JPS60152693A - Zinc-lead co-deposition electroplating bath - Google Patents

Abstract

PURPOSE:To provide a titled electroplating bath which yields a smooth and good zinc-lead plating film by incorporating an adequate amt. of bivalent lead ion having a suitable concn. and a the nonionic surface active agent expressed by the specific general formula as a levelling agent in a chloride bath, etc. of bivalent zinc ion. CONSTITUTION:A smooth and good zinc-lead co-deposited plating film having excellent corrosion preventiveness is obtd. by an acidic zinc-lead co-deposition electroplating bath contg. bivalent lead ion having the conc. of <=1/50 the concn. of zinc ion in a molar ratio and contg. further the nonionic surface active agent expressed by the general formula ( I ) (where R1; 1-4 C alkyl group or phenyl group, R2 and R3; hydrogen or methyl group, m and n; 1-30 interger), (II) (where R; 1-18C alkyl group, m; 2-20 interger) in the range of 0.1-30g/l as a levelling agent in a chloride bath of bivalent zinc ion, borofluoride bath, silicofluoride bath or a mixed bath of chloride and borofluoride or silicofluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plating bath capable of obtaining a zinc-lead plating film with excellent corrosion resistance by eutectoiding zinc and lead during electroplating.

Zinc plating has excellent corrosion resistance and is inexpensive, so
This is the most widely used plating method. In addition to being used by plating specialists for products in all fields, it is also widely used as a surface treatment for steel sheets supplied by steel manufacturers as galvanized steel sheets. In recent years, it has become a problem that automobile parts exported to cold regions are rapidly corroded by antifreeze IL agents sprayed on roads.
Much research has been done on how to obtain galvanized coatings that can withstand harsh corrosive environments.

Among them are zinc-iron, zinc-nickel.

Alloy electroplating such as zinc-cobalt-chromium, zinc-cobalt-molybdenum, zinc-cobalt-nickel, zinc-nickel-chromium (vanadium, tungsten), zinc-nickel-cobalt-chromium, zinc-cobalt, etc.
Multilayer electroplating of zinc/manganese, chrome (nickel, tin)/zinc, etc., dispersion plating of zinc-aluminum,
Hot alloy plating, such as zinc-aluminum, zinc-magnesium, and zinc-manganese, has been studied mainly by steel manufacturers, and nine publications have been published. However, it seems that there are advantages and disadvantages in terms of uniformity of film composition, price of the 9 alloy components, bath management, equipment, workability of the film, etc., and currently it is not possible to narrow down which method is the best. Seem.

On the other hand, lead is a relatively inexpensive metal and itself has excellent corrosion resistance. Although it is also used as a turn sheet, the plating film made of lead alone is very soft and easily scratched, and until now there are no suitable additives for lead plating other than peptone and glue. Since it has not been developed, it is difficult to use lead alone. In addition, lead is a potentially sensitive metal.9 Regarding zinc-lead alloy electroplating, which has essentially a different anti-corrosion mechanism than zinc, primary ■ or ■
Although this is thought to be due to the reasons described in 2.1, there have been no reports of any serious use of baths for industrial use.

■Since zinc and lead do not dissolve in each other, a uniformly dispersed alloy cannot be prepared by melting methods, and there is no history or data on zinc-lead alloy plating in hot-dip plating.

■Lead is much more harmful than zinc (Pb: E=-0,
126V, Zn: E = -〇, 736V) (7
) T:, When attempting to eutectoid by electroplating,
Lead is substituted and precipitated by the precipitated zinc, making it difficult to obtain a uniform and dense plating film. Furthermore, in order to suppress lead precipitation, it is necessary to reduce the lead concentration in the bath to a very low level, and with conventional techniques, it has been difficult to maintain this constant.

■In the case of trace amounts of lead dull materials, when heat treated after plating, lead may be concentrated at the interface between the base material and the plating film, causing peeling.

In this way, lead in galvanizing is often considered to be a factor that has an adverse effect or is difficult to control, and therefore it is thought that lead has often been left out of the scope of consideration. However, since lead is a metal with a high hydrogen overvoltage, it is possible that the addition of lead increases the hydrogen overvoltage of the eutectoid plating film and suppresses the serotype reaction. F. Mansfeld
They also report that when 0.2 to 1.0% lead is added to zinc, the hydrogen generation reaction rate is lower than that of pure zinc.

