Influence of The KF Concentration on The Coating Process And Properties of Potentiostatic Deposited Fluoride Conversion Film on AZ31 Mg Alloy

Magnesium (Mg) and its alloy have closer density and elastic modulus (density: 1.7–2.04 g/cm-3, Young's modulus: 41–45 GPa) to those of natural bone (density: 1.8–2.1 g/cm-3, Young's modulus: 10–30 GPa) than traditional implants such as 316L stainless steels, Ti6Al4V alloys, Co-Cr based alloys, thus when implanted they can minimize the stress shielding effect that can cause delay in healing process of damaged bones and implant loosening [1-3]. Additionally, Mg can be excreted in terms of soluble MgCl2 through urine, and Mg is considered as a beneficial element in maintaining the normal function of the human metabolism and the growth of new bone tissue [2,3]. Moreover, Mg can totally degrade in the physiological system (pH 7.4-7.6), thus eliminating the need for secondary surgery [1-5]. These intriguing characteristics make Mg and its alloys have great potential in orthopaedic application. Nevertheless, most of currently developed high purity Mg and Mg alloys fail only within 1~2 months in the human body fluids [4], while damaged bones need at least 3 months to heal [4], thus negatively affecting the bone tissue regeneration. Meanwhile, the generation of subcutaneous hydrogen gas (H2) and the accumulation of bubbles in gas pockets adjacent to the implant will occur during their degradation. If the volume of accumulated H2 reaches a high level, it will cause separation of tissue and tissue layers [4-7]. Consequently, in order to decrease their degradation rate and thus accumulation of H2 to match the healing rate of damaged bones, fluoride conversion film (FCF) has been developed, attributed to the harmlessness of the fluorine ions releasing into the organism [8], its good biotissue compatibility [9-12], excellent cell adhesion [13-14], and its characteristics to accelerate the osseointegration rate [15], enhance bone healing [16] and prevent the biofilm formation [17-19]. The original method to fabricate FCF on Mg substrate was immersion of Mg substrate in 40% or 48% hydrofluoric acid, HF [19-25], however, the high toxicity Influence of The KF Concentration on The Coating Process And Properties of Potentiostatic Deposited Fluoride Conversion Film on AZ31 Mg Alloy Liping Wu, Lin Zhao, Junhua Dong*, Wei Ke, Xiaofang Li Environmental Corrosion center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110016, China