What Are the Different Uses of Galvanized Iron?

Galvanized iron refers to a zinc-iron alloy product made by galvanizing the iron sheet through a galvanizing process. The galvanized iron sheet is not easy to rust. Commonly known as lead iron, white iron. If the coating is damaged, a zinc-iron galvanic cell can be formed. Iron is used as the positive electrode, and the iron is protected by the cathodic protection principle of the sacrificial anode.

1.Classification of galvanized iron alloy

According to the different iron content of the alloy plating, electroplated zinc-iron alloy plating can be divided into two types: high-iron alloy plating and low-iron alloy plating.

2. Use of galvanized iron alloy

(1) Application of high-speed iron alloy coating: It is mainly used as the bottom layer of electrophoretic coating of automobile steel plates. It can improve the binding force with paint after being phosphated beforehand; Chrome plating after polishing can be used as protective decoration of hardware products Plating layer; can be used as the bottom layer of decorative copper-zinc alloy to improve its corrosion resistance.

(2) Use of low iron alloy coating: often used as passivation treatment. Low-iron alloy coatings with iron content of 0.3% ~ 0.6% have high corrosion resistance after passivation treatment. Among them, black passivation has the highest corrosion resistance and does not use silver salts. This is the largest of low-iron zinc-iron alloy coatings. advantage.

Composition of galvanized iron solution

1.Main salt

In alkaline zincate plating zinc iron alloy solution,

Composition of galvanized iron solution

1.Main salt

Zinc chloride, ferrous chloride, zinc sulfate, ferrous sulfate, and iron sulfate are the main salts, and their role is to maintain zn ²⁺ and Fe ²⁺ in the plating solution at a certain ratio, thereby maintaining the composition of the plating alloy. Since the change of Fe ²⁺ in the plating solution has a greater influence on the iron content in the plating layer, the composition of the plating solution must be strictly controlled during the plating process.

2.Conductive salt

For high-iron alloy coatings, the addition of conductive salts has a greater impact on its alloy composition. The content of conductive salt should be controlled within a certain process range. The content of conductive salt is high, the conductivity is good, and the dispersion and covering ability of the plating solution are improved. The content of conductive salt is low, the conductivity is poor, the tank pressure is increased, and the cathode current density is narrowed. , The brightness is reduced, and the plating is easy to burn when the current is slightly larger.

3.Polyethylene glycol

The iron content in the coating will decrease as the content of polyethylene glycol increases. Polyethylene glycol is good for the appearance of the coating.

4.Ascorbic acid

Ascorbic acid plays a stabilizing role in the plating solution, prevents Fe ^{2+ from} being oxidized, and has a good stabilizing effect when the content is 1 g / L.

5.Additives

The low iron alloy coating is used as a protective coating. The coating needs to be passivated. The crystallization of the coating affects the quality of the passivation film.

6. Buffering agent The buffering agent for the pH of the plating solution is usually a weak acid or a weak acid salt. At high current density, the hydrogen evolution of the cathode is serious, and the pH near the cathode surface rises rapidly, causing the plating solution to be unstable. At this time, the pH of the plating solution can be stabilized with a buffer.

7.pH

The effect of pH value on the composition of the coating layer is related to the cathode current density, and its influence law varies with the current density. The pH value of the acidic plating solution is most stable between 4 and 5; if it is too high, the Fe ³⁺ content in the plating solution increases, causing the current density to be unstable.

8.Temperature

When a soluble anode is used, the temperature of the plating solution must not be too high, so as to prevent the content of Fe ³⁺ from increasing with the temperature of the plating solution, thereby affecting the stability of the plating solution. In the weakly acidic plating solution, the iron content in the plating layer increased slightly with the increase of the plating solution. When the temperature is too high, the additives are liable to decompose and the coating is rough; when the temperature is too low, potassium chloride is liable to crystallize and precipitate.

9.Cathode current density

The effect of cathodic current density on the iron content of the coating varies greatly depending on the plating solution system. The iron content of the plating layer in the chloride plating solution changes with the current density much less than that in the sulfate plating solution. The effect of current density on the composition of the coating is related to the ratio of main salt content and conductive salt.

Preparation of acid galvanized iron solution

The preparation method of the electroplating solution is as follows:

1. Dissolve zinc chloride and potassium chloride in 1/3 volume of water, add zinc powder (1g / L) and powdered activated carbon (1 ~ 2g / L), stir thoroughly for 30min and let it stand for filtration. The pH value of the 5% hydrochloric acid solution is adjusted to 3.5 ~ 4.

2. Dissolve ascorbic acid and stabilizer in water, then pour it into a solution of ferrous sulfate dissolved in 5-10 times water, and pour it into the tank after clarification.

3. Dissolve the polyethylene glycol in hot water, dissolve the thiourea in water, add it to the plating tank, and stir well.

4. Add additives diluted with water, add water to the required volume, and test plating after several hours of electrochemical treatment.

crafting process

Process of acid galvanized iron alloy: workpiece chemical degreasing hot water washing flowing water washing pickling and rust removal twice flowing water washing electrochemical degreasing hot water washing flowing water washing weak corrosion flowing water washing galvanized iron alloy recycling Running water washing Exiting light Running water washing Passivation Running water washing Aging inspection Finished product. ^[2]