Galvanized Steel: Material Properties, Process, and Uses

Galvanized steel plays a significant role in the field of material science and engineering due to its unique set of properties. It has wide range of applications especially in construction, household and various automotive components. The protection of zinc coating is what makes it unique from other types of steel which eventually favor it in extended lifespan. In this article, you will be able to explore the material’s properties, manufacturing process and its vast use in industry. So, regardless of your educational background, get ready to equip knowledge of this versatile materia.

Figure 1: Galvanized steel

What is Galvanized Steel?

A type of steel that comprise of zinc coating through a renowned process of galvanization. The respective coating is done by metallurgical bonding of zinc and steel with the sole purpose of increasing its properties like corrosion resistance and durability. Hence, this protective layer makes it able to withstand aggressive environment. Moreover, it increases the life span of steel making it durable and cost effective [3] [4].

Figure 2: Galvanized steel sheet

Why is Galvanized Steel Important?

This steel type has its importance due to its exceptional corrosion resistance and long lifespan. The protective coating of zinc acts as a blockade that prevents oxygen and air from direct contact with steel, eventually minimizing the chances of degradation and rust. This ability to withstand different environmental conditions makes this material a perfect choice for industrialists to use it in applications such as construction and infrastructure. In addition to this, it requires low maintenance comparatively making it a cost-efficient choice.

What is Galvanized Steel Used for?

This zinc protected steel has a variety of applications due to its unique set of properties. Some of them are listed below:

Construction

• Structural beams
• Roofing
• Walling

Automotive

• Car bodies and parts

Infrastructure

• Bridges,
• Guardrails
• Light poles

Household Appliances

• Washing machines
• Refrigerators

Agriculture

• Fencing
• Silos

Figure 3: Applications for galvanized steel

Advantages and Disadvantages of Galvanized Steel Material

Below are some of the advantages and disadvantages of galvanized Steel:

Figure 4: Advantages and disadvantages of Galvanized steel

How is Galvanized Steel Made

This steel is made through a process of galvanization in which immersion of steel is done in molten zinc. Below is the brief description of galvanizing steel:

The Galvanization Process

The most prominent galvanizing process that ensures good corrosion resistant property is hot dip galvanizing which comprise of several steps that are discussed as following:

Surface Preparation

First, the steel undergoes surface preparation before it is zinc coated. It can be done in three stages which are described under:

• Degreasing and Cleaning:Dirt, oil and other sorts of contaminants are removedby using alkaline solution to ensure zinc coating defect free.
• Pickling:once it is cleaned, the steel is immersed in either sulfuric or hydrochloric acid which further removes oxide or any rust present on steel surface.
• Fluxing:After that, the steel is submerged in a flux solution which constitutes of zinc ammonium chloride that leads in forming a protective layer that prohibits oxidation before galvanizing. This process also helps in increasing the adhesion capability of zinc coating with steel.

Hot-Dip Galvanizing

The process includes dipping the clean steel into a molten zinc bath, usually sustained at a temperature of 450°C. The process includes following steps:

• Immersing Steel in a Molten Zinc Bath:This immersion leads to the reaction between zinc and steel resulting in the formation of zinc alloy layers ensuring the steel is entirely coated with zinc.
• Formation of Zinc-Iron Alloy Layers:This formation takes place during immersion providing a strong bond and increases the corrosion resistance. Common layer that forms during immersion are gamma, delta along with zeta phase enhancing the overall durability.
• Controlling Zinc Coating Thickness:This can be controlled by adjusting certain parameters including immersion time, temperature of the bath and the speed at which the steel is withdrawn from the bath.

Post-Treatment

Once the steel is galvanized, it undergoes following stages for post treatment:

• Cooling and Solidification of the Zinc Coating:The zinc coated steel is allowed to cool in air or through a certain cooling process once it is taken out from zinc bath.
• Inspection for Defects and Coating Uniformity:Visual inspection is done in order to check any coating defect. Moreover, the thickness and uniformity is also assessed via specialized instruments.
• Application of Additional Treatments:as per the requirement of the application, additional process could be done to galvanize steel. For improved adhesion and surface hardness, galvannealing is done. In addition to this, zinc phosphate coating could be done for enhanced corrosion resistance.

Figure 5: Step wise process for Galvanizing steel 

Material Properties of Galvanized Steel

Galvanized steel has unique set of properties which are elaborated below:

Corrosion Resistance

This steel has excellent corrosion resistance because of zinc coating that acts as a sacrificial barrier. The phenomena behind this sacrificial behavior and the protection of steel from rust is discussed below:

The Zinc Layer as a Sacrificial Barrier

The zinc layer of galvanized steel acts as a sacrificial barrier which eventually provides resistance against corrosion in aggressive environmental conditions. Zinc is highly attracted to oxygen and moisture present in the environment as compared to steel therefore zinc corrodes first while protecting the steel component. This action of sacrifice extends the life of steel.

How Zinc Protects Steel from Rust

The formation of zinc oxide and zinc hydroxide takes place once the zinc undergoes corrosion. This formation of oxides develops a passive layer over the surface of steel component and provides physical barrier against oxygen and moisture from getting direct contact with the steel component. In some cases, if this coating is damaged, the remains of zinc still provide protection to steel through sacrificial action.

The Electrochemical Process of Zinc Corrosion

This. The electrochemical process leads to the corrosion of zinc in such a way that the zinc coating acts as an anode while the steel component acts as cathode. The electrolyte in this case is oxygen or moisture that helps in electron flow. As a result of this oxidation take place at zinc while reduction at cathode which eventually leads to process that prevents the formation of rust on the steel component.