In addition, the inventors have experienced a case in which about 1% lead was detected in a case where a cathodic protection zinc plate for a ship had a problem with poor dissolution. These results indicate that trace amounts of lead suppress corrosion of zinc.

The present invention was made in view of the problems mentioned above, and it is an object of the present invention to provide a plating bath capable of suppressing the non-dense substitutional precipitation of lead and achieving smooth and good zinc-lead eutectoid electroplating. purpose.

Two configurations of the present invention will be explained below.

That is, containing divalent lead ions at a concentration of 1150 or less of zinc ions in a molar ratio in a divalent zinc ion chloride bath, borofluoride, silicon fluoride, or a mixed bath of chloride and borofluoride, or chloride and silicon fluoride. and as a smoothing agent.

General formula, where R1 represents an alkyl group or phenyl group having 1 to 4 carbon atoms, R2 and R3 represent hydrogen or a methyl group,
m and n represent integers of 1 to 30.

(B) Re0-(CI+2-(:1120) m II and 1R represent an alkyl group having 1 to 18 carbon atoms.

m represents an integer of 2 to 20.

0.1 g ll of nonionic surfactant shown in
This is an acidic zinc-lead eutectoid electroplating bath having a zinc-lead content in the range of 30 g/l to 30 g/l.

In addition, here, the amount of surfactant added to the nonionic yarn is 0.1g.
The reason for limiting it to /A~30g/I2 is 0.1g
/j! If it is less than 30 g/l, the effect of suppressing substitutional precipitation will not be sufficient, and it is not preferable, and if it is more than 30 g/l, bubbles will be generated frequently, which is undesirable from the viewpoint of pollution prevention such as environmental pollution. It is.

Next, the composition of the plating solution and working conditions will be shown in Examples, but the present invention is not limited to these Examples. The composition and conditions of one plating bath can be changed as appropriate in accordance with the purpose of obtaining a eutectoid film.

Example 1 +1) ZnCl2 1 mol/1 f21 P b CI 2 0.005% l/ll (
31CH3COONa 10 g I1(4) Nonionic surfactant (B) 3 g/n (51pH 3,5 (6) Bath temperature 25°C From a plating bath with this composition, cathode current density 0°02A
The film obtained by plating a mild steel plate to a thickness of about 8 μm with /ca had a slightly glossy grayish white color, and the lead content in the plating film was 5.6%. As the cathode current density decreases, the lead content in the plating film increases to 0.
8.7% at 01^/cd, 14.5 at 0.005^/d
%Met.

Example 2 fll Z n CI 2 1 mo/L// 1f21
P b CI 2 0.002%/I// 12(3
1CH3COONa 10 g ll1 (4) Nonionic surfactant (A) 3 g/12 (51 pH 3,5 (6) Bath temperature 25°C In a plating bath with this composition, cathode current density 0°02A/
- The film obtained by plating a mild steel plate to a thickness of about 8 μm had a slightly glossy grayish white color, and the lead content in the plating film was 2.4%. When the concentration of other components is kept constant and the concentration of lead ions is varied, the lead content in the electrodeposit changes linearly. Figure 1 shows this change. This shows that the composition of the electrodeposit can be easily controlled by controlling the lead concentration in the bath.

Example 3 +1) T(BF4 0.50 mol/β(2) ZnO
O, 25 mol/l (31MgCI2 ・61120 0.25 mol/1(
4) PbCl2 0.005 mol/1 (5) Nonionic surfactant (B) 3 g/β (61 pH 1,9 (7) Bath temperature 25°C From a plating bath with this composition, cathode current density 0°02A
The film obtained by plating a mild steel plate to a thickness of about 8 μm at /cd was semi-glossy with a slightly yellowish brown color, and the lead content in the plating film was 8.4%.

