Chromium on Aluminum

Application Note EDXRF1606

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The measurement of chromium (Cr) conversion coating on aluminum is demonstrated.


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 coating also helps in the retention of paint for the final finished product.

NEX QC+ high-resolution EDXRF analyzerModel: NEX QC+


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

Element: Cr
Units: mg/ft²
Sample I.D. Standard value Calculated value
STD 1 6.1 6.1
STD 2 13.2 13.7
STD 3 15.0 14.4
STD 4 30.8 31.3
STD 5 33.4 33.0
STD 6 23.3 23.3
STD 7 99.5 99.5

EDXRF1606 correlation plot Cr on aluminum - revisedCorrelation plot Cr on aluminum

Recovery and repeatability

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

Element: Cr
Units: mg/ft²
Sample I.D. Standard value Average value Std. dev % Relative
STD 1 6.1 6.06 0.03 0.5%
STD 7 99.5 99.0 0.2 0.2%


The performance shown here demonstrates NEX QC+ provides excellent sensitivity and performance for the measurement of chromium conversion coatings on aluminum.

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