JPS61133394A - Method for plating zn-ni alloy with high electric current - Google Patents

Abstract

PURPOSE:To electroplate a Zn-Ni alloy having superior corrosion resistance by adding a specified amount of Na2SO4 to a plating bath contg. Zn<2+> and Ni<2+> acidified with sulfuric acid and by regulating the ratio between Zn<2+> and Ni<2+> to a specified value. CONSTITUTION:Na2SO4 is added to a plating bath contg. Zn<2+> and Ni<2+> acidified with sulfuric acid by 0.6-1.0mol/l, and the ratio between Zn<2+> and Ni<2+> is regulated so as to satisfy Ni<2+>/(Zn<2+>+Ni<2+>)=0.55-0.65. Electroplating is carried out with the resulting plating bath at about 0.6-0.8m/sec flow rate, about 50-70 deg.C bath temp. and 80-200A/dm<2> current density to obtain a Zn-Ni alloy layer having about 10-13wt% Ni content. The Zn-Ni alloy layer has improved corrosion resistance and is hardly microcracked.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to the electroplating of Zn-former yarn alloy, in which the old content in the plating layer can be reduced to 10 to 13 with good corrosion resistance even when plated at high current density. t%.

(Prior art) The amount of electroplating deposited is determined by (current density) x (plating time), so in a continuous electroplating line, the current density must be increased to maintain the same amount of plating by reducing the fin speed. There is a need to.

However, simply increasing the current density to match the line speed may cause concentration polarization or insufficient conductivity, resulting in an increase in voltage.For this reason, when plating with conventional high current densities, it is difficult to plate on the surface to be plated. The plating solution may be sprayed at high speed, or a conductive agent [Na25Oa, (NH, hsO,, Na
Various methods such as adding Cl or the like or increasing the bath temperature are used to suppress the increase in voltage as the weave density increases. This means that Zn-Ni
The same applies to the case where alloys are plated at high current density.

By the way, when plating Zc+-Nij% alloy at high current density, 1sO4 or (Nlln)*SO4 is used as a conductive agent.
When used, a double salt with low solubility is formed and the bath composition cannot be adjusted to the desired composition. Therefore, Na5SO4, which does not have such problems, is generally used. As shown in Figure 1, the effect of Na1SO4 as a conductive agent is that the electrical conductivity increases with the addition amount up to about 7091 (0.5 mol/e), but it is not effective even if it is added beyond that amount. becomes saturated, so conventional Na25
When adding On, the amount was at most 0.5 mol/C or less [Corrosion resistance of Zr+-Ni composite electroplated steel sheet, Shibuya 11 Ka, Iron and Steel,! @See No. 7 of 1966 ('80) J.

However, conventionally, by adding 0.5 mol/8 or less of NatSOn to a Zn-old yarn alloy plating bath containing 11% and 12+, it is possible to obtain Ni content of 1 to 13 series alloy plating (γ single phase), which has the best corrosion resistance. ) in the plating bath at a current density of 20^/da" or more, set the value of )lie 7 (lnn +Ni2+) in the plating bath to 0.7 to 0.75, and set the bath temperature to 60°C or more to plate the surface to be plated. This was done while injecting 1 liquid at a flow rate of 0.6 to 0.8 s 8 ee. The composition is amazing! This is because they are easily affected by the flow rate of the liquid, and in areas where the flow velocity distribution is disturbed, a mixed phase of (γ + η) occurs in the former case, and a mixed phase of (γ + α) in the latter case, resulting in a decrease in corrosion resistance. This is because if the temperature is lower than 60° C., the flow velocity distribution becomes a mixed phase of (7+η) at the 6-fold portion, as described above.

