JPH01247592A - Continuous aluminum electroplating method - Google Patents

Abstract

PURPOSE:To stably carry out Al plating when a steel member is electroplated with Al in a molten salt plating bath contg. an Al halide and an alkylpyridinium halide, by using a porous basket made of a specified metallic material and packed with many Al balls as the anode. CONSTITUTION:When the surface of a steel sheet as the cathode is plated with Al in a mixed molten salt consisting of an Al halide such as Al chloride and an alkylpyridinium halide such as butylpyridinium chloride as a plating bath, a metal basket packed with many Al balls is used as the anode. The basket is produced by nitriding, boriding or carburizing the surface of a porous net of Ti, Ta, Nb, Zr, etc., or coating the net with a Pt family metal, the oxide thereof or other metal oxide so as to prevent corrosion by the molten salt plating bath. Al plating can stably be carried out without causing the corrosion of the basket by the plating bath and in the case where an Al plate is used as the anode, plating work becomes unstable owing to the consumption of the plate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of plating aluminum using a non-aqueous plating bath.

(Prior art and its problems) Aluminum electrochemically has a more base potential than hydrogen, so when plating is done in an aqueous solution, hydrogen is generated at the cathode.
It becomes difficult to plate aluminum. To prevent this, electroplating of aluminum has conventionally been carried out using a plating bath made of molten salt or a non-aqueous solution.

Non-aqueous plating baths include AICh and LiA1)
LiAlH4 or LiH dissolved in ether is typical, but LiAlH4 and LiH may react with oxygen or moisture and decompose or explode, resulting in a decrease in current efficiency and In addition to the disadvantages of reduced lifespan, these hydrides are expensive and have limited use due to price.

In order to solve the above problems, a bath containing a molten salt of aluminum halide and alkylpyridinium halogen (IJI) and an aromatic organic solvent has been proposed (JP-A-62-70592 and JP-A-62-70592). 1986-
No. 70593), these baths allow electroplating of aluminum at room temperature with low risk of explosion and inexpensive reagents.

(Problems to be Solved by the Invention) However, the above method poses a major problem when it is implemented industrially. In other words, when aluminum plating is performed on a steel plate in a molten salt of aluminum halide and alkylpyridinium halide using an aluminum plate as an anode and a cold-rolled steel plate as a cathode, good plating can be obtained as long as the anode current density is low. However, when plating is performed at a higher anode current density, the resulting plating becomes gray and forms dendrite-like crystals. It is assumed that this is because when the current density is increased, organic matter adheres to the anode surface due to a side reaction, making the current distribution unrestricted and, as a result, the plating becomes gray. However, for industrially efficient plating, it is essential to increase the anode current density.

In order to increase the current density and improve productivity while preventing the resulting plating from turning gray, it is necessary to use an aluminum plate larger than the material to be plated and to sufficiently stir the liquid. However, increasing the size of the aluminum plate causes an increase in the size of the plating tank, nonuniform current distribution, and increased consumption of inert gas used to prevent oxidation of aluminum complex ions in the bath.

Furthermore, when plating is performed using an aluminum plate as an anode, the aluminum plate wears out and the current distribution becomes uneven, resulting in uneven plating thickness, so the aluminum plate must be replaced. If this is done, the frequency of replacement will increase, resulting in the inconvenience of having to stop operation each time.

Generally, in electroplating in an aqueous solution, an anode basket is used to carry out continuous operation, the spherical metal to be plated is placed in the anode basket, and a direct current is applied to dissolve the spherical metal and the metal to be plated is placed in the bath. Plating is performed continuously while replenishing ions. Although this method eliminates the drawbacks caused by the use of aluminum plates, the anode basket is required to be corrosion resistant to the plating solution, and titanium is generally used as the anode basket for electroplating in the aqueous solution.

However, in the above method using a non-aqueous molten salt of aluminum halide and alkylpyridinium halide, the molten salt is highly corrosive, and if a titanium anode basket is used as in aqueous electroplating, the elution of titanium may occur. A new problem arises in that the eluted titanium adheres to the plated material.

(Object of the Invention) The present invention provides a method for plating aluminum on a steel plate or the like using a conventional bath containing an aluminum halide and an alkylpyridinium halide, in which a metal aluminum ball is housed instead of an aluminum plate as an anode. Plating is carried out by applying electricity using an anode basket that is corrosion resistant to the plating solution. This eliminates uneven current distribution due to aluminum elution when an aluminum plate is used as an anode, and operational problems due to replacement of the aluminum plate. The purpose of the present invention is to provide a continuous aluminum plating method that avoids stoppage.

