Impact of Surface Preparation on the Quantification of Diffusible Hydrogen Content in Aluminum Alloys

The impact of final surface preparation immediately prior to hydrogen content measurements in aluminum alloy samples was investigated using thermal desorption analysis (TDA). Samples ground in water showed an apparent hydrogen signal. Glow-discharge optical emission spectroscopy (GDOES) confirmed that the analyzed hydrogen originated from the subsurface layer. X-ray photoelectron spectroscopy (XPS) revealed the presence of a thin aluminum oxide/hydroxide layer on the surface. Formation of these compounds indicates that hydrogen was introduced into the material by the reaction of oxide-free aluminum with water molecules during the grinding, followed by its entrapment at near-surface interstitial lattice sites. Chemical pickling in concentrated nitric acid and combined grinding, chemical pickling, and electrochemical polishing approaches are proposed as proper surface-preparation techniques for samples without and with adherent corrosion products, respectively.