Aluminum Window and Door Finishes: Powder Coating, PVDF, Anodizing and Electrophoresis

Every aluminum window and door leaves the factory with a finish, and that finish decides more than the color. It decides how the frame stands up to sun, salt spray and rain, and how much maintenance the owner signs up for later. There are four finishes to choose from, and each one has its own clause in China’s national standard for aluminum building profiles, so this choice can be made on numbers rather than adjectives.

The profile underneath

All four finishes sit on the same base alloy: 6063-T5 and 6063-T6, extruded to GB/T 5237.1—2017 at high-precision tolerance. As a reference, T5 temper carries a tensile strength of at least 160 N/mm² and T6 at least 205 N/mm². Where the project uses thermal break profiles — under GB/T 5237.6—2017 both the longitudinal and transverse shear characteristic values are at least 24 N/mm at room temperature — the same four finishes apply, so choosing a thermally broken frame does not narrow the finish options. See also how to choose thermal break aluminum casement windows.

Powder coating — GB/T 5237.4—2017

Powder coating is the default for most projects because it opens the widest color range: any RAL color, on flat, sand-texture, wood grain or metallic surfaces. The requirements are a minimum local coating thickness of 40 μm on decorative faces, indentation hardness of at least 80, adhesion grade 0 dry, wet and after boiling water, no cracking or detachment after impact testing, salt spray resistance with filiform corrosion penetrating no more than 4 mm to either side of a scribe, and no film loss or visible change after mortar testing.

PVDF, or fluorocarbon coating — GB/T 5237.5—2017

PVDF is a multi-coat system of two, three or four coats, with average film thickness rising accordingly: at least 30 μm for two coats, 40 μm for three and 65 μm for four. Everything else is specified as tightly as with powder, and in places tighter: hardness of at least 1H, adhesion grade 0 dry, wet and after boiling water, and a salt spray limit of no more than 2 mm single-side penetration from the scribe — half the allowance powder coating gets. Surfaces come flat, sand-texture or metallic, again across the RAL range. Projects that need the thickest film and the tightest corrosion limit in the standard move up to three or four coats.

Anodizing — GB/T 5237.2—2017

Anodizing differs in kind: it does not add a coating onto the aluminum, it converts the surface of the aluminum itself into an oxide. That is why anodized frames carry a metallic look no paint quite reproduces. The oxide film comes in four classes — AA10, AA15, AA20 and AA25 — from thinnest to heaviest. Sealing quality after nitric acid pre-immersion is held to a weight loss of no more than 30 mg/dm². Surfaces are sand or bright finish, and the color range is the four the oxide itself can produce: silver white, bronze, champagne and black. 6061-T6 is offered for anodized profiles as well. The trade-off is that the palette is fixed: if the project needs a specific corporate color, anodizing will not reach it and the answer is powder or PVDF.

Electrophoresis — GB/T 5237.3—2017

Electrophoresis sits between the two: an anodic oxide is formed first, then a paint film goes over it, giving what the standard calls a composite film. It comes in three grades. Grade A requires local oxide ≥9 μm, paint ≥12 μm and composite ≥21 μm. Grade B requires ≥9, ≥7 and ≥16 μm. Grade S requires ≥6, ≥15 and ≥21 μm. Beyond that, composite film alkali resistance is at least 9.5 grade, abrasion resistance is at least 3300 g for grade A, 3000 g for B and 2400 g for S, paint adhesion reaches grade 0 dry and wet, and film hardness is at least 3H for grades A and B against 1H for grade S. Colors follow the same four as anodizing.

How to choose

A specific RAL color or a wood grain look? Powder coating is the only one of the four that lists wood grain among its surface categories — see our guide to wood grain and custom RAL colors. A metallic look rather than a painted one? Anodizing, and pick the AA class for the exposure. The thickest film and tightest corrosion limit available in the standard? PVDF, three or four coats. Both the protection of an oxide layer and the hardness and abrasion figures of a paint film? Electrophoresis.

If a thermally broken window is part of the same project, the finish and the thermal break are independent choices and do not constrain each other. All four finishes are available across our window, door and curtain wall systems. Tell us the project location, exposure and target color, and we will tell you which of the four fits, and quote accordingly.