Study On Biocorrosion Behavior And Calcium Phosphorus Coating Of Mg-Nd-Zn-Zr Alloy By IECAP Processing

In order to develop high performance bio magnesium alloy and its coating preparation process,we studied the effect of a new hot extrusion process?iECAP?on biological corrosion behavior of Mg-Nd-Zn-Zr alloy,and the effect of electrochemical deposition process on the mechanism of calcium phosphate coating.The effect of iECAP process on the corrosion behavior of Mg-Nd-Zn-Zr alloy in simulated body?SBF?fluid was studied by changing the extrusion temperature.The results show that the corrosion resistance in SBF of extruded alloy is better than that of as-cast alloy.The corrosion changed from local corrosion to uniform corrosion after extrusion.The corrosion resistance increased gradually when the extrusion temperature increased from 400 ? to 500 ?.After the immersion of simulated body fluid,a layer of corrosion products and a small amount of crystalline precipitate were formed on the surface of alloys,the main components were Mg?OH?₂,HA and?Ca,Mg?₃?PO₄?₂,etc.The effects of p H,temperature,current density and time on the calcium phosphorus coating were studied by adjusting the electrochemical deposition parameters.When the p H value increased from 3 to 5,the morphology of the coating changed from needle-like into ribbon-like,and then into spherical-like,the content of FHA reduced at the same time.p H value determines the quantity of OH-in the electrolyte,with the increase of p H value,the quantity of OHincreased,which is beneficial to increase the nucleation rate.Thus the needlelike morphology grew up into ribbon-like,when p H value increased from 3 to 4.However,calcium and phosphorus ion will form precipitation,when the quantity of OH-is excessive,which is not conducive to the nucleation.Thus the content ofFHA in the coating decreased.When the deposition temperature increased from50 ? to 80 ?,the morphology of the coating changed from needle-like into ribbon-like and spherical-like,the content of FHA in the coating increased at the same time.Temperature determines the free energy of the system,the higher the temperature is,the greater the free energy will be.It will lead a increase of nucleation rate.When the current density increased from 0.25 m A/cm² to 1m A/cm²,the coating consist of ribbon-like and spherical-like structures,and the ribbon-like structure became finer.The current density decided the generation rate of H2 and OH-,and they determined the size of the ribbon-like structure together.When the time increased from 2 h to 8 h,the coating consist of ribbonlike and spherical-like structures,and the coating became more loose.Time leads to differences in growth of crystal grain,some grains grow preferentially and some grains growth is restrained.In conclusion,the p H value of the greatest impact,followed by temperature,and the current density and time had little effect.In addition,the main component of the coating is FHA.