Magnetic Induction or Eddy Current Testing: Non-destructive methods that directly measure coating thickness in microns. Cross-Sectional Microscopy: Cutting and examining the coated sample under a microscope for precise measurement.
Calculating the thickness of a zinc layer (such as in galvanized coatings) involves knowing the mass of the zinc per unit area and the density of zinc. Here’s the step-by-step method:
Thickness (μm)=Mass per unit area (g/m²)Density of zinc (g/cm³)×10Thickness (μm)=Density of zinc (g/cm³)Mass per unit area (g/m²)×10
Where:
Density of zinc = 7.14 g/cm³ (standard value for pure zinc)
The ×10 factor converts cm to μm (since 1 cm = 10,000 μm and we divide by area in m²).
Measure the mass of the zinc coating per unit area (g/m²):
This can be obtained via weighing before and after galvanizing or using a magnetic thickness gauge that provides coating weight.
Example: If a steel sheet gains 300 g/m² of zinc after galvanizing, the coating mass is 300 g/m².
Apply the formula:
Thickness=300 g/m²7.14 g/cm³×10≈420 μmThickness=7.14g/cm³300g/m²×10≈420μmMagnetic Induction or Eddy Current Testing: Non-destructive methods that directly measure coating thickness in microns.
Cross-Sectional Microscopy: Cutting and examining the coated sample under a microscope for precise measurement.
If a galvanized sheet has a zinc coating weight of 150 g/m², the thickness is:
Thickness=1507.14×10≈210 μmThickness=7.14150×10≈210μm
Hot-dip galvanizing typically ranges from 50–150 μm (varies by standard, e.g., ISO 1461).
Electrogalvanized coatings are thinner (~5–25 μm).
For alloy coatings (e.g., Zn-Fe, Zn-Ni), adjust density accordingly.