Depassivation of aluminium by magnesium addition and mechanical working

The focus of this study involves incorporating Magnesium (Mg − 2.5 wt% and 6.5 wt %) into pure Al and subjecting the resulting alloy to Mechanical Working (20% and 30% Height reduction). To establish relationship between deformation, Microstructure and electrochemical properties, alloys were developed by liquid metallurgy route and followed by 20% and 30% height reduction. Compare to EMF value Mg is higher electronegative than aluminum and affects the chemical properties of the Al-Mg (5xxx) system by altering its microstructure from a uniform to a complex containing many secondary compounds. Addition of Mg in to Al, make it more active and accelerating the corrosion rate. According to physical metallurgy Mg composing secondary phase particles (e.g., Al 3 Mg 2 ) are structured at the end of grains or grain boundary. These area is act as local anode compare to Al matrix which act as cathode. The formation of corrosion cell lead the local dissolution. The alloy underwent mechanical working (20% and 30% height reduction) to enhance its depassivation by transforming the microstructure from coarse to fine grains. Addition of Mg and mechanical working both lead to produce smaller grains due to grain refinement phenomena. The change in microstructure will disorganize passive alumina film. In Sea water or chlorine containing surrounding alumina film became less stable and tends to localized breakdown Spectroscopy was used for the chemical analysis to confirm the presence of Mg, and XRD was conducted. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to study the microstructures of pure Al and cast alloys. Corrosion behavior evaluation included the standard weight loss method and potentiodynamic study for all the developed and mechanically worked alloys. The results imply that increased Mg content accelerates the corrosion rate by forming Al-Mg intermetallic compounds on the grain boundaries and promoting corrosion through mechanically induced sites and grain refinement. The alloy with a 6.5% Mg content exhibited the best corrosion performance when subjected to 20% mechanical working.