried out for one minute, the electrolytic chemical conversion treatment is conducted for one minute with the test pieces 10a and 10b as the cathodes, and the upper limit of the current value is controlled to 3 A in this case.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical conversion treatment method for coating steel and aluminum as a coating base, and more particularly to a method for simultaneously performing chemical conversion treatment on steel and aluminum.

[0002]

2. Description of the Related Art In recent years, some automobile bodies use an aluminum plate formed of an aluminum alloy in addition to the conventional steel plate for the purpose of weight reduction. By the way, when painting a body that also uses an aluminum plate in this way, it is necessary to apply a coating base by chemical conversion treatment to each, but conventionally, as this coating base, the steel plate is generally treated with zinc phosphate, and, Chromate chromate treatment is applied to the aluminum plate for the body, and therefore each has a different treatment process.

However, when the undercoating is separately performed for the steel plate and the aluminum plate in this way, the undercoating work becomes complicated and the productivity is remarkably deteriorated. Incidentally, it is possible to treat the aluminum plate and the steel plate at the same time using a zinc phosphate solution for steel, but in this case, there is an oxide film on the surface of the aluminum and the pH of zinc phosphate is about the same as the aluminum plate. Cannot be etched. Therefore, for example, Japanese Patent Application Laid-Open No. 63-15789 proposes a method of simultaneously performing a base treatment on an aluminum plate and a steel plate using a phosphoric acid treatment liquid containing a fluoride as an etching agent for aluminum.

[0004]

However, such a conventional simultaneous processing method allows the undercoating to be performed on the same line between the steel plate and the aluminum plate. However, the difference in the etching amount between these steel plates and the aluminum plate is required. This reduces the amount of crystal precipitation on the surface of the aluminum plate. In addition, the surface of an aluminum plate is ground by sanding or the like for reshaping after molding the car body.However, by polishing the surface of the aluminum plate in this way, the etching reaction becomes even stronger, and this polished part is not The amount of crystals precipitated by the chemical conversion treatment is significantly reduced as compared with the processed portion, and the coating becomes insufficient. Furthermore,
The same phenomenon occurs at the edge of the aluminum plate,
Insufficient coating. When the formation of the chemical conversion treatment film is insufficient in this way, the adhesion of the coating film when coated is deteriorated and the corrosion resistance is significantly deteriorated.

By the way, there is generally known a method of forming a coating film by an energization chemical conversion treatment, but this energization conversion treatment can promote the formation of a coating film on both a steel plate and an aluminum plate. However, when the surface treatment is performed only by the energization chemical conversion treatment, the adhesion between the chemical conversion treatment film and the treatment object is significantly deteriorated because the deposition mechanism does not involve the etching reaction of the treatment object, and actually, There was a problem that it could not be used.

In view of such conventional problems, therefore, the present invention, in the case of simultaneously performing chemical conversion treatment in the state where steel and aluminum are mixed, adheres to the surface of aluminum and its polished portion, and further to its edge portion, in adhesion and The purpose is to uniformly deposit crystals with excellent corrosion resistance in the same amount as steel.

[0007]

In order to achieve such an object, the present invention provides a conventional chemical conversion treatment step of immersing an object to be treated in which steel and aluminum are mixed in a simultaneous phosphating solution, After the chemical conversion treatment step, an energization chemical conversion treatment step of energizing the object to be treated as a cathode for a predetermined time is provided.

Further, the time for the normal chemical conversion treatment step is about 1
It is desirable to set the time for the energization chemical conversion treatment step to about 1 minute and the total chemical conversion treatment time to about 2 minutes.

[0009]

In the chemical conversion treatment method of the present invention having the above-mentioned constitution, by performing the normal chemical conversion treatment step in the previous stage, it is possible to form a coating film having good adhesion with etching reaction on both steel and aluminum. it can. Next, by performing an energization chemical conversion treatment step after the normal chemical conversion treatment step, a defective portion of the coating film which is insufficient in the normal chemical conversion treatment is compensated for, and a sufficient thickness is provided on the aluminum surface and the polished portion, and further on the edge portion. Can be formed.

Further, the time for the conventional chemical conversion treatment step is about 1
Minutes, and by setting the time of the energization chemical conversion treatment step to about 1 minute and the total chemical conversion treatment time to about 2 minutes,
It is possible to form a film in an ideal state within a short time.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an example of a test piece 10 as an object to be used in the chemical conversion treatment method of the present embodiment. The test piece 10 has a rectangular shape and is made of a steel plate and an aluminum plate to be subjected to a chemical conversion treatment test. Prepare each formed one. Then, in the figure, the shaded portion is masked 12 on the front and back to expose the white background portion, and the exposed portion 1
4 has a horizontal length L1 of 1.25 cm and a vertical length L2 of 1
Set to 0 cm. The area of the exposed portion 14 at this time is 1.25 × 10 × 2 = 25 cm ^{2 on the} front and back sides.