Example 4 +11 HBF4 0.50 mol/1 (21Zn0 0.25% L/Il (3) MgCI2 ・6H201 mol/It(41Pb
Cl2 0.005 mol/1(5) Nonionic surfactant (B) 3 g/l! (61 pH 1,9 (7) Bath temperature 25°C From a plating bath with this composition, cathode current density 0°02A
The film obtained by plating a mild steel plate to a thickness of approximately 8 μm at /cd was slightly yellowish brown and gray with a slight luster, and the lead content in the electrodeposit was 12.6%. .

Example 5 (11HBF4 0.50 mol/1 (2) ZnO0.25 mol/1 (31ZnCl2 0.75 mol/l (41MgCI2 ・61120 1 mol/l (5)
PbCl2 0.005 mol/7! (6) Nonionic surfactant (B) 2 g/7! (7) pH 1,7 (8) Bath temperature 25°C From a plating bath with this composition, cathode current density 0°02＾/
- The electrodeposit obtained by plating a mild steel plate to a thickness of about 8 μm was a satin-like semi-gloss with a yellowish brown color, and the lead content in the plating film was 15.1%.

Example 6 (11H2S i F4 0.25 mol/1121 Z
nOO, 25 mol/β f31Mgc]2 ・61120 1 mol/1 (41P
bCl2 0.005 mol/1 (5) Nonionic surfactant (A) 1 g/7! (61 pH 1,1 (7) Bath temperature 25°C From a plating bath with this composition, cathode current density 0°04A
The electrodeposited material obtained by plating a mild steel plate to a thickness of about 8 μm with /at() had a glossy, dark appearance, and the lead content in the plating film was 15.8%.

Example 7 1) H2S iF4 0.25 mol/7! (2) Z
nOO, 25 mol/β (3) Z n C120, 75 mol/l (41 MgC
12・61120 1 mol/l1 (51P b Cl
2 0.005 mol/β(6) Nonionic surfactant (B
) Ig/1 (7) pH 1,1 (8) Bath temperature 25°C From a plating bath with this composition, cathode current density 0°04＾/
(The electrodeposited material obtained by plating a mild steel plate to a thickness of approximately 8 μm with !II+ had a glossy, dark appearance, and the lead content in the plating film was 15.8%. The addition of sodium acetate, magnesium chloride, or boric acid in the above examples is not an essential component for the purpose of the present invention, which is to achieve a smooth zinc-lead eutectoid coating.

Added to facilitate pH adjustment of the plating bath. It has been added.

Next, regarding the corrosion resistance of these zinc-lead eutectoid coatings, the corrosion resistance against salt water becomes better as the lead content increases from 0.1%.

A range of about 0.5% to about 8% is good. The amount of iron dissolved in the salt water due to corrosion when immersed in 5% salt water was measured, and the results plotted against the lead content in the plating film are shown in Figure 2.

- Less melting of the base iron within the lead content range specified in H.

It can be seen that it has excellent corrosion resistance. Furthermore, the lead content was 10%, which did not show good corrosion protection in such an environment.
Regarding eutectoid coatings exceeding 1:2, for example, pure zinc plating coatings with a thickness of about 14 μm completely melt in a few minutes in 1:2 hydrochloric acid. The zinc-lead eutectoid coating required about 80 minutes to completely dissolve. Such good hydrochloric acid resistance is exhibited when the lead content is about 5% or more.

[Brief explanation of the drawing]

2. Figure 1 is a graph showing the relationship between the lead concentration in the plating bath and the lead content in the electrodeposited material, and Figure 2 is a graph showing the relationship between the lead content in the plating film and the melting amount of the base iron.

Claims (1)

[Claims] A concentration of zinc ions in a molar ratio of 1150 or less in a divalent zinc ion chloride bath, borofluoride bath, silicofluoride bath, or a mixed bath of chloride and borofluoride or chloride and silicofluoride. Contains divalent lead ions and acts as a smoothing agent. General formula: However, R1 is an alkyl group having 1 to 4 carbon atoms or a phenyl group, R2 and R3 are hydrogen or a methyl group, and 1
m and n represent integers of 1 to 30. (B) However, R represents an alkyl group having 1 to 18 carbon atoms. Ox represents an integer from 2 to 20. 0.1 g/l of nonionic surfactant shown in
An acidic zinc-lead eutectoid electroplating bath having a content in the range of 30 g/jl to 30 g/jl.