Alumin-Art Plating Company, Inc.

With 40 years of experience Anodizing aluminum Alumin-Art is confident we can give you just the finish you need.  From small to large, simple to complex our operators have the experience and knowlegde to provide the highest quality coating quickly and reliably.

Technical Information

     The anodizing of aluminum is a well understood process that has found use in virtually every industry that utilizes aluminum.  The process forms a film of aluminum oxide on the surface of the workpiece that is identical, in fact, to the oxide formed when bare aluminum is left in the open air.  The difference is that by electrolytically forming this oxide the coating can be built in a very uniform, dense fashion.  This coating has several properties that make it valuable in many industries.

     First, the corrosion resistance of the coating is exceptional.  When corrosion is understood as simply oxidation then the oxide formed on the surface of the aluminum during anodizing cannot be further oxidized when exposed to the atmosphere when the workpiece is in the field.  Corrosion resistance testing is performed monthly by an independent laboratory on panels processed at Alumin-Art Plating Co., Inc. by the same internal procedures used to process customer orders.  Current corrosion resitance as required by MIL-A8625F (the industry standard anodizing specification) is 336 hours accelerated salt spray testing (the method is defined in ASTM B117).

     Second, is the ability of the oxide to absorb colored dyes after anodizing is complete.  When the oxide is formed the coating is quite porous (these pores are very small, so small, in fact, that they can only be viewed with an Electron Microscope).  The porous nature of the oxide is what allows dye to be absorbed, much like a sponge.  A wide range of colors are available.   Once dyed the coating must be sealed.   The most common form of sealing by far is hydrothermal; the pores of the coating are quite simply filled with water (near boiling, aided by the use of Nickel acetate) and form bohemite.  The sealed coating has greater corrosion resistance and will no longer absorb dye.  The sealing process also inhibits color fading of the dye; keep in mind, however, that all organic dyes will eventually fade as a result of exposure to UV energy.  The ability of an organic dye to resist fading is called lightfastness; the lightfastness scale is 1-10, 1 being the least reistant to fading, 10 being the most fade resistant.

     The last property dicussed here (though there are certainly many more properties that make anodizing useful) is the coatings resistance to electrical current.  This is often desired when aluminum will be used as an electrical enclosure, for example.  The oxide of aluminum has a very high degree of electrical resistance.  During the formation of the oxide it is necessary to apply enough current to overcome this resistance at a given potential.  While anodizing the coating being formed is also being continuously dissolved by the electrolyte (in this case Sulfuric acid).  The oxide formation happens very rapidly initially, as the current is able to "push past" the resistance of the oxide being formed.  At these early stages oxide formation is occuring much more rapidly than the coating is being dissolved.  As the coating thickness increaeses, however, so does its resistance.  Oxide formation slows down.  Eventually, oxide formation and dissolution will occur at the same rate; at this point, no more oxide can be formed at the given potential and thickness as well as electrical resistance is maximized.  Keep in mind that this coating is quite resistant to the flow of electricity and if an enclosure is anodized it may be necessary to mask areas for grounding purposes prior to anodizing.