Anodizing is not like electroplating and other organic coatings, it is
unique to aluminum. It has greatly extended the applications of aluminum
products and uses after it was developed in early 1930's, where the
metal or else not be utilized. The anodic finish is now available from
aluminum finishing job shops all over the world and is quite
inexpensive.
Anodizing will convert the surface of aluminum to an oxide. Though it
would naturally form aluminum oxide on its surface, it will be a very
thin film. It offers a thicker oxide coating several times thick if
required. The rigidity of this aluminum oxide coating challenges that of
diamond. Due to this anodizing improves abrasion resistance. It can
also appreciably modify and improve the appearance of aluminum. By the
usage of dyes and special procedures, the finisher can make aluminum
look like stainless steel, pewter, copper, or brushed bronze. The
process will improve corrosion resistance, particularly when the metal
surface is in exposure to humid, industrial, and marine atmospheres. The
electrical insulating property of the anodic finish finds its
application when dielectric properties are significant for electrical
components. This type of aluminum is simple to clean and it resists heat
to the high temperature where the metal itself melts.
We can define anodizing as an electrochemical conversion process, and
not an applied coating. The surface of the metal is converted to
aluminum oxide as a result of reactions going on at the anode in an
acidic solution. Oxide formation generally gets inward, towards the
source of the fresh metal. The first formed oxide will remain in contact
with the anodizing solution all through the process cycle; the last
formed oxide is at the metal interface. The coating will be nearly 30-50
pct thicker than the original metal it replaces.
Structure of most coatings is predominantly porous. There will be a very
slight non-porous barrier film at the interface. Process control starts
with the quality of the metal, its precleaning and racking, and finally
ends with unracking, possible "clean-up" and final inspection. The job
shop finisher or captive department generally has the least control over
a very important requirement for good anodizing that is the metal
quality. Type of mill product, alloys, worth, temper and so on has
significant effects on the appearance, oxide coating property and
functional properties like abrasion and corrosion resistance of the end
product.
The finisher must know about the metal that is to be treated. Some
process changes should be made, and particular quality standards will be
difficult to attain other than the proper alloy is being anodized.
These can be formed in a range of chemical solutions, though only a
handful is in industrial use. The advantage of anodized aluminium
is the potential of colored anodizing dye. These dye seeps into the
microscopic pores of the anodized layer and colors it. This layer is
then sealed and the color appears as part of the metal itself. This can
be used for great artistic effect, making aluminum parts with strikingly
tasteless colors to ornament your motor bike or, more topically,
telescope.
