JPH086172B2 - Method for forming soft chrome plating film with excellent drawability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applied to automobile parts, household appliance parts, containers, and the like.
The present invention relates to a method for forming a soft chrome plating film having excellent corrosion resistance and workability.

[Conventional technology]

Chromium has a beautiful metallic luster, scratch-resistant hardness, high corrosion resistance and heat resistance, and is therefore widely used as a plating metal. Gloss and hardness are used for interior and exterior parts of automobiles, nameplates, furniture, toys and containers, and hardness and heat resistance are used for home appliances parts. Is used everywhere.

In particular, a film with less friction and an abrasion resistant film, which utilizes its hardness and a smooth plated surface, are major features of this plated film.

The electroplating method and the chrome-penetration plating method have hitherto been used as methods for forming a plating film utilizing the excellent characteristics of chromium. In the chromium permeation plating, chromium is diffused and permeated into the surface layer of the member to be plated at a high temperature to form an alloy layer of the member metal and chromium on the surface. This method requires a long processing time and is expensive, so that it is mainly used for special ones requiring heat resistance. The most widely used method is electroplating using a Sargent bath. In this method, chromium metal is electrolytically deposited on the surface of a member to be plated, which is used as a cathode, from a sulfuric acid aqueous solution containing chromium ions to form a film. One of the drawbacks of chromium electroplating is the phenomenon of cracks in the plating layer. It is thought that this occurs because the plating film has internal stress and the film is hard, but the hardness of the electroplating film is actually higher than that of the chromium metal itself.
It is more than twice as large. The Vickers hardness of pure chrome metal mass is about Hv = 130, whereas it is Hv = 300 or more for chrome plating film and Hv = 1,300 for hard film. The cause of this hardness is the internal stress generated during electrolytic deposition,
It is thought to be due to the storage of hydrogen and the heterogeneous structure due to the mixture of oxides. The electroplating film of chromium has a drawback that cracks occur because it releases stress and strain due to these.

The large difference in the hardness of the plating film is due to the difference in the electrolytic conditions, and the influence of the bath temperature is particularly large.
For example, in hard chrome plating, which requires abrasion resistance, this is utilized to obtain a large hardness by lowering the bath temperature. On the other hand, on the contrary, in order to reduce the generation of cracks, it is sufficient to increase the bath temperature and electrolyze under conditions that tend to soften the film, but there is also a limit, and Hv = 300 is the limit. Bright chrome plating was obtained at a bath temperature of 55 ℃, but the electrolytic deposition efficiency in this case is 12 to 15%. Although the deposition efficiency is low, one of the drawbacks of the electroplating of chromium is that most of the remaining electrolytic current is spent on the deposition of hydrogen, and when the bath temperature is increased, the electrolytic deposition efficiency further decreases.

There are also attempts to improve the coating by adding additives to the plating bath. For example, in the case of adding a large amount of silicate salt,
No cracks were observed in the static state after plating,
A crack was generated when a slight load was applied (see Metal Surface Technology 22, (6), P270, 1971).

Although chromium metal itself has a high degree of corrosion resistance, if a crack occurs, it cannot be expected to have anticorrosion ability as a film, so conventionally, a nickel plating layer was formed under the chromium plating layer, The layer has been used to expect gloss and hardness. In the case of a steel member, an electro-deposition stress is generated in the nickel plating layer, and in order to alleviate this, copper plating is further performed under the nickel layer, and three-layer plating is required. Heretofore, only the beautiful luster and hardness of chromium metal have been utilized as the plating film, and it has been abandoned to utilize its corrosion resistance.

[Problems to be solved by the invention]

As described above, in the conventional chrome plating, since the electroplating method is used, it becomes a hard film having internal stress, cracks occur in the film, and it is difficult to sufficiently exert the corrosion resistance of the chromium metal, Further, it is more difficult to process after plating. For this reason, many advantages of chrome metal cannot be utilized as a plating film, and since plating is performed after processing, it is necessary to process complicated shapes one by one, and it is difficult to obtain a uniform plating film. At the same time, the processing cost was high.

