JPH09324298A - Treatment of surface of aluminum or aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adhesion of plating by subjecting Al or an Al alloy to electrolytic etching in a soln. contg. chlorine ions. SOLUTION: As for this treating method, Al or an Al alloy is subjected to electrolytic etching in a soln. contg. chlorine ions, therefore, in Al in which the state is not the same metallographycally and the noble part and the base part are present electrochemically, the part in which electric current concentrates is partially formed, and cylindrical fine tunnel pits with <=3μm diameter innumerably grow from the Al surface toward the inside approximately vertically. The increase of the surface area by this formation of the tunnel pits reaches ten times or above to improve the adhesion. Moreover, plating is easily precipitated into the tunnel pits to form innumerable anchors, and, even in the case of plating high in internal stress and easy to peel in the Al or Al alloy inferior in adhesion, excellent adhesion can be obtd. by the synergetic effect of the increase of the contact area and the anchor effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for Al or Al alloy, which is used as a pretreatment for plating the surface of Al or Al alloy without using an intermediate layer.

[0002]

2. Description of the Related Art The conventional plating method of this kind of Al or Al alloy involves one of the inventors, and the Al or Al alloy is positively or negatively charged in an alkaline or acidic electrolyte with a counter electrode. Negative voltage is alternately applied to slightly dissolve the surface of the metal to be treated at the anode to remove the oxide film, and generate negative hydrogen at the cathode to generate hydrogen, destroy the oxide film and activate it in a reducing atmosphere. By repeating the above, a plating film having excellent adhesion and gloss was obtained (Japanese Patent Publication No. 2-40751).

[0003]

However, such conventional Al or Al alloy plating method can obtain plating with good adhesion to many Al alloys by electrolytic activation, but a strong oxide film is likely to occur. Some of the pure Al-based and corrosion-resistant Al alloy-based platings cannot withstand the harsh conditions of use, and also have the disadvantage that the adhesion may not be sufficient in thick plating with large stress.

An object of the present invention is to eliminate such inconvenience.

[0005]

In order to achieve the above object, in the surface treatment method of Al or Al alloy according to the present invention, Al or Al alloy is electrolytically etched with a solution containing chlorine ions. , Al having a noble portion and a base portion that are electrochemically different from each other in terms of metallography and has a partially concentrated current, and has a diameter of 3 μm
The following cylindrical fine tunnel pits grow innumerably from the Al surface toward the inside (see FIG. 1). The increase in surface area due to the formation of this tunnel pit
Since it is 10 times or more, when plating is applied, the adhesion area of the plating is significantly increased and the adhesion is improved. Furthermore, plating easily deposits in the tunnel pits to create innumerable anchors (see Fig. 2), and internal stress in Al or Al alloys with poor adhesion due to the synergistic effect of the increased adhesive area and anchor effect. Excellent adhesion can be obtained even with plating that is easily peeled off.

Further, if a positive or negative voltage is alternately applied between the Al or Al alloy and the counter electrode, etching and reduction are repeated as many times as the number of conversions of the application, and microscopically. At the moment of the anode, it is corroded by the electrolytic solution containing chlorine ions, but at the moment of becoming the cathode, the etching of that part stops and hydrogen gas is generated, so even if it becomes the anode in the next cycle Is etched.
As a result, when positive or negative voltage is alternately applied, fine tunnel pits are generated, and the surface area is about 20 to 30 times, as compared with the case where they are not applied alternately. The adhesion area is increased and the adhesion is improved. Further, the oxide film formed slightly by hydrogen gas generated at the time of the cathode is destroyed, and activation is promoted in a reducing atmosphere to further improve the adhesion.

Further, if the positive or negative voltage application ratio can be changed, as shown in FIG. 3, the reduction effect of etching and hydrogen gas generation can be adjusted by changing the applied voltage ratio. The surface condition can be adjusted to suit the type of material and the type of plating.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the surface treatment method for Al or Al alloy according to the present invention, the solution containing chlorine ions means an acid containing chlorine atom such as hydrochloric acid, sodium chloride or ammonium chloride,
An alkali, a salt, or a mixed solution of these is used.

As a method of alternately applying positive or negative voltage, alternating current is used, for example. In this case, the number of cycles is the number of conversions of application.

