Aluminum anodizing thickness affects corrosion resistance, wear performance, color, electrical behavior and final dimensions. Buyers should specify the anodizing type, required thickness or range, sealing, visible surfaces, masking areas and inspection method instead of writing only “anodized aluminum.”
How Thick Is Aluminum Anodizing?
The values below are common procurement ranges for discussion, not automatic acceptance limits. The final requirement must follow the drawing, applicable standard and approved process.
| Anodizing category | Common discussion range | Typical purchasing focus |
|---|---|---|
| Decorative / conventional sulfuric anodizing | Often about 5–25 µm | Appearance, corrosion protection, sealing and color consistency |
| Hard anodizing | Often about 25–75 µm; other values may be specified | Wear, hardness, electrical insulation and dimensional allowance |
Terms such as Type II and Type III are commonly associated with MIL-PRF-8625 classifications. They should not be treated as a complete thickness instruction by themselves: class, color, sealing, thickness, masking and test requirements still need to be defined.
Does Anodizing Make Aluminum Thicker?
Yes. The anodic oxide is formed by converting the aluminum surface. Part of the layer develops above the original surface and part develops inward. A frequently used estimating rule for conventional anodizing is that roughly half of the total coating thickness contributes to outward growth, but the actual ratio varies with alloy and process.
This is a planning example, not a universal conversion. Close-tolerance drawings should state whether dimensions apply before or after anodizing and should use the processor’s qualified growth data.
Type II vs Type III Anodizing
| Item | Type II | Type III |
|---|---|---|
| Primary intent | General protective and decorative anodizing | Hard, wear-resistant anodic coating |
| Thickness | Usually thinner | Usually thicker and more dimensionally significant |
| Color | Clear or dyed options are common | Natural color may be darker and alloy-dependent; dye options require confirmation |
| Design concern | Appearance, sealing, outdoor exposure and fit | Wear surfaces, threads, bores, sharp edges and coating buildup |
How Is Anodizing Thickness Measured?
Non-destructive eddy-current instruments are widely used on non-conductive anodic coatings over conductive aluminum. The gauge, calibration standard, probe geometry and measurement location must suit the component. Methods such as ASTM B244 and ISO 2360 are commonly referenced for this principle.
- Calibrate on a suitable uncoated substrate and certified reference foils or standards.
- Measure flat, representative areas away from edges, holes and strong curvature unless those areas are specifically required.
- Take multiple readings and report the agreed statistic, not only the highest value.
- Identify the part, lot, locations, instrument and calibration status in the inspection record.
For disputed or high-precision work, cross-sectional microscopy or another agreed reference method may be used. Instrument readings should not be confused with color, sealing quality or corrosion performance; those may require separate tests.
Alloy, Geometry and Color Affect the Result
Two parts processed in the same bath can differ in appearance because alloy chemistry, extrusion or rolling condition, heat treatment, surface preparation and geometry affect oxide formation. For visible assemblies, use material from controlled lots and approve a physical color/finish sample.
- 6063 profiles: often selected for architectural and visible extrusions because of their anodizing response.
- 6061 components: commonly anodized for industrial parts, but final color and finish depend on material and process.
- High-copper or high-silicon alloys: may respond differently in color and coating appearance; confirm feasibility before ordering.
- Threads and close bores: may need dimensional compensation or masking.
What Buyers Should Put on the Drawing
| Requirement | What to define |
|---|---|
| Base material | Alloy, temper and product form |
| Anodizing | Standard/type, class, thickness or range and sealing |
| Appearance | Color, gloss, visible faces and approved sample |
| Dimensions | Whether limits apply before or after coating; critical fits and threads |
| Masking | Contact points, threads, bores, bonding faces and rack-mark zones |
| Inspection | Measurement method, locations, number of readings and report format |
Frequently Asked Questions
How much thickness does anodizing add in millimetres?
Convert micrometres to millimetres by dividing by 1,000. A 20 µm total coating equals 0.020 mm. Only the outward-growth portion increases the external dimension, so do not add the full coating thickness to each surface without qualified process data.
How thick is a Type II Class 2 coating?
“Class 2” generally identifies dyed anodizing, not one universal thickness. The purchase specification must state the required thickness or range together with color, sealing and acceptance criteria.
Is Type III always better than Type II?
No. Type III is selected when hard, wear-resistant coating is required, but it adds more dimensional and appearance constraints. Type II is often more suitable for decorative or general protective applications.
Can anodizing thickness be checked with a handheld gauge?
Yes, an eddy-current coating-thickness gauge is commonly used when it is properly calibrated and the part geometry permits reliable readings. Critical acceptance should follow the agreed test method and sampling plan.
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Post time: Sep-29-2026