In order to solve these problems, the present invention has been made, and by forming a chrome-plated film under the limited conditions of ion plating, a film that is soft, has no cracks, and has good workability. The purpose is to obtain.

[Means for solving problems]

That is, the method according to the present invention reduces the pressure in the vacuum container to 1
× 10 ^-4 Torr and below, within the scope of 1,500V bias voltage from 200V between the deposition source and the object to be plated, the hardness 120~180Hv by ion plating on the surface of the object to be plated
And a method of forming a soft chromium plating film having excellent drawability, which comprises forming a chromium film having a film thickness of 2 to 7 μm.

In the method using ion plating, a material to be plated (hereinafter referred to as a substrate) is placed in a vacuum vessel, and the plating material is placed in a crucible below the vacuum vessel. The material in the crucible is heated and vaporized by a suitable heating source such as an electron beam, a laser, or a plasma gun. When this vaporized gas is passed through the plasma, some of the gas is ionized and has an electric charge (ionization). When a bias voltage is applied with the crucible as a positive electrode between the crucible and the substrate, the ions are attracted to the negative electrode substrate and collide with the surface thereof. Here, the ions are discharged and are deposited together with the non-ionized atoms to form a film.

The ion plating method is suitable for controlling the thickness of a thin film (μm or less), and is also suitable for plating a metal or alloy such as aluminum or titanium which cannot be electrodeposited by electroplating with an aqueous solution. For this reason, this is a technique that is unlikely to be considered as a method for treating a corrosion-resistant plating film that requires 10 μm or more and is conventionally treated by electroplating.

The inventor was conducting research on thin film plating, but for chromium metal, compared to a film formed by electroplating,
It was found that the film formed by the ion plating method was fairly soft.

As a result of further investigation, the conditions for obtaining a chrome-plated film that is soft and does not have surface defects such as cracks were investigated.

First, unlike electroplating, the same results were expected in the same manner as in ion plating, such as the generation of hydrogen and vacuum vapor deposition without the presence of chromium oxide (a method that does not ionize vaporized elements in the ion plating method). Then, softening of the film was observed, but the extent was not sufficient. Therefore, it became clear that the ion plating method should be used. Next, when the ionization rate (percentage of chromium atoms ionized in plasma {bias current / deposition rate and equivalent current} × 100) was examined, the higher the ionization rate, the more the film tended to soften. However, even if it was lowered, the effect was sufficiently recognized. From this, it was found that the ionized chromium is important and is involved in the formation of the soft film. When the bias voltage for accelerating this ion was examined, it was necessary to have a certain value or more, and the lower limit was 200V. The upper limit does not exist for softening, but it is desirable to treat at 1,500 V or less because the plated surface becomes rough at 1,500 V or more. As for the degree of vacuum, as expected, the higher the degree of vacuum, the better the film obtained.
10 ^-4 Torr is enough.

Furthermore, it was also found that the coatings obtained under these studied conditions were free of defects such as pinholes even though they were fairly thin coatings.

The present invention has been made based on the above findings, and in the present invention, a chromium plating film having a hardness of 120 to 180 Hv is formed on an object to be plated. The lower limit hardness of 120 Hv is set to be about the same as the hardness of pure chromium metal, and when the hardness exceeds 180 Hv, it is about the same as the vacuum deposition film,
The object of the present invention cannot be achieved. The plating method of the soft chromium plating film and the performance of the obtained film will be described below by using specific examples.

〔Example〕

FIG. 1 is a sectional view showing an outline of an ion plating apparatus used for confirming the present invention. 1 is a substrate to be plated, 2 is a crucible for containing a vapor deposition material, and 3 is a chromium metal which is the vapor deposition material. 4 is a vacuum container which is the main body of the apparatus, and 5 is plasma.

