Chemical imaging based on diffusive gradient in thin films (DGT) technique in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) enables the visualization and quantification of chemical processes occurring at reactive interfaces in situ. Over the last 30 years, DGT has become a versatile tool for studying chemical concentration and bioavailability in the water–soil-sediment–biota systems [1]. The recent application of DGT LA-ICP-MS in materials science opened the door for studying metal corrosion processes at unprecedented spatiotemporal resolution.

In this study, we have developed and applied DGT LA-ICP-MS for the in situ investigation of pitting corrosion, a highly localised form of corrosion that initiates the formation of cavities in the metal, which is difficult to detect due to the small size of early pits. The 7075 aluminium (Al) alloy (AA7075), containing Zn (w = 5.6-6.1 %), Mg (w = 2.1-2.5 %), and Cu (w = 1.2-1.6 %), is used as sample material that is being widely applied in aircraft structural parts where susceptibility to pitting corrosion is critical because pits can act as starters for fatigue cracks. Advanced polyacrylamide-based DGT binding gels with a highly homogeneous distribution of Chelex (iminodiacetate) only, or both Chelex and Metsorb (TiO2) binding phases are evaluated and applied for the simultaneous and quantitative sampling of corrosion products of Al, Mg, Zn, and Cu. The novel approach is combined with microscopic images to obtain detailed information on surface structural changes during AA7075 corrosion.

The study's results show that applying DGT LA-ICP-MS using Chelex gels enables accurate in situ visualization of corrosion reactions on AA7075 exposed to NaCl solution (w = 1.5 %) at pH 4.5 and room temperature with different exposure times. The development of the method for the analysis of highly localised pitting corrosion has also revealed less localised crevice corrosion resulting from stagnant solution flow. Thus, the presented results open up the prospect of applying the DGT method for the monitoring different corrosion processes.