Top 12 Metal Surface Finishing Types You Must Know

When we machine metal, there are usually many steps to complete, and surface finishing is often the last step, and it is also the most important part.

In this article, we will learn about the 12 most common metal surface finishing, including anodizing, black oxide, PVD coating,bead blasting, polishing, electroplating, etc. These processes can change the properties of the metal surface, but many people may not know their differences, specific functions, and which surface finishing they need for the project. Let's start learning!

What is Surface Finishing?

Surface finishing is a process of artificially forming a surface layer on the surface of a material that has different mechanical, physical and chemical properties from the material. Its processes cover a wide range of industrial processes that can remove, add or change the surface of a material or finished product.

The main purpose is to improve the appearance of the product, enhance its mechanical or chemical properties, and meet the corrosion resistance, wear resistance, chemical resistance, hardness, weldability, wettability, conductivity or other special functional requirements required by the product.

1. Anodizing

What is Anodizing?

Anodizing is an electrolytic passivation process that enhances the corrosion resistance, durability and appearance of metals, especially aluminum. During the electrolytic oxidation process, the surface of aluminum and aluminum alloys is usually converted into an oxide film, which has protective, decorative and other functional properties.

Advantages of Anodizing

• Corrosion resistance
• Improved durability
• Enhanced wear resistance
• Increased hardness
• Better adhesion for paint and glue
• Improved aesthetics
• Long-lasting finish

Applicable Materials of Anodizing

The most commonly used material for anodizing is aluminum. Non-ferrous metals or their alloys (such as magnesium, titanium and their alloys) can also be anodized.

Available Colors of Anodizing

Anodizing can present a variety of colors, which mainly depends on the electrolyte, dye, process parameters, etc. Common colors include red, golden yellow, blue, green, silver, etc.

Applications of Anodizing

Anodizing is widely used in aerospace, automotive, electronics, machinery manufacturing and other industries, and is ideal for engine parts, automotive parts, engine components, wheel hubs, aluminum alloy decorative panels, molds and more.

Resources

If you want to know more about anodized aluminum, you can read this article.

2. Black Oxided

What is Black Oxided?

Black oxide is a chemical conversion coating, also known as "chemical oxidation" or "black tinting", that improves the corrosion, wear and decorative properties of metals by forming a protective layer of black oxide on the metal surface.

It is commonly used on metals such as steel, aluminum, and copper, and produces a variety of black shades, including matte black, gloss black, and deep black.

Advantages of Black Oxide

• Corrosion resistance
• Improved aesthetics
• Enhanced wear resistance
• Reduced light reflection
• Cost-effective solution

Applicable Metal Materials of Black Oxide

Black oxide is mainly used for stainless steel, carbon steel, copper alloy and titanium alloy. Some precious metals, such as gold, silver and platinum, can also be black oxidized to obtain special surface effects, but this process is not suitable for all metals.

Available Colors of Black Oxide

The colors formed by the black oxide process are not limited to black. Although the name "black oxide" might lead one to believe that only black can be formed, it can actually form a wide range of colors, including the most common matte black, glossy black, dark black, and inky black. There are also gray-black, dark gray, silver-gray, bronze, dark brown, reddish brown, and more.

Applications of Black Oxide

Black oxide is widely used in electronics, automobile, machinery manufacturing and other industries. It is an ideal choice for electronic components, electrical housings, auto parts, engine parts, molds, gears, bearings, washers, and mechanical parts.

Resources

Perhaps you also want to know the difference between anodizing and black oxide, then you must not miss this blog.

3. Physical Vapor Deposition (PVD)

What is PVD Coating?

PVD is the abbreviation of Physical Vapor Deposition. It refers to the use of low-voltage, high-current arc discharge technology under vacuum conditions. The gas discharge is used to evaporate the target material and ionize the evaporated material and the gas. The accelerated effect of the electric field is used to deposit the evaporated material and its reaction products on the workpiece. The deposited atoms or molecules will form a thin film on the surface of the substrate.

Advantages of PVD Coating

• Enhanced hardness
• Improved wear resistance
• Increased corrosion resistance
• Enhanced surface aesthetics
• High temperature stability
• Environmental friendly

Applicable Metal Materials of PVD Coating

PVD coating can improve the wear resistance, hardness, corrosion resistance and fatigue resistance of metals. Commonly used metal materials include: stainless steel, aluminum alloy, titanium alloy, carbon steel, alloy steel, etc.

Available Colors of PVD Coating

PVD coatings can present a variety of colors, depending on the target material used, process parameters and post-processing methods. Commonly available colors: gold, silver, blue, black, gray.

