Aluminium alloys are used in aerospace field due to their good properties of strength, weight-to-strength ratio and cost. On the other hand, they manifest weak corrosion resistance. Therefore, they need a strong corrosion protection treatment which enables them to resist at the aggressive work-field environment. Usually, the protection system consists of a multi-layer system, with oxide layer on the surface, a corrosion inhibitor primer and a topcoat. The materials analysed in this work were Aluminium 2024 and 6061. The first one was both anodised and chromate converted while the second one only chromate. The aim of this study is to analyse the acid pickling process and its parameters, namely acid concentration, temperature of bath and immersion time, on the subsequent processes of chromic acid anodising and chromate conversion coating (alodine 1200S).