Potential–controlled deposition of MgF2 film on AZ31 Mg alloy for enhanced corrosion resistance and biocompatibility

A high–quality magnesium fluoride (MgF 2 ) film was fabricated on AZ31 magnesium alloy via a novel potentiostatic deposition technique in a mildly alkaline NH 4 F solution to enhance its corrosion resistance and biocompatibility. This study systematically established the applied potential as the critical parameter governing the film's formation mechanism, microstructure and functional properties. The optimized film, deposited at a specific negative potential, exhibited superior performance characterized by a dense, crystalline morphology, the highest fluorine content and the greatest thickness. Electrochemical tests in simulated body fluid revealed a polarization resistance nearly two times higher and a corrosion current density two orders of magnitude lower than that of the bare alloy, alongside a significantly reduced hydrogen evolution rate. Furthermore, this optimized film enhanced surface hydrophilicity and markedly improved the viability and proliferation of L929 fibroblast cells. This work establishes potentiostatic deposition in NH 4 F solution as a highly promising one–step surface engineering strategy, offering superior control over the formation of protective and biocompatible MgF 2 films compared to traditional conversion coatings. • A novel one-step potentiostatic deposition method for MgF 2 films in a safe NH 4 F solution is presented. • The applied potential is a key governing parameter for film thickness, F/O ratio and crystal size. • The film deposited at –1.3 V SCE is the thickest and most fluorine–rich. • The optimal MgF 2 coating reduces the corrosion current by two orders of magnitude. • The film exhibits excellent hydrophilicity and no cytotoxicity (Grade 0).