JPS5836071B2 - Manufacturing method for silver-plated iron and iron alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the method of plating iron or iron alloys with silver or silver alloys, and is particularly intended to improve the corrosion resistance of silver-plated stainless steel and the like. It is.

General 1.Pure iron and iron alloys such as stainless steel and Fe-Ni
are relatively inexpensive metals that have excellent corrosion resistance, mechanical strength, and electromagnetic properties; however, many of these metals have strong passivation films on their surfaces, resulting in poor electrical connectivity and soldering properties, making them difficult to use for electronics. As a material for electrical parts, its use is limited.

Examples include electronic contacts, connectors, switches, terminals, etc. that require spring properties.

For this reason, precious metals such as silver and gold are used by plating at least a portion of the surface of stainless steel to economically utilize the strength of the base material and the electrical connectivity and solder properties of precious metals. It is something.

Conventionally, silver plating is performed directly on passive metals such as stainless steel, which involves activating the stainless steel by dipping or cathodic reduction, and then silver plating the pin. Since holes are formed, the activated stainless steel is easily oxidized due to the pinholes, and high corrosion resistance cannot be expected.

Furthermore, surface properties such as electrical connectivity and solderability were also significantly reduced.

The reason for this is that an electrolytic corrosion system is formed through the pinholes in the silver plating, and the activated stainless steel becomes an anode and is severely corroded.

In other words, when comparing the areas of the cathode silver and the stainless steel exposed through the pinhole, this electrolytic corrosion reaction occurs because the former has an extremely large surface area, and the cathode reaction (yo2
+H2 0+2 e-"20H) polarization is difficult to occur and is therefore strongly promoted.

In this way, corrosive substances such as red rust generated in stainless steel contaminate the surface of precious metals such as silver through pinholes, impairing the electrical connectivity and soldering properties as described above, and may develop into pitting corrosion.

This is because activated stainless steel has the same corrosion potential as pure iron or steel during plating, and it goes without saying that the same thing occurs when pure iron or steel is plated with Ag. do not have.

The present invention is based on the discovery of a method for producing silver or silver alloy plated stainless steel, etc., which has excellent corrosion resistance by inactivating the activated base metal in silver or silver alloy plated iron and iron alloys.

That is, the method of the present invention involves activating the surface of iron and iron alloys and plating them with silver or silver alloys, then cathodizing them in an aqueous solution containing hexavalent chromium ions, and then rolling them. It is characterized by:

The method of plating silver or silver alloy in the method of the present invention may be carried out by any method such as electroplating or electroless plating, or by activating the surface of stainless steel etc. by dipping or cathodic reduction using a conventional method, or by a conventional method. After performing steps such as further protecting the activation by strike plating with nickel or copper, plating is performed.

As silver plating baths, cyanide baths, nitric acid baths, etc. are widely used.

Also, as silver alloy plating, Ag-Cu, Ag-In, Ag
-Sb, Ag-Pb, Ag-Zn, etc.

In the present invention, after performing silver or silver alloy plating as described above, 6
Cathode treatment is performed using a solution containing valent chromium ions.

The reason for this is that by performing silver or silver alloy plating, pinholes formed in these plating layers are closed, thereby improving corrosion resistance.

As the solution containing hexavalent chromium ions, chromium trioxide, sodium chromate, sodium dichromate, potassium chromate, potassium dichromate, etc. are used.

Also, the concentration of hexavalent chromium is more than ioowA, especially iooo ~ 5
A range of 0 0 01'lm is desirable.

The reason is that if it is less than 1001'l'', the chromium film will not adhere and will be effective in filling the pinholes as described above [, (
L★ga◎ゐ.

Also, if the concentration is too high, for example 5 0 0 0 0
When more than 1 plm of wastewater accumulates, it becomes difficult to treat the wastewater, resulting in environmental hygiene problems.

To treat this chromium ion, silver or silver alloy plated stainless steel is immersed in the aqueous solution of the chromium compound mentioned above, and electrolytic treatment is performed using this as a cathode. /dm2 or more, especially 0.1~
A combination of a current density of 0.5 A/dm2 and a treatment time of 2 seconds or more, especially 5 to 30 seconds, is practical.

