The anodized aluminum is usually connected with professional camping equipment, car and bike parts, and its "unique, shiny color”. Sometimes – you will find anodized parts in houses, where "accents made from the anodized aluminum” should highlight the uniqueness of particular products.
Yes, from the perspective of an average person – that is true. But anodization itself is much more than "an aluminum with nice, anodized color”. First of all – this is a process that increases corrosion resistance and makes aluminum alloys possible to use in the electronic industry.
What is an aluminum anodization and what are the advantages of that process?
Anodized aluminum (called sometimes oxidized) is an alloy with a thin layer of oxide coating (alumina trioxide, Al2O3), achieved in an electrochemical process called anodization. That additional coating provides better corrosion resistance and hardness than a natural layer of oxidized aluminum that develops in contact with air.
Thus – anodization makes additional corrosion prevention unnecessary (like painting or varnishing). Thanks to those features, aluminum anodized parts can be used in a vast variety of environments, even aggressive and highly corrosive (eg. in contact with corrosive substances). It is worth mentioning that many CNC-made parts are subjected to anodization in the final stages of production to provide better part characteristics.
Anodization itself is an electrochemical process whose goal is simple: provide better wear resistance of exposed parts and elements (in addition: to giving nice color). Many types of alloys can be anodized and the process itself is regulated by international norms (ISO: 7599 for decorative anodization and 10074 for hard anodization). The results of aluminum anodization are:
- better corrosion resistance,
- better resistance to mechanical damage and surface abrasion,
- possibility to change color,
- better surface finish,
- higher UV resistance, especially the final color of the anodized surface,
- the anodized surface can be polished, thus it is easier to clean and maintain its esthetic valours.
What is an aluminum anodization process?
Three types of aluminum anodization differ mainly in the agent used to accelerate the oxidation process, the quality of the gained coat on the surface, and complexity:
- Type I anodizing – uses chromium acid as an electrolyte agent. It is a good method of anodizing elements with a complex surface structure that can trap electrolytes. Another advantage of that method is the higher hardness of the final coat, yet the color of the achieved layer is much darker, thus not very pleasing aesthetically and harder in coloring,
- Type II anodizing – is the most popular type of that process. As an electrolyte agent uses sulfuric acid that produces a good-quality surface with the potential for coloring,
- Type III anodizing (known as "hard anodization”) – is the most complicated and less popular of the three, yet provides the best properties of achieved surfaces. An electrolytic agent also uses sulfuric acid, but in a much higher concentration than in type II, and the voltage and current used in that process increase accordingly during the electrolysis. Although less popular in a typical application, that type of aluminum anodization is widely used in the production of automotive and military parts.
It is worth mentioning that each of the anodization types allows the colorization of aluminum (and that is the main cause of the connection between process and aesthetic features). It could be achieved by the addition of other elements during electrolysis (that gives shades of browns and black) or the usage of organic pigments (SANDALOR® process) that allows achieving up to 25 color options.
What does the process of aluminum anodization look like?
The aluminum anodization process has multiple stages and can be complicated. On the other hand (simplified) can be summarized in the following steps:
- before the beginning of the anodization process begins, the subjected element must be cleaned and degreased,
- another step is chemical polishing or pickling (usually in caustic soda),
- after another rinsing, the actual process of anodization begins in an electrolytic batch (in acid and with the utilization of current, according to the chosen type of process),
- in final rinsing it is possible to color aluminum (by the usage of the colorizing additives) – this is a non-obligatory step,
- anodization finishes by sealing the surface – in cold (by the usage of a passivator) or in hot, almost-boiling weather.
The process itself (types I and II anodization) is possible to perform at home with a little equipment, but still, remember the usage of acids is always potentially dangerous. Type III anodization is way more complicated and requires more professional tools to perform. That is why it is a good idea to get professional aluminum anodization services.
What is the usage of anodized aluminum?
Anodized aluminum has many applications – from many industries to daily applications. The main reason for that variety of use is the anodized coat itself. Said layer is non-conductive (keep in mind: aluminum electrical conductor) thanks to that anodized aluminum alloys are often used in the production of electronic and electric parts.
High rigidity and overall hardness of surface make that type of finish popular in many industries, especially in automotive – as an additional layer of protection for crucial parts (eg. pistons, valves, or transmission elements) or strictly aesthetical elements.
High stain and corrosion resistance make it a good material for kitchen appliances (selected series of aluminum alloys safe to use close to food).
All mentioned reasons combined make anodization popular in military and outdoor industries. Thermoses, pickaxes, or receivers of guns (or other important parts) are subjected to that processing to achieve better wear resistance and rigidity.
But still: the most "visible” application of anodized aluminum can be seen in houses and homes as a part of interior design – as anodized profiles or bars.
Is the anodized aluminum safe for people?
Yes: anodization is safe for people and their health. Every aluminum alloy that can be used around food – can be anodized and achieve all of the features of that process: low reactivity, high rigidity, easy-to-clean surface, and good heat conductivity.
That is why anodized aluminum is commonly used in houses and healthcare. Said process decreases wear and tear, especially during repetitive cleaning and sterilization (also with the usage of aggressive chemicals). These features make that type of alloy perfect for hospitals and other "health-related” applications.
Aluminum anodization in CNC machining
Aluminum part anodization is an important finishing step for many CNC machining processes (milling or turning). Utilization of that form of preserving the part surface provides much better protection (mechanical and chemical) of the produced part. It is even more important in machining personalized projects and the production of automotive and bike parts and profiles.
The cost of aluminum anodization varies between the type of process, the desired color of coating, the overall size, and the complication of ordered parts. In RADMOT we can oxidize aluminum profiles up to 600 mm (a bit over 23.6 inches). Still: anodization is an additional cost for machining parts, yet can provide longevity of parts and thanks to that: more savings in the future.
Aluminum colorization: anodization or powder paint?
There are a few possibilities to color aluminum – from painting with hard lacquer (eg. car body), through powder painting to the mentioned anodization. And although the last type of coat of color is limited by its technology (the pallet is small), the gained surface finish is for sure the most wear resistant.
Oxidized aluminum provides way better protection against UV radiation than other types of coloring alloys. It is worth mentioning that the paint does not interact with the metal itself; anodization makes a color an inseparable element of the aluminum surface.
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At RADMOT, we can offer CNC milling services, CNC turning services as well as many additional services, including washing, aluminum anodizing, laser marking and assembly.
Contact us and tell us what you need. We have been providing CNC services for almost 40 years. Our quote is completely free. And if you have any doubts about what technology will work best for you, our expertise is at your service.