Furthermore, the application ratio of the positive or negative voltage is adjusted by the positive and negative holding time, the magnitude of the positive and negative voltages, and the like.

[0011]

[Examples] Examples will be described below. In the table showing the test results, ◯ indicates that no adhesion failure is observed, and Δ indicates that adhesion failure is also observed. , X indicates that most of them had poor adhesion.

Example 1 ADC12 was added to sodium carbonate 1
In an alkaline solution containing 00 g / l and 5 g / l of sodium hydroxide, and in a solution containing 5 g / l of sodium chloride added thereto, 50 ° C. 13.3 Hz, inversion ratio of 76% (cathode base), 10 A / dm ² Electrolytic etching is performed for 2 minutes under the conditions described above, and chromium plating is performed for 15 minutes at a current density of 40 A / dm ² , then a tape adhesion test (a method in which cellophane tape is pressure-bonded to the cut surface with a cutter knife and peeled off) ) And a heat test (natural cooling or water cooling by holding at each temperature for 1 hour) were as shown in Table 1.

[0013]

In electrolytic etching in an alkaline solution of sodium carbonate and sodium hydroxide, even if the chromium plating is deposited, it becomes a scaly plating and is easily removed or peeled off. On the other hand, when a salt containing chloride ions such as sodium chloride is added to the alkaline solution, tunnel pits are formed, the adhesion area is increased and the anchor effect is promoted, and plating with good adhesion is obtained. Of course, as in the case of hydrochloric acid, electrolytic etching using a sodium chloride single solution also produces tunnel pits, and plating with good adhesion can be obtained.

(Example 2) Pure Al of A1080 was electrolytically etched for 3 minutes in a 10% hydrochloric acid solution at room temperature under a condition of 13.3 Hz and 10 A / dm ² to change the inversion ratio to 40 A / d.
The result of chrome plating for 15 minutes at a current density of m ² is
The results are shown in Table 2.

[0016]

Plating with good adhesion can be obtained by converting the polarity and applying positive and negative voltages alternately to carry out electrolytic etching.
Good adhesion in a wide range of negative ratio. Since it is not etched by the cathode direct current, tunnel pits are not formed and the adhesion is poor. Adhesion is inferior in anode DC etching because it is less likely to form tunnel pits than in positive / negative alternating etching due to polarity conversion, but adhesion is improved because anode pits are also formed in tunnel pits.

(Example 3) A1100, A2017, A5052, A
6061, ADC12 in an alkaline solution containing 100 g / l of sodium carbonate and 5 g / l of sodium hydroxide at room temperature for 12.4
Hz, inversion rate 86% (cathode base), 10 A / dm ² for electrolytic degreasing for 2 minutes, then in a 10% hydrochloric acid solution at room temperature, 12.4 Hz, inversion rate 86% (cathode base), 10 A / d
Tunnel etching is performed for 3 minutes under the condition of m ² to obtain 40 A /
Table 3 shows an adhesion adhesion comparison test (cutting test-peeling of cut surface and the above-mentioned test) between the chrome plating and the chrome plating by the zinc substitution method, which were carried out at dm ² for 120 minutes (film thickness of about 50 μm).

[0019]

Since the chromium plating has a large internal stress, when a thick film is formed, sufficient adhesion cannot be obtained by the zinc substitution method. As can be seen from the results in the above table, direct adhesion to the base material by tunnel etching gave better adhesion than plating with an intermediate coating such as the zinc substitution method for all Al and Al alloys. Plating is obtained.

(Embodiment 4) A1100, A2017, A5052, A
6061, ADC12 in an alkaline solution containing 100 g / l of sodium carbonate and 5 g / l of sodium hydroxide at room temperature for 12.4
Hz, inversion rate 86% (cathode base), 10 A / dm ² for electrolytic degreasing for 2 minutes, then in a 10% hydrochloric acid solution at room temperature, 12.4 Hz, inversion rate 86% (cathode base), 10 A / d
Adhesion comparison test between electroless nickel plating performed by tunnel etching under the condition of m ² for 3 minutes and electroless nickel for 90 minutes (film thickness of about 15 μm) and electroless nickel plating by zinc substitution method is shown in Table 4. It was as follows.

