JP3385561B2 - Al material on which phosphate film is formed and method for forming phosphate film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphate film-forming Al material used for automobile bodies, for example.

[0002]

BACKGROUND OF THE INVENTION In recent years, application of aluminum alloy (hereinafter abbreviated as Al) plate to body panels and the like has been promoted for the purpose of reducing fuel consumption and weight of automobiles. By the way, a steel plate is mainly used for the body panel, and therefore a phosphating process is required. That is, from the viewpoint of corrosion resistance, the automobile manufacturing line includes a step of phosphate treatment (formation of phosphate coating) after assembling the body from each part.

It is preferable that the Al plate is subjected to chromate treatment rather than zinc phosphate treatment in terms of corrosion resistance, but for this purpose, a treatment line dedicated to the Al plate must be provided, which results in high cost. Therefore, since the existing steel plate treatment line is used as it is, it is necessary to perform the zinc phosphate treatment in a system in which an Al plate and a steel plate are mixed. It has been pointed out that if an Al plate and a steel plate coexist during this phosphate treatment, problems will occur in the formation of the phosphate film and the sharpness after painting.

For example, when an Al plate is treated with a phosphate solution, the Al surface is dissolved in the phosphate solution, Al ³⁺ is eluted into the phosphate solution, and the formation of a phosphate film is inhibited. It will come to be. Also, under the current steel plate treatment conditions, even if the Al plate is treated with a phosphate solution, only a very small amount of phosphate film is formed, and it is sufficient for an Al plate with only a small amount of phosphate film formed. The surface properties of the cold-rolled steel sheet on which various phosphate coatings have been formed are greatly different, and the glossiness and sharpness of the coating film after coating may differ, resulting in poor appearance. . When the zinc phosphate coating on the Al plate is small, not only the appearance of coating is different, but also the corrosion resistance after coating becomes poor.

As a means for solving such a problem,
It has been known to add K ⁺ and F ⁻ to the phosphate solution. That is, Al ³⁺ + 2K ⁺ + Na ⁺ + F ⁻ → K ₂
Dissolved Al using the reaction that becomes NaAlF ₆ (precipitate)
By removing ³⁺ and adding F ⁻ , it becomes possible to form a phosphate film on the Al plate. However, if an Al plate and a steel plate are to be processed at the same time, the liquid composition and the amount of replenishment must be changed depending on the ratio of the areas to be processed, and many types of vehicles can be manufactured on the same phosphate treatment line. When performing, if the above means is adopted, the load amount of the Al material must be limited.

Therefore, as an alternative to this, a Zn plating layer, Zn--Fe, Zn--Co, Zn is formed on the surface of the Al plate.
A technical idea has been proposed (JP-A-61-157693) in which a Zn-based alloy plating layer such as Ni or a Fe-based alloy plating layer such as Fe-Sb has a thickness of 1 g / m ² or more. . Moreover, after cleaning the surface of the Al plate, a Zn plating layer is applied in an amount of 0.05 to 1.0 g /
A technical idea of increasing the thickness of m ² is proposed (JP-A-4-2680).
No. 77).

Further, a technical idea is proposed in which after the surface of the Al plate is cleaned, a Zn plating layer is made to have a thickness of 0.05 to 1.0 g / m ² by a zinc displacement plating method and an electrogalvanizing method (Japanese Patent Laid-Open No. Hei 10 (1999) -58242). No. 4-268078). or,
Fe, Co, Ni, Cu, Cr, Mn on the surface of the Al plate
A technical idea of discontinuously coating one or more selected from the above has been proposed (Japanese Patent Laid-Open No. 5-112892).

However, in any of these proposals, an extra step is required in addition to the phosphate treatment, so that it is troublesome and costly. or,
In an Al-Mg-based alloy containing Mg, the surface oxide film is 70 Å or less, and the Mg concentration in the oxide film is 20 atomic% or less.
A Mg-based alloy material has also been proposed (JP-A-5-70970).

However, even the proposal is not sufficient.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly conducted research on phosphatability, and as a result, the phosphatability is A
It has been found that it is closely related to the surface characteristics of the oxide film on the surface of the 1-material. In particular, for example, the zinc phosphate film formation reaction in the zinc phosphate treatment consists of dissolution of Al in the anode part and zinc phosphate film formation in the cathode part, and a zinc phosphate film is formed by the cathode reaction. Have found that the corresponding anode reaction needs to take place actively. That is, it has been found that it is important to form an oxide film having a characteristic that a large amount of current flows due to anodic polarization.

The present invention has been achieved based on such knowledge, and an object of the present invention is a technique capable of extremely easily forming a dense and thick phosphate film on an Al material used as an automobile body. Is to provide. The object of the present invention is to obtain a current value of 200 to 70 flowing when an electric potential is scanned at a sweep rate of 30 mV / min from the immersion potential to the anode side of 0.5 V in a 10 wt% nitric acid aqueous solution at 20 ° C.
Surface property of 0 μA / cm ² (Phosphate treatment
This is achieved by an Al material forming a phosphate coating characterized in that it has the surface characteristics of a floor Al material) .

