Galvanization: A Basic Guide to Understand

different galvanized parts

Galvanization can be found everywhere in life. For example, building frames, ladders, balconies, etc. are all made of galvanized metal. In the custom machined parts industry, it is no exception. From CNC machined parts to sheet metal fabrication, galvanized metal has become one of its indispensable material choices.

Galvanization is a rust-prevention procedure in which a zinc coating is applied to steel or iron to provide protection. There are various galvanizing methods that exist and hot-dip galvanizing is the most popular and widely utilized.

However, the galvanizing process is a complex procedure, and knowing more about galvanizing can help prototyping and manufacturing projects make better choices and run more smoothly.

What is galvanization/galvanizing?

Galvanization or Galvanizing (or zinc protect) is the process of adding a layer of zinc to the outer surface of a metal, i.e. iron or steel. Zinc iron alloy is a highly corrosion-resistant type of metal that insulates iron from oxygen and water so that it can’t undergo the chemical reactions required for rusting. The resulting coating is usually about 6 to 20 μm, about three times the thickness of electroplated coating steel. It usually consists of a pure zinc layer and an alloy layer.

galvanizing parts

Materials for galvanizing

The main substrates that can be galvanized are steel and iron. But of course, other metals can also be galvanized. The material used for galvanizing is pure zinc. A similar surface treatment to galvanizing is tin plating. But tin plating is not as reliable as galvanizing. If the coating is damaged, the tin will corrode the iron underneath, so tin plating is generally only suitable for food storage.

Types of galvanization

We will discuss different types of galvanization. Though hot-dip galvanizing has been utilized to protect steel for generations, the galvanizing process continues to evolve with new technologies and creative chemistries. Additionally, the electro galvanization, cold and sherardizing galvanized process utilized in order to produce a specialized coating on steel or iron.

Hot-dip galvanization

Hot-dip galvanizing is the most common method of galvanization, in which the metal is completely immersed in a pool of molten zinc to form a zinc coating on the surface of the metal. Hot-dip galvanization layer is formed in three steps with zinc in the liquid state. The iron-based surface is dissolved by the zinc solution to form a zinc and iron alloy phase layer; the zinc ions in the alloy layer further diffuse into the substrate to form a zinc and iron intercalation layer; The alloy layer is wrapped around the surface of the zinc layer.

Compared with electro-galvanizing, hot-dip galvanizing is a more economical choice. Not only for the steel inside to ride to the protection, anti-corrosion function, the surface of the parts after hot-dip galvanizing is also brighter and more beautiful.

In addition, hot-dip galvanizing of steel parts is equivalent to an annealing treatment, which can also improve the mechanical properties of steel materials, eliminate the stress of welding when forming steel parts. It helps to better turn and mill the steel parts. The galvanized steel can also be used in high-temperature applications up to 392 °F, but use above that temperature can cause the zinc carbonate layer to peel off the surface.

Electrogalvanization

Electro galvanizing combines galvanization with electroplating by introducing an electric current into an electrolyte solution applied to the steel, which passes through a zinc bath with a zinc anode and steel conductor, reducing the positively charged zinc ions to zinc metal, which is then deposited on the positively charged steel, rather than being immersed in a molten zinc drum as in hot-dip galvanizing.

However, compared to hot-dip galvanization, the production line for electro-galvanizing is very expensive. The advantage is that its coating is thinner and more detailed, more uniform and non-porous, with a better surface finish.

Moreover, galvanizing is now involved in a wide range of industries, especially for fasteners. It has been used in machinery manufacturing, electronics, precision instruments, aerospace, etc. The galvanized layer can be passivated by chromic acid to form a variety of colors, with a certain degree of decoration. Also, the galvanized layer has good ductility. It can be cold-punched, bending and other molding processes without damaging the coating.

Sherardizing (Mechanical Galvanization)

In a closed rotating drum containing zinc powder, the glass ball, which is the impact medium, rotates with the drum, generating mechanical and physical energy by friction and hammering against the surface of the plated part. This method of galvanizing, also known as mechanical galvanizing or dry galvanizing, is suitable for relatively small parts and parts that require partial coating internally.