Applications of PVD Coating

This technology is widely used in aerospace, automotive, electronics, machinery, construction and other industries. PVD coating can give parts durability, corrosion resistance, wear resistance and aesthetic value. It is an ideal application choice for aerospace components, medical devices, automotive engine parts (such as pistons and camshafts), and electronic components.

4. Bead Blasting

What is Bead Blasting?

Bead blasting is a surface removal process in which fine sand, metal, plastic or other abrasive particles are sprayed at high pressure onto a workpiece to produce a finely textured surface (the process of cleaning and roughening the surface of a substrate using the impact of a high-speed sand stream).

Advantages of Bead Blasting

• Removes rust and corrosion
• Improves surface finish
• Enhances paint adhesion
• Cleans and prepares surfaces efficiently
• Versatile for various materials
• Cost-effective
• Eco-friendly option

Applicable Metal Materials of Bead Blasting

Bead blasting is a widely used surface finishing process that can be used on a variety of materials, including metals, glass, plastics, ceramics, and wood. Common metal materials include stainless steel, alloy steel, carbon steel, aluminum alloy, copper alloy, and titanium alloy.

Will Bead blasting create other colors?

Bead blasting does not change the inherent color of the material itself. However,  metal will appear darker after bead blasting and have a matte finish, giving it a more rugged look.  For example, sandblasted aluminum will appear a deeper gray, while sandblasted copper will appear a deeper red.

Application of Bead blasting

Bead blasting is widely used in the automotive, aerospace, machinery manufacturing, electronics and other industries. It is an ideal choice for automotive engine parts, wheels, gears, bearings, molds, and electronic product housings.

5. Polishing

What is Polishing?

Polishing refers to a finishing method that uses mechanical, chemical or electrochemical effects to reduce the surface roughness of a workpiece to obtain a bright and smooth surface. It cannot improve the dimensional accuracy or geometric shape accuracy of the workpiece, but its purpose is to obtain a smooth surface or mirror gloss, and is sometimes used to eliminate gloss (matte).

Advantages of Polishing

• Enhanced Aesthetics
• Improved Durability
• Better Cleanability
• Increased Chemical Resistance
• Improved Light Reflection
• Reduced Friction and Wear
• Surface Preparation for Coating

Applicable Metal Materials of Polishing

Many metal materials can be polished, but different metal materials require different polishing methods and process parameters. Commonly used metal materials for polishing include stainless steel, aluminum, copper, brass, etc.

Does Metal Polishing Create a New Color?

Metal polishing does not produce new colors. It mainly changes the optical properties of the metal surface, thereby changing the color and brightness of its reflected light, giving the metal surface a different visual effect.

Application of Polishing

Polishing is widely used in the automotive, aerospace, medical, consumer electronics and mold manufacturing industries. It is an ideal choice for automotive engine parts (such as crankshafts and camshafts), aerospace parts (such as turbine blades, bearings and seals), medical devices, camera lenses, injection molds, etc.

6. Electroplating

What is Electroplating?

Electroplating is an electrolytic process that coats one metal surface with a thin film of another metal. It creates a strong metallurgical bond between the base material and the coating, producing a functional and durable coating.

During this process, the metal workpiece is immersed in a bath of electrolyte along with a cathode and an electric current is applied. This results in the controlled removal of a thin layer of metal from the surface, effectively eliminating defects such as scratches and burrs.

Advantages of Electroplating

• Enhanced corrosion resistance
• Improve wear resistance
• Improve appearance
• Increase conductivity
• Improve thermal conductivity
• Reduce coefficient of friction
• Enhance weldability

Applicable Metal Materials of Electroplating

There are many common electroplating materials, which are widely used in various industrial fields, mainly nickel, chromium, zinc, copper, gold, silver and rhodium.

Available Colors of Electroplating

Electroplating can produce a variety of colors, depending on the color of the electroplating material itself and the electroplating process.

For example: nickel plating is silvery white or light gold (slightly dark), gold plating is golden yellow, copper plating is reddish brown, chrome plating, silver plating, and tin plating are all silvery white.

Electroplating technology can achieve a variety of surface effects to meet the needs of different industries and applications.

Application of Electroplating

Electroplating is widely used in industries such as automotive, medical, electronics and home appliances, and is ideal for automotive engine components (such as crankshafts and piston rings), circuit boards, connectors, medical devices, household housings, etc.

7. Electrophoretic Coating

What is Electrophoretic Coating?

Electrophoretic is an electrochemical surface finishing technology that deposits charged paint particles in an aqueous solution onto the surface of a conductive substrate under the action of an electric field, thereby forming a uniform and dense coating. This process is usually used for the purpose of corrosion protection, decoration and improving product durability.

