Surface modification of anodized Mg in ammonium hydrogen fluoride by various voltages

In recent years, extensive research has been carried out on the potential of using magnesium for biodegradable implants. However, the fast rate of corrosion of magnesium remains one of the major limitations of using Mg and Mg alloys as implants. The present work aimed to deposit a corrosion-resistant coating onto pure Mg (≥ 99.93%) in a saturated ammonium hydrogen fluoride solution at 120-200 V by micro arc fluorination (MAF) to improve resistance to corrosion. The treated samples were then characterized by SEM, EDS and XRD to assess morphological, chemical and structural characteristics. Electrochemical corrosion and immersion tests were used to evaluate the level of corrosion resistance. To test the coatings in vitro, MC3T3-E1 cells were cultured on the surface and cell viability was analyzed. A layer of dense ceramic coating with micro pores was observed on the surface. The thickness of the coatings ranged from approximately 2.5 to 5.5 μm. XRD and EDS analyses indicated that the coatings formed on the magnesium surface were composed of MgF2. Electrochemical and immersion tests performed in the SBF proved that the anodic fluorination coatings significantly improved the corrosion resistance of pure Mg. In the in vitro assay, both the proliferation and adherence rates of cells grown on the MgF2 coatings improved compared with the untreated group.