Posted July 15, 2021

What is the Difference Between Anodizing and Electroplating?

 An anodized bolt and a plated socket showing the difference between anodizing and electroplating

CNC mills and lathes are advanced manufacturing instruments that create precision parts used in various industries. However, no matter how precisely made, the part will always have som marks from the equipment. These “as-milled” surfaces may be acceptable for prototype parts or components hidden from view, but most require a surface finish applied for protection and aesthetics. Two of the most common surface finishes include anodizing and electroplating, which differ significantly regardless of the similar applications. This article will explore this further and answer the question: what is the difference between anodizing and electroplating?

Anodizing Machined Parts

Anodizing, used primarily for aluminum parts, creates a surface finish offering corrosion resistance and durability. It also provides an aesthetically pleasing appearance. Aluminum forms a naturally occurring layer of oxide that offers minimal protection when exposed to the atmosphere. Anodizing increases this layer’s thickness, making the part more robust and able to withstand harsh environments. The anodizing process creates a natural range of colors, including gold, brown, gray, and black, and provides better adhesion for painting, silk screening, and powder coating. Anodizing also allows for dyes to create additional colors.

Increasing the natural oxide layer on the surface of a part through anodizing uses an electrochemical process. After being cleaned and prepared, the operator will suspend the part in an anodizing tank of diluted acid and water that conducts electrical current. With cathodes introducing electricity to the tank, the aluminum surface of the part combines with negatively charged oxygen ions and builds up the aluminum oxide layer. The electrochemical process changes the thickness and texture of the part’s surface, giving it a strong decorative finish that is corrosion-resistant.

There are different versions of the anodizing processes depending on the needs of the treated part:

  • Type I: Hard anodizing uses a chromic acid-based chemical bath to produce a thin, durable finish with a high level of resistance to corrosion. Finish thicknesses range from 0.00002 inches to 0.0001 inches (0.00127 mm to 0.00254 mm).
  • Type II: Decorative anodizing uses sulfuric acid, which allows metals to absorb most colored dyes. The thickness of this finish can increase to 0.001 inches (0.0254 mm).
  • Type III: Hardcoat uses sulfuric acid and additional electrical current to produce the thickest anodized finish. This finish will range in color from gray to bronze and can achieve thicknesses up to 0.003 inches (0.0762 mm).

The next section looks at using electroplating finishes on a part to contrast it with anodizing.

Using Electroplating to Finish a Part

Electroplating creates a surface finish by depositing one type of metal in thin coats onto a part made out of different metals. The metal plating protects the part by increasing its strength, heat resistance, and creating an insulating barrier. Plating also enhances the part’s surface properties. For example, platings can reduce friction, improve electrical conductivity, or prepare the surface for paint adhesion. The plating increases the thickness of a part by applying several thin metal layers to build it up. The part’s appearance will also improve with a glossy sheen or smoothing the surface with a more uniform finish.

Electroplating uses an electrochemical process, although it has some differences from anodizing. First, the operator cleans the part in chemical baths to ensure that it has a strong bond for the electrodeposition process. Next, the operator suspends the part in a bath of electrolyte solution. They carefully monitor this solution to ensure that it is clear of any foreign metals that could compromise the plating process. A power supply then provides current to the bath flowing from a positively charged electrode, or anode, to the part to be plated, which serves as the cathode in this circuit. The anode contains the metal for plating, and the flow of current slowly pulls this metal from the anode and deposits it onto the part.

There are different metals that you can specify for electroplating, including the following:

  • Zinc works well as a plating finish over steel or iron, preventing those metals from corroding. However, zinc plating does not work well for components exposed to marine environments or temperatures greater than 500˚ F (260˚ C).
  • Tin serves as a standard surface finish due to its low cost. It provides a soft and ductile covering with corrosion resistance and solderability for electronic components in various high-tech industries.
  • Copper offers various surface finishes for metal, including dull, semi-bright, satin, polished, or gloss coatings. It has high electrical and thermal conductivity, magnetic repellence, antibacterial and ductile properties.

The automotive, electronics, medical, aerospace industries, and many others use electroplated parts. By understanding these surface finishes deeper, the next step involves identifying the differences between them.What is the Difference Between Anodizing and Electroplating?

Anodizing and electroplating comprise electrochemical processes that produce high-quality surface finishes on machined parts. Anodizing increases the thickness of the natural protective layer of oxides, while electroplating deposits metal layers on the part instead. They both use a similar electrochemical process to deposit material on a metal surface, but the natures of those materials differ completely. This chart summarizes the differences between the two:

 

Definition

Application

Purpose

Anodizing

Building up a coating of protective metal oxides on a metal surface with an electrochemical process

Aluminum and other metal components for aircraft, electronics, architectural materials, and home products

Provides a protective barrier to corrosion that adds durability and pleasing aesthetics

Electroplating

Depositing thin layers of metal on another metal surface using an electrochemical process

Automotive, aerospace, energy, medical, electronics, military, and tools using metal components

Improve surface quality such as resistance to damage or corrosion, reflectivity, frictionless, electrical conductivity, and appearance. 


At Plethora, we offer many surface finishes on the parts we build. These finishes include alodine coating, powder coating, passivation, electropolish, blasting, and of course, anodizing and electroplating. We strive to provide the industry's best finishing services to match our advanced CNC machining capabilities. We are ISO 9001 certified, supporting our primary goal of manufacturing your parts to the highest quality. Our online DFM and quoting systems are ready to receive your data so we can begin working together on your next project. To get started, upload your design files to Quote My Part or call us at 415-726-2256.
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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: materials, Design, Manufacturing, finishing, CNC machining, Quality, Prototyping, electroplating

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