A study on corrosion characteristics of AA2024 under different conditions

In this work the corrosion characteristics of bare aluminum based alloy (AA2024) and zinc coated AA2024 are studied in the aqueous solution having three different pH (2, 7 and 12). Apart from the traditional methods of aluminum coating (chromate conversion coating and zincating), this thesis suggests an alternative way to coat aluminum with a metal. A novel ionic liquid consisting of only cations and anions electrolyte is used for this purpose. AA2024 alloy in a deep eutectic solvent (DES) having zinc ions cannot be coated by zinc by applying anodic potential directly due to the typical characteristic of aluminium alloy which has Al2O3 thin layer occurring naturally on the aluminium surface. To electrodeposit zinc on aluminium alloy, an extreme anodic voltage (+1.65) is firstly applied for removing Al2O3 layer in Ethaline and then the cathodic potential (-1.5 V) is immediately applied in order to deposit zinc in-situ on newly prepared aluminium alloy surface which does not have Al2O3 anymore. Galvanised AA2024 displays the characteristic of an amorphous structure observed by SEM and XRD. Bare AA2024 has pitting corrosion at high potential in three aqueous medium use in this work (10 mM HCl, 0.5 M NaCl, 10 mM KOH). Zinc coated AA2024 has passivation behaviour in alkaline and acidic media. Corrosion resistance of zinc coated AA2024 alloy is almost as high as that of bare AA2024 in three different media. The work reported in this thesis presents that zinc coated AA2024 has more than six times higher corrosion resistance than bare Al2024 in alkaline medium (pH = 12).