Many aluminum alloy products look great when new but begin to suffer from paint peeling or blistering after a year or two of use; this is usually caused by cutting corners during pre-treatment or failing to meet required baking temperatures. You can evaluate quality using the following methods:

1. Inspect the appearance (most intuitive)

Good: The surface is flat and smooth (or has a uniform sand-grain texture) with no sagging (paint runs), particulate impurities, or pinholes; there is no color inconsistency, and coverage is uniform even at edges and recessed areas.

Bad: Visible dust particles on the surface, severe "orange peel" texture, or exposed base material at the edges (indicating the coating is too thin).

2. Test adhesion (most critical)

Professional test (Cross-hatch test): Use a specialized cross-hatch cutter to score a 1mm x 1mm grid pattern into the paint (cutting all the way down to the aluminum substrate), then apply 3M tape firmly and rip it off quickly. A high-quality coating will not lose any grid squares; a poor-quality coating will suffer from large-scale paint detachment.

DIY method: Use a fingernail or coin to scratch hard at the edges; if the coating peels off easily in flakes, the adhesion is extremely poor (indicating inadequate cleaning or a lack of passivation during pre-treatment).

3. Test hardness and wear resistance

Press hard with an HB or 2H pencil to scratch the surface; a high-quality coating should not show obvious scratch marks.

Gently scratch with a key; a good coating will only show a metal mark (which can be wiped off), whereas a poor coating will produce powder or expose the base material.

4. Ask about the "pre-treatment" process (an insider's perspective)

There is a saying in the coating industry: "30% coating, 70% pre-treatment."

Before spraying, aluminum must undergo: degreasing (oil removal) → water rinsing → alkaline washing → water rinsing → passivation (chromate or chrome-free passivation).

If a manufacturer skips the "passivation" step to save money, or fails to rinse thoroughly, there will be no "bonding layer" between the paint and the aluminum, inevitably leading to large-scale peeling or flaking later on. When purchasing, always ask if the manufacturer has a complete pre-treatment line. 5. Check weathering resistance reports (for outdoor products)

For aluminum alloy products intended for outdoor use (such as doors, windows, and curtain walls), you must require the manufacturer to provide test reports for salt spray resistance and artificial accelerated aging (UV exposure). Standard powder coatings generally require a salt spray resistance of over 500 hours, while fluorocarbon coatings require even higher performance.