Investigation of spots on the surface of Al-castings

Castings made of Al-alloy were after mechanical machining cleaned, wrapped with plastic envelope and stored for two months. During that period, a local corrosion appeared in the form of darker spots on the surface of the castings. Results of XPS investigation of spots on Al-castings are presented. On the surface and in the corrosion products the rests of washing media were present. The main reason for the spots was condensed-water corrosion inside the plastic envelope. The rests of detergent together with the presence of condensed humidity enabled corrosion process to occur during the storing period.