Author: Tony Hunt

Aluminum is an amazing metal.  About 8.23% of the earth’s crust is aluminum, making it the most abundant metal in the earth’s crust.  It is 2.9 times lighter than iron and 1.7 times lighter than titanium, yet, when mixed with other metals to create alloys it can functionally compete with steel and titanium in many applications.

Aluminum reacts rapidly with oxygen, creating a very thin layer of aluminum oxide on its surface.  Aluminum oxide volume is 1.5 times larger than the aluminum used to form the layer.  This means that the oxide film is under compressive stress and will not only cover the metal continuously, but can protect the substrate even under deformation.  This layer is 2 to 3 nanometers thick.  It is impermeable to air, water, and many chemicals.  Without this layer, all aluminum would continue to react until it became a pile of aluminum “rust,” and all those aluminum tire rims, pots, airplanes, and backpacking frames would become powder in just a few hours.

Not only is aluminum oxide a good protective layer, but it is very hard and wear resistant.  Aluminum oxide has a Mohs hardness rating of 9.  In comparison, a diamond is a 10 and a hardened steel file is between a 7 and 8.  There are specially produced or rare items that are harder than Aluminum oxide (and some are harder than diamonds), but they are generally man-made or brought to earth by meteorites. Aluminum oxide is also a great insulator.  Aluminum is an excellent conductor of electricity, but when it is isolated by Aluminum oxide, it becomes a poor conductor. Naturally occurring Aluminum oxide is known as corundum, sapphire, and ruby.  Hence the name of our company, Sapphire Metal Finishing, Inc. 

Anodizing is the process of growing a thick layer of Aluminum oxide on the surface of a piece of Aluminum.  It makes aluminum chemically resistant, abrasion resistant, and/or electrically non-conductive.  Anodizing also makes it possible to dye aluminum.  Thick man-made aluminum oxide has small pores that are able to absorb dye. At Sapphire Metal Finishing, we specialize in aluminum anodizing services. We offer a variety of colors, including black, red, orange, blue, tan, olive drab, gold, some miscellaneous colors and undyed/clear/gray anodizing.  Contact us today to learn more!

To maximize the durability and performance of aluminum parts, many companies source aluminum anodizing services to both enhance the surface finish and add an effective layer of protection to their workpiece. Anodizing aluminum is a popular, efficient coating method, that is often more cost-effective and durable than many traditional surface applications, like painting. Using a controlled electrochemical process, aluminum anodizing creates an exceptionally hard, durable, corrosion-resistant, and non-conductive anodic oxide finish on aluminum parts. Along with durability, this anodized layer results in a smooth, attractive surface that can be dyed in many colors.

Also referred to as an “aluminum oxide finish”, anodic oxide finishes are electrochemically fused to the surface, leaving a permanent protective layer that will never peel or chip like paint or even powder-coated surfaces. This is because the electrochemical fusion process allows the new anodic oxide layer to become physically bonded to the aluminum workpiece. Additionally, the surface finish on anodized aluminum products can enhance the adhesion of secondary coatings like paint.

Relative to other available aluminum finishes, anodizing is very environmentally friendly.  Most chemicals used in the process are non-hazardous and are often used in fertilizers and water purification facilities.  Very, very small amounts of nickel and trivalent chromium are used in the seal and dye processes.  These are separated from the waste stream and handled by certified waste handling operations.

The anodizing process can be divided into three general categories: Surface preparation, anodizing, and finishing.

In surface preparation, the parts may be tumbled or bead blasted.  They are thoroughly cleaned in a non-etching caustic detergent.  They may then be etched to make the surface more matte and offset the anodizing growth to maintain dimensions.  It is then important that alloy metals and native oxide on the surface are removed.

During the anodizing process, the aluminum is submerged in a bath of acid electrolytes. Once submerged, the aluminum workpiece acts as an anode, with a cathode being placed beside it.  Electric current is forced through the bath, resulting in the bath solution releasing oxygen ions that will react with the aluminum workpiece forming an anodized surface finish.

The anodized surface may then be dyed.  There are about 40 billion pin holes in the sapphire-like aluminum oxide layer.  Microdroplets of pigment are adsorbed into these pin holes.  The pigments can be seen through the transparent aluminum oxide, changing the apparent color of the part.  The part is then sealed.  This process is done to trap the pigments in the pinholes and to protect the exposed aluminum in the bottom of the pinholes from environmental conditions.

Whether you need a single part finished, or an entire production line – we have the experience, in-house capabilities, and dedicated staff to make it happen. We also offer custom aluminum anodizing services, aluminum chem film services, and aluminum chromate conversion coating services. For more information on any aspect of our business, call Sapphire Metal Finishing at 208-614-4050, visit our contact page, or use our quote generator tool for quick price estimates.

The colors of anodized aluminum are typically deep, rich, bright, and very appealing. However, there is a common misperception that aluminum anodization colors are permanent and will not fade over time. Most dyes used in anodizing are organic dyes that eventually break down over time when exposed to UV light. In some cases, poor quality anodizing is the root cause of fading, but generally there are other more important causes than the quality anodization processes.

Continue reading “Why Does Anodizing Fade and What to Do to Stop It”

At Sapphire Metal Finishing, we work with OEMs and various manufacturers to provide customized solutions for their aluminum anodizing requirements. Many of our customers are unsure of the difference between Type II and Type III anodizing and which option is best for their parts and components.

Continue reading “The Differences in Type II And Type III Anodizing”

The process of anodizing aluminum enhances the corrosion resistance and durability of the surface of the metal by adding an anodic oxide finish. This is done through an electrochemical process that is carefully controlled to provide a specific amount of oxidation to the surface aluminum. Continue reading “Things You Need To Know To Prepare Parts For Aluminum Anodizing”