FIG. 2 shows a state in which test pieces 10a and 10b formed of a steel plate and an aluminum plate are suspended from a support rod 16, and in this state, the chemical conversion treatment liquid 18 is immersed in a liquid tank 20. .

By the way, a cold-rolled steel plate is used as the steel plate, and a normally used GC-45 is used as the aluminum plate.
Use the pickling material. Further, as the chemical conversion treatment liquid 18, a simultaneous zinc phosphate chemical conversion treatment liquid containing fluorine is used, and an experiment is carried out in a state where this is maintained at 40 ° C. still,
Of the cations in this treatment liquid, it is desirable to contain nickel, which is effective for the anti-blister performance of the coating film, at a high concentration of about 2000 ppm. Further, the test piece is washed with tap water and with deionized water.

Here, in this embodiment, the test piece 1 is used.
0a, 10b is subjected to the chemical conversion treatment by immersing it in the above-mentioned simultaneous zinc phosphate treatment liquid, the ordinary chemical conversion treatment step is performed for one minute only by the ordinary immersion treatment, and then the test pieces 10a, 10b are immersed in the same liquid. The energization chemical conversion treatment step with the cathode as the cathode is performed for 1 minute, and the total treatment time is set to 2 minutes. In this energization chemical conversion treatment step, the upper limit of the current value is 3A.
Controlled as.

Therefore, in the chemical conversion treatment method of this embodiment, the normal chemical conversion treatment step is performed by simultaneously immersing the test piece 10a of the steel plate and the test piece 10b of the aluminum plate in the simultaneous zinc phosphate chemical conversion solution containing fluorine. As a result, it is possible to form a coating film of zinc phosphate crystal having good adhesion with an etching reaction on both the test pieces 10a and 10b. At this stage, it is undeniable that the film formation on the test piece 10b made of an aluminum plate is insufficient as compared with the test piece 10a made of a steel plate due to the difference in the etching amount.

Next, an energization chemical conversion treatment step is performed after the normal chemical conversion treatment step to compensate for the film formation of the test piece 10b, which was insufficient in the normal chemical conversion treatment, and to add phosphorus in the treatment liquid to the relevant portion. Zinc acid crystals can be positively deposited. That is, the coating film made of the zinc phosphate crystal produced by the normal chemical conversion treatment has an electric insulating property, and the portion where the coating film becomes insufficient by applying current to the test pieces 10a, 10b, that is, the surface of the aluminum plate. In addition, a hydrogen reduction reaction occurs at the edge portion, and due to this increase in PH, it is possible to form a film of zinc phosphate crystals without the etching reaction of the unprocessed material.

That is, in this embodiment, a film having good adhesion is formed in the first half of the normal chemical conversion treatment step, and then the insufficiently formed part of the film is effectively formed in the latter half of the current chemical conversion treatment step. The coating film having excellent adhesiveness and corrosion resistance can be sufficiently formed through both of these treatment steps.

Further, in the latter half of the energization chemical conversion treatment step, the respective cations (+2 valences) of Zn, Ni and Mn contained in the chemical conversion treatment solution are selectively taken into the film of the non-processed material which is the cathode. Therefore, the proportions of Zn, Ni, and Mn in the coating film are increased as compared with the ordinary dipping method, and the alkali resistance performance of the coating film is improved, whereby the corrosion resistance performance can be further improved.

Next, experimental results by the chemical conversion treatment method of this embodiment will be shown together with other comparative examples. In addition, as another comparative example, the test piece 10a under the same conditions as the experiment conducted in this example,
Two sets of 10b are prepared, one set of these two sets is subjected to the normal chemical conversion treatment step only for 2 minutes, and this is set as Comparative Example 1, and the other set is subjected to the energized chemical conversion treatment step for 2 minutes. This is Comparative Example 2.

That is, the following Table 1 shows the surface (normal portion) and the edge portion of the aluminum plate, which is analyzed by EPMA (electron probe microanalyzer) "unit: cps (count value)" and coating weight (C / W) ". [Unit: g / m ^2] ”is the result of each of the present Example, Comparative Example 1, and Comparative Example 2. Further, Table 2 shows the results of the EPMA analysis and the coating weight measurement similarly performed on the normal portion and the edge portion of the cold rolled steel sheet (SPC), respectively.

[0021]

[Table 1]

[0022]

[Table 2]

In the EPMA analysis, as indicated by a circle mark in FIG. 1, a substantially central portion P of the exposed portion 14 of the test piece 10 is shown.
Was observed as a normal portion, and the side edge corner portion Q of the exposed portion 14 was observed as an edge portion. Further, the C / W measurement is obtained by removing the coating film with nitric acid and measuring the weight difference before and after the peeling. In this C / W measurement, the normal part and the edge part are the same test piece for one material, and therefore have the same value.

Further, the following Table 3 compares the total counts of the normal part and the edge part in the aluminum plate and the SPC, and shows them in the present Example, Comparative Example 1 and Comparative Example 2, respectively, and Table 4
Indicates the count numbers of Mn and Ni in the same count number, respectively.

