Corrosion and Electrochemical Behavior of Scandium-Doped Aluminum–Magnesium Alloys Coated with Polymeric Organosilicon Layers

The comparative corrosion resistance of additively manufactured and cast Al–Mg–Sc alloy 1575 remains uncertain because assessment methods and exposure durations yield conflicting results. This study examined fabrication method and organosilicon surface modification effects in 0.6 M NaCl, approximating seawater chloride concentration. Selective laser-melted and cast specimens were investigated by corrosion potential measurements, anodic polarization, electrochemical impedance spectroscopy, scanning reflectometry, gravimetry, profilometry, and optical microscopy. Protective vinyl- and aminosilane-derived layers and their mixtures were evaluated. The additively manufactured alloy showed a pitting potential of −0.400 V, 84 mV more positive than the cast alloy, indicating greater resistance to pitting initiation. A vinyl–aminosiloxane layer increased pitting potentials by 171 and 162 mV, respectively. However, impedance and long-term corrosion tests indicated greater overall corrosion resistance of the cast alloy. Additively manufactured specimens developed pits, whereas cast specimens underwent selective and quasi-uniform dissolution. Organosilicon layers reduced corrosion in both materials, depending on surface condition and degradation mechanism. Neither fabrication method was consistently superior: corrosion rankings depended on exposure duration, assessment method, and corrosion mechanism.