The Difference Between Chem Film vs. Anodize, Part 2: What Is Anodize?

Read Part 1 of our three-part series The Difference Between Chem Film vs. Anodize here!

Continuing our exploration of metal finishing techniques, the second part of our series focuses on anodizing, a popular method used to protect and enhance the surface of aluminum parts. Anodizing not only improves corrosion resistance but also allows for the addition of vibrant colors and increased surface hardness. In this segment, we will take a closer look at the process of anodizing metal. By the end of this blog series, you’ll have a comprehensive understanding of chem film vs. anodize, helping you choose the optimal finish for your metal projects.

What Is Anodizing?

Anodizing is essentially an electrolytic passivation process that thickens the natural layer of oxide on aluminum surfaces, helping metal parts resist wear and corrosion. Compared to naked aluminum, anodization improves the bond between adhesives, undercoats, and metal surfaces, much like chem film. This relatively thick, porous layer also absorbs dyes to create a unique decorative look, while its nonconductive nature helps insulate components against electricity. Anodized threaded components are also considerably less prone to galling.

Anodized coatings augment these properties of aluminum and other nonferrous metals: 

• Adhesive bonding
• Cleanability
• Decreased coefficient of friction
• Corrosion resistance
• Electrical insulation
• Paint adhesion
• Wear resistance

Impurities within limit corrosion resistance, so anodization is less effective for aluminum alloys, including materials like copper, iron, or silicon. Anodized metal surfaces also conduct heat less efficiently, expand more readily when heated, and have higher melting points.

Types of Anodization

There are many types of anodizing, though manufacturers mainly use three types. The anodization specification is Mil-A-8625, a standard for military and aerospace applications.

These are: 

• Type 1 anodizing: Using chromic acid, this method neither causes damage nor fatigue to aluminum, resisting stress while also offering good self-healing and corrosion resistance properties; however, manufacturers who use this anodization technique must deal with stricter environmental regulations, as chromic acid is both carcinogenic and noxious. Silvex does not offer this type of Anodize due to the environmental hazards associated with
• Type 2 anodizing: The most common type of anodizing, this approach uses sulfuric acid rather than chromic acid, producing porous surfaces that are easily dyed; this method for anodization is less expensive as it uses less energy and requires no special waste treatment, while the chemicals used are also more economical.
• Type 3 anodizing: Also referred to as hard anodizing, this method also utilizes sulfuric acid as an electrolyte solution, with higher current densities and voltages, along with lower temperatures, that produce highly porous yet considerably thicker metal surfaces, making it more durable due to the thicker coating, however, it doesn’t suit parts that require tight tolerances, though it does offer superior wear and abrasion resistance.

Used to prime surfaces for adhesives and paint, type 1 anodizing suits components that require tight tolerances, as it doesn’t notably alter dimensions; it’s commonly used for aircraft components. Type 2 anodizing is often used for decorative purposes since it readily absorbs adhesives, dyes, and paints; it’s used for architectural purposes, consumer electronics and goods, kitchenware for the military, optical components, and armed forces. The aerospace and defense industries extensively use type 3 anodized components, which are used for compressor fittings, gears, hinges, insulation plates, linear guides, pistons, valves, vehicle components, and other parts.

Having delved into the world of anodizing, we’ve uncovered how this versatile process improves corrosion resistance and adds aesthetic value and surface hardness to aluminum parts. From decorative finishes to protective layers, anodizing proves to be a powerful technique in various industries.

Join us for Part 3 of our series, where we will compare the real-world applications and industry uses of chem film and anodizing, helping you make an informed choice for your projects.