JPS6270593A - Aluminum electroplating bath and plating method by said plating bath - Google Patents

Abstract

PURPOSE:To develop an electroplating bath of Al which is inexpensive and has excellent current efficiency and long service life by compounding a specific org. solvent with a molten salt bath consisting of an Al halogen compd. and alkyl pyridinium halogen compd. CONSTITUTION:The plating bath prepd. by compounding 10-75vol% arom. org. solvent such as benzene with the molten salt bath in which 40-80mol% Al halogen compd. AlX3 (X is a halogen atom of Cl, Br, I, etc.) and 20-60mol% alkyl pyridinium halogen compd. C5H5N-R-X (R is an alkyl group of 1-5C, X is a halogen atom) is used as the plating bath to be used in the stage of electroplating Al to the surface of a cold rolled steel sheet, etc. A consumable anode consisting of an Al plate is used for the anode and the electroplating is executed by passing DC or pulse current of 0.1-10A/dm<2> current density in the plating bath kept at 0-40 deg.C in a dry oxygen-free atmosphere of N2, Ar, etc. The life of the plating bath is thus extended and the Al plating layer having the excellent resistance to heat, oxidation and corrosion is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrolytic aluminum plating bath that has a long bath life, is less dangerous, is inexpensive, and has high current efficiency, and a plating method using the plating bath.

(Prior Art) It is difficult to perform electroplating of aluminum in an aqueous plating bath because aluminum has a large affinity for oxygen and its potential is less noble than that of hydrogen. For this reason, electroplating of finished aluminum has conventionally been carried out in a non-aqueous plating bath, particularly an organic solvent-based plating bath.

As this organic solvent-based plating bath, ^Icl3 and Li
AIH or LiH dissolved in ether ^
ICl3 and L18111. A typical example is a plating bath prepared by dissolving .

(Problem to be solved by the invention) However, all of these plating baths contain highly active Li^1114 and LiH, so if oxygen or moisture is present, they will react with them and decompose. However, the current efficiency was reduced and the bath life was also shortened. For this reason, during plating, the plating bath was sealed with an inert gas to prevent it from coming into contact with oxygen or moisture, but since complete sealing is difficult, the longer the plating time, the lower the current efficiency and the shorter the bath life. ization was inevitable.

In addition, LiAIH and LiIt react violently with oxygen and moisture, so if a large amount of oxygen or moisture accidentally gets mixed in,
There was also a risk of explosion.

Furthermore, since Li^l114 and LiH are expensive, plating costs are high, and their uses are limited due to price.

(Means for Solving the Problems) In view of the problems mentioned above in conventional non-aqueous electrolytic aluminum plating baths, the present invention provides a plating bath that solves these problems and a plating method using the plating bath. It provides:

The present inventors conducted various studies in order to develop a plating bath free from the above-mentioned problems, and as a result, they developed a molten salt bath consisting of an aluminum halogen compound and an alkylpyridinium halogen compound.

We have also discovered that in order to efficiently perform high-purity aluminum plating with a good appearance using this molten salt bath, it is necessary to perform the plating under specific electrolytic conditions.

That is, the present inventors have developed an aluminum halide compound (^
IX1, where X is Cl, Br, I) 40-80 mol% and a furkylpyridinium halogen compound (C, 115N-
An electrolytic aluminum plating bath characterized in that an organic solvent is blended into a molten salt bath formed by melting 20 to 60 mol% of R-X, where R is an alkyl group having 1 to 5 carbon atoms and X is a halogen atom. Using this plating bath, the bath temperature is 0-40℃ by direct current or pulsed current in a dry oxygen-free atmosphere.
He developed an electrolytic aluminum plating method characterized by plating under electrolytic conditions of a current density of 0.1-10^/dm2.

When the concentration of a molten salt bath consisting of an aluminum halogen compound and an alkylpyridinium halogen compound is in the above range, it becomes a liquid at around room temperature and ionically dissociates, so that electroplating of aluminum is possible using the molten salt bath alone. For example, a molten salt bath consisting of aluminum chloride and butylvinonium chloride undergoes ion dissociation as follows.

However, this molten salt bath is somewhat viscous, and the plating solution is often carried away by the material to be plated, and there is a limit to plating at high current density due to conductivity.

Therefore, in the present invention, since the above-mentioned ionic dissociation does not change even if an organic solvent is added, an organic solvent is added to the molten salt bath to reduce the viscosity of the bath and reduce the amount of plating solution taken out by the material to be plated. At the same time, it also improves conductivity,
This made it possible to perform plating at high current density.

