Can a very thin conversion film be accepted by color?
Different metals respond differently in the same bath. Steel appearance cannot represent aluminum, and film color is not a quantitative deposit measurement.
Provide a separate blank for each substrate
Retain steel, aluminum and blank coupons from the same production period. Measure zirconium by the agreed method. Test adhesion and target durability with the same topcoat, recording each substrate separately.
Why does steel pass while aluminium fails in the same bath?
Check pretreatment, rinsing and bath conditions separately for each metal. Steel or galvanized sheet pretreatment: At equivalent degreasing and rinsing conditions, compare adhesion and corrosion after painting. Aluminum pretreatment: Identify the alloy and prior processing. Run a line trial with representative parts.
Checking Bath control parameters and Zirconium per unit area
Bath control parameters (Grade-specific units): Request composition, pH and the monitoring method. Zirconium per unit area (mg/m²): Specify the measuring instrument, calibration and untreated substrate blank. Coating corrosion resistance (Time and rating): Keep paint film thickness and exposure conditions constant.
What to record
- Substrate
- Rinsing conditions
- Zirconium content and method
- Topcoat
- Adhesion result
Technical references
Products and processes
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