anodized aluminum is an extremely durable surface finishing method, enhance corrosion-resistant, and highly aesthetic surface; but many people don’t know how it work. and what is exactly anodized aluminium, even though this process have widely usage on our current life. keep reading we will dig it more detail today.
What is aluminum anodizing?
Treat aluminium or aluminium alloy products as an anode, and put them into an electrolyte solution to form a thin film of aluminium oxide on the surface; normally the thickness of film around several hundred microns, Compared to the natural oxide film of aluminium alloys, its corrosion resistance, wear resistance and decorative properties are significantly improved and enhanced.
Why You Might Want to Anodize Aluminum
there many reason you prefer to anodizing your aluminum or aluminum alloy parts, after you anodized aluminum parts, a very thin layer of oxide form on parts surface. this layer is quite thin, just several microns, wont effect precision machined parts. besides this, anodizing also have many advantages; such as below point.
1. Prevention of corrosion of aluminium products
Normally aluminum products will oxide in air. But this naturally oxidized film is very unstable, on the contrary; The anodized film itself is sufficiently stable in the atmosphere; And great denseness and corrosion resistance.
2. Protection – decorative products
After anodizing, Most Aluminum or aluminium alloy products can achieve clear oxide film.This oxide film can absorb a wide range of organic and inorganic dyes, resulting in a variety of vibrant colors. This colorful film acts as both an anti-corrosion layer and a decorative layer
3. Hardening wearing layer
You can achieve Al₂O₃ layer after anodizing, This film not only has a high hardness and thickness, but also a low roughness; The porous, thick oxide film is capable of reserving lubricating oil, so it can be effectively applied to aluminium products working in a frictional state.
4.Electrical insulating layer
The oxide film obtained a high electrical resistance and is therefore useful for improving the electrical insulation of certain products.
5. Painted undercoats
Due to the oxide film has good adsorption capacity, it can be used as a base layer for spray paint and other organic films, so that the paint are firmly bonded to the product, thus increasing its corrosion resistance
How Aluminum anodizing works?
Generally speaking, aluminium or aluminium alloy is used as the anode and lead plates are used as the cathode. Aluminium and lead plates are put together in an aqueous solution, which contains sulphuric acid, oxalic acid, chromic acid, etc., and electrolysed to form an oxide film on the surface of the aluminium and lead plates. The most widespread of these acids is the anodic oxidation with sulphuric acid
Aluminium Anodizing Process
This is because after anodizing, the surface of the aluminium is smooth and anti-corrosive and anti-static, and it remains as bright as new for 20 years. So what are the specific steps of anodizing?
- Surface Pre-treatment, we need remove burrs and flashes; also polish part surface. increase adhesive of oxide film
- Hanging the parts on jig.
- Degreasing; Removal of grease from surfaces by mechanical, chemical or electrolytic methods
- Cleaning; Removal of grease and dirt from surfaces with weak acids, alkaline solutions, solvents
- Desmutting; Removal of impurities adhering to aluminium surfaces
- Anodizing; Electrolytic oxidation process. In this process; Produces a dense, porous, strongly adsorptive Al2O3 film layer.
- Colouring; Use a proper electrolyte; the aluminium will produce a colored oxide film during the anodizing process.
- Pore Sealing; the pores of the porous oxide film generated after the anodizing are closed, so that the anti-pollution, anti-corrosion and anti-wear properties of the oxide film are enhanced.
Commonly used electrolytes for Anodizing
Commonly used processes for anodizing aluminium alloys are: sulfuric acid anodizing, chromic acid anodizing, oxalic acid anodizing and phosphoric acid anodizing. The most commonly used is sulfuric acid anodizing; Here below you can find each electrolytes advantages and disadvantages.
| Electrolytes | Adavantages | Disadvantages |
| Sulphuric Acid Anodising | Widely used, Low Cost, good film transparency, good corrosion and friction resistance and easy coloring;good film adsorption, colorless and transparent, simple process and easy operation | |
| Chromic acid anodizing | Oxide layer thin;maintain the original precision and surface roughness of the work-piece; the corrosion resistance is strong, | the porosity is low and difficult to dye; Oxide layer is soft, with poor wear resistance |
| Oxalic Acid Anodizing | Porosity of the oxide film is low;Great wear resistance; | Cost Higher,poor stability; Color unstable |
| Phosphoric acid Anodizing | Phosphoric acid film has strong water resistance,the bonding of the adhesive is better | Oxide film is thin (only 3um) and the pore size is large. |
Application
Anodizing is surface treatment for metal, Most metal can run anodizing with proper treatment. such as Stainless steel; Zinc alloy; Aluminum alloy; Magnesium alloy; Copper and Titanium alloy.
Conclusion
As a top die casting manufacturer, we have fluent experience to handle anodizing products, such as aluminum; Zinc and magnesium, we knew the whole process well, and understand which process is more suitable for different parts. please contact us if you have anodizing problem.