JPS6020467B2 - Colored chromate treatment method for zinc-nickel alloy plated products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a colored chromate treatment method for electric Zn-mounted NJ-plated products, which have significantly superior corrosion resistance compared to Zn-plated products.

In recent years, various alloy platings of Zn and different metals have been studied for the purpose of improving the corrosion resistance of Zn plating.

Among these, Zn--Ni alloy plating has been put into practical use because it is particularly excellent in terms of corrosion resistance, gloss, and physical properties. This Zn-Ni alloy plating has the best corrosion resistance when the Ni content in the plating film is 11 to 18%.
Compared to plating, the time for red rust development in the salt water tread test is extended by 5 to 1 pi. However, these Zn--Ni alloy plating methods have so far only been adopted mainly by steel manufacturers as a continuous plating method for thin steel plates (strips). In addition, the chromate treatment on the Zn-Ni alloy plating on these steel plates is called clear (glossy, transparent) chromate, in which the amount of chromium in the chromate film is 50 mg/filter or less, and its corrosion resistance meets JIS-Z2371. According to the Motozuku salt water mist test, the time it takes for white rust to appear is approximately 7 hours or less, and it has sufficient corrosion resistance as it is for pavers used in harsh corrosive environments. It's hard to say.
One of the reasons why Zn-Ni alloy plating has not been put into practical use for decoration and anti-corrosion purposes is that, unlike ordinary Zn plating, Zn-Ni alloy plating has traditionally been coated with a highly corrosion-resistant colored coating. One reason is that it was difficult to form a chromate film.

Therefore, the present inventors have conducted various studies in order to produce a colored chromate film with good corrosion resistance and heat resistance on Zn-Ni alloy plated products. As a result, Zn-Ni alloy plated products were coated with Cr60 at 0.5~100 t/d, SO
By treating reeds with a chromic acid solution containing 0.025 to 1.5 in weight ratio to Cr80 and adjusting the pH to 1.3 to 2.7, it exhibits beautiful iridescent interference colors, We succeeded in producing a colored chromate film containing a Cr content of 100 mm or more and having much better corrosion resistance and heat resistance than conventional Zn-plated colored chromate. This ku.

The composition of the mate solution is different from that of the secondary chromate solution used in the treatment of Zn plated products or Zn-Ni alloy plated products. The point and fence limited to 1.5 are 1.3~
2.7. When the concentration of SO reed is less than 0.025 in weight ratio to Cr60 concentration, Zn-Ni
No colored chromate film is formed on the alloy plating film, but on the other hand, if it is over 1.5, the chromate film becomes thinner.
Corrosion resistance decreases. In addition, if the chromate solution has a spot of 1.3 or less, the chromate film will not be colored and the chromate film will not be colored.
The amount of adhesion will be small, and the corrosion resistance will be low (normal Z
For n marking, for example, C's 3100 ta'so, H cross 045
A colored chromate film with good appearance and corrosion resistance can be produced even from a chromate solution with a pH of 0.5 to 0.8.

). Moreover, if the mottling is 2.7 or more, the reactivity of the chromate solution decreases, and a good colored chromate film cannot be formed on the Zn--Ni alloy plating. To adjust the mother chromate solution, in addition to adding alkali hydroxides such as NaOH and KOH to raise the pH, 03 and Zn(
It is also possible to add OH)2, NiC03, Ni(OH)2, etc. Also, to lower the pH, C
Use rQ or day 2S04. In addition, in order to increase the shine of colored chromate treatment on Zn plating and the gloss of the film, the plated item is usually immersed in a dilute aqueous nitric acid solution or soaked in a chromate treatment solution prior to chromate treatment. NO; but Zn-N according to the present invention
When performing colored chromate treatment on i-alloy plating, NO;
must not be used as they inhibit the formation of chromate films.

The concentration of Cr60 is almost the same as that of colored chromate solution with Zn plating.

If the thickness is less than 0.5 ta', the chromate film becomes thin and sufficient corrosion resistance cannot be obtained.

In addition, increasing the concentration to a high concentration of 100 m/s or more is not preferable because it increases the cost and increases the burden of wastewater treatment. The chromate treatment of a Zn-Ni alloy plated product using a chromate solution as described above may be carried out in exactly the same manner as the conventional treatment using a chromate solution.

