Magnetron-sputtered Al–Mg coatings – structural, microgravimetric and voltammetric characterisation in water, chloride and Cu(II) environment

Abstract

Al–Mg films were formed on glass and quartz substrates by magnetron sputtering technique using Al–5Mg casting alloy as a sputtering target. The content of elements in the films was similar to that of the sputtering target. The X-ray diffraction indicated a crystalline structure of the sputtered deposits with pronounced 〈1 1 1〉 texture of Al. Initial corrosion stages of the coatings were studied in water, 3.5% NaCl and 3.5% NaCl + 50 ppm Cu(II) solution by electrochemical quartz crystal microbalance (EQCM). Microgravimetric measurements in water and NaCl solution indicated a perfect anticorrosive stability of the coatings. Copper inhibited corrosion during the first corrosion stages (t<1 min) whereas with the increase in immersion time the inhibition effect was reversed to strong corrosion acceleration. Atomic force microscopy (AFM) showed that copper deposits were similar in shape and size on both sputtered and cast alloys. Measurements of breakdown potentials indicated superiority of sputtered coatings with respect to the cast alloy in both NaCl and NaCl + Cu(II) solutions.