Abstract
In deaerated 0.1 M KF solution at pH 5, pH 7.5 and pH 9, fluoride films were deposited on AZ31 magnesium (Mg) alloy at − 1.4 V vs saturated calomel electrode (SCE). The morphology, phase composition, elemental and compositional depth distribution of different fluoride films and their influences on the corrosion resistance of AZ31 Mg alloy were explored in detail. The results indicated that the films deposited at weak acidic and nearly neutral pH consisted of two layers with amorphous Mg(OH)2 and MgF2 as the inner layer, and Mg(OH)2, MgF2 and KMgF3 crystals the outer layer. The film deposited at alkaline pH was a monolayer structure consisting of amorphous Mg(OH)2 as the major constitute and MgF2 as the minor constitute. The protectiveness of fluoride film was intimately related to its composition and structure. The content and crystal regularity of KMgF3 were the two main factors influencing the protectiveness of fluoride film. The fluoride film deposited at pH 7.5 offered the best protection to AZ31 Mg alloy.