Effect of native air-formed oxidation on the corrosion behavior of AA 7075 aluminum alloys

• Microstructure of AA 7075 alloy plays a key role in its local corrosion.
• Mg2Si structure change significantly over time under air exposure conditions.
• Local oxidation process of Mg2Si phase was studied by AFM and SEM/EDX.
• Air-formed oxidation improve corrosion resistance of aluminum alloy over time.
• This is due to modification of passive layer structure as proven with XPS.

The effect of native air-formed oxidation on the corrosion behavior of AA 7075 aluminum alloy and selective corrosion of anodic Mg2Si precipitates was presented. Oxidation of Mg2Si leads to formation of Mg(OH)2 protrusions depleting magnesium in this precipitate as shown by AFM, SEM and EDX results. Spectroscopic studies prove that composition changes occurring within the passive layer may be a cause of observed improvement of electrochemical properties under prolonged exposition to air. Influence of cathodic phases containing AlFe(Cu,Mn,Cr) is limited in these conditions.