Cold galvanization

This method requires only the equipment normally used to apply paint. Cold galvanization is the application of zinc-rich paint to the surface of steel parts, but the coating is a less durable and less protective coating of the steel parts, so it is rarely used.

How Does the hot-dip galvanization work metal parts: Step by step

Hot-dip galvanizing is the most common type of galvanizing and is often used to treat metal parts. The process has the following main steps.

Pre-treatment

Removal of oil in a degreasing solution (usually alkaline chemicals) followed by pickling in a bucket of diluted hot sulfuric acid, repeated water washing and pickling to ensure a clean steel surface for subsequent galvanization.

Auxiliary plating agent treatment

The steel is immersed in a solution of plating aid (usually ammonium chloride and zinc chloride) to prevent premature oxidation of the metal before galvanizing, then drying and preheating it.

Galvanization

After treating the steel, it is submerged in a pool of molten zinc, where a chemical reaction occurs between the iron and zinc, resulting in an iron-zinc metal compound, which is the zinc coating.

Post-treatment

Cooling, passivation, testing, etc. Of course, if you want to adjust the performance of the zinc coating, you can add metals such as magnesium and aluminum to improve its corrosion resistance, optimize its appearance, etc. In addition, the silicon, manganese, and carbon dioxide content of the chosen steel will also affect the function of the coating.

The benefits of galvanization

galvanized metal parts

Galvanization is a cheap process as compared to most treated steels. In addition, galvanized steel is quickly ready to use when delivered. It does not require additional preparation of the surface. And the life expectancy of high-strength steels increases up to 50 years.

Many different industries utilize galvanized steel primarily because it has such a wide array of benefits for industries.

Prevention of rusting

A protective coating is formed on the surface to prevent corrosive substances from reacting with the underlying steel or iron. Even if the zinc coating is damaged, the zinc will corrode before the iron, and the remaining zinc will dare with the atmosphere to form a dense patina insoluble in rainwater, which then protects the exposed steel or iron.

Corrosion protection

The zinc coating on galvanized metal prevents corrosive substances from reaching the weaker underlying base metal, which extends the life of the base material.

Durable

The zinc coating produced by galvanizing is so strong and durable that a piece of industrial steel is expected to last more than 50 years in a normal environmental shell, and another 20+ years even when used in water, and without maintenance. This durability also increases product longevity and reliability.

Economical/low cost

Galvanizing is a fairly simple and low-cost surface treatment process compared to most treated steels. Moreover, galvanized steel is delivered ready for use without additional surface preparation, inspection, painting/coating, etc., and requires no maintenance, resulting in additional cost savings.

galvanizing cost

Applications of galvanized steel

The ability to prevent corrosion of steel has led to the widespread use of galvanizing in several industries. The most common is in the construction industry, where hundreds of thousands of tons of galvanized construction steel are produced each year for structures such as building frames, street furniture, fire escapes, ladders, and balconies.

Also, galvanized steel is common in the transportation industry, including highway guardrails, road or railroad fences, ship hoisting wire ropes, road or railroad noise barriers, wind and snow barriers, street signs, street lights, etc.

Those in the automotive industry, such as the skeleton foundations of cars, such as bumpers, cross members, frames and chassis can also be made of galvanized steel.

There are also custom fabrication industry areas where various nuts, bolts, and sheet metal parts are required to be galvanized to provide protection against corrosion and help extend the life of the metal, and to a lesser extent, as appearance parts with color and quality requirements for appearance.

galvanizing application

Galvanization or not?

Galvanization is one of the most common surface treatments for parts made of steel. Galvanized coatings enhance the life, corrosion resistance, and surface finish of their parts. In addition, galvanized materials are widely used as galvanized sheet metal for sheet metal manufacturing processes such as bending and stamping, CNC machining, etc.

WayKen is an expert in prototyping and low volume manufacturing, where we offer cost-effective galvanizing services and other finishing services. We can help you choose a practical solution for your project with different surface finishes. 

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