Elementor #31952

In CNC machining, anodizing is one of the most reliable surface finishing processes. It improves corrosion resistance, surface hardness, wear resistance, and overall part durability. That is why it is widely used in aerospace, medical devices, automotive, and consumer electronics.

This guide answers a common engineering question: which metals can actually be anodized, and is aluminum the only option? The answer depends on the electrochemical behavior of the material, not just the metal type itself. Let’s break it down.

1. How Anodizing Works?

Anodizing is an electrochemical oxidation process. The metal part is placed in an electrolyte solution (typically sulfuric acid, though oxalic or chromic acid may be used for specific applications) and acts as the anode in an electrical circuit. When current is applied, oxygen ions react with the metal surface to form a controlled oxide layer. The resulting oxide is porous immediately after formation, which allows for subsequent dyeing or sealing if needed.

Unlike painting or electroplating, anodizing does not add a separate material on top. The oxide layer grows directly from the base metal, creating a strong metallurgical bond. This makes the finish much more durable and wear‑resistant than ordinary coatings.

2. Which Metals Are Valve Metals?

Only certain metals can form stable, functional anodized layers. These are called valve metals. They have a self‑limiting oxide growth behavior: once the oxide layer forms, it controls further current flow and allows stable layer formation. In industrial practice, the most commonly anodized valve metals are those that balance process stability with practical utility.

Common valve metals include:

• Aluminum
• Titanium
• Magnesium
• Zirconium
• Niobium
• Tantalum
• Zinc (limited industrial use)

Among these, only aluminum and titanium are regularly seen in high‑volume CNC manufacturing. The others appear in niche applications or specialized industries, and their anodizing processes are often more complex or costly.

3. Aluminum: The Industry Standard for Anodizing

Aluminum is the most widely used metal for anodizing in CNC manufacturing. It naturally forms a stable, dense, and hard oxide layer (aluminum oxide). The process is stable, cost‑effective, and compatible with large‑scale production.

Industrial applications of aluminum anodizing include electronic housings, automotive components, aerospace structures, and architectural profiles.

Alloy composition matters

Not all aluminum alloys anodize equally well. Based on our shop experience:

In our daily work, we frequently use Type III hard anodizing on 6061 aluminum to produce CNC parts for clients across medical, automotive, and consumer electronics industries. For a better surface appearance, we often apply sandblasting before anodizing to create a uniform matte finish.

Aluminum anodizing is what we do best. If you need custom CNC machining with anodizing, we can help.

4. Titanium Anodizing: Colors and Performance

Titanium can also be anodized, forming a stable titanium dioxide (TiO₂) layer. This provides strong corrosion resistance and excellent biocompatibility, making titanium suitable for medical implants and aerospace components.

One unique feature of titanium anodizing is color without dyes. By adjusting the voltage during anodizing, you can produce different colors through optical interference. No pigments or dyes are used. These structural colors are highly durable and resistant to fading.

Titanium anodizing is more expensive and more sensitive to surface conditions than aluminum. At Beska, we offer it for medical and aerospace prototypes. Contact our engineers to discuss your requirements.

5. Magnesium in Lightweight Engineering

Magnesium is the lightest structural metal used in engineering. However, its natural corrosion resistance is poor. Therefore, magnesium alloys often require surface protection through anodizing or plasma electrolytic oxidation (PEO). In advanced PEO processes, a ceramic‑like oxide layer is formed on the surface, significantly improving hardness (up to 1000 HV) and corrosion resistance (salt spray resistance can exceed 1000 hours).

Typical applications of magnesium anodizing or PEO include:

• Lightweight automotive parts such as transmission cases and steering wheel frames
• Portable electronics housings (notebooks, cameras) where weight reduction is critical
• Aerospace structures including gearbox housings and seat components

Magnesium anodizing is rarely requested in standard CNC projects. If you are considering magnesium parts, we recommend discussing your specific application with our engineers to select the right surface treatment.

