JPH0830278B2 - Method for electroplating aluminum or aluminum alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for electroplating aluminum or aluminum alloys using a molten salt bath.

[0002]

2. Description of the Related Art Aluminum plated products have many advantages such as excellent corrosion resistance, beauty, and nontoxicity.

However, since electrodeposition from an aqueous solution is impossible, at present, it is mainly produced by the molten metal immersion plating method.

However, this method is difficult to perform thin plating, and the working temperature exceeds 700 ° C., so that an alloy layer with the base material is generated, or the base material is thermally adversely affected.
There are many problems.

Therefore, recently, there is a movement to solve the above problems by an electroplating method as an alternative method to the molten metal immersion plating and open the way to industrialization.

As described above, since electroaluminum plating cannot be electrodeposited from an aqueous solution, a method using a molten salt bath capable of electrodeposition is considered, and many electroaluminum plating methods based on this method have been proposed. It has been made and is being put to practical use.

This molten salt bath, for example, a method using a two-component system or a three-component system of AlCl ₃ -XCl (X: alkali metal) has a working temperature of 150 to 200 ° C. and a molten metal dipping method (for example,
Since it is much lower than 700 ° C), there is no adverse effect on the formation of the alloy layer or the base metal, and thin plating is possible. The above problems have been solved for some time, but the following problems are still present. It leaves a problem.

That is, in all of the conventional electroplating methods of aluminum using a molten salt bath, the deterioration of the bath over time is large, which results in a decrease in electrodeposition current efficiency (hereinafter simply referred to as current efficiency), powdery deposition, etc. However, it has been a serious problem for industrialization of electroaluminum plating.

The causes of the deterioration of the bath with time have not been fully clarified yet, but the three main causes are considered to be as follows.

Due to the moisture absorption of the plating bath, ionic species harmful to plating such as oxychloride are generated.

In the plating tank, various metals melt from the plating base material into the plating bath. These metal ions are almost all harmful except some. Among them, Fe ions are considered to be particularly harmful.

At the stage of depositing Al ³⁺ → Al ⁰ at the cathode (for example, a steel plate), harmful low-valence ions of Al are produced, and these are accumulated in the bath as the electrolysis proceeds.
The existence of these low-valence ions is not clear in the plating bath at 200 ° C or lower.

Of these problems, various metal ions such as Fe ions in the bath can generally be replaced and removed by stirring the molten salt bath with a pure metal aluminum rod or plate.

For example, as shown in Japanese Patent Laid-Open No. 61-243190, this method is also applied to replace and remove by suspending aluminum powder.

When the insoluble anode is used, the low valence ions of Al are oxidized at the anode, so that deterioration with time is prevented for the time being.

[0016]

However, it is difficult to completely remove the moisture due to the moisture absorption in the bath by only suspending the aluminum powder, which is a big problem.

[0017]

The electroplating method of the present invention has an arbitrary size (for example, a thickness of 0.1
Small amount of metallic sodium or metallic potassium (~ 5mm, small size 2-5mm square pieces) (eg 1g / l)
It is characterized in that aluminum or aluminum alloy is electroplated on the base metal using a molten salt bath in which is dispersed.

[0018]

[Operation] That is, by dispersing and stirring a small amount of metallic sodium or metallic potassium in a molten salt bath,
It reacts with a small amount of moisture absorbed in the bath to generate oxides and hydrogen gas, and deterioration over time is prevented.

Therefore, the electrodeposition of powdery plating is avoided and a beautiful plating is deposited.

Incidentally, the oxide of sodium or potassium is removed by filtration according to the soiling of the bath at appropriate times.

However, it usually reacts with free chlorine ions existing in the bath or in the atmosphere outside the bath or nascent chlorine to form sodium chloride or potassium chloride, which is a common ion that originally constitutes the bath, for plating. It does not have a bad influence on it.

Oxygen released at that time reacts with a counter electrode such as a pure aluminum plate or aluminum powder to form alumina. Then, if necessary, an alkali metal piece may be newly added.

As the molten salt bath used in the present invention, an anhydrous bath of a mixed molten salt of AlCl ₃ -XCl (X: alkali metal), which is usually used, is used.

It should be noted that electroplating with a molten salt, for example, electroplating with a molten salt of aluminum itself is already known and well understood by those skilled in the art, so further reference will be made to simplify the description. Omit it.

[0025]

EXAMPLES The present invention will be further described with reference to examples.

[0026]

[Example 1] Using a circulation cell type molten salt dedicated cell in which the space portion is maintained in an argon gas atmosphere, AlCl ₃ -N
19 of aCl-KCl (AlCl ₃ : 60, NaCl: 26, KCl: 14 mol%)
0 plating bath which is heated to keep ℃, AlCl ₃ · 4 as a moisture
Add 5g / l in the form of H ₂ O, thickness 0.1-5mm, size 2-5m
Add 1g / l of small pieces of metallic sodium cut into m squares, make cold cathode steel plate (1dm ² ), cathode 99.99% aluminum plate, flow rate 0.5m / sec, current density 10A / dm ² , energizing amount 120
Electrolysis was carried out at 0 coulomb / dm ² .

The experimental results for confirming the effect of metallic sodium on the deterioration of the bath due to water absorption are shown in FIG.

Initially, the addition of water caused the electrodeposited state to become powdery, and the current efficiency was 30% or less, but the state was gradually recovered by the addition of about 1 mm × 2 mm × 3 mm of metal sodium pieces, 1 g / l. As shown in the figure, after 30 minutes, the current efficiency was 85% or more, and white smooth plating was obtained, and the addition of the small pieces of metallic sodium according to the method of the present invention is effective in preventing the deterioration of the bath due to water absorption. Was confirmed.

[0029]

As is apparent from the above description, in the electroplating method of the present invention, in electroaluminum plating using a molten salt bath, a trace amount of water in the bath is effectively removed, and the bath deteriorates with time. Can be prevented.

Moreover, since there is no need to provide a step related to this removal, there is an effect that the process is simple and the application to actual operation is extremely easy.

Therefore, it can be said that the present invention greatly contributes to the industrialization of electroaluminum plating using a molten salt bath.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the time after the addition of small pieces of sodium metal and the current efficiency in electroplating with a molten salt bath.

Claims (1)

[Claims] 1. A method of electroplating aluminum or an aluminum alloy on a substrate metal using a molten salt bath, characterized in that pieces of metallic sodium or potassium of any size are dispersed in the molten salt bath. And a method of electroplating aluminum or aluminum alloy.