Anodizing is a processing technology favored by aluminum alloy industry. Today, I will tell you about five advantages of anodizing aluminum alloys.

 

Aluminum alloy substrates are particularly susceptible to scratches and wear, and hardness of aluminum alloys cannot be compared with steel. However, surface of anodized aluminum alloy profile will be very hard, wear-resistant, and not easy to scratch. This is due to greatly increased hardness of surface oxide film.
Hardness of Aluminum Anodizing
Hardness of aluminum anodized film is generally 200~500HV. Anodizing is an exothermic process, and high temperature will increase hardness of anodizing.
Heating aluminum anodized film removes moisture in it. In addition, crystal structure of anodized film will also change. Within a certain range of dehydration and structural changes of anodized film, hardness of anodized film increases with extension of heating time. If aluminum anodic oxide film is maintained to protect aluminum substrate, anodic oxidation performance will deteriorate instead, and hardness of anodic oxide film cannot be maintained. Therefore, in order to maintain change of anodic oxide film hardness during heating within performance range of anodic oxide film.

Since surface of aluminum alloy is endowed with a dense oxide film, this oxide film can better prevent direct contact between aluminum and air.
When aluminum and its alloys are anodized, following reactions occur at anode: 2Al ---> 6e- + 2Al3+; following reactions occur at cathode: 6H2O +6e- ---> 3H2 + 6OH-. At the same time, acid chemically dissolves aluminum and formed oxide film, and reaction is: ① 2Al + 6H+ ---> 2Al3+ + 3H2; ② Al2O3 + 6H+ ---> 2Al3+ + 3H2O.
Film layer on the surface of aluminum shell that is heated and extruded is very weak, and aluminum is a kind of active metal, which is easily combined with oxygen, water and other substances in air, then chemically reacts to form Al2O3 and Al(OH)3. Corrosion resistance is greatly reduced; film layer will thicken after anodizing to resist corrosion of acid and alkali substances, thereby improving service life of aluminum shell.

 

Before aluminum profile is anodized and sealed, surface will have a lot of dense pores, which can easily absorb some metal salts or dyes, so that surface of aluminum product will form colorful colors.
Anodic oxidation film of aluminum and aluminum-magnesium alloy in sulfuric acid solution is colorless and transparent, while oxide film of aluminum alloy containing manganese or silicon is light gray or brown gray.
Film thickness of pure aluminum can reach 40um, and thickness of general protective-decorative oxide film is 5-20um. Sulfuric acid oxide film is porous, has strong adsorption capacity, and has a porosity of 10-15%. Film layer is suitable for dyeing or electrolytic coloring, and is used for decoration or identification marks. In order to improve protective performance of film, sealing treatment should be carried out. When service conditions are harsh or corrosion resistance requirements are high, additional painting is required. Paint film and oxide film have good bonding force.

Anodizing will reveal metallic texture of the entire aluminum alloy workpiece.
Xinhao L series aluminum shell
Xinhao G series aluminum shell
Xinhao Q series aluminum shell

Anodizing is fundamentally different from sandblasting or spraying or electrophoresis. Anodic oxidation film is attached to the surface of product, not inner oxide film is integrated with product. It is an electrochemical reaction that occurs on the surface inward. Therefore, anodized film will not appear phenomenon of film peeling similar to that of sandblasting.
Electrochemical reaction of anodic oxidation
Aluminum and aluminum alloy anodic oxidation solution generally adopts an acidic solution with medium solubility, such as sulfuric acid, oxalic acid, etc., aluminum and aluminum alloy parts are used as anode, lead plate is used as cathode, and direct current is passed through. Reaction on cathode is:
2H++2e→H2↑
And on anode, mainly discharge of water:
H2O—2e→[O]＋2H+
2AI+3[O]→AL2O3+ 1670kJ