The ability of Mg2Ge crystals to behave as ‘smart release’ inhibitors of the aqueous corrosion of Zn-Al-Mg alloys

Abstract

In-situ scanning vibrating electrode technique and time-lapse microscopy are used to investigate the influence of germanium additions (0.19–1.8 wt.%) on the corrosion performance of zinc-aluminium-magnesium model alloys immersed in 0.17 mol.dm−3 NaCl. The addition of Ge results in the formation of Mg2Ge and a decrease in the fractional area of eutectic phase. A 58 % decrease in SVET derived mass loss is achieved at 1.8 wt.% Ge. It is proposed that Mg2Ge crystals are anodically attacked and behave as reservoirs of Mg2+ ions. Mg(OH)2 is precipitated and local electrolyte pH stabilises to values at which the zinc surface is passive.