sign in sign up
<<
Home , Anodizing

Types of Anodizing

Type II and Type III Anodizing

There are 2 main methods, which are natural anodizing (Type II) and hard anodizing (Type III). Type II being the more common of the two. Type II uses a sulfuric based chemical bath allowing tints and colors to be added to the parts. It produces finishes 2-25um thick and grey in color. The finish can be colored to a range of vivid shades. Type III anodizing produces films up to 115 um and is used when a super hard surface is desired for more demanding applications that require high wear and temperature resistance. It uses the same acid bath as Type II but done at a cooler temperature. Colors are not common but shades of greys can be achieved by altering temperature and voltage. Type III has a much thicker abrasion resistant . Type II Type III Resistance > 336 hrs. salt spray 1000 - 2000 hrs. salt spray Wear Resistance Good Excellent Thickness Range 1.778 – 25.4 um 12.7 – 114.3 um (According to MIL-A-8625) Insulating Properties Good (non-conductive) Excellent (Extremely non-conductive) Appearance Clear or dyed Grey colors Penetration/Growth 65% Penetration 50% Penetration 35% Growth 50% Growth

Compatible Materials and Colors

Aluminum, aluminum alloys, , and can be anodized. Aluminum is by far the most common due to its high strength to weight ratio and availability. Anodized aluminum is capable of achieving many colors as dyes can be used to get the desired shade.

Influence of Aluminum Alloy Components on Color and Transparency High-purity aluminum contains practically less than 0.05% of other . For aluminum alloys, usually aluminum will be alloyed with magnesium, , manganese, or to improve the mechanical properties.

Alloy Series Alloy Element Properties 1xxx Aluminum (99.0% min) Soft Conductive 2xxx Copper Very strong Hard 3xxx Manganese Strong 4xxx Silicon Strong 5xxx Magnesium Strong Ductile 6xxx Silicon & Magnesium Strong Ductile 7xxx Zinc Very Strong

However, its suitability for decorative purposes (coloring) decreases. Example causes of color differences in aluminum alloy:

Alloy Element Alloy element % Effect Remark Copper Up to about • No appreciable influence on color, Al 2xxx series 0.2% transparency or hardness of the and 7xxx series anodic layer. However, in the contain more typical amounts of alloy additive than 0.2% Cu (AlCuMg group etc.) it produces an uneven, blotchy grey and brownish appearance. • Also, alloys with copper tend to increase the incidence of galvanic corrosion pitting during the coloring process. Manganese & At about 0.1% • Cause a yellow tinge to the surface • A higher content results in darker colors. Magnesium > 5% • Causes dullness in the surface.

Silicon Up to 1% (in The oxide layer is only subtly dulled. Silicon can lead solid solution) to the oxide Over 1% (in Cause grey dulling layer a grey non-solid tinge, though solutions) this depends 3-6% Grey tint heavily on the form of the silicon in the alloy. Zinc Above about 2% Cause only marginally account for some Al 7xxx series dulling and make no appreciable contain more difference to the color, unless they are than 2% Zn combined with other elements.

Titanium can be anodized in a wide variety of colors, as well as achieving very thin transparent anodized layers. Titanium anodizing does not use dyes to alter the colors, differing the voltage produces an array of colors that are seen as light waves reflect off the oxide layer. This means that the color will not fade like dyed parts.

Magnesium is more difficult to color, as the oxide layer is not as thick leaving the surface of the material much less porous for dyes to settle. Anodized magnesium’s color is often on the grey scale. It is possible to color but it is much trickier. Magnesium is often anodized with very thin films so that the parts are better primed for painting.

Stainless Steel can be anodized to different colors, including black. However in comparison to titanium anodizing, stainless steel colors are not so durable and require some type of protective coating to become durable