Since this plating bath contains an organic solvent, it is flammable, but since it does not contain any active ingredients, it is stable and there is no risk of explosion if it comes into contact with oxygen or moisture.

In the case of the plating bath of the present invention, aluminum plating is performed using an aluminum halogen compound as in the conventional plating bath, but in the case of the present invention, the aluminum halogen compound is not limited to ^ICl3, and ^lBr3 and ^113 can also be used. be. However, ^Icl3 is cheap, and
It is preferable from a safety point of view as it is less violent.

Further, as the alkylpyridinium halogen compound, it is preferable to use one in which the alkyl group has 1 to 5 carbon atoms. This is because when the number of carbon atoms in the furkyl group is 6 or more, it becomes difficult to become liquid at room temperature when mixed with an aluminum halide compound.

Further, as the organic solvent, aromatic solvents such as benzene, toluene, xylene, etc. are preferable in terms of solubility.

The blending ratio of Rakuchu's aluminum halogen compound and flukylbylinonium halogen compound is such that the concentration of Moesha is 40~
Preferably, it is 80 mol% (the latter concentration is therefore between 20 and 60 mol%).

This is because when the content of the aluminum halide compound is less than 40 mol%, the alkylpyridinium cation concentration increases as is clear from the above ion dissociation, and the alkylpyridinium cation reduction reaction proceeds at the same time during aluminum electrodeposition. This is because it causes deterioration, a decrease in current efficiency, and poor surface appearance of the plating layer. Moreover, if it exceeds 80 mol%, the conductivity of the bath will become low and the vapor pressure will also become high.

In addition, the blending ratio of the organic solvent to the total amount of the aluminum halogen compound and the flukylvinonium halogen compound is 10 to 75 vol% (therefore, the total amount of both halogen compounds is 25 to 90 vol%). It is preferable to do so.

When the proportion of the organic solvent is less than loVOI%, the properties are almost the same as those of a molten salt bath, and the effect of adding the organic solvent is hardly recognized. Furthermore, if the proportion of the organic solvent exceeds 75 vol%, the concentration of the aluminum halide compound in the bath will be low, resulting in a drastic decrease in current efficiency during aluminum electrodeposition, and if ignited, there is a risk of fire.

Although the plating bath is safe even when exposed to oxygen or moisture, in order to prevent oxidation of the aluminum complex ions, plating is preferably carried out in a dry oxygen-free atmosphere (for example, in dry N2 or Ar). Further, the electrolytic conditions are a bath temperature of 0 to 40 DEG C., a direct current or a pulse current, and 0.1 to 10^/daI2, whereby efficient, highly pure and uniform plating can be performed. If the bath temperature is lower than 0''C, it will be difficult to plate with high current density, and conversely, if the bath temperature is higher than 40℃ and the current density is higher than 10Δ/dm2, the plating layer will turn gray. At the same time, the crystals also become coarse dendrite crystals, resulting in poor appearance and workability.Pulse current makes the crystals finer and provides better workability than direct current.

Generally, in order to achieve uniform plating through continuous plating, it is necessary to replenish the plating bath with ^1 ions and to control the ^1 ions in the bath at a constant level. It is advantageous to use a soluble aluminum anode as the anode in the plating bath because AI ions are automatically replenished according to the amount of current applied. For example, ^lc1. containing an aromatic organic solvent. -B
When plating is performed using an aluminum anode in a PC (butylpyridinium chloride) PS plating bath, ^I ions are automatically supplied from the anode as follows.

8l+4cI--nAIC1,-+ 3 e-81+
7^IC+,--,4^12CI? -+ 3 e-The attached drawing uses an aluminum plate for the anode. ! 9A
-4-9"I+1! Palm i or 1 ml"-
Δ1 in the bath when plating is applied
This shows the change in ion concentration, and the ^1 ion concentration remains almost constant even if plating continues for a long time.

When performing continuous plating using an insoluble anode such as Ti-Pt type anode, replenishment of ^1 ions is as follows: ^Ic1. , ^I
It is sufficient to replenish a halogen compound such as B "3, ^II. However, in the case of continuous flashing using an insoluble anode, a halogen bus generation reaction occurs at the anode interface during electrolysis, and the halogen component in the bath decreases. This causes the bath composition to fluctuate and shortens the life of the bath.

The present invention will be explained below with reference to Examples.

