What is anodizing?
How long does it take?
How do you color aluminum?
What are the electrical properties of Anodizing?
Can I expect uniform color?
What about rack marks?
What alloys are recommended for anodizing?
What casting alloy is recommended for anodizing?
What is a Hull cell?
A coating of aluminum oxide is grown from the aluminum by passing an electrical current through an acid electrolyte bath in which the aluminum is immersed. The coating thickness and surface characteristics are tightly controlled to meet end product specifications.
It only takes a few hours to process and pack a part. Most anodizers need anywhere from a few days to a few weeks to plan, process and invoice for projects.
There are four ways to color aluminum:
MPP currently provides colors using dyes as well as 2 step.
The dielectric strength of an anodic coating should be approximately the same as that of Alumina. The Handbook of Chemistry and Physics, 43rd Edition, (Published by The Chemical Rubber Publishing Co, Cleveland, OH) gives the dielectric strength of Alumina as between 40 - 160 volts/mil. In metric units that is 1.6 - 6.4 V/uM
Almost all appearance features of the anodic coatings are somewhat variable. That means, “it depends”. There will be some variation in the appearance from batch to batch and even piece to piece. MPP strives to minimize these variations. If appearance uniformity is critical, agreed upon “range samples” should be approved before the parts are processed.
Electrical contact must be made to each part that is anodized. The more electrical current required, the bigger the electrical contact must be. The size of the contact therefore depends on the anodizing process and the size of the part being anodized
Most aluminum alloys will build aluminum oxide in an anodizing tank. 2000 series Alloys are generally the most difficult to anodize and 5000 or 6000 series are the easiest. For the best appearance and performance, 5005 AQ alloy for sheet and 6063 alloy for extrusion are recommended. 5052 alloy for sheet and 6061 alloy for extrusions are popular, but they may have more appearance variations.
Castings are challenging to anodize because they are often porous. The alloy preferred for anodizing castings is 518. C443 is also good, but it is not inherently corrosion resistant.
The Hull cell is a type of test cell used to qualitatively check the condition of an electroplating bath. It allows for optimization for current density range, optimization of additive concentration, recognition of impurity effects and indication of macro-throwing power capability. The Hull cell replicates the plating bath on a lab scale. It is filled with a sample of the plating solution, an appropriate anode which is connected to a rectifier. The "work" is replaced with a hull cell test panel that will be plated to show the "health" of the bath.