The type of finish a project gets is hotly debated these days. Metal components of manufactured goods, particularly aluminum, tend to receive one of two types of coatings: anodized or powder coating.

When it comes to anodizing aluminum vs. powder coating, it can be difficult to see the difference between the two. The final result of the two processes appear to be similar. However, they are two very different processes down to the chemical reactions involved in producing them. These differences amount to substantial differences between how the coating on the finished product reacts, the amount of time it lasts, and the ultimate lifespan of the finished product.

Options When Anodizing Aluminum

At the most basic level, the difference between anodizing and powder coating is that powder is an organic coating, or a coating containing carbon, while anodizing is a metal oxide coating. In the aluminum anodizing process the metal workpiece is inserted into an acid bath where it serves as the anode—negative pole—in an electrical circuit. This frees up aluminum atoms that bond with oxygen that form a thicker layer of aluminum oxide than would be formed naturally. This creates a hard surface that resists corrosion and wear.

While there are different levels of anodizing, they are all creating a similar oxide layer. The difference lies mainly in the strength of the acid. Stronger acids increase the thickness of the oxide layer. Thicker layers can withstand more. There are roughly four types of anodizing:

Type of Anodizing

Features

Chromic Acid

Chromic acid baths create a thin layer of metal oxide on the anode (work piece) surface. It is the most common type of anodizing and one of the first types used as it is an extension of the chrome plating process. 

 

The process, however, has traditionally used hexavalent chromium, a known carcinogen. So alternatives like trivalent chromium or boric acid are being used instead.

Boric Acid

This is an alternative to chromic acid. Anodizing boric acid provides a safer, less toxic solution while allowing for equivalent results. 

 

While boric acid is a safer and quicker acid than chromic acid, its adoption has lagged somewhat because it’s a patented process.

Sulfuric Acid

Sulfuric acid (also the bath to create hardcoat anodizing) is used to create Type 2 anodizing, creating a thicker oxide coating. Notably, this thicker coating also reduces the electrical conductivity of the aluminum which may be a useful feature for parts in certain applications. 

Hardcoat Anodize

Hardcoat anodization is an extension of sulfuric acid anodization with more exacting process controls and longer immersion times. It can also be combined with different materials like polytetrafluoroethylene (PTFE) molecules to create a slippery lubricated surface.

Of the four anodization processes, the most directly comparable to powder coating is hardcoat anodizing. The process allows for the introduction of different materials into the anodization process that creates a unique surface with different properties that can make the resulting product more useful in certain roles, like bearings, that make contact with other parts under corrosive or high-heat environments.

The advantages of powder coatings is that there is a wide range of options available from color to the chemistry of the coating used. However, an important difference is that powder coating is essentially a very strong paint and not suitable for surfaces that will encounter direct contact, mechanical wear, or intense heat or chemical corrosion.

Types of Powder Coating

Powder coats start off—unsurprisingly—as a fine powder that is applied to a part or component. The powder is fine enough that it electrostatically sticks to the component. Once a satisfactory coating of powder is applied the part is then baked or exposed to UV light to melt the powder into a uniform film across the surface of the workpiece. Since there is no liquid solvent involved, this process can allow for some very thick coating across a workpiece without creating runs or sagging in the coating. The biggest advantage of powder coating though is probably the sheer variety of coating types available.

Type of Powder Coating

Features

Epoxies

These are highly durable powders that have excellent chemical and corrosion resistance but poor weathering resistance. UV exposure can cause chalking and fading.

Polyesters

The most common type of powder coating, polyester powder offers a wide variety of colors and excellent mechanical properties with great flexibility. Low curing temperatures make these coatings easy to apply to a wide variety of materials. They also weather fairly well for a few years.

Super Durable Polyesters

Essentially, these are polyester powder coats that are engineered to resist UV and chemical degradation for longer periods making them more suitable for outdoor use.

Epoxy-Polyester Hybrids

Blended epoxy and polyester powders offer a range of properties depending on whether the epoxy or the polyester is the more prevalent of the two. Polyester powders allow for thinner coatings and enhanced appearance while epoxies allow for greater chemical and corrosion resistance.

Fluoropolymers

Powder coats that are based on fluoropolymers offer the best in UV resistance and long-term durability under weathering. These are used for architectural structures and other outdoor systems. They are widely used to coat 6061 and 6063 aluminums.

Urethanes

Another common powder coating type is urethane coatings. These offer a good blend of durability and weathering resistance and are commonly used in coating automotive parts like rims.

These different powder coating types can also be combined either by multiple powders going into a single layer before curing, or additional layers being added after curing. This allows for a variety of effects. On the cosmetic side different colors and finishes can be added. On the more practical side, combining different layers like covering an epoxy base coat with a fluoropolymer protects the epoxy coat from UV rays that would damage it. This ability to mix and match as needed, and get desirable results is the biggest advantage of powder coating vs anodizing.

Advantages and Disadvantages of Anodizing Aluminum vs. Powder Coating

The major advantage of anodizing aluminum vs. powder coating is that anodizing creates a coating that is ionically bonded to the aluminum substrate. It is substantially more difficult to remove than a layer of powder coating which is a film that is mechanically bonded to the aluminum like a glue or layer of paint. Since aluminum forms a layer of oxides when exposed to the atmosphere under normal circumstances the anodized layer is in some respects self repairing even if it is scratched or damaged through to the substrate. Although this freshly generated layer will be much thinner than an anodized one.

This strong electro-chemical bond means that anodized coatings are much stronger and longer lasting than most powder coatings are. The disadvantages of anodizing aluminum are cost, smaller color and texture selection, and inconsistent alloy reaction.

In contrast, powder coating can be applied to any aluminum alloy. In fact it can be applied to plastics, carbon fiber, fiberglass, and all manner of composites. While it does not bond to the substrate at the molecular level, the bond it does have with the substrate isn’t exactly weak. Although you wouldn’t expect a powder coated surface to hold up inside of an automotive engine, powder coating is frequently used to give engine manifolds and automotive rims a more colorful and pleasing appearance. Anodizing is also used in this role, although it is used more often for production parts rather than custom products from small shops.

When it comes to anodizing aluminum vs. powder coating there isn’t really a clearly superior choice, because even though they are different processes they are comparable in many ways. The only clear advantage is that anodizing performs significantly better under UV and other weathering conditions than powder coating. Although fluoropolymers weather better than other powder coating options they’re still not as long lasting as anodized equivalents. This means anodizing is a better option for architectural aluminum that is expected to last for decades while powder coating may be a more affordable option for architectural trim aluminum that may be replaced as soon as trends change. Whatever coating option is chosen, it should be paired with quality aluminum.

Still wondering about anodizing aluminum vs. powder coating? Industrial Metal Service knows aluminum, specializing in 6061 and offering a range of cast aluminums like ALCA-5 or Alimex that respond well to anodizing. Whatever your coating process is, IMS delivers process ready aluminum cut to your specifications nationwide on time and for a fair price. Call or request a quote to work with an aluminum supplier that you can rely on.

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IMS Team

Industrial Metal Service has decades of experience and over 1.1 billion pounds of metal sold and recycled. Our founder, Jeff, has spent his life in the industry and prides himself on offering fair, efficient, trustworthy, knowledgeable, outstanding customer service. We offer metal salesmetal recycling pickup service, and other associated services, such as precise metal sawing, machinery teardown, and warehouse cleanupGive us a call and we’ll get it done.