[0022]

In contrast to the electroless nickel plating having durability and adhesion, the electroless nickel plating on the intermediate coating such as the zinc substitution method cannot obtain sufficient adhesion,
In the tunnel etching method, electroless nickel is directly deposited in the tunnel pit, and the adhesion area is increased and the adhesion is improved by the anchor effect.

(Example 5) A1100, A2017, A5052, A
6061, ADC12 in an alkaline solution containing 100 g / l of sodium carbonate and 5 g / l of sodium hydroxide at room temperature, 1
2.4Hz, inversion rate 86% (cathode base), 10A / dm ²
Electrolytic degreasing for 2 minutes under the conditions of 10% hydrochloric acid solution at room temperature, 12.4Hz, inversion rate 86% (cathode base), 10A /
Tunnel etching is performed for 3 minutes under the condition of dm ² , nickel for 60 minutes (film thickness of about 20 μm), chromium for 2 minutes (film thickness of about 20 μm)
Table 5 shows the adhesion comparison test between the nickel / chromium plating having a thickness of 0.2 μm) and the nickel / chromium plating by the zinc substitution method.

[0025]

Nickel-chromium plating by the tunnel etching method has excellent adhesion to all Al or Al alloys like other platings.

In the case of decorative nickel / chromium plating which requires anticorrosion, the zinc substitution method complicates the multi-step process and makes it extremely difficult to control, and impurities and chemicals in other tanks are brought in, resulting in a marked deterioration in adhesion. However, since the method of the present invention can simplify the process and reduces the number of chemical species, it is very advantageous for line control and adhesion.

[0028]

EFFECTS OF THE INVENTION The surface treatment method for Al or Al alloy according to the present invention is for electrolytically etching Al or Al alloy with a solution containing chlorine ions. In Al where there is a base part and a base part, there is a part where current concentrates partially and the diameter is 3μ.
Innumerable cylindrical fine tunnel pits of m or less grow almost vertically from the Al surface toward the inside. The increase in surface area due to the formation of this tunnel pit is more than 10 times,
In the case of plating, the adhesion area of the plating is significantly large and the adhesion is improved. Furthermore, even if plating easily deposits in the tunnel pits and countless anchors are formed, and in the case of Al or Al alloy with poor adhesion due to the synergistic effect of the increase in the adhesive area and the anchor effect, even large plating such as internal stress that easily peels off. Excellent adhesion can be obtained.

Further, if a positive or negative voltage is alternately applied between the Al or Al alloy and the counter electrode, etching and reduction are repeated as many times as the number of conversions of the application, so microscopically. At the moment of the anode, it is corroded by the electrolytic solution containing chlorine ions, but at the moment of becoming the cathode, the etching of that part stops and hydrogen gas is generated, so even if it becomes the anode in the next cycle Is etched.
As a result, when positive or negative voltage is alternately applied, fine tunnel pits are generated, and the surface area is about 20 to 30 times, as compared with the case where they are not applied alternately. The adhesion area is increased and the adhesion is improved. Further, the oxide film formed slightly by hydrogen gas generated at the time of the cathode is destroyed, and activation is promoted in a reducing atmosphere to further improve the adhesion.

Further, if the application ratio of the positive or negative voltage can be changed, as shown in FIG. 4, the reduction effect of etching and hydrogen gas generation is adjusted by changing the ratio of the applied voltage, The surface condition can be adjusted to suit the type of material and the type of plating. Such a surface condition has a great effect on surface treatment other than plating, for example, improvement of adhesion such as painting.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of Al or an Al alloy with tunnel pits formed according to the present invention.

FIG. 2 is a cross-sectional view of Al or Al alloy in a state where a plating layer penetrates into a tunnel pit according to the present invention.

FIG. 3 is a voltage waveform diagram in a state in which the application ratio of the positive or negative voltage is changed in the present invention.

Claims (3)

[Claims] 1. A method for surface treatment of Al or Al alloy, which comprises electrolytically etching Al or Al alloy with a solution containing chlorine ions. 2. The surface treatment method for an Al or Al alloy according to claim 1, wherein a positive or negative voltage is alternately applied between the Al or Al alloy and the counter electrode. 3. The surface treatment method for Al or Al alloy according to claim 2, wherein the application ratio of positive or negative voltage can be changed.