Corrosion Behavior Of AZ31b Magnesium Alloy By Ultrasonic Rolling In Simulated Body Fluid Containing Uric Acid

Magnesium alloy has received wide attention as a potential bio-implant material,due to its good biocompatibility and degradability,and the density and elastic modulus close to that of human bone.However,the poor corrosion resistance of magnesium alloy results in the failure of mechanical support at the initial implantation stage.The plastic deformation caused by ultrasonic rolling can improve the mechanical properties of magnesium alloy,and then affects the corrosion properties.The organic composition in the body fluid will also affect the corrosion performance.Therefore,investigating the effect of ultrasonic rolling passes and uric acid content on the corrosion behavior of AZ31B magnesium alloy in dynamic and static simulated body fluids（SBF）is informative for the potential application of magnesium implants in patients with hyperuricemia.（1）First,the surface roughness of magnesium alloy samples after turning and ultrasonic rolling with different passes was tested.Then,the short-term immersion corrosion test was carried out in static high uric acid simulated body fluids to analyze the electrochemical corrosion behavior and soaking corrosion morphology.It was found that ultrasonic rolling could improve the surface roughness and corrosion resistance of AZ31B.The increase of rolling passes can reduce the surface roughness value of magnesium alloy,but the electrochemical activity is enhanced,and the corrosion morphology shows that the corrosion product spalling rate is accelerated.（2）The magnesium alloy after ultrasonic rolling were immersed in static simulated body fluid with different concentrations of uric acid for short-term and long-term immersion corrosion tests.The electrochemical corrosion behavior,immersion corrosion rate and corrosion morphology were analyzed.In the short-term immersion corrosion test,the corrosion products flaked off seriously when uric acid concentration was 210μmol/L,so the corrosion inhibition ability was weak.The corrosion products were lighter in spalling when uric acid concentration was 630μmol/L,so the corrosion inhibition ability was strong.In the long-term immersion corrosion test,the corrosion rate of magnesium alloy in SBF containing uric acid is greater than that without uric acid.The corrosion rate was the maximum when the uric acid concentration was210μmol/L,it decreased when the uric acid concentration reached 420μmol/L,and it increased again when the uric acid concentration further increased.The macroscopic morphology of the corrosion surface layer showed deep pore-like distribution when the uric acid concentration was lower than 420μmol/L,and the loose trachoma-like corrosion products gradually appeared around the corrosion pits when it was higher than 420μmol/L.The ionized O^-of 2,6,8-trihydroxypurine formed by uric acid through proton migration reaction will attract Ca²⁺and Mg²⁺in the solution,which makes the corrosion product layer with the increase of uric acid concentration more effective in preventing corrosion.Higher uric acid concentration promotes ionization of2,6,8-trihydroxypurine and produces more H⁺,which makes the corrosion product layer more easily destroyed.（3）COMSOL was used to simulate the environment of flowing body fluids,and a circulation device was constructed to simulate the flow of body fluids.Short-term immersion corrosion tests of ultrasonic rolling magnesium alloy in simulated body fluids with two concentrations of uric acid were carried out,and electrochemical corrosion behavior and immersion corrosion morphology were analyzed.A test was carried out to simulate the corrosion loss in body fluids with high concentration of uric acid in hydrostatic fluid.It was found that the flow of body fluids made the corrosion products flake off faster,weakened the hindrance to corrosion,and thus accelerated the short-term immersion corrosion rate of magnesium alloys.