6. Metals That Cannot Be Effectively Anodized

Some metals are not suitable for anodizing due to their electrochemical properties. The most common ones include:

Iron, steel, and stainless steel

These metals do not form stable, protective oxide layers through anodizing. The oxide that does form is porous and lacks adhesion, so corrosion continues underneath. In fact, anodizing iron or steel would simply accelerate rusting. For these materials, recommended surface treatments include electroplating (such as zinc or nickel plating), powder coating, or physical vapor deposition (PVD).

Copper and copper alloys

Copper can form an oxide layer, but it is not stable enough for structural protection. The oxide tends to be soft and easily damaged, and it does not stop further oxidation. Copper anodizing is occasionally used for decorative coloring or for limited electrical insulation on small components, but it is not common in industrial CNC machining.

Noble metals (gold, silver, platinum)

These metals are chemically stable and do not form functional oxide layers under normal anodizing conditions. They are already highly resistant to corrosion, so anodizing offers no benefit and is not performed.

Anodizing works well only on specific metals (primarily valve metals), and for everything else a different surface finishing method is required.

7. Industry-Specific Recommendations for Anodizing

The choice of material and anodizing type often depends on the target industry. Below are practical recommendations based on common requirements in four key sectors.

Medical Devices

Titanium and 6061 aluminum are preferred. Type II anodizing provides color coding and corrosion resistance; Type III hard anodizing is used for wear‑resistant surgical tools. Key requirements include ISO 13485, biocompatibility per ISO 10993, and documented process controls. Typical applications include orthopedic implants, surgical instrument handles, dental tools, and device housings.

Aerospace

7075, 2024, and 6061 aluminum plus titanium are commonly used. Type III hard anodizing (25–50 µm) is preferred for wear and corrosion resistance; Type I chromic acid anodizing is used for some legacy specifications. This sector requires strict thickness control, salt spray testing (ASTM B117, 500+ hours), and full lot traceability. Typical parts include landing gear components, hydraulic manifolds, brackets, and fuselage fittings.

Automotive

6061 and 6063 aluminum are most common, along with 5000 series for trim. Type II anodizing is used for decorative trim (bright colors, matte or gloss finishes); Type III hard anodizing is applied to suspension and wear surfaces. Requirements include high salt spray resistance, UV stability, and consistent color across production volumes. Typical uses include interior trim, shift knobs, EV heat sinks, brake caliper pistons, and under‑hood brackets.

Consumer Electronics

6063 aluminum offers the best surface finish, with 6061 as an alternative. Type II anodizing provides unlimited color options, matte or glossy finishes, and a premium tactile feel. Key requirements are uniform color across large batches, scratch resistance, and consistent gloss level. Typical applications include smartphone cases, laptop enclosures, headphone components, and power bank shells.

Matching the anodizing process to industry‑specific priorities (biocompatibility, wear resistance, color consistency, or surface aesthetics) ensures optimal part performance and cost efficiency.

8. How Beska Handle Anodizing for Custom CNC Parts

We machine and anodize aluminum and other metals to meet customer requirements. Our in‑house anodizing line is set up for both decorative and hard anodizing.

• Types offered: Type II (sulfuric acid, decorative and protective) and Type III (hard anodizing, wear resistant)
• Maximum part size: 800 mm × 500 mm × 300 mm
• Typical oxide thickness: 5–25 µm for Type II, 25–75 µm for Type III
• Quality control: coating thickness gauge, color spectrophotometer, salt spray test chamber

The goal is always the same: deliver CNC parts that resist corrosion, hold up under wear, and match your specifications without unnecessary delays or extra handling. For example, we always plug holes and threads before anodizing. If we skip this step, the oxide buildup would shrink the openings and cause assembly problems.

Conclusion & Get Your Quote

Anodizing is not a universal finish for every metal. It works best on valve metals, with aluminum being the most practical and cost‑effective choice for the vast majority of CNC machined parts. Titanium and magnesium are suitable for specialized high performance applications, while steel and copper require alternative surface treatments.

At Beska, we combine precision CNC machining with in house anodizing (Type II and III) for aluminum, titanium, and other select metals, so you get a single partner for both machining and finishing with faster lead times and better quality control. When you are ready to start your project, simply upload your CAD file for a free DFM and quote within 24 hours, or reach out to our engineers directly.

FAQ