The Infulence Of Ion Concentra-Tions In Saline Solution On The Degradation Behavior Of Pure Magnesium

Magnesium alloys have excellent biodegradable characteristic,good mechanical prop-erties and biocompatibility.However,the fast corrosion rate restricts their clinical applications.Therefore,it's important to study the degradation behavior of magnesium alloys in physio-logical environment for their clinical applications.In this paper,the effects of chloride ion concentration,pH value,glucose in the immersion solutions and their coupling with stress on the degradation behavior of pure magnesium were systematically studied by self-made stress corrosion experiment platform,electrochemical analysis,microscopic morphology observa-tion,hydrogen evolution test.It is indicated that:In simulated body fluid(SBF),increasing the chloride ion concentration or glucose addi-tion can speed up the corrosion of pure magnesium and increase the hydrogen evolution rate,while increasing the pH value of the solution has the opposite effect.Meanwhile,for different immersion solutions,the corrosion rate of pure magnesium is accelerated with increasing the stress.In nitric acid solution,the corrosion current density of pure magnesium increases with the increase of stress.In the solutions containing a certain concentration of chloride ions(0.5mol/L and 1mol/L),the polarization resistance of pure magnesium decreases and the corrosion current density increases with the increase of stress,especially the chloride ion concentration is 1mol/L.However,in the SBF with pH=8.0 or adding glucose,the effect of stress on the electrochemical corrosion behavior of pure magnesium is not obvious,which may be related to the passivation films on the magnesium surface.With the increase of chloride concentration in the solution,the river-like corrosion mor-phology on pure magnesium surface is intensified.When the concentration of chloride ion in the solution exceeds 0.5mol/L,the pitting corrosion due to chloride ions is aggravated and the corrosion surface presents honeycomb-like.In SBF adding 0.9g/L glucose,there is a slight pitting corrosion on the magnesium surface,while the pitting corrosion is not obvious on the magnesium surface in SBF with pH=8.0 owing to the formation of passive films.Stress mode has an influence on the corrosion behavior of pure magnesium.The corro-sion pits on magnesium surface under the tensile stress are deeper than those under the com-pressive stress.Under these two kinds of stress modes,magnesium surface all appear pitting corrosion,presenting river-like corrosion morphology.In the SBF,with the extension of the stress corrosion time,the capacitive arc radius gradually increases in the high frequency re-gion of the impedance spectrum of pure magnesium,indicating that the polarization resistance gradually increased,and the polarization resistance under the tensile stress is greater than that under the compressive stress during the initial period of corrosion.