[0025]

[Table 3]

[0026]

[Table 4]

From the above experimental results, it can be seen from Tables 1 and 2 that the aluminum plate and the SPC are energized as in this Example and Comparative Example 2, so that the count values of Zn, Ni and Mn in the normal portion and the edge portion are increased. Respectively increase,
In particular, the increase is remarkable at the edge portion. In addition, as a result, in this example and comparative example 2, C / W was increased as compared with comparative example 1, and it was confirmed that the film formation was sufficiently performed.

Next, from Table 3, both the aluminum plate and the SPC are
In Comparative Example 1, the total count number of the edge portion, that is, the coating amount is significantly smaller than that in the normal portion. However, by performing the energization treatment in the present Example and Comparative Example 2, the normal portion and the edge portion are processed. It was confirmed that the coating amounts were substantially equal by and.

Further, from Table 4 it can be seen that in Comparative Example 1, Mn and Ni in the edge portion of the aluminum plate are significantly less than in the normal portion, but in the present Example and Comparative Example 2, the difference is very small. It has been confirmed that

Therefore, from the above experimental results, in the present example and the comparative example 2 in which the energization treatment is performed, the formation of the coating film is promoted in both the aluminum plate and the SPC as compared with the comparative example 1 in which the energization is not performed. It becomes remarkable in. Also,
By performing the energization treatment, the amount of the coating film formed at the edge portion is approximately the same as that of the normal portion, and a substantially uniform coating film can be formed over the entire object to be processed.

By the way, from the above experimental results, it seems that both the present example and the comparative example 2 in which the energization process is performed are effective in forming the film, but the energization chemical conversion process of the comparative example 2 involves the etching reaction of the non-processed material. Since there is only a precipitation mechanism that does not exist, the adhesion between the coating film and the object to be treated is significantly deteriorated. On the other hand, in the present example, a coating film with good adhesion was formed by the normal chemical conversion treatment without energization in the first half, and then the portion of the film that was insufficient in this normal chemical conversion treatment was treated with the latter half of the current chemical conversion treatment. Since it was generated effectively by processing,
It is possible to obtain a coating having excellent adhesion and corrosion resistance.

Therefore, by using the chemical conversion treatment method of this embodiment as a coating base for an automobile body in which an aluminum plate and a steel plate are used in combination, the aluminum plate and the steel plate can be processed in the same line. The production efficiency can be greatly improved.

Further, in the present embodiment, the time for the normal chemical conversion treatment step was set to about 1 minute, the time for the energization chemical conversion treatment step was set to about 1 minute, and the total chemical conversion treatment time was set to about 2 minutes. Since the film can be sufficiently generated in an ideal state within a short time, the production efficiency of the product can be improved also from this point. Each processing time is not limited to the time set in this embodiment (every 1 minute).

[0034]

As described above, in the chemical conversion treatment method according to the first aspect of the present invention, the current chemical conversion treatment is performed after the normal chemical conversion treatment step is performed on the object to which the steel and the aluminum are mixed. By carrying out the steps, it is possible to uniformly form a coating having good adhesion and corrosion resistance to a sufficient thickness not only on steel but also on the surface of aluminum and the polished part, and even the edge part. Therefore, by using the chemical conversion treatment method of the present invention as the coating base of the object to be treated in which steel and aluminum are mixed, it is possible to perform chemical conversion treatment of these steels and aluminum at the same time, and it is possible to significantly improve the work efficiency. it can.

In the second aspect of the present invention, the time for the normal chemical conversion treatment step is set to about 1 minute, and the time for the energization chemical conversion treatment step is set to about 1 minute, and the total chemical conversion treatment time is set. By setting the time to about 2 minutes, it is possible to form a film in an ideal state within a short time, and it is possible to achieve various excellent effects such that the work efficiency can be further improved.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a test piece used in an experiment to which the chemical conversion treatment method of the present invention is applied.

FIG. 2 is an explanatory diagram showing a part of an experimental apparatus to which the chemical conversion treatment method of the present invention is applied.

[Explanation of symbols]

10 test piece (processing object) 10a steel plate test piece 10b aluminum plate test piece 12 masking portion 14 exposed portion 18 chemical conversion treatment liquid (simultaneous phosphate treatment liquid)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C25D 11/36 E 7179-4K 301 7179-4K

Claims (2)

[Claims] 1. A normal chemical conversion treatment step of immersing an object to be treated consisting of steel and aluminum in a simultaneous phosphating solution, and after the normal chemical conversion treatment step, current is applied for a predetermined time with the object to be treated as a cathode. An energization chemical conversion treatment step, and a chemical conversion treatment method comprising: 2. The general chemical conversion treatment step is set to approximately 1 minute, the energization chemical conversion treatment step is set to approximately 1 minute, and the total chemical conversion treatment time is set to approximately 2 minutes.
The chemical conversion treatment method according to claim 1, wherein the chemical conversion treatment method is defined as minutes.