(Problems to be Solved by the Invention) However, even if the current density is increased to correct high current density plating with such bath composition and bath temperature, 80 A/
dm" is the limit, and when it exceeds 80 A/ds", the plating layer is a single phase of γ, but the average Ni content in the plating layer increases to around 14-1%, and countless microcracks form in the plating. This occurs in the layer and reduces corrosion resistance. The reason why the old content in the plating layer increases is that the Ni2+ concentration in the plating bath is about 2.3 times higher than the Zn'+ concentration.
Even though the total Ni concentration is considerably higher, the precipitated Zn-N1 alloy has a Ni content of 10%, which is opposite to the bath composition, so at high current density, the Ni concentration is considerably higher. Q
It is assumed that the diffusion of Zn2+ becomes rate-determining for the Zn-old thread alloy precipitation, and as a result, the Ni content in the plating bath becomes high (it is assumed that the Ni content in the plating bath becomes high). An increase in the Ni content of the
As shown in the figure, the amount of precipitated Zn' increases as the electric density increases, but it is easy to understand that the amount of Zn' precipitated decreases. On the other hand, the reason why numerous microcracks occur in the plating layer is not necessarily clear, but it is thought that an increase in the old content in the plating layer is involved.

(Means for solving the problem) Therefore, the present inventors conduct plating in which the Ni content in the plating layer is stable and in the range of 10 to 13 wt%, which has the best corrosion resistance, and the generation of microcracks is small. As a result of various researches to develop a high current density plating method that can
som o. e~i. By adding omol/e, lie and N
i2+ and old%/(Zn”+1%)=0, 55~0.6
They found that if the current density was adjusted to 5, the desired plating layer could be obtained even if plating was performed at a high current density.

In the present invention, NatSo is added to the plating bath at a concentration of 0.5% compared to the conventional method.
Adding 0.6 mol/e or more of N
Although the mechanism of action of atSOn on electrodeposition is not clear, the knowledge that adding 0.6 mol/n or more can increase the average prior content in the plating layer by around 2 wt% may be helpful. That is, NazSO- is 0.6
By adding mol/e or more, the Ni concentration in the plating solution can be reduced and the Zn concentration can be increased. In other words, Ni” / (Zn” + Ni”) < 0
．． It can be set to 7. As shown in Figure 2, when the current density becomes high, the amount of Zn precipitated decreases, and conversely, the amount of N; N1 content in 14wt%
It can be reduced from more than 10 to 13 wt%. Therefore, as a result of various studies on ways to increase the amount of Zn precipitated, the above method was discovered.

In this way, it became possible to increase the amount of Zn precipitated, so it was possible to increase the amount of Zn and Ni2+. NazS in the bath
By adding 0.6 mol/C or more of O<, the plating solution flow rate is 0,
6-0.8m/see, bath temperature 50-70℃
As a result of studying a plating bath composition that would result in a Ni content of 10 to 13 wt% in the plating layer and less occurrence of microcracks in the plating layer under a plating condition range of current density 80 to 200 A/da'', NazSO4a degree 0.6
~1.0 mol/8, and Zn> and 1 total are Ni''/
(Zn" + Na total) = 0.55 to 0.65, especially when plating at a current density of 150 to 200 A/da", the NazSO- concentration should be set to 0.8 to 1.0 mol/C. "/(Zn2++ Ni")=0.55-
They found that it is sufficient to set it to 0.65.

Here, the reason why N12SO+1 degree is set to 0.6-1.0 mol/8 is that if it is less than 0.6 mol/e, the effect of increasing the Ni content in the plating layer is small, and conversely, if it is less than 0.6 mol/e, the effect of increasing the Ni content in the plating layer is small. This is because if it is extremely depleted, N12SO+ will recrystallize when the plating solution is stored in a low-temperature environment such as in winter, and it will take time to dissolve, reducing operability. Also Ni”
/(Zn" + Ni") = 0.55-0.65
The reason for this is that if it is less than 0.55, the plating layer composition becomes susceptible to the influence of the plating g flow rate, and areas where the flow velocity distribution is disordered become a mixed phase of (γ+R), resulting in a decrease in corrosion resistance. On the other hand, if it exceeds 0.65, the average old content in the plating layer will increase, causing countless microcracks to occur in the plating layer and reducing corrosion resistance.