(Example 1) For the substrate 1, a mild steel plate having a thickness of 0.6 mm was used. Put chromium metal 3 in crucible 2 and put the inside of vacuum container 4 at 5 × 10 ^-5
After a vacuum of Torr was applied, a bias voltage of 200 V was applied between the substrate 1 and the crucible 2, and the chromium metal 3 was irradiated with an electron beam to generate it. The vaporized chromium atoms are partially ionized when passing through the plasma 5, accelerated by an electric field, and deposited on the substrate together with the chromium atoms to form 2 μm.
A film having a thickness of m to 7 μm was formed. The plasma was generated by a DC arc.

In Example 2 and Example 3 and Comparative Examples 1 to 3, the plating conditions were changed, and the comparative examples included conditions outside the range. Table 1 shows these ion plating conditions.

In Comparative Example 1, the degree of vacuum is low, and in Comparative Example 2, the bias voltage is low. Further, in Comparative Example 3, since the vaporized atoms are not ionized, the conditions for vacuum deposition are not for ion plating.

Regarding the chrome plating layer formed in this way,
The hardness, drawability, pinholes and cracks were examined. The hardness was examined by the Vickers hardness test, and the drawability was examined by using a cup squeezer with a punch diameter of 33 mm, a die and a clearance of 0.85 mm, and squeezing at a speed of 10 mm / min to examine the reflection of cracks. The pinholes and cracks were observed by enlarging the pressed and bent plated surface 400 times with a microscope. The results of these investigations are shown in Table 2 together with the electroplated chromium layer. The electroplated chrome layer was electrodeposited on the same steel plate as in the example using a Sargent bath, and had a thickness of 5 μm.

In all of the examples, the hardness was low, the drawability was good, and there was no film defect even with a film as thin as 2 μm. On the other hand, in Comparative Example 1 in which the degree of vacuum is low, Comparative Example 2 in which the bias voltage is low, and Comparative Example 3 in which vacuum deposition is performed, the film hardness is softened, but it is not sufficient to withstand drawing. Of the conditions of the ion plating, there is no limitation on the vapor deposition rate and the ionization method, and the vacuum degree and the bias voltage may be set within the ranges described above. The higher the ionization rate, the better, but a rate as low as 0.5% is sufficient.

FIG. 2 shows a comparison of the hardness of the chrome coating obtained by the present invention with the hardness of other methods and the hardness of pure chrome metal.

As described above, the electroplated chrome coating is the hardest, and the vacuum deposited film is softer than the electroplated film, but its degree is insufficient. I got that.

〔The invention's effect〕

According to this invention, the same hardness as pure chromium metal,
A soft chrome-plated film is obtained, and the film has no defects and no cracks, so that its properties including the corrosion resistance of chromium metal can be sufficiently exhibited. Therefore, even a thin film can exhibit sufficient anticorrosion ability, and the need for base plating such as nickel plating is eliminated, resulting in a reduction in processing cost. Furthermore, since this soft film can withstand drawing, it can be used not only as a surface coating of flexible materials, but also after plating, which simplifies the part manufacturing process and facilitates plating. High efficiency can be achieved.

[Brief description of drawings]

FIG. 1 is a sectional view showing the outline of an ion plating apparatus embodying the present invention, and FIG. 2 is a comparison diagram of the hardness of a chromium plating layer according to the present invention and other chromium. 1 ... Substrate, 2 ... Crucible, 3 ... Chrome metal, 4 ...
Vacuum container, 5 ... Plasma

Claims (1)

[Claims] 1. The pressure in the vacuum chamber is set to 1 × 10 ⁻⁴ Torr or less, and the bias voltage between the vapor deposition source and the object to be plated is within the range of 200V to 1,500V. Hardness 120-180Hv by plating and film thickness 2-7
A method of forming a soft chromium plating film having excellent drawability, which comprises forming a chromium film of μm.