You may have already heard about the versatile application of anodized aluminum components across various industries. There are anodized aluminum parts in everything we use on a daily basis, such as our smartphones, bicycles, and kitchen utensils, to more complex objects like firearms, multi-tools, and even window frames. There likely isn’t a car or a plane out there without some anodized component integral to its functionality and sturdiness. If you’ve noticed the possibilities for protective coatings on things you use nearly every day, perhaps you were wondering about starting a small business for anodizing aluminum components. You should get acquainted with as much of the process as you can before purchasing the machinery. There are multiple steps to getting aluminum anodized, but there are also a few steps in pretreatment and cleaning anodized aluminum that we will focus on in this particular blog.
Industry-Specific Aluminum Anodization Terms
During your research into the anodization of aluminum, you will come across some terms that will be mentioned on and off to explain the process. Some of these terms relate to the chemistry of the process, while some refer to the physics and electronic aspects. This is because anodization is an electrochemical process that results in the passivation of an aluminum surface, producing a thick oxide coating that becomes corrosion and tarnish-resistant. Bare aluminum is prone to corrosion, but the process of aluminum oxidation creates an anodized aluminum surface that saves it from further corrosion. This artificially oxidized aluminum component is also more durable, adherent to paint, and resistant to abrasions.
Now that we know the core of the process and its aim, we are going to discuss some processes that each aluminum extrusion needs to go through before becoming fully functional kitchenware, a tool, or aluminum siding for your home.
Pretreatments of Anodizing Process
Anodized aluminum extrusions need to be subjected to a thorough cleaning process before being submerged into the chemical bath with an electric current. These cleaning procedures require more than a simple cleaning solution. The anodizing process cannot begin if the aluminum surface contains any grease, oil, or dirt. The surface also has to be as smooth as possible to achieve premium results. This is why we will explain the process of rinsing, etching, and deoxidizing, as they are the most important steps in the cleaning process.
Cleaning – Removing Organic Soil
Aluminum parts sometimes contain oil and grease, which are often referred to as organic soil. These contaminants are normally removed with a non-etching alkaline soil cleaner. Even if your aluminum component is already a formed object, it’s absolutely vital to remove any organic contaminants before immersing it in the chemical bath. If you fail to observe this step carefully, the organic matter left on the component will react with the anodizing electrolyte solution and leave marks on the surface. Each time a step in pretreatment is performed, a ritual of rinsing with cold, flowing water needs to be completed.
Deoxidizing – Removing Inorganic Soil
As its name implies, deoxidizing is the process of removing oxide buildup on the surface of aluminum via oxidation-reduction reactions (redox). Sometimes there are excess alloyed metals remaining on the surface of aluminum, and deoxidizing removes them with the help of mineral acids. There are three acids we can use: nitric-acid-based, chromic-acid-based, and hydrofluoric-acid-based. Deoxidizing can be light-duty or heavy-duty, with etching or with no etching, or it can be used after alkaline etching as a rinse neutralizer.
Etching
We’ve already mentioned some ways of etching. The most efficient and vital part of surface preparation can be done in two ways: using an acid solution or using an alkaline solution. Etching is performed to even out or smooth the outer layer of metal and provide a uniform surface. This upper layer is sometimes referred to as ‘disturbed,’ since it often contains nano-sized grains. A good pretreatment guarantees the removal of these grains, a smooth surface free of imperfections, and a corrosion resistance of the highest quality.
Acid etching comprises a mixture of phosphoric acid and a surfactant, while alkaline etching is made up of caustic soda, a surfactant, and a chelating agent. With the application of these acids, sometimes there is residue, which is called smut.
Desmutting
Desmutting is the act of removing excess alloyed metals from the surface of aluminum after etching, and it can be done using any mineral inorganic acid, although most often nitric acids are used. You shouldn’t confuse it with deoxidizing, as the latter uses redox reaction to remove aluminum oxide only. Another difference is that you may not always be able to deoxidize aluminum before processing it, but you can always give it a thorough desmutting.
Rinsing
We’ve touched on the importance of rinsing only briefly. The truth is, its importance cannot be overstated. It can be quick, but a thorough rinse is always recommended. Some time in the rinse tank is needed for contaminants to dilute off the surface of aluminum components. A mechanical stirrer or air usually contribute to the best results. Depending on the part size and application, you need to pay attention to the water flow, water temperature, and quality. Whatever the case may be, the water needs to be purified. Regular tap water may have high mineral content, so it’s best you use distilled water during your process.
List of Pretreatment Steps
For a perfect aluminum finish, the most important steps you can take are in the beginning of the process. Anodized surfaces will look clean and polished only with the proper application of the following steps:
-
- Cleaning Organic Soil
- Rinsing
- Deoxidizing
- Rinsing
- Etching
- Rinsing
- Desmutting
- Rinsing
- Anodizing
Conclusion
To achieve a perfect anodized coating, it’s going to take more than rubber gloves and a soft cloth. Only once you’ve mechanically cleaned it can you really say that your aluminum surface is perfect. Aluminum requires cleaning and maintenance, but the end result is well worth it.
If you are interested in having your parts processed, please contact us at www.aerospacemetalsllc.com