(Means for Solving the Problems) The present invention provides an aluminum electroplating bath that contains an aluminum halide and an alkylpyridinium halide as molten salts and may further contain an aromatic organic solvent. This is a method of aluminum plating a plating material, in which a corrosion-resistant anode basket containing a metal aluminum ball is used as an anode, and direct current or pulse current is applied to the material to be plated, thereby continuously plating the material with aluminum. According to the method of the present invention, of the metal aluminum balls constituting the anode and the anode basket, only the metal aluminum balls are almost selectively dissolved, and the anode basket base itself is not eluted. Therefore, the non-uniformity of the current distribution is eliminated, and if the number of metal aluminum balls decreases due to elution, it is sufficient to simply add the metal aluminum balls from above into the anode basket without stopping the current supply, and the formed plating layer is It stabilizes and further improves operational efficiency.

The present invention will be explained in more detail below.

The anode basket substrate in the method of the present invention must have corrosion resistance to aluminum halides and alkylpyridinium halides. As the substrate, conductive metals such as titanium, tantalum, niobium, and zirconium, or their base alloys can be used in a desired shape such as porous, lattice, or net shapes.

In order to improve the physical strength and chemical corrosion resistance of the surface of these metals and metal alloys while maintaining their metallic conductivity, the surface of these metals, etc. is nitrided by known means such as chemical vapor deposition or physical vapor deposition. Boridization or carbonization coating treatment can also be performed,
As a result, it is possible to obtain an anode basket substrate that can withstand wear when metal aluminum balls are introduced and does not elute into the electrolytic bath. Note that the metals mentioned above can be used alone as an anode basket without the coating, except for titanium alone.

The thickness of these surface coating layers is 0.5 μm or more, preferably 2 μm or more.
A thickness of μm or more is sufficient. If the coating thickness is less than 0.5 μm, the surface treatment will not be sufficient, and if titanium is used as a substrate in the presence of pinholes or the like, elution of the substrate may occur.

In place of the nitrided, borided or carbide coating layer, a platinum group metal, a platinum group metal oxide, or aluminum, germanium, gallium, vanadium, titanium, silicon, manganese, indium,
At least one coating layer selected from metal oxides of bismuth, tin, antimony, tantalum, niobium, zirconium, molybdenum, tungsten, and hafnium may be formed.

These coating layers are electrically conductive coating layers that are stable against corrosive plating solutions, and the coating layers protect the substrate from corrosion and conduct the current applied to the anode basket from the coating layer to the anode basket. It has the function of flowing into a metal aluminum ball. Also, since it has higher hardness than aluminum, it can withstand wear when inserting metal aluminum balls.

The thickness of the oxide coating layer is 0.5 μm or more, preferably 1 μm.
m or more is sufficient. In addition to chemical vapor deposition or physical vapor deposition as in the case of the nitrided, borided or carbonized coating layer, the oxide coating layer can be formed by dissolving the metal salt of the metal in a solvent, applying it to the substrate, and then applying it to the substrate in a reducing atmosphere or Thermal decomposition method, which converts into the desired coating form by heat treatment in an oxidizing atmosphere, and plating methods, such as electroless plating and electroplating, can be used. Plating method is preferred. The coating thickness can be determined by repeating the above operations in the case of pyrolysis, by adjusting the plating time and current density in the case of plating, and by controlling the deposition time in the case of smoke deposition. It can be adjusted to the desired thickness.

Next, the metal aluminum balls used in the method of the present invention are:
It may have any shape such as spherical, ellipsoidal, or polyhedral, and may have irregularities.

Furthermore, the smaller the particle size, the larger the surface area per unit weight, and the particle size range is preferably about 1 to 50++ uw.

Further, in the present invention, aluminum chloride, aluminum bromide, and aluminum iodide can be used as aluminum halides constituting the molten salt, and as alkylpyridinium halides, the N-alkyl group has 1 to 5 carbon atoms, and halogen Compounds in which is chlorine, bromine or iodine can be used, the most preferred compound being N-butylpyridinium chloride. The composition of both is 40 to 80 mol% aluminum halide.
, alkylpyridinium halide 20-60 mol%
When an organic solvent is used, it is preferable that the amount of the aromatic organic solvent is 10 to 75% by volume based on the total amount of both the halides. Benzene, toluene, xylene, etc., which have excellent ability to dissolve compounds, are desirable.

The materials to be plated with aluminum are made of conductive metals such as steel, such as home appliance parts, electronic parts, automobile parts, and aircraft parts.Depending on the shape, the material may be used as a cathode and the surface may be plated with aluminum. However, if it cannot be used alone as a cathode due to constraints such as shape, a separate cathode may be installed, electrically connected to the cathode, and energized to perform plating.

