X-ray photoelectron spectroscopy (XPS), combined with scanning electron microscopy (SEM), weight loss tests and atomic absorption spectroscopy (AAS), has been applied to investigate the corrosion protection properties of zinc phosphate when coated on 7075-T6 aluminium alloy. XPS is consistent with the coating process leading to both physically adsorbed and chemically absorbed zinc. The former is washed away by ultrasonic washing, but the chemically absorbed component, identified as ZnO(x), is incorporated into the aluminium oxide layer. This layer helps suppress the dissolution of aluminium during the corrosion process.