By the chromate treatment of the present invention as described above, Zn-N
It is possible to form a thick and beautiful chromate film on the i-alloy plating film, which has an average chromium content of 100 mm or more, which was previously impossible. By the way, the Zn-Ni alloy plating film tends to become inactive very easily, and if it is left for a long time after plating, or if the Ni content in the plating film exceeds about 12%, it cannot be treated with the above chromate solution. However, a colored chromate film may not be formed.

In such cases, the temperature of the chromate treatment solution should be adjusted to 35 to 5
It is best to flood to 0°C. In addition, Zn in the above chromate solution
When electrolyzed using the -Ni alloy plating film as an anode, a good colored chromate film is produced. Electrolysis is performed in a chromate solution for a few seconds. In this way, a portion of the plating film is dissolved, and thereafter, the reaction for forming the chromate film can proceed easily. Note that if electrolysis is performed constantly during the chromate treatment, the chromate film will peel off due to the 02 gas generated from the plated surface, so a good chromate film will not be obtained. However, if electrolysis is performed with a weak current of about 0.01 to 0.2 A/d, the chromate film will not peel off due to the generated O2 gas. In addition to this method, 0.0. A good colored chromate film is produced by applying electroplating of Zn to a level below the surface level and then treating it with the above chromate solution. Zn-
The thin Zn plating that is further plated on the Ni alloy plating is easily dissolved in the above chromate solution and the chromate production reaction progresses, so the chromate production reaction continues on the underlying Zn-Ni alloy plating. progresses. In this case, flash plating with a Zn plating of 1 to IQA/d for 2 to 3 seconds is sufficient. Although there is no problem in applying more Zn plating than this, all Zn plating needs to be dissolved in the chromate solution, so considering the deterioration of the chromate solution, processing time, etc. It is desirable to do so. Next, examples of the present invention will be described.

Example 1 A steel plate was plated with Zn-Ni alloy with a Ni content of 10% for 3r.
It was applied to a film thickness of m.

This can be achieved by the following conditions.

Mate processed. Chromate solution composition N is also Cr207, 2 days 20 10#/event (60 in C = 3.49 evening/so) ratio S04
2 evening/evening (SO reed = 1.96 evening/do) (S 戊)
/Cr60=0.56)PH
I. 8 Processing conditions Bath temperature
3pu0 soaking time
19 Sand Interval Example 2 A steel plate was plated with a Zn-Ni alloy with a Ni content of 10% to a thickness of 1 Am, and then chromate-treated under the following conditions.

Chromate liquid composition N et Cr207・2 days 20 20 evenings/so (Cr80 = 6.50%) (Contains 340% of Cr2(S04)) (S 207/Cr60 = 0.11) PH 2.1 (Adjust with C 3)
Processing conditions Bath temperature 5
0q0 Groove Immersion Time 29 Sand Interval Example 3 A steel plate was plated with a Zn-Ni alloy with a Ni content of 8% for 3 times, and then chromate-treated under the following conditions.

Chromate solution composition C of 3 2 nights/event (Cr60 = 1.04 evenings/event)
So) ratio S04 0.1 evening/evening (SO=0.09
8 evening/evening) Solution 1.8 (S戊-/Cr6
10 = 0.0 place) Processing conditions temperature
4020 immersion time
19-stage Example 4 A steel plate was plated with a Zn-Ni alloy with a Ni content of 12% for 2 rms, and then chromate-treated under the following conditions.

Chromate liquid composition Na2Cr207・2 days 20 30 evening/soku Cr60 ill. 82 ta'so) (S'-/
Cr60=0.081)PH
20 Processing conditions Bath temperature
50 pm electrolysis IA/
Turtle sea bream soaking time as anode for 5 seconds at d second (successively after electrolysis) Example 5 Ni content in steel plate 12
% of Zn--Ni alloy plating was applied, and this was subjected to chromate treatment under the following conditions.

350 ta'〆(Cr
60 = 26.0 evening/so) ratio S04 10 evening/
So (SO = 9.8 evening / evening (S 戊 - / Cr6 ten = 0. spot) Na pay P04 2 evening / so PH 1.4 (pH adjusted with NaOH)
Excessive processing conditions 3
000 bonding time 1 Sunama Example 6 A steel plate was coated with Zn--Ni alloy plating with a Ni content of 15% three times, and further Zn plating with a thickness of 0.1 French was applied thereon.