In order to perform aluminum plating using a plating bath, an anode basket, a metal aluminum ball, and a material to be plated made of each of the above-mentioned compounds, the bath temperature is set to 0 to 150°C, preferably 0 to 40°C, and the cathode current density is set to 1. ~50A/
dm"preferably 20 to 30 A/dm".

Conventionally, it is not preferable to set the bath temperature to 40° C. or higher because the resulting plating layer becomes gray, but in the method of the present invention, the plating layer does not become colored and plating can be performed at high temperatures.

In the case of the conventional technology that uses an aluminum plate with the same area as the material to be plated as an anode, the optimal cathode current density range is 0.1 to IOA/dit, and within this range, a material with high current efficiency and high purity can be obtained. Although a plated layer is obtained, the method of the present invention further increases the cathode current density to achieve the above-mentioned 20 to 3.
Good plating can be obtained even at 0A/dm2,
Furthermore, when the Metsuki liquid is stirred by a jet stream, it becomes 50A.
Even at a high current density of /dm'', it is possible to obtain good aluminum plating with high current efficiency.

In order to prevent hydrolysis and oxidation of the aluminum halide, it is desirable to operate the plating in a dry oxygen-free atmosphere, such as a dry nitrogen or dry argon atmosphere, and it is particularly advantageous to operate in a dry nitrogen atmosphere at low cost. Can be done.

The above-mentioned mixture of aluminum halide and alkylpyridinium halide liquefies and ionically dissociates at temperatures of 0 to 40° C. and higher to form aluminum complex ions. When direct current or pulsed current is applied in this state, the dissociated aluminum complex ions are reduced and precipitated onto Murakami to be plated, and the material to be plated is plated.

As the plating operation progresses, the aluminum complex ions in the plating bath decrease, but the metal aluminum balls in the anode basket dissolve and compensate for the decrease, so that the aluminum concentration in the plating bath is maintained approximately constant. Also, as the plating operation progresses, the amount of the metal aluminum balls decreases, in which case new metal aluminum balls may be added to the anode basket, and an anode basket with an opening may be used. It is possible to continuously form aluminum plating on the plated surface without having to stop the plating operation.

(Examples) Examples of the present invention will be described below, but these examples do not limit the present invention.

A net-like basket made of etitanium was washed with a hot oxalic acid aqueous solution, further washed with ion-exchanged water, dried, and then a hydrochloric acid solution containing 15 mol% ruthenium chloride and 85 mol% titanium chloride was applied with a brush. It was dried at room temperature and further fired at 500°C. This operation was repeated to produce an anode basket having a coating layer with a thickness of about 5 μm. On the other hand, the steel plate was subjected to pre-plating treatments such as solvent vapor cleaning, alkaline degreasing, and pickling, then dried, and 60 mol% of aluminum chloride and 40 mol% of butylpyridinium dichloride were kept in a nitrogen atmosphere.
mol% in a molten salt plating bath (bath temperature 20°C), the steel plate was used as a cathode, and the anode basket containing a metal aluminum ball (purity 99.99% by weight, diameter 10mm) was used as an anode to apply a direct current ( IOA/dm”)
Continuous aluminum plating was performed by applying current.

Table 1 shows the appearance and current efficiency of the plating after a predetermined period of time. As can be seen from Table 1, the plating layer of the aluminum-plated steel sheet obtained in this example exhibited a white color, and the current efficiency also showed an ideal value of 98 to 100% over a long period of time. Furthermore, the aluminum-plated steel sheet obtained in this example had a uniform thickness and dense crystals, and even when the obtained steel sheet was repeatedly bent, no cracking or peeling occurred, and both workability and adhesion were good.

This ff1LL Aluminum plating was performed in the same manner as in Example 1 except that an aluminum plate (purity 99.99% by weight) was used as the anode. Table 1 shows the appearance and current efficiency of the plating after a predetermined period of time.

Table 1 The surface of a titanium basket was treated by ion blasting and coated with titanium carbide to form an anode basket.

Aluminum plating was carried out on a steel plate serving as a cathode in the same manner as in Example 1 except that this anode basket was used, the bath temperature was 30°C, and the molten salt was 60 mol% of aluminum promide and 40 mol% of methylpyridinium chloride. went.

The plated layer obtained on the steel plate had a uniform thickness, a white color, and dense crystals as in Example 1. Further, even when the steel plate was repeatedly bent, no cracking or peeling occurred, and both workability and adhesion were good. Furthermore, the current efficiency was almost 100% after 10 hours of energization, similar to Example 1.
There is no deterioration of the plating bath and the purity of the plating layer is 99%.
．． It was 97% by weight or more.