Further, the current value flowing when the potential is scanned from the immersion potential to the anode side of 0.5 V at a sweep rate of 30 mV / min in a 10 wt% nitric acid aqueous solution at 20 ° C. is 200 to 70.
The surface property is 0 μA / cm ² and the time until a rapid change in the potential curve after immersion in the phosphating solution occurs within 55 seconds (before the phosphating treatment,
This is achieved by an Al material forming a phosphate film characterized by having the surface characteristics of the Al material) .

Further, the current value flowing when the potential is scanned from the immersion potential to the anode side of 0.5 V at a sweep rate of 30 mV / min in a 10 wt% nitric acid aqueous solution at 20 ° C. is 200 to 70.
An Al material having a surface property of 0 μA / cm ² is treated with a phosphating solution to achieve a phosphate film forming method. Also, from the immersion potential in a 10 wt% nitric acid aqueous solution at 20 ° C, 0.5 V, 30 m to the anode side.
The current value flowing when the potential was scanned at a sweeping rate of V / min was 200 to 700 μA / cm ² , and the time required for a rapid change in the potential curve after immersion in the phosphate treatment solution was 55. Al with surface properties within seconds
This is achieved by a method for forming a phosphate film, which comprises treating the material with a phosphating solution.

In the present invention, in the 10 wt% nitric acid aqueous solution at 20 ° C., the immersion potential is 0.5 V and the anode side is 30 mV.
/ The current value flowing upon potential scanning at a sweep rate of min is limited such that 200~700μA / cm ^2, the phosphate film when the current value in the anode polarization is 200 .mu.A / cm ² less than This is because the film was hard to be formed, the adhesion amount was small and the film thickness was thin, and the crystal was also coarse. The Al material is A
In the case of the 1-Mg-based alloy, it was difficult to obtain a large current value in anodic polarization exceeding 700 μA / cm ² , so it was set to 700 μA / cm ² or less. A preferred range is 200 to 500 μA / cm ² .

Further, the time until the rapid change in the potential curve after immersion in the phosphating solution is set to 55 seconds is longer than 60 seconds, the phosphate film is formed. This is because it was difficult and the crystals tended to be coarse. The preferable range is 30 to 55 seconds. The current value in anodic polarization is determined as follows. First, an Al material having a predetermined oxide film
The sample is dipped in a wt% nitric acid aqueous solution, and the value of the current flowing through the potential is measured by scanning the potential from the dipping potential to the anode side of 0.5 V at a sweep rate of 30 mV / min at 20 ° C. In FIG. 1 showing this polarization measurement result, the anode current value is obtained from the tangent line of the curve before and after the current increases.

The potential measurement in the phosphating solution is 43 ° C.
Zinc phosphate treatment liquid (PBL3020 manufactured by Nippon Parkerizing Co., Ltd., total acidity 23 points, free acidity 0.9
Points, accelerator concentration 3.0 points), SC
E Measure the potential with the reference electrode. In FIG. 2 showing the potential change thus obtained, −1100 immediately after the immersion.
It shows a base potential of about mV and gradually changes, but then a sharp shift to a noble potential of about -500 mV is observed. The time until the midpoint of this abrupt change is taken as the time until the abrupt change in the potential curve after immersion in the phosphate treatment liquid occurs. Incidentally, the time until this abrupt change occurs is a time that is not so much involved in the formation of the zinc phosphate film, after which the zinc phosphate film starts to be formed. Therefore, this time should be short.

After the cleaning treatment, oil or the like may be applied to the surface of the Al material for storage. In such a case, the above measurement is performed after degreasing with an organic solvent. Hereinafter, specific examples will be described.

[0018]

【Example】

[Example 1] A rolled material of an Al-Mg alloy (JIS 5182) was immersed in a sulfuric acid aqueous solution having a pH of 1 at 60 ° C for 2 minutes, and an oxide film on the surface of the rolled material was washed with an acid.
After this, a degreasing agent (L4 manufactured by Nippon Parkerizing Co., Ltd.)
428, 2%) at 43 ° C. for 1 minute for degreasing, followed by washing with water, and subsequently using a colloidal titanium solution (PL-Z, PL-ZN manufactured by Nippon Parkerizing Co., Ltd.) at 25 ° C. for 10 minutes. A pretreatment for zinc phosphate treatment was performed over a period of 2 seconds.

Then, the total acidity was adjusted to 23 points, the free acidity was adjusted to 0.9 points, and the concentration of the accelerator was adjusted to 3.0 points, in a PBL3020 solution (zinc phosphate treatment solution) manufactured by Nippon Parkerizing Co., Ltd. at 43 ° C. It was dipped for 2 minutes and treated with zinc phosphate. [Example 2] A rolled material of Al-Mg alloy (JIS 5182) was immersed in a phosphoric acid aqueous solution having a pH of 2 for 2 minutes at 55 ° C, and the oxide film on the surface of the rolled material was washed with an acid.

