Hydrogen Determination in Aluminum and Aluminum Alloys

Significance of the Topic

Hydrogen solubility in molten aluminum and its reduction during solidification can lead to trapped gas pores that compromise mechanical properties and surface quality. Reliable quantification of both surface and bulk hydrogen is essential for quality control in aluminum production and downstream applications.

Study Objectives and Overview

This application note describes a procedure for determining hydrogen content in aluminum and its alloys using the LECO RHEN602 hydrogen determinator. Objectives include separation of surface and bulk hydrogen fractions, optimization of furnace parameters, and validation of precision and accuracy for typical aluminum grades.

Methodology and Instrumentation

The RHEN602 employs an electric resistance furnace with a stepped temperature program, argon carrier gas, and a thermal conductivity detector. The analysis sequence comprises five programmable steps:

• Step 1: Liberate surface hydrogen
• Step 2: Allow surface hydrogen to separate from bulk
• Step 3 (optional): Ensure complete surface hydrogen removal
• Step 4: Liberate bulk hydrogen
• Step 5: Power reduction to prevent aluminum boil‐over

Sample preparation involves machining solid samples to 10.5 × 24 mm dimensions, cleaning with acetone, and minimizing exposure to atmospheric moisture. Calibration uses certified reference materials or gas dosing. Key furnace and analysis parameters include multiple outgas cycles, programmable delays for surface and bulk acquisition, and power settings to control temperature ramps and holds.

Used Instrumentation

LECO RHEN602 hydrogen determinator with electrode furnace and thermal conductivity detector
Graphite crucibles and compatible electrode tips
NIST or equivalent reference materials for calibration

Main Results and Discussion

Typical results demonstrate low hydrogen levels and good repeatability:

• 6061 aluminum alloy: Surface ≈ 0.023 ppm H, Bulk ≈ 0.060 ppm H, Total ≈ 0.083 ppm H (s = 0.003)
• AlMg 5% alloy: Surface ≈ 0.051 ppm H, Bulk ≈ 0.163 ppm H, Total ≈ 0.214 ppm H (s ≈ 0.010)
• AlMgSi 0.5% alloy: Surface ≈ 0.029 ppm H, Bulk ≈ 0.135 ppm H, Total ≈ 0.164 ppm H (s ≈ 0.007)

Results confirm effective separation of hydrogen fractions and tight standard deviations, indicating robust precision. Surface hydrogen represents a small portion of the total content, underscoring the importance of bulk analysis.

Benefits and Practical Applications

The described approach offers:

• Rapid and accurate hydrogen quantification for process control
• Distinction between surface‐adsorbed and trapped hydrogen
• Enhanced product quality by early detection of porosity risk
• Applicability to a range of alloys and sample forms

Future Trends and Potential Applications

Advances may include integration with automated sample loading, real‐time process monitoring in casting lines, refined calibration using synthetic gas standards, and coupling with other detectors for multi‐element analysis. Further miniaturization and improved software algorithms could drive detection limits lower and expand field applications.

Conclusion

The LECO RHEN602 system provides a validated, high‐precision method for hydrogen determination in aluminum and its alloys. By separating surface and bulk hydrogen contributions, the protocol supports rigorous quality assurance in industrial production and research settings.

Reference

1. Talbot DEJ, The Effects of Hydrogen in Aluminum and Its Alloys. Maney, London, 2004.
2. Hess PD, Turnbull GK, Proceedings of International Conference on the Effects of Hydrogen on Materials Properties and Selection and Structural Design, Champion, 1973, pp. 277–287.
3. Ransley CE, Talbot DEJ, The Routine Determination of the Hydrogen Content of Aluminum and Aluminum Alloys by the Hot‐Extraction Method. Journal of the Institute of Metals, Vol. 84, 1955–1956, p. 445.