Surface functionalisation of additively manufactured AlSi10Mg by organophosphonic acid and PDMS grafting

Additive manufacturing (AM) of aluminum alloys enables lightweight and customized components but typically results in rough, chemically inhomogeneous surfaces that promote corrosion and hinder the application of protective thin films. In this study, a combined surface modification strategy consisting of UV-induced grafting of polydimethylsiloxane (PDMS) and subsequent adsorption of octadecyl phosphonic acid (ODPA) molecules was applied directly to as-manufactured AlSi10Mg surfaces. Thin film formation for the individual and combined modifications was confirmed by polarization modulation infrared reflection–absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). Both techniques revealed a pronounced reduction in the PDMS-related signals after ODPA adsorption, indicating a preferential substitution of PDMS by ODPA at Al-rich surface sites, while Si–O–Si linkages remained stable. Water contact angle (WCA) measurements demonstrated a strong decrease in surface energy, with modified surfaces exhibiting stable hydrophobicity (≈130°) after immersion in NaCl solution for up to 9 h. Electrochemical impedance spectroscopy (EIS) using a droplet-cell setup showed that the combined PDMS + ODPA modification increased the impedance at 0.1 Hz by up to sixfold compared to the unmodified reference during short immersion intervals. However, prolonged exposure led to electrolyte permeation and a subsequent decrease in electrochemical impedance values. The presented surface modification therefore represents a promising approach to suppress initial and atmospheric corrosion processes. • Grafted molecular ODPA and macromolecular PDMS films lead to durable low energy surfaces • Post-adsorption of ODPA on PDMS-grafted surfaces leads to an increase of corrosion resistance • PM-IRRAS and XPS reveal a partial displacement of PDMS by ODPA at Al-rich oxide surface sites • ODPA/PDMS layers are shown to be suitable for a temporary corrosion protection of AM manufactured AlSi10Mg