Advantages of Electrophoretic Coating

• Uniform coating
• Excellent anti-corrosion performance
• Good adhesion
• Environmentally friendly
• High efficiency and automation
• Improved appearance
• Wide applicability

Applicable Metal Materials of Electrophoretic Coating

Electrophoretic coating is an environmentally friendly coating technology, but it is mainly used for metal materials, especially aluminum alloys and steel, followed by aluminum alloys and magnesium alloys.

Available Colors of Electrophoretic Coating

Electrophoretic coating can form a variety of colors. By selecting and mixing different coatings, electrophoretic coating can meet diverse color requirements. Common colors include black, white, red, blue, green, etc.

Application of Electrophoretic Coating

Electrophoretic is widely used in the automotive, home appliances, construction, electronics, medical equipment and other industries. It is an ideal choice for wheels and hubs, air conditioning radiators, building steel structures, circuit boards, medical equipment housings, etc.

8. Brushed Metal

What is Brushed Metal?

Wire drawing is a surface finishing method that forms uniform lines on the surface of the workpiece by grinding the product to achieve a decorative effect. According to the different lines after wire drawing, it can be divided into: straight wire drawing, random wire drawing, corrugation, and spiral wire drawing. This finishing not only improves the aesthetics of the metal, but also has some practical functional advantages.

Advantages of Brushed Metal

• Improve aesthetics
• Anti-fingerprint
• Enhance wear resistance
• Anti-slip
• Blemish coverage
• Environmentally friendly

Applicable Materials of Brushed Metal

Brushed metal can be applied to a variety of materials, common metals include: stainless steel, aluminum, copper, titanium, carbon steel, alloy steel, nickel.

Available Colors of Brushed Metal

Brushed metal itself is a physical finishing process that does not directly change the color of the metal. However, by combining it with other surface fishining techniques (anodizing, electroplating, etc.), the metal surface after brushing can present a variety of colors.

Application of Brushed Metal

Brushed metal is widely used in home appliances, electronics, construction, automobile and other industries. It is an ideal choice for home appliance housings, electronic product housings, stainless steel elevator panels, and automobile interior panels.

9. Photochemical Etching

What is Photochemical Etching?

Etching is usually referred to as photochemical etching, which refers to the removal of the protective film of the area to be etched after exposure and development. During etching, it comes into contact with chemical solutions to achieve the effect of dissolution and corrosion, forming a concave-convex or hollow-out effect.

Advantages of Photochemical Etching

• Achieve high precision
• Strong flexibility
• Clean surface
• Simple process
• Cost-effective
• Good compatibility
• No mechanical stress

Applicable Metal Materials of Photochemical Etching

Etching can be applied to a variety of metal materials, the most common of which are: stainless steel, aluminum, copper, nickel, titanium, brass, zinc, gold and silver

Available Colors of Photochemical Etching

Metal etching does not directly change the color, but it can affect the optical properties of the metal surface, thereby indirectly changing its color. For example, stainless steel can appear a darker silver-gray with a fine texture after etching. Aluminum can appear a darker gray with a matte effect after etching. Copper will form green copper oxide after etching, which is the common copper rust.

Application of Photochemical Etching

Photochemical etching is widely used in electronics and semiconductors, aerospace, medical equipment, automobiles, consumer electronics and other industries. It is an ideal choice for circuit boards, microelectronic components, aviation precision parts (turbine blades, fuel nozzles and structural components), surgical instruments, automotive engine parts, and audio precision parts.

10. Powder Coating

What is Powder Coating?

Powder coating is a dry process for spraying various metal products through a spray bed or fluidized bed. It adsorbs the powder coating on the surface of the workpiece by electrostatics, and then cures in an oven to produce a bright protective coating, mainly used to protect metal products from corrosion and damage.

Advantages of Powder Coating

• Durable finish
• Environmentally friendly
• Wide color variety
• Resistant to chipping and scratching
• Uniform coating thickness
• Cost-effective
• Reduced VOC emissions

Applicable Metal Materials of Powder Coating

Powder coating is suitable for a variety of metal materials, the most common of which are carbon steel, stainless steel, alloy steel, aluminum alloy, zinc alloy, magnesium alloy, copper alloy and titanium alloy.

Available Colors of Powder Coating

Powder coating can be presented in a variety of colors to meet different decorative and functional needs. Common colors are black, gray, blue, red, copper, gold and silver

Application of Powder Coating

Powder coating is widely used in automobiles, home appliances, construction, furniture, industry and other industries. It is an ideal choice for automobile engine parts, wheels, home appliance housings, metal furniture, pipes and valves.

11. Plasma Electrolytic Oxidation (PEO)

What is Plasma Electrolytic Oxidation?

Plasma electrolytic oxidation, also known as plasma electrolytic deposition, is a surface finishing technology performed in a plasma environment.