The concentration of Zn'+ and NI2+ is (Zn''+12+)
1.0 to 1.4 mol/e is sufficient.

The plating method of the present invention uses Zn containing ions other than Zn'+ and Ni, such as iron ions, chromium ions, and cobalt ions.
- Plating at quotient current density in Ni1 alloy plating bath! 1
It is possible.

Note that 0.6 to 1.0 mol/e of Ha2SO< is added to the plating bath containing Zn% and 12+, and plating is performed at a high current density to make the average old content in the plating layer 10 to 13 w[%]. As a method, Ni” / (Zn” + Ni”) = 0
．． 7, and the concentration of Zn′ and 1 total is (Zn” +
It is possible to consider a method of increasing Ni") = 1.4 mol/C or more, but this method increases the viscosity of the plating solution and increases the amount of light plating solution drawn out by the material to be plated, making it expensive. Not only does it waste a lot of money, but it also increases the cost before the plating bath is built, so it is not a preferable method.

(Example) After degreasing and pickling a cold-rolled steel plate with a thickness of 0.8 m by a conventional method, a Zn single-layer alloy was coated with 209% per side of a Zn single-layer alloy in various sulfuric acid acid plating baths containing Zn2+ and 12+ to which NIL2SO was added. /+s" electroplating to investigate the occurrence of cracks in the plating layer and the corrosion resistance (salt water atmosphere test based on JIS Z 2371). Table 1 summarizes the plating conditions and the investigation results.

As is clear from Table 1, if plating is performed using the method of the present invention,
Even if the current density is set to 80 to 200 A/da, the old content in the plating layer is 10 to 13-t%, and almost no scratches occur in the plating layer.
It is economical because the temperature can be lowered to ℃.

Figure 3 shows the composition of the plating layer plated using methods 1 to 4 of the present invention shown in Table 1. This is a summary of how the precipitation amount of Zn and Hi changes depending on the degree of F, and in the case of the method of the present invention, IJ421! Both the reduction in the amount of Zn precipitated and the increase in the amount of Zn precipitated due to the increase in current density are smaller than in the case of the conventional method shown in Figure 1. Even when plating is performed at a high current density, the old content in the plating light layer is lower than that in the conventional method. You can see that it doesn't get very expensive.

(Effect) As explained above, the method of the present invention has a drop of 80A/-12
Zn- has excellent corrosion resistance even when plated at higher current densities than
Is it possible to plate old thread alloy? Monkey. Also, increase the bath temperature to 70℃.
Since it can be done as follows, it can be attached at low cost.

[Brief explanation of the drawing]

#I1 diagram is old" / (Zi" + Ni") = 0.
7. NatSO in a plating IK bath with a pH of 1.7 and a bath temperature of 55°C.
- is a graph showing the relationship between Ha, SO, addition amount and plating bath electrical conductivity. Figure 2 shows the old %/
(7n% +lli%) = Q. F, Na, 5O4G, 5Mos, /e, current density and Z when plating with different current densities at a bath temperature of 60°C
Figure 7 shows the relationship between nB and the amount of C/Ni precipitation. Figure #I3 is a graph showing the relationship between the current density and the amount of Zn and old precipitation in the case of 1 to 41% plating according to the method of the present invention in the yl example.

Claims (2)

[Claims] (1) Add 0.6 to 1.0 mol/l of Na_2SO_4 to a sulfuric acid acid plating bath containing Zn^2^+ and Ni^2^+, and add Zn^2^+ and Ni^2^+. Ni^2^+
/(Zn^2^+Ni^2^+)=0.55~0.65
Zn-Ni is characterized in that it can be electroplated after adjusting to
High current plating method for alloys. (2) Z according to claim 1, characterized in that electroplating is performed at a current density of 80 to 200 A/dm^2
High current plating method for n-Ni alloy.