| Magnesium alloy has become one of the most promising metal medical materials in 21 th century due to the high specific strength,excellent biocompatibility and degradability.However,the poor corrosion resistance is the largest obstacle which hinders its application in clinical field.So,how to improve its corrosion resistance is the significant research direction of biomedical magnesium alloy.Mg-Zn