Corrosion behavior of Al–Zn–Mg–Cu alloy in high pressure CO2 environment

This study investigates the corrosion behavior of Al-Zn-Mg-Cu alloys treated by non-isothermal aging (NIA) in a simulated shallow oil and gas well high-pressure CO 2 environment (1-4 MPa, 60°C) and the effect of pressure on the dynamic behavior of the passivation film, using electrochemical techniques, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The results show that the corrosion current density of the H10 sample treated by NIA at 4 MPa (1.07×10 -7 A/cm 2 ) is an order of magnitude lower than that of the T6 sample (1.21×10 -6 A/cm 2 ), and its passivation film exhibits higher stability due to the uniform distribution of η' phases and the optimized grain boundary structure. The high-pressure environment promotes CO 2 dissolution to form H 2 CO 3 , which leads to environmental acidification and localized dissolution of the passivation film, causing the corrosion morphology to shift from uniform corrosion to pitting corrosion. In addition, under high pressure, the ratio of Al 2 O 3 /Al(OH) 3 decreases, and the proportion of unstable hydroxides such as Zn(OH) 2 and Mg(OH) 2 increases, weakening the protective properties of film. This also accelerates the coarsening of η phases, intensifies micro-galvanic corrosion, and accelerates the breakdown of the film, leading to alloy failure.