Distinguish average thickness from local thickness
A thickness class sets requirements for both average coating thickness and the minimum measured locally. These are different limits. For example, a coating described as AA20 does not mean that every point must measure exactly 20 μm, nor does it describe an unrestricted 16–20 μm range.
The common AA classes below provide a useful basis for discussing an order. State the applicable standard and edition in the specification; do not assume that similarly named classes in different standards are interchangeable.
| Thickness class | Minimum average thickness | Minimum local thickness |
|---|---|---|
| AA10 | 10 μm | 8 μm |
| AA15 | 15 μm | 12 μm |
| AA20 | 20 μm | 16 μm |
| AA25 | 25 μm | 20 μm |
Describe the actual exposure before choosing a class
For dry indoor partitions, decorative trims or automation frames, appearance and handling resistance may be the main priorities. An AA10 specification can be a starting point for discussion, but wear, cleaning chemicals and electrical requirements may call for a different process or coating specification.
Outdoor windows, railings and façade components need a review of local exposure and the applicable building specification. AA15 or a thicker class may be considered where suitable. Coastal, marine-adjacent or heavily polluted sites often require a more demanding assessment, including AA20 or AA25 where specified. These are discussion points, not automatic approvals for every location.
Tell the supplier how close the installation is to salt spray, whether rain washes the surfaces, how water drains and how the profiles will be cleaned. Sheltered areas can accumulate contaminants. A thickness class alone cannot establish a guaranteed service life.
Treat sealing as a separate quality requirement
The anodizing process creates a porous oxide layer. For finishes requiring sealing, the selected sealing process helps close those pores and contributes to stain and corrosion resistance. A thicker film does not compensate for inadequate sealing or poor preparation.
Guantian coordinates anodizing with audited Foshan finishing partners. The production requirements cover the chosen coating and sealing process, while returned profiles are checked at the Sanshui QC stage before packing. Depending on the agreed inspection plan, evidence can include thickness readings and dye-spot or acid-dissolution sealing checks. Agree the test method and acceptance criteria rather than requesting only a generic certificate.
Confirm appearance and precision fits
Alloy, temper, pretreatment and color influence the appearance of anodized aluminum. A finish approved on one alloy or a flat plaque may look different on another section. Use a representative production sample when color, gloss or visible extrusion features matter.
Anodizing changes dimensions, and pretreatment may also remove material. Review narrow slots, threaded holes, mating faces and electrical contact areas before manufacturing. The appropriate allowance depends on the actual process; a universal growth value can lead to a poor fit.
Specify the inspection locations
Mark significant surfaces and agreed measurement areas on the drawing. Eddy-current gauges are used for coating-thickness checks, with equipment and measurement procedures suitable for the substrate and section geometry. Define sampling, reporting and any difficult-to-access features before the order is released.
The specification should also identify acceptable appearance, jigging-mark locations, sealing verification and any corrosion or wear testing. Keeping these requirements with the approved sample gives purchasing and quality teams a common basis for acceptance.
Frequently asked questions
Why not specify the thickest coating for every part?
A thicker film can add process time and cost and affect appearance or precision fits. Select the coating around the actual duty and acceptance requirements rather than assuming that more thickness always improves the finished product.
Does 6063 always look better after anodizing than 6061?
6063 is commonly chosen for decorative extrusions, but appearance also depends on the material condition, pretreatment and finishing route. Compare representative samples when appearance is important.
Is 16 μm the local minimum for AA25?
No. In the common AA classes shown here, AA20 has a 16 μm minimum local thickness, while AA25 has a 20 μm minimum local thickness.
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