Plasma electrolytic oxidation of Zircaloy-2 at constant rms current is examined in silicate and aluminate electrolytes, revealing significantly different behaviors in the growth kinetics and properties of the coatings. Coatings thicken continuously in the silicate electrolyte, while in the aluminate electrolyte, the thickness reaches a relatively constant value. The latter coincides with changing appearances of discharges and detachment of an outer coating layer. Dissolution of zirconium is faster in the silicate electrolyte in the early stage of PEO, but is faster in the aluminate electrolyte following coating breakdown. The pre-spallation coating formed in the aluminate electrolyte shows superior wear resistance, which can be ascribed to its relative compactness, associated with the presence of tetragonal zirconia stabilized by aluminium species. (C) 2012 Elsevier Ltd. All rights reserved.