Corrosion Behavior Of Magnesium Fluoride Chemical Conversion Coating On AZ80 Magnesium Alloy In Aggressive Ion Solution

Magnesium alloy has good bio-mechanical properties and bio-compatibility.As a biodegradable medical implant material,it has achieved good results in clinic.It is a complex physiological environment in organism.Medical implant materials are accelerated by blood pressure,blood flow velocity and corrosive ions,among which corrosive ions are the most important factors affecting the corrosion of implant materials.One of the factors is to systematically study the degradation mechanism of corrosive ions on magnesium alloys,which plays an important role in the clinical application of magnesium alloys as biomedical materials.The excessive corrosion rate of magnesium alloy has been a bottleneck restricting its development.However,surface treatment is one of the important ways to improve the corrosion degradation of magnesium alloy.Among them,the chemical conversion film is the most commonly used method in the surface treatment technology of magnesium alloy because of the simple conversion process and low price.In this paper,the corrosion degradation behavior of AZ80 magnesium alloy magnesium fluoride chemical film in aggressive saline solution in physiological saline and plasma was studied.In order to improve its excessive corrosion rate,the conversion of potassium fluoride with green and shorter conversion time was used.A magnesium fluoride chemical film was prepared on the surface of the alloy.The corrosion rate of the alloy was analyzed by immersion and electrochemical tests.The macroscopic and microscopic morphology and corrosion products of corrosion were analyzed by SEM and XRD.The effects of magnesium fluoride chemical film on the corrosion degradation behavior of aggressive ions in magnesium alloy were investigated.The results are as follows:The chloride ion can accelerate the corrosion,which leads to the further destruction of existing weak areas and the emergence of new weak areas.In addition,the corrosion rate increases with the increase of chloride ion concentration.Bicarbonate can slow down corrosion,mainly because Mg₅?CO₃?₄?OH?₂·5H₂O,which is more stable than Mg?OH?₂,is formed in solution.With the appearance of sulfate ions in solution,the corrosion rate becomes faster,possibly because the corrosion product film of Mg₂?OH?₂SO₄·5H₂O on the surface is porous and can not effectively prevent chloride ions from entering the matrix.Monohydrogen phosphate and glucose can effectively reduce the alloy.The corrosion rate is mainly due to the formation of stable Mg₃?PO₄?₂.In immersion experiments,the corrosion rates of the alloys in Cl^-+HCO₃^-?Cl^-+HCO₃^-+SO₄^2-?Cl^-+HCO₃^-+SO₄^2-+HPO₄^2-?Cl^-+HCO₃^-+SO₄^2-+HPO₄^2-+C₆H₁₂O₆were 81%,74%,84%and 86%lower than those calculated by weight loss in Cl^-respectively.The potassium fluoride chemical film can reduce the average hydrogen evolution rate of the alloy in physiological saline,bicarbonate-containing and monohydrogen phosphate.Compared with non-chemical film alloys,the average corrosion rate of chemical film alloys is reduced by 8.2%,19.4%,22.8%,respectively.chemical conversion film can effectively reduce the open circuit potential of the alloy and increase the charge transfer resistance.