It generates plasma by applying high-frequency voltage in the electrolyte, and uses high-energy particles in the plasma to bombard the metal surface, causing physical and chemical changes such as oxidation and deposition on the surface, forming a dense oxide film or composite film layer.

Advantages of Plasma Electrolytic Oxidation

• High hardness and wear resistance
• Excellent corrosion resistance
• Good insulation
• Enhanced decorative properties
• Improved lubricity
• Increased biocompatibility
• Environmentally friendly and low cost

Applicable Metal Materials of Plasma Electrolytic Oxidation

Plasma electrolytic oxidation is primarily applicable to aluminum and its alloys, and it can also be used for magnesium and titanium and their alloys.

Does PEO produce new colors?

Plasma electrolytic oxidation itself does not produce new colors, but it will produce different visual effects by changing the structure and optical properties of the metal surface, such as color depth, glossiness, and texture changes. For example, aluminum alloy will appear gray or silver after plasma electrolytic oxidation.

Application of Plasma Electrolytic Oxidation

Plasma Electrolytic Oxidation is widely used in electronics, automotive, machinery manufacturing, construction and other industries. It is ideal for electronic equipment, automotive engine parts, gears, bearings, housings, crankshafts and sensors.

Resources

If you want to know more about Plasma Electrolytic Oxidation, you can read this article.

12. Spray Painting

What is Spray Painting?

Spray painting is a fast and efficient method of applying adhesives, primers, varnishes, oils, sealants, varnishes and enamels to a surface using a spray gun. The finishing techniques available and the time required for the process are determined by the surface of the material.

Advantages of Spray Painting

• Enhanced aesthetics
• Protection against corrosion
• Improved durability
• Resistance to environmental elements
• Easy maintenance
• Versatile color options

Applicable Metal Materials of Spray Painting

There are many metal materials that can be used for painting, including stainless steel, carbon steel, alloy steel, aluminum, titanium, copper, zinc, magnesium and nickel.

Available Colors of Spray Painting

There are many colors available for spraying, you can choose the right color according to your needs. Common colors are black, white, gray, blue, yellow, red, green, gold, silver and copper.

Application of Spray Painting

The process is widely used in the automotive, aerospace, construction, machinery manufacturing, and electronics industries, and is ideal for automotive parts, airframes, mechanical parts, consumer electronics, and construction materials.

How to Choose?

For many people, choosing the best method may be a little difficult. Therefore, we give you reference from 4 aspects: function, color requirements, materials, and budget to help you choose the right surface finishing.

According to Function

Depending on the different functions, you can choose different surface finishing.

• For metal parts that are prone to rust and corrosion, you can choose electroplating, chemical conversion film, and spraying to improve the corrosion resistance of the parts.
• For metal parts that need to resist wear and friction, you can choose electroplating, sandblasting, and spraying to enhance wear resistance.
• For metal parts that need to improve aesthetics, you can choose electroplating, spraying, and polishing.
• For metal parts that need to enhance conductivity, you can choose electroplating to improve the conductivity of the parts.

According to Color Requirements

Depending on the material and performance, different surface finishing can provide different color options, color durability and other properties:

Spraying produces rich colors, which can achieve single color, multi-color, and pattern color, and can control the surface gloss, but the durability is affected by the performance of the coating.

The color produced by electroplating is relatively simple, and the common color is metallic, but the durability is good.

The color produced by anodizing is relatively simple, and the common colors are black and silver, but it has strong corrosion resistance and is suitable for aluminum alloy materials.

According to the Material

Selecting the appropriate surface finishing from the material side requires a combination of material properties and applicability of the surface finishing; not all processes are suitable for any type of metal.

In general, aluminum, stainless steel or steel are suitable for most processes. For example, aluminum alloys are suitable for anodizing, steel for plating. If you want to process copper or titanium alloys, you need the right process.

According to the Budget

Choosing the right surface finishing method from a budget perspective requires a comprehensive consideration of cost and effect, as the costs of different materials vary greatly.

Spraying and sandblasting are suitable for mass production and products with low surface requirements, and have low processing costs.

Electroplating and anodizing are suitable for products with high surface requirements but limited budgets.

Thermal spraying and laser surface finishes are suitable for products with extremely high surface performance requirements and are not sensitive to cost.

Conclusion

Hopefully, after reading this article, you will have a better understanding of different surface finishes for metals, and will be able to simply understand which surface finishing is suitable for your project in terms of materials, performance, and budget.

If this article is helpful to you, please share it with more people, thank you very much! Furthermore, if you want to know more about other surface finishes, please continue to follow our blog or contact us directly, and we will solve your needs as soon as possible.

If you have metal parts planning needs, please feel free to contact us. DEK is your best manufacturing partner, specializing in CNC machining, metal 3D printing, die casting, and sheet metal manufacturing. Contact us now!