Do-it-yourself galvanizing of body metal

To protect the iron of the car from rust, zinc is not used by car manufacturers too often. However, many people know that do-it-yourself galvanizing of metal is a very effective way to protect the metal of a car body from corrosion. To date, there are several ways to do-it-yourself galvanize the metal of a car body, even at home.

Most metals, for example, such as zinc, tin and aluminum, oxidize when in contact with air, which forms a dense oxide film on their surface. It does not allow oxygen to penetrate deeper than the surface layer of the metal, thereby stopping its oxidation. But in the case of iron oxidation, such a film is not formed. Since iron oxides and hydroxides are loose and do not protect this metal from further oxidation.

Coating the metal of the car body with zinc protects it from corrosion for two reasons. First, because the dense film of zinc formed on the surface of the metal does not allow the interaction of the latter with atmospheric oxygen. Secondly, iron and zinc are a galvanic pair, in which zinc is a much more active element. This means that if the integrity of the galvanized iron film is violated, zinc will be the first to react with oxygen, protecting the iron of the machine. Galvanizing and tinning a car at first protect the iron of a car from rust in the same way. The difference is found in mechanical damage to the coating of the car body. Tin, unlike zinc, is a less active metal than iron. Therefore, if the protective coating is damaged, it does not slow down the corrosion of the car body iron, but accelerates it, remaining untouched itself.

In order to galvanize metal, there are several ways:

• Galvanized zinc. When zinc is deposited on a metal surface from a solution of salts containing zinc. This treatment is characterized by the lowest energy consumption and allows you to control the thickness of the applied layer. As an electrolyte for this method, zinc sulfate dissolved in water is most often used.
• Hot galvanized. Occurs when a prepared machine part is immersed in molten zinc at a temperature of 470 oC. Preparation of the metal surface consists in its degreasing and etching. The method is distinguished by the result with the best protective properties, as well as an unstable coating thickness. It is usually used for metal structures used in construction.
• Diffusion galvanizing. There are two kinds. One is the heat treatment of the steel surface with zinc powder, called sherardization. It occurs at a temperature of 290 to 450 oC. Another type of such galvanizing is performed in zinc vapor at a temperature of just under a thousand degrees Celsius.
• Shopping. Galvanizing in this way consists in spraying molten zinc onto the surface of machine body parts from a special spray gun.
• Gas-dynamic galvanization. This is the coating of the surface of the car body with zinc using ultrasound. It is distinguished by the ease of applying a protective layer on the surface of parts of any shape and very good adhesion of the coating to steel. But a set of equipment for this is difficult to acquire.
• Cold galvanized. When a polymer primer containing zinc powder is applied to the prepared surface of the car body in any way. After drying, the applied layer acquires the protective properties of the primer and zinc coating. This composition is called zincor. This method is more suitable than others for processing a car at home.

Galvanic zinc plating can be done with both complex and simple electrolytes. The complex ones include zincate, cyanide and ammonium electrolytes. The group of simple electrolytes includes, for example, chloride, boron fluoride and sulfate. The difference between these two groups of electrolytes is that the polarization of simple electrolytes is less, so the crystals of zinc deposited from them are larger. Due to availability and good results, sulphate electrolytes are often used for electrogalvanizing. The most preferred concentration of zinc sulfate in the electrolyte for use at 20 oC is 200 to 300 g per liter of solution. To improve the properties of the electrolyte, various reagents are added to it. Sodium sulfate increases the electrical conductivity of the solution. Additives of aluminum sulfate stabilize the acidity of the mixture. Due to the fact that this reagent is a very good thickener, the solution becomes a little thicker, and this favorably affects the finish structure of the coating. The addition of surfactants and colloids to the electrolyte further improves the quality of the deposited film. For galvanization at room temperature, surfactants of the cationic type are better suited. For example, such as dioctadecyldimethylammonium chloride, hchloride, or didecyldimethylammonium bromide. And of the colloids - dextrin and wood glue.

Galvanic galvanizing does not proceed well under all conditions. Below we present the optimal set of conditions and composition of the electrolyte.

Conditions.

• Temperature from 15 to 30 oC.
• Hydrogen index (pH) from 3.6 to 4.4.
• The current density is 1–4 A/dm2.

The composition of the electrolyte.

• Zinc sulfate 200–300 g/l.
• Aluminum sulphate 20–30 g/l.
• Sodium sulfate 50–100 g/l.
• Dextrin 8–10 g/l.
• DCU 0.5–1 g/l.

Surface preparation.

Applying any coating to a car body requires careful surface preparation. Do not do without it before galvanizing. Before immersing a car part in a container with electrolyte, its surface must be thoroughly cleaned of dirt and oxides. Degrease and pickle with a special compound. If after galvanizing it is planned to paint the surface of a body part, it should be phosphated. For this, a 30-second treatment with a Mazhef solution is suitable, which must be diluted to a concentration of 30-40 g / l with the addition of 30-60 g / l of zinc nitrate.

Of course, it is hardly possible to do galvanic galvanizing of the entire car body at home. Therefore, at home for do-it-yourself galvanizing of a car body, cold galvanizing is more suitable.

Cold galvanizing technologies

Cold galvanizing stands out from all galvanizing methods due to its ease of implementation. Therefore, it is most suitable for do-it-yourself car processing at home. The composition for cold galvanizing is usually a polymer primer with a high zinc content.

Advantages of this method of protection.

• The simplicity of the technical process, which allows you to process the car body with your own hands, even at home.
• The complete absence of restrictions on machined auto parts in size and shape. In this way, you can galvanize the entire car body at home.
• A wide range of temperatures in which it is permissible to apply a zinc-containing primer. Usually such a primer can be applied at a temperature of -20 to +40 oC. Before you start applying the primer, you need to make sure that the surface is at least three degrees warmer than the dew point.

The weak side of this method of protecting cars from corrosion is the low strength of the protective film. However, this can be ignored. Since the soil on the car body from above is usually protected by more durable coatings, for example, paint and varnish and anti-gravel.

Cold galvanizing agents

The market offers many different compositions for cold galvanizing. We will only mention the most popular ones.

1. Galvanol. The most famous Russian primer for cold galvanizing cars. It is a one-component composition with zinc additives for car protection.
2. Cynotan. A little less well-known domestic primer for cold galvanizing. It is a one-component composition with zinc powder for car protection.
3. Zinconol. Polyurethane primer with zinc.

All of them are easy to use even at home.