Voltammetric and structural characterization of sputter deposited Al–Mg films

Al–Mg films with Mg content 0–98% were formed on glass substrates by magnetron sputtering. The voltammetric studies in 3.5% NaCl and 3.5% NaCl+50 ppm Cu(II) solutions showed that the corrosion resistance of samples increased with increase in Al content; this was evident from higher both open circuit and breakdown potentials. Sputtered films of Mg–3Al, Al–4Mg and Al had a superior resistance to corrosion when compared to their cast counterparts, which are widely used for practical applications. XRD data showed that the increase in magnesium content caused a change of the deposit structure from cubic to hexagonal. The grain size of sputtered samples was less than the size of cast counterparts (100–170 nm for sputter deposits and 225–300 nm for casts depending upon chemical composition). The copper deposits, which developed in Cu(II) solution, and the inherent domains of localized corrosion were demonstrated by AFM. The superior corrosion resistance of magnetron sputtered Al–Mg films was attributed to a higher passivation capacity of the (hydro)oxide layer developed on the sputtered deposits with reduced grain size and more uniform microstructure.