Aluminum plating was attempted in the same manner as in Example 2, except that no coating layer was formed on the surface of this MU coarse λ titanium basket.

At the beginning of energization, formation of an aluminum plating layer on the steel plate serving as the cathode was observed, but corrosion of the basket progressed as soon as energization started, and it became impossible to continue the plating operation after about 3 hours had passed.

Senshu Panshu Parts were plated in substantially the same manner as in Example 1.

Bolts that have been previously subjected to solvent cleaning, alkaline degreasing, and acid cleaning are placed in a barrel and immersed in a molten salt plating bath (bath temperature 60°C) consisting of 67 mol% aluminum chloride and 33 mol% butylpyridinium chloride kept in a nitrogen atmosphere. The current density is 5A/d+++, with the contact in the barrel as the cathode and the anode basket containing a metal aluminum ball (99.99% purity, diameter 101) as the anode.
Aluminum plating was applied to the bolts by applying a direct current of ”.

The resulting plating layer had excellent adhesion, was white, had a uniform thickness, and had dense crystals.

Comparison (1) Aluminum plating on bolts was carried out in the same manner as in Example 3 except that an aluminum plate (purity 99.99% by weight) was used instead of the anode basket as an anode. The resulting plating layer was non-uniform, with plating concentrated on the screw threads, poor adhesion to various parts, and the appearance of the plating layer was gray.

(Effects of the Invention) When applying aluminum plating to steel plates, etc. using a molten salt plating bath, the present invention provides a corrosion-resistant solution to the molten salt plating bath containing metal aluminum balls instead of an aluminum plate as an anode. Anode basket is used.

Firstly, in the conventional aluminum plating method using a molten salt plating bath, the current distribution becomes uneven due to elution of the aluminum plate serving as the anode, resulting in uneven thickness of the two main layers. In the invention, the metal aluminum balls melt almost selectively and the anode basket itself does not melt, so there is no disturbance in the current distribution.
A uniform plating layer with a beautiful appearance and excellent heat resistance, oxidation resistance, corrosion resistance, etc. can be obtained.

Second, in the conventional plating method, the anode elutes and requires frequent replacement of the anode and the electricity supply needs to be stopped each time the anode is replaced, which reduces operational efficiency, whereas the present invention In this case, there is no need to replace the anode, and only the metal aluminum balls need to be replenished, and the efficiency does not decrease.

Third, in order to perform aluminum plating industrially, it is essential to increase the amount of aluminum plating that can be obtained within a certain period of time by increasing the current density. By increasing the current density, the resulting plating layer is prevented from deteriorating even if the current density is increased. However, as the anode becomes larger, the plating apparatus itself becomes larger, which increases the cost of the apparatus itself, the cost of ancillary equipment, and the installation area, which is not preferable. In contrast, in the present invention, the surface area of the metal aluminum balls used is large, and the actual anode area can be dramatically increased without increasing the size of the anode basket.・It is possible to obtain a large amount of plating within a relatively short period of time without increasing the current density, which is particularly advantageous when performing industrial large-scale plating processing.

Patent applicant: Nisshin Steel Co., Ltd.

Claims (5)

[Claims] (1) A method of aluminum plating a material to be plated using an aluminum electroplating bath containing an aluminum halide and an alkylpyridinium halide as a molten salt, in which a corrosion-resistant anode basket containing a metal aluminum ball is used as an anode. A method characterized in that the material to be plated is continuously plated with aluminum by applying current to the plated material. (2) The method of claim 1, wherein the substrate of the corrosion-resistant anode basket is a metal substrate selected from the group consisting of titanium, tantalum, niobium, zirconium, and alloys thereof. (3) The method according to claim 1 or 2, wherein the corrosion-resistant anode basket is a basket whose base surface is coated with nitridation, boronization, or carbonization. (4) The base surface of the corrosion-resistant anode basket is made of platinum group metal, platinum group metal oxide, aluminum, germanium, vanadium, titanium, silicon, manganese,
indium, bismuth, tin, antimony, tantalum,
3. A method according to claim 1, comprising a coating of one or more selected from the group consisting of metal oxides of niobium, zirconium, molybdenum, tungsten and hafnium. (5) Plating conditions are dry oxygen-free atmosphere with bath temperature of 0 to 1.
5. The plating according to any one of claims 1 to 4, wherein the plating is carried out at 50° C. with a direct current having a current density of 0.1 to 50 A/dm^2 or a pulsed current having an average current density of 0.1 to 30 A/dm^2. Method.