Factors Affecting Corrosion Resistance

Major factors that affect the resistance against corrosion are:

Thickness of the Zinc Coating

The thickness of zinc coating has a strong influence on corrosion resistance. Coatings that comprise of adequate amount of thickness offer greater resistance against corrosion as compared to thin coatings.

Type of Zinc Coating (Galvanized vs. Electroplated)

Galvanized coating offers greater superior resistance as compared to electroplated coatings because it comprises of a thicker layer and has the ability to withstand aggressive conditions. On the other hand, electroplated coatings are suitable for mild environmental conditions.

Environmental Conditions (Humidity, Temperature, Pollutants)

The nature of the environment that the steel component has to withstand has a great influence in its ability to resist corrosion. Aggressive conditions that involve humidity, elevated temperature and other pollutants can speed up corrosion.

Galvanized Steel Chemical Composition

Below is the chemical composition of galvanized steel:

Table 1: Chemical composition of galvanized steel

Galvanized Steel Mechanical Properties

Below are the mechanical properties briefly described of galvanized steel [21] [22] [23]:

Density of Galvanized Steel

Galvanized steel has a density that lies between 7.85 to 8.15 g/cm³.

Durability

It has exceptional durability due to factors mentioned below:

Resistance to Harsh Environments

Its resistance against aggressive environmental condition that includes pollutants, moisture and vice versa due to the sacrificial act of zinc coating.

Protection Against Weathering and UV Radiation

The coating of zinc provides good protection against UV radiation as well as weathering enhancing the lifespan of steel components.

Withstanding Extreme Temperatures

It can withstand extreme range of temperature without causing any sort of degradation in the material component.

Imperviousness to Moisture and Chemicals

The ability of galvanized steel to bear aggressive conditions due to the protective coating makes them capable enough for high demand applications.

Strength

Galvanized steel maintains the natural strength of steel while increasing several mechanical properties:

Tensile Strength and Yield Strength

• Galvanized steel keeps hold of its high tensile strength as well as yield strength, which are vital for structural components.

Ductility and Impact Resistance

• It exhibits competent ductility along with impact resistance that allows it to endure abrupt shocks without breaking.

Hardness and Wear Resistance

• The zinc coating improves the surface hardness as well as wear resistance of this steel, compelling it to be suitable enough for applications demanding abrasion resistance.

Modulus of elasticity

This material has the modulus of elasticity of approximately 200 GPa showing its ability to resist load without deforming plastically.

Bulk modulus

Galvanized steel comprises of a bulk modulus of 160 GPa.

Poisson’s ratio

Similarly, the poison’s ratio for galvanized steel is 0.3.

Shear modulus

The zinc coated steel has a shear modulus of 80 GPa showing its ability to withstand shear forces.

Summary of Mechanical Properties Table of Galvanized Steel

Table 2: Mechanical Properties of galvanized steel

Formability

Galvanized can form various shape without negotiating its mechanical properties:

Cold Forming Processes

It can undergo several cold forming processes including bending, rolling and stamping which shows its tendency to attain various shapes and readily available for variety of applications without compromising its structural integrity.

Fabrication Techniques

This zinc coated steel can undergo various fabrication techniques such as welding, cutting and drilling depending on the demand of the applications. However, care should be done while performing any technique to avoid causing any damage to zinc coating.

Machining Capabilities

This material has the ability to go machining which eventually allows the industrialist to perform various operation such as turning, drilling or milling according to the need an requirement of the application.

Galvanized Steel Finishes

Galvanized steel acquires a good surface finish. Major surface properties it possesses are mentioned below:

Surface Properties

• Have good smoothness which makes the steel component appealing in terms of aesthetic look.
• The coating of zinc promotes exceptional adhesion of coatings and paint with long lasting assurance.
• Has good printability which makes them flexible enough in terms of finishing various architectural applications.

Cost-effectiveness

Galvanized steel has a higher initial cost due to the process of applying zinc coating on steel. Therefore, it is costly as compared to various other materials but if we are concerned about long-term saving then this material is much more beneficial as it requires low maintenance, can withstand aggressive environment and vice versa.

Alternatives to Galvanized Steel

If we are concerned about any alternative to galvanized steel, consider the factors like cost, environmental conditions it can bear, mechanical properties and vice versa. However, following are the best alternative materials to consider:

• Stainless steel
• Aluminum
• Coated carbon steel
• Plastics
• Composites

Advantages of Galvanized Steel CNC Machining Parts in Manufacturing

CNC machining is one of the latest technologies of machining a certain material into a certain shape or size depending on the nature and demand of the application. The difference between traditional and CNC machining lies in terms of accuracy and precision. Like all other materials, galvanized steel has good capability to be CNC machined due to its forming ability without compromising its mechanical properties. There are many advantages of galvanized steel CNC machining parts in manufacturing. Some of them are mentioned in the figure below:

Figure 6: Advantages of Galvanized Steel CNC Machining Parts

Conclusion

In conclusion, galvanized steel is one of the most versatile materials which is widely acceptable for numerous applications whether you are choosing it for manufacturing, construction or any other sector. Moreover, the zinc coating or we should say the protecting coating which give the steel an immense amount of protection against aggressive conditions makes it a popular choice among the applications that require resistance against highly corrosive environment. Finally, its machining capabilities make this material a good candidate where high precision and accuracy among the steel components is required. Hence, making this material a worthwhile contribution in manufacturing practices.