What Are the Types of Metal Part Finishing Processes?

Metal part finishing processes are the last step in the manufacturing process of metal parts. This process involves changing the surface of your part, with the ultimate aim of improving its appearance or durability.

This can be achieved through different methods. In this article, we’ll give you a breakdown of the common types of metal finishing processes used in custom parts manufacturing. From anodizing, coating, passivation, electroplating and others.

What Are the Categories of Metal Finishing Processes?

Finding the type of metal finishing technique that best matches your application can be difficult. But it becomes easier if you start by the category in which they fall into: additive/altering and subtractive/refining finishes. Below, we’ll explain the differences between these categories and list the common types of metal finishing processes under each.

Additive and Altering Finishes

Additive/altering processes change the metal surface by adding material, or chemically modifying, its composition. In short, it’s used when you want to improve the part’s corrosion resistance, aesthetics. Or prepare the surface for bonding, painting, or electrical conductivity.

The Common Additive/Altering Metal Finishing Processes:

• Anodizing
• Electroplating
• Electroless Plating
• Powder Coating
• Chromate Conversion Coating
• Phosphate Coating
• Hot Blackening
• Painting

 

Subtractive and Refining Finishes

Subtractive and refining processes improve the metal surface by removing imperfections, contaminants, or excess material. These processes are ideal when your goal is to reduce surface roughness, remove sharp edges, and achieve a polished or consistently matte texture.

Common Subtractive/Refining Metal Finishing Processes:

• Electropolishing
• Abrasive Blasting
• Buff Polishing
• Brushing
• Grinding

 

What Are the Common Metal Part Finishing Processes?

There are multiple finishing methods used across different industries. But some are requested more often than others. We’ve listed the most common ones requested by buyers on Haizol’s platform. Oftentimes, these are preferred due to their performance, cost, and material fit.

What Is Anodizing?

Anodizing modifies the aluminum surface by growing a durable, corrosion-resistant oxide layer that can also be dyed for decorative finishes. It’s commonly applied to aluminum, which serves as the anode in an electrolytic bath. Ultimately causing a controlled oxidation reaction.

After anodizing process, the porous oxide layer can be dyed to match a specific color or to achieve a decorative finish that resembles other metals.For example, anodized aluminum can be dyed to resemble copper, brass, or bronze.

• Electrochemical process.
• Frequently applied to anodizing Aluminium.
• Can be dyed to match a specific color.

What Is Hard Coat Aluminium Anodizing?

Hard coat anodizing is a more robust version of standard anodizing. Similar to standard anodizing. It uses an electrochemical reaction to build up an oxide layer. But the difference lies in the thickness, hardness, and abrasion resistance of the resulting finish. However, hard coat anodizing creates a thicker/harder surface that offers better wear resistance and smoother finish.

There are many colour options. The typical options are darker tones such as dark bronze and black due to the thickness of the oxide layer. Sticking with these colours helps you avoid custom setup charges. Apart from that, limiting color variations and batching more parts per dye color can reduce overall anodizing costs. Keep in mind anodizing small batches can be costly. Fixed setup costs apply no matter the quantity.

• Better wear resistance than standard anodizing.
• Choosing standard dark colors helps avoid custom dye setup charges.
• Small-batch anodizing can be costly.

 

What Is Passivation Stainless Steel?

Passivation chemically removes surface iron from stainless steel to restore its natural corrosion resistance. While stainless steel naturally forms a protective chromium oxide layer. It can still corrode if iron particles become embedded in for example machining, forming, or handling. These contaminants can lead to localised rusting. Often referred to as rouging. Especially in environments with moisture, chlorides, or chemicals.

Passivation stainless steel typically involves treating the surface with nitric or citric acid to dissolve exogenous iron without affecting the steel’s appearance or dimensions. This process restores the metal’s passive oxide layer and helps prevent future corrosion.

• Improves the stainless steel resistance to corrosion.
• Risk for localised rusting.

 

What Is Chromate Conversion Coating?