Thereafter, zinc phosphate treatment was performed in the same manner as in Example 1. [Example 3] A rolled material of an Al-Mg alloy (JIS 5182) was immersed in a nitric acid aqueous solution having a pH of 1 for 1 minute at 60 ° C, and the oxide film on the surface of the rolled material was washed with an acid.
Thereafter, the same procedure as in Example 1 was carried out to carry out zinc phosphate treatment.

[Comparative Example 1] Al-Mg without acid cleaning
Rolled alloy (JIS 5182) rolled into PBL3020
It was dipped in 2 minutes and was treated with zinc phosphate. [Comparative Example 2] A rolled material of an Al-Mg alloy (JIS 5182) was immersed in a caustic soda aqueous solution having a pH of 14 at 50 ° C, and the oxide film on the surface of the rolled material was washed with alkali.

Thereafter, zinc phosphate treatment was performed in the same manner as in Example 1. [Comparative Example 3] A rolled material of an Al-Mg alloy (JIS 5182) was immersed in a sodium phosphate aqueous solution having a pH of 8 at 50 ° C for 3 minutes, and the oxide film on the surface of the rolled material was washed with a weak alkali. .

Thereafter, zinc phosphate treatment was performed in the same manner as in Example 1. [Comparative Example 4] A rolled material of Al-Mg alloy (JIS 5182) was immersed in a phosphoric acid aqueous solution having a pH of 4 at 40 ° C for 1 minute to wash the oxide film on the surface of the rolled material with an acid. Thereafter, the same procedure as in Example 1 was carried out to carry out zinc phosphate treatment.

[Comparative Example 5] Al-Mg alloy (JIS
The rolled material of 5182) was immersed in a nitric acid aqueous solution having a pH of 1 at 30 ° C. for 15 seconds to wash the oxide film on the surface of the rolled material with an acid. Thereafter, the same procedure as in Example 1 was carried out to carry out zinc phosphate treatment. [Characteristics] The zinc phosphate coating formed as described above was examined, and the results are shown in Table 1.

Further, the anode current value (2
0.5V from immersion potential in 10wt% nitric acid aqueous solution at 0 ° C
Current value flowing when potential scanning was performed on the anode side at a sweep rate of 30 mV / min) and zinc phosphate treatment liquid PBL3
The time required for a rapid change in the potential curve after immersion in 020 was measured, and the results are also shown in Table-1.
Shown in.

Table-1 Anode current value Potential change time Zinc phosphate treatability (μA / cm ² ) (sec) Adhesion amount (g / m ² ) Film form Example 1 300 45 1.2 Dense Example 2 250 50 1.1 Dense Example 3 300 35 1.3 Dense Comparative Example 1 150 62 0.6 Coarse Comparative Example 2 10 20 0.3 Coarse Comparative Example 3 70 62 0.6 Coarse Comparative Example 4 170 59 0.4 Coarse Comparative Example 5 180 65 0.6 Coarse It can be seen from this that the Mg-based Al alloy material having the surface characteristics as in the present invention is excellent in zinc phosphate treatment. That is, a dense and thick phosphate film can be formed very easily.

[0027]

[Effect] The phosphate film is well formed, and the cost of forming the film is low.

[Brief description of drawings]

FIG. 1 Graph of anodic polarization measurement results

FIG. 2 Graph of changes in electrode potential

Continuation of front page (56) Reference JP-A-1-240675 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22/00-22/86

Claims (4)

(57) [Claims] 1.Surface of Al material before phosphating
Characteristics 0.5 from the immersion potential in a 10 wt% nitric acid aqueous solution at 20 ° C
Potential scanning on the V anode side at a sweep rate of 30 mV / min
The current value that flows whenIs200-700 μA / cm²so
Al which forms a phosphate film characterized by being
Material. 2.Surface of Al material before phosphating
Characteristics 0.5 from the immersion potential in a 10 wt% nitric acid aqueous solution at 20 ° C
Potential scanning on the V anode side at a sweep rate of 30 mV / min
The current value that flows whenIs200-700 μA / cm²so
And in the potential curve after immersion in the phosphating solution
It takes less than 55 seconds before a sudden change occurs.
An Al material on which a phosphate film is formed. 3. A value of a current flowing when an electric potential is scanned at a sweep rate of 30 mV / min from the immersion potential to the anode side of 0.5 V in a 10 wt% nitric acid aqueous solution at 20 ° C. to 200 to 700.
A method for forming a phosphate film, which comprises treating an Al material having a surface characteristic of μA / cm ² with a phosphate treatment liquid. 4. A value of a current flowing when an electric potential is scanned from an immersion potential to a 0.5 V anode side at a sweep rate of 30 mV / min in a 10 wt% nitric acid aqueous solution at 20 ° C. to 200 to 700.
μA / cm ² and the time until a rapid change in the potential curve after immersion in the phosphate treatment solution is 5
A method for forming a phosphate film, which comprises treating an Al material having a surface property of 5 seconds or less with a phosphate treatment liquid.