Zirconium on Aluminum

Application Note EDXRF1630

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Scope

The measurement of zirconium (Zr) conversion coating on aluminum is demonstrated.

Background

Aluminum and steel are often coated with a protective conversion coating, also called passivate or passivation coating, to prevent oxidation and corrosion of the base metal. Conversion coatings include chromium (Cr), titanium (Ti), vanadium (V), manganese (Mn), nickel (Ni), or zirconium (Zr). A phosphate coating may be applied as well to minimize wear on cutting tools and stamping machines. Aluminum is often coated for use in aircraft parts, aluminum window frames and other similar industries where the aluminum is exposed to weathering. Steel for the automotive industry is typically first galvanized with a zinc coating before the conversion coating is applied. Protected steel is also used for outdoor sheds and other similar uses where steel is exposed to weathering. Conversion coatings also help in the retention of paint for the final finished product.

800x610 NEX QC+ (S in Crude screen)_picture_2020.06.25Model: NEX QC

Calibration

An empirical calibration was built using a set of standards assayed by careful weigh-strip-weigh. 

Element: Zr
Units: mg/ft²
Sample I.D. Standard value Calculated value
STD 1 0.98 1.150
STD 2 2.21 2.227
STD 3 3.52 3.484
STD 4 4.81 4.679
STD 5 6.71 6.618
STD 6 15.26 15.333

EDXRF1630 Correlation plot Zr on aluminumCorrelation plot Zr on aluminum

Recovery and repeatability

To demonstrate repeatability (precision), three calibration standards were chosen. Each sample was measured in a static position for ten repeat analyses with typical results shown below.

Element: Zr
Units: mg/ft²
Sample I.D. Standard value Average value Std. dev % Relative
STD 1 0.98 1.165 0.056 5.7
STD 4 4.81 4.707 0.050 1.0
STD 6 15.26 15.193 0.077 0.5

Sample surface and positioning

Aluminum may be surfaced with different patterns to give products various esthetic looks or physical properties. Such surfacing techniques may leave the aluminum smooth, may be brushed aluminum with a directional grain pattern, or may be a hatched or other pattern. The samples demonstrated here had a brushed, directional grain pattern.

Conclusion

The performance shown here demonstrates NEX QC provides excellent sensitivity and performance for the measuring zirconium conversion coatings on aluminum.

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