Furthermore, the present invention performs rolling processing, and the rolling reduction rate is not particularly limited, but a normal rolling car performs rolling processing with one trowel of 2.5 or more, and the reason for this is 2. If the rolling ratio is less than .5, the effect of the rolling process will not be exhibited and the pinholes formed by the plating layer of silver or silver alloy cannot be filled with a chromium film.

Further, by removing the chromate film adhering to the surface of the plated layer by rolling, electrical connectivity and solder properties can be improved without impairing corrosion resistance.

In addition, rolling increases the mechanical strength, improves the adhesion and abrasion resistance of the silver or silver alloy plating layer, makes the crystals uniform, and improves the surface gloss.

If the known chromate treatment is simply performed without rolling, the above-mentioned characteristics of Ag plating will be greatly impaired, even if the corrosion resistance can be improved.

Next, examples of the present invention will be described.

Example I A SUS304 plate was subjected to cathodic degreasing (2.5 A/dm2) for 1 minute in an alkaline aqueous solution, and then 1 minute
After activation by cathodic treatment for 1 minute in 0HCA, immediately washed with water, first perform silver strike plating under the same conditions as the first step, and then thicken under the same conditions as the second step. A silver-plated SUS plate (sample ■) obtained by performing silver-plating with a thickness of 1 μm was rolled as it was (sample ■), and the plate was treated with 5 parts sodium dichromate solution.
．． 5A/dm210 seconds cathode treatment (sample ■
) was subjected to 25% rolling with a rolling machine (sample ①) and was placed in a constant temperature and humidity chamber at 60° C. and a relative humidity of 95% for 500 hours to observe the occurrence of iron rust.

The results are shown in Table 1. Table I (1) Iron rust was observed in spots. (II) Same as above. (If) No iron rust occurs (5) No iron rust occurred and the surface had gloss.

As described above, it was found that corrosion resistance was significantly improved by attaching a chromium film.

Next, the contact resistance and solderability of the above samples were measured.

That is, the contact resistance was determined by pressing a silver bar with a tip of 5 cm with a force of 250 g.

The solderability was determined by immersion in a eutectic solder bath at 235°C for 3 seconds using a 25% rosin flux according to the MIL-STP method.
It was pulled up and the wetted area of the surface was measured.

The results are shown in Table 2.

Table 2 Contact resistance 0 Solder wettability (%) (I) approx. 100XIO-3 50 (II) 45 60 (nD approx. 200X10-3 35 (IV) 1.IXIF3 Even for those coated with chrome as in 98 and above If rolling is not performed, the electrical connectivity and solderability are significantly reduced, but rolling can significantly improve the electrical connectivity and solderability.

Example 2 A 52% Fe-48% Ni alloy plate was subjected to the same activation treatment as in Example 1, and then plated with a 1μ thick silver-antimony alloy under the following conditions.

AgCN 150. ! i'/7
KCN 50g/IJ Potassium antimonyl tartrate 50 g/1 Sodium potassium tartrate 50 g/IK O H
7 g/1 liquid temperature 20
℃ Cathode current density IA,/dm2 This silver alloy plated plate was treated as it was (Sample I) in the same manner as in Example 1.
) Also, the plate subjected to rolling processing (sample ■), the plate subjected to chromium treatment (sample ■), and the plate subjected to rolling processing (sample ■) were subjected to the conditions shown in Example 1, respectively. Corrosion resistance, electrical connectivity, and solderability were measured.

The results are shown in Table 3.

As is clear from the table above, silver alloy-plated iron-nickel (here, as in Example 1, electrical connectivity and solderability are poor if only a chromium coating layer is provided, so rolling is performed to significantly improve the electrical connectivity and solderability. did.

As detailed above, according to the method of the present invention, it is possible to produce a composite material in which iron or iron alloy is plated with silver or silver alloy and has excellent corrosion resistance, electrical connectivity, and solderability.

In particular, when passive metals such as stainless steel are plated, there is a great risk of losing their corrosion resistance, which is one of their most important utility values, but the method of the present invention can restore corrosion resistance without losing the characteristics of silver plating. Therefore, its industrial value is great.

Claims (1)

[Claims] 1. After activating the surface of iron or iron alloy and plating with silver or silver alloy, cathode treatment is performed in an aqueous solution containing hexavalent chromium ions, and then rolling processing is performed. Method for producing silver-plated iron and iron alloys.