Chromate conversion coating creates a very thin, corrosion-resistant film on light metals like aluminum, zinc, and magnesium. It’s especially useful as a prep step before painting or bonding.

These metals naturally form oxide layers. However, those layers can be inconsistent/disrupted during machining, forming, or surface preparation. When that happens, corrosion becomes a greater risk. Especially in environments with moisture, salt, or industrial chemicals.

The coating is applied through a chemical reaction between the solution and the metal surface. Ultimately, forming a thin, protective film that improves performance without changing the part’s dimensions.

• Prevents corrosion.
• Improves coating and bonding performance.
• Maintains dimensional accuracy.

 

What Is Electroplating Stainless Steel ?

Electroplating stainless steel creates a thin clear metal coating on a non-metallic parts surface by reducing dissolved metal cations. This layer provides protection from corrosion, less friction, and reduces tarnishing to the part.

In essence it’s a process that applies a thin layer of metal onto the surface of a stainless steel part. Usually, it’s done using an electric current (to reduce dissolved metal ions from a solution) which then deposits onto the surface. The result? A clean, uniform metal coating that helps to protect the part from corrosion. It also reduces surface friction and minimises tarnishing over time.

• A clear metal coating on non-metallic parts.
• Improve appearance and extend the part’s lifespan.

 

What Is Electropolishing Stainless Steel ?

Electropolishing is an electrochemical process used to smooth and brighten the surface of stainless steel parts. Often called reverse plating. It removes a thin layer of material using an electrolyte solution and an applied electric current. It’s used to eliminate small imperfections, burrs, and surface contamination. Ultimately, creating a cleaner, more polished finish with improved corrosion resistance.

• Electrochemical process.
• Eliminate small imperfections and improve corrosion resistance.

 

Why Should We Use Metal Finishing?

Metal finishing improves corrosion and wear resistance, enhances surface adhesion, and extends the lifespan of metal parts. It’s often essential in applications where parts are exposed to harsh environments or require precise surface properties for coating, bonding, or assembly.

Metal finishing enhances parts in several ways, including:

• Improving appearance
• Enhancing coating or bonding adhesion
• Increasing corrosion resistance
• Reducing tarnishing
• Adding chemical resistance
• Removing surface flaws
• Controlling surface friction

How to Choose the Right Metal Finishing Process

The best finishing method depends on your (1) base material, (2) performance requirements, and (3) post-processing steps like bonding, painting, or sterilization. No single finish works for every part or industry. Our engineers often start with three key factors: environment, wear, and appearance.

At Haizol, we've processed thousands of RFQs for custom parts. Based on buyer behavior and supplier feedback, here’s a simplified guide to how engineers choose the right surface treatment:

Scenario	Recommended Finish	Why
Aluminum part that needs corrosion protection + color	Anodizing	Adds oxide layer + allows decorative dye
Aluminum in high-friction/wear setting	Hard coat anodizing (MIL-A-8625 Type III)	Improves surface hardness up to 60+ Rockwell C
Stainless steel in medical or food use	Electropolishing	Reduces Ra value, removes microburrs, easy to clean
Stainless steel with iron contamination from machining	Passivation (ASTM A967)	Removes embedded iron and restores corrosion resistance
Aluminum or zinc part before painting	Chromate conversion coating (RoHS-compliant Type II)	Improves paint adhesion without dimensional change
Aesthetic or decorative part	Electroplating (nickel, chrome)	Smooth, uniform appearance with added corrosion layer

 

Conclusion: What Are the Types of Metal Part Finishing Processes?

Each metal finishing process serves a specific purpose. Whether it's protecting against corrosion, improving surface appearance, or preparing parts for bonding or coating. Understanding the differences helps you choose the right metal part finishing services for your material, budget, and application.

If you’re curious about the cost of manufacturing your metal parts with finishing included, send in your request for quotation today. As the leading marketplace for custom parts manufacturing, we’ll connect your request to verified factories in Asia. Completely free and with no markups.