Real-time zinc-nickel coating measurements Thickness and composition analysis using the Niton XL5 Plus Handheld XRF Analyzer

Significance of the Topic

The control of zinc-nickel (Zn-Ni) electroplated coatings is critically important in industries such as automotive, aerospace and electronics where corrosion resistance and regulatory compliance (REACH, RoHS) are required. Zn-Ni alloys typically contain 85–93% Zn and 7–15% Ni and are widely used as a cadmium replacement. Non-destructive, near-line methods for simultaneous thickness and composition assessment increase productivity, reduce scrap of high-value parts, and speed process control.

Objectives and Study Overview

This application note demonstrates the use of the Thermo Scientific Niton XL5 Plus handheld X-ray fluorescence (HHXRF) analyzer for real-time, non-destructive determination of Zn-Ni coating thickness and Ni concentration. The work compares empirical calibration models built in the analyzer’s User Mode against laboratory reference values to validate accuracy for quality control applications on plated steel parts.

Methodology and Instrumentation

The analytical approach combines HHXRF signal intensities and empirical calibration to deliver both coating thickness and composition simultaneously. Key methodological points:

• Instrument: Thermo Scientific Niton XL5 Plus handheld XRF analyzer (HHXRF).
• Calibration dataset: 24 reference samples of low-alloy steel plated with Zn-Ni, previously characterized in the laboratory for coating thickness and Ni content.
• Data collected: XRF peak intensities for Zn, Ni and Fe plus background regions across the calibration set.
• Calibration model: Mathematical regressions linking measured intensities to reference coating thickness (µm) and Ni concentration (wt%). Models were entered into the analyzer’s User Mode for routine measurement.
• Measurement conditions: Typical analysis time reported in validation was 30 seconds per measurement.

Instrumentation Used

Instrumentation and algorithmic features relevant to the study:

• Niton XL5 Plus handheld XRF analyzer — allows near-line, non-destructive testing without cutting parts.
• Standardless fundamental parameters (FP) capability present in the instrument for multi-layer thickness estimation, but empirical calibration was preferred here to obtain simultaneous composition and thickness.
• User Mode software for creation and deployment of empirical calibration curves on the analyzer itself.

Key Results and Discussion

Calibration performance:

• Calibration regressions for both Zn-Ni coating thickness and Ni concentration show near-ideal linearity: regression slopes ~0.999 and R² values of 0.9986–0.9991, indicating very strong correlation between measured and reference values.

Validation performance:

• Independent validation samples (not used in calibration) demonstrated excellent agreement with laboratory reference values. Example results (selected):
• Sample A: reference thickness 4.91 µm vs measured 4.88 µm; reference Ni 13.27 wt% vs measured 13.41 wt%.
• Sample G: reference thickness 11.80 µm vs measured 11.86 µm; reference Ni 15.9 wt% vs measured 16.66 wt%.
• Across a range of thicknesses (≈2–12 µm) and Ni concentrations (≈6–16 wt%), the instrument delivered accurate results suitable for process control.

Interpretation:

• Empirical calibration on a representative set of plated samples enables the handheld XRF to quantify both layer thickness and composition with laboratory-comparable accuracy for routine QC.
• The results confirm that, while FP algorithms can estimate layer thickness standardlessly, empirical calibrations are advantageous when simultaneous, quantitative composition information is required.

Benefits and Practical Applications

The validated method provides clear advantages for metal finishing and QA/QC workflows:

• Real-time, near-line measurements accelerate process adjustments and reduce rework.
• Non-destructive testing preserves valuable or assembled components, avoiding sectioning or destructive sampling.
• Ease of deployment and low operational burden lower total cost of ownership compared with frequent lab-based analyses.
• Suitable for industries requiring traceable, fast assessment of Zn-Ni coatings on fasteners, connectors and structural parts exposed to corrosive environments.

Future Trends and Applications

Potential developments that will enhance handheld XRF applications for coating control:

• Expanded calibration libraries for a wider variety of substrates, multi-layer systems and alloy chemistries to broaden applicability.
• Integration with production-line automation and MES systems for continuous in-line quality assurance.
• Improved algorithms, including hybrid FP-plus-empirical and machine learning models, to reduce calibration burden and improve robustness across variable substrates.
• Enhanced uncertainty estimation and on-device QA checks to support auditability and compliance with standards.
• Miniaturization and connectivity improvements enabling cloud-based calibration updates and remote support.

Conclusion

The Niton XL5 Plus handheld XRF analyzer, when calibrated using representative Zn-Ni plated reference samples in User Mode, reliably quantifies coating thickness and Ni concentration in real time. The approach combines the practicality of non-destructive HHXRF with empirical calibration to deliver lab-comparable accuracy for near-line quality control. This capability helps manufacturers meet corrosion-protection specifications, reduce scrap, and speed production decisions.

Reference

1. M. Bauer. Measuring Metal Coating Thickness at Line Using the Thermo Scientific Niton XL5 Plus XRF Analyzer. Thermo Fisher Scientific, 2021.