(Example) Example 1 A cold-rolled steel plate (thickness: 0.5 mm) was subjected to plating pretreatment such as solvent vapor cleaning, alkaline degreasing, and pickling using a conventional method, and then dried and immediately kept in an N2 atmosphere in advance. Benzene was added to a molten salt bath consisting of 60 mol% of ^1cL and 40 mol% of butylpyridinium chloride at a ratio of 6.
Plating bath formulated to be 0 vol% (bath temperature 20°C)
), and aluminum ram plating was performed. For plating, a cold-rolled steel plate is used as the cathode, and an aluminum plate (purity 99.993+) is used as the cathode.
ut%, plate thickness 5 mm) as an anode, the test was carried out for 5 minutes at a current density of 5Δ/dII+2 using direct current.

The plating layer of the obtained aluminum-plated steel sheet had a uniform thickness, a white color, and dense crystals.

Furthermore, even when the steel plate was repeatedly bent, no cracks or peeling occurred, and both processing and adhesion were good.

Current efficiency is calculated from the amount of current flowing and the amount of plating deposited.
It was 100%.

Example 2 A cold-rolled steel plate with a thickness of 0.5 wl11 was aluminum plated in the same manner as in Example 1. Plating is carried out by cold rolling in a plating bath in which toluene is mixed in a molten salt bath of 311.70 mol% and 30 mol% of ethylpyridinium chloride at a bath temperature of 30°C and 30 mol% of ethylpyridinium chloride, which is maintained in an atmosphere of A, at a bath temperature of 30°C. A steel plate was immersed, and using the steel plate as a cathode and an aluminum plate (same as in Example 1) as an anode, immersion was carried out using direct current at a current density of 5^/dm2 for 5 minutes.

The quality of the plating layer of the obtained aluminum-plated steel sheet was the same as in Example 1, with a uniform thickness, white color, and m-density of crystals. Furthermore, even when the steel plate was repeatedly bent, no cracks or peeling occurred, and both processing and adhesion were good. Furthermore, the current efficiency was 95%.

Example 3 A cold-rolled steel sheet with a thickness of 0.5 mm was subjected to plating pretreatment and drying in the same manner as in Example 1, and aluminum plating was performed in each of the plating baths of Examples 1 and 2 using pulsed current. Plating with pulsed current has a duty ratio of 1/10 to 1/100 for each plating bath. Average current density 0.1~10^/
dm2, the thickness of the plating layer was uniform, and the appearance and
Both workability and adhesion were the same as those of direct current plating.

We also plated a Cu alloy and a Ni alloy in the same manner as above, and found that excellent ^1 plating was possible.

(Effects) Since the plating bath of the present invention described above does not contain any components that react violently with oxygen or moisture, the bath life is long and the danger is low. In addition, alkylpyrinonium halogen compounds are cheaper than Li^IH and LiH, have high bath current efficiency, and can be plated at high current density, which, together with their long bath life, make them attractive for plating. This can be significantly reduced.

Therefore, if the plating bath of the present invention is used, it can be applied to home appliance parts, electronic parts such as IC9-D7 frames, automobile parts, and aircraft parts that require electrolytic aluminum plating materials and products from the viewpoint of heat resistance, oxidation resistance, corrosion resistance, etc. They can be supplied to parts and other fields at low cost.

[Brief explanation of drawings]

The attached drawing is a graph showing the change in the ^1 ion concentration in the bath when continuous plating is performed using the plating bath of the present invention, and an aluminum anode is used as the anode for long time plating.

Claims (5)

[Claims] (1) Aluminum halogen compound (AlX_3, where X is Cl, Br, I) 40 to 80 mol% and alkylpyridinium halogen compound (C_5H_5N-R-X, where R is an alkyl group having 1 to 5 carbon atoms, and X is a halogen atom)
An electrolytic aluminum plating bath characterized in that an organic solvent is blended into a molten salt bath formed by melting 20 to 60 mol% of aluminum. (2) The electrolytic aluminum plating bath according to claim 1, wherein the organic solvent is aromatic. (3) The electrolytic aluminum plating bath according to claim 1, wherein the blending ratio of the organic solvent is 10 to 75 vol%. (4) Aluminum halogen compound (AlX_3, where X is Cl, Br, I) 40 to 80 mol% and alkylpyridinium halogen compound (C_2H_5N-R-X, where R is an alkyl group having 1 to 5 carbon atoms, and X is a halogen atom)
Using an electrolytic aluminum plating bath in which an organic solvent is blended with a molten salt bath of 20 to 60 mol%, the bath temperature is 0 to 0 using direct current or pulsed current in a dry oxygen-free atmosphere.
An electrolytic aluminum plating method characterized by plating under electrolytic conditions of 40° C. and a current density of 0.1 to 10 A/dm^2. (5) The electrolytic aluminum plating method according to claim 2, characterized in that plating is performed using an aluminum anode as an anode.