This was subjected to chromate treatment under the conditions shown below.

Chromate liquid composition Na2Cr207・2 days 20 150 evening/so (Cr60=52.4 evening/evening) wide S04
10 evening/evening (SO=9.8 evening/evening) (S-
/Cr60=0.19)HC〇〇Na
l-5 poly/〆PH
I. 6 Processing conditions temperature
30:00 bond soaking time
19 Sand Comparative Example 1 Zn--Ni alloy plating with a Ni content of 10% was applied to a steel plate for 3 hours, and this was treated under the following chromate treatment conditions for normal Zn plating.

Chromate liquid composition C-3 100 m/s (Cr6 152.0 m/s) Ratio S04 10 m/s (SO reed-9.
8 Yu/So) vs. 0.6(S戊-/Cr6
10=0.19) Processing condition temperature
3pi○ immersion time
lq Akima Comparative Example 2 Zn with Ni content of 10% on steel plate
-Ni alloy plating was applied for 3rm, and this was treated under the following chromate treatment conditions for light Zn plating.

Chromate liquid composition C-3 10/so (Cr6 152/so) ratio SOchi 1/Z (SO reed-0.
Evening) PH I. 2 (S-/Cr6-=0.19) Processing conditions temperature
30℃ immersion time
3 Tochi Akima Comparative Example 3 Zn plating was applied to the steel plate with 4r kite,
Chromate treatment was performed under the following conditions.

Chromate solution composition N is also Cr207, 2 days 20 10 evenings/evening (Cr60 = 349 evenings/evening) QS04 1 evening/Z (SO reed-=0. side evening/Z
)HN03 2ta'so(S go-/Cr60=0
．． 28) pH
I. 7 Processing conditions Bath temperature
3bi○ immersion time
19 Next, regarding each plating/chromate treatment test piece obtained in the above Examples and Comparative Examples, [1
'Analysis of Cr content in the chromate film, '2) Corrosion resistance test using salt water mist, '3) Heat resistance test of chromate using low heat.

The analysis method and test method are as follows. '1} Analysis of Cr content in chromate film Each test piece was soaked in HCI for 100 minutes to dissolve all the chromate film, and the eluted Cr content was analyzed and quantified using an atomic absorption spectrophotometer. The amount of Cr (male/female) per surface area of the test piece (chromate film) was determined.

■ Corrosion Resistance Test Each test piece was tested in accordance with JIS-Z2371, and the time until white corrosion products (white sapi) and reddish-brown corrosion products (red sapi) were generated from the surface was checked using a salt water mist test. , their corrosion resistance was confirmed.

Heat resistance test The temperature of each electric heating furnace equipped with a temperature controller is set to l.
Set to oo15, 20025 and 0.

The above test pieces were placed in these furnaces and left at the specified temperature for 2 hours, then each test piece was taken out and examined to see if the chromate film was destroyed by the heat and turned black. was confirmed visually. Table 1 shows these results.

As is clear from the results shown in Table 1, Zn-N
It becomes possible to perform high-quality colored chromate treatment on i-alloy plated products, and the corrosion resistance and heat resistance of the plated products can be dramatically improved.

Claims (1)

[Claims] 1. When chromating a zinc-nickel alloy plated product containing 20% by weight or less of nickel, the chromate treatment is performed using Cr^6^ + concentration = 0.5 to 100 g/lS.
O^2^-_4 concentration/Cr^6^+ concentration = 0.025~
1.5 (weight ratio) A method for colored chromate treatment of zinc-nickel alloy plated products, characterized in that the treatment is carried out using a treatment solution having a pH of 1.3 to 2.7. 2. When chromating a zinc-nickel alloy plated product containing 20% by weight or less of nickel, after applying electrogalvanization to a film thickness of 1 μm or less on the plated product, Cr^6^+concentration= 0.5-100g/lSO^2^
-_4 concentration/Cr^6^+concentration=0.025~1.5(
A method for colored chromate treatment of zinc-nickel alloy plated products, characterized by forming a chromate film using a treatment liquid having a pH of 1.3 to 2.7 (weight ratio).