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What Is Anodizing?

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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 26 June 2014
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Anodizing is a protective and decorative surface treatment used to enhance the working qualities and visual appeal of items made from a range of metals including aluminum alloys, zinc and titanium. The treatment involves manipulation of the natural oxide layers on the metals to produce thicker and more durable films. These enhanced oxide layers lend the items increased resistance to wear and corrosion and provide surfaces which are more receptive to paints, dyes, and adhesives. When applied thinly, anodized films also tend to cause light interference resulting in attractive surface patterns and multicolor effects. In addition to the improved wear and corrosion resistance offered by anodizing, treated parts are also less inclined to exhibit galling of friction surfaces.

Oxide formation on the surfaces of metals is a naturally occurring phenomenon that results from exposure to oxygen and moisture in the air. Although oxidation on ferrous metals, also known as rust, can cause the eventual destruction of the material, metals such as aluminum alloys, zinc, titanium, magnesium and tantalum can benefit from an oxide layer. If manipulated to be thick enough, these oxidative layers can offer corrosion and wear resistant properties to these metals. This is the principle that underpins the anodizing process used to impart protective and attractive finishes on many non-ferrous metal items.

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The anodizing process involves passing an electric current through an electrolyte solution between a positively charged anode, in this case the anodized item, and a negatively charged cathode. This resultant reaction changes the crystal structure of the anode surface and causes a layer of oxide to be deposited on it in what is known as an electrolytic passivation process. The characteristics of this oxide film can be manipulated during this process, thereby allowing for a high degree of control over the end result. Generally the synthesized layers are more robust than those occurring naturally. As a matter of interest, the anode role played by the product is the source of the anodizing name.

Anodized oxide layers are generally fairly porous by nature and require the application of sealant to ensure maximum corrosion and wear resistance. The film's adhesion to the metal is far stronger than conventional plating or painting films though, thus making anodized finishes particularly durable. This durability offers an excellent base for the post-treatment application of paints and dyes, with colored anodized finishes exhibiting outstanding longevity even with continuous use. Anodizing also helps prevent galling, or adhesive wear, of threaded or sliding parts at their points of friction.

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Discuss this Article

GenevaMech
Post 8

@Alchemy- Anodizing aluminum at home is easy. I have a small set up in my basement that I use for different anodizing projects. you will be able to do color fading and other little tricks in no time. All you need is a bucket, distilled water, battery acid, dyes, and a source of electricity. Good luck.

PelesTears
Post 7

I make custom components for paintball and airsoft guns and I anodize all of my metals at home. You can easily set up a DIY anodizing kit in your garage or basement that will allow you to anodize aluminum. You only need a few supplies, and nothing that is really expensive. You should do a quick search and you will find a number of "how to" videos on setting up a home anodizing kit.

Alchemy
Post 6

Does anyone know if you can get a DIY anodizing kit so I can anodize some metal parts in my garage? I want to anodize a few small pieces of metal with color if I could. If these kits are available, what is the best kit to buy?

Babalaas
Post 5

@Cougars- Black anodizing is a process where the metal is dyed black during the anodizing process. The dye fills in the pores created by the anodizing process. Once the dye is added, the anodizing process moves to the sealing phase where nickel acetate is added to seal the porous metal surface.

Another process for black anodizing is to adhere the metal dye to the surface of the porous material through electrolysis. This is the anodizing process that is used to create the cookware fiorite raves about in the first post.

The only change in the process of anodizing other colors is the color of the dye. Red anodized metals will use red dye versus black dye, and so on for all other colors. Essentially, the two processes are the same.

cougars
Post 4

What is the difference between black anodizing and color anodizing?

aplenty
Post 3

@istria- I think that chrome plating is a similar process to anodizing. I used to work in the front office of an anodizing service and we did both chromium plating and chromic acid anodization. They both use the electroplating process and the procedure only varies in a few steps.

istria
Post 2

Is it possible to chrome plate something that is anodized? Does the chrome plating adhere better when the item is anodized? I would like to have some custom pieces made for my autocross car that are basically chrome plated anodized components. I like the fact that the metals that are usually anodized are lighter than steel, but I like the look of chrome.

Fiorite
Post 1

I have always wondered why my pots and skillets were so durable, but I never thought they were so because of "rust". I recently bought one of those really nice anodized cookware sets complete with copper bottoms and riveted stainless handles. I have had the pans for about seven months and I do not have a single scratch in any of them.

I use these pans every day because I am a chef by trade, but I was a little nervous when I first purchased them because of past experiences with non-stick pans. Most of my other non-stick pans lost their non-stick qualities within weeks of purchase. Eventually they had to be thrown out because they would peel and I would get black flecks in foods cooked at high temperatures.

I still love to use stainless pots and pans in my work kitchen, but I prefer my new anodized pans at home. My electric range does not crank out the same Btu's that the stoves at my work do, so everything I cook in my stainless pans sticks unless I use large amounts of oil or fat. I can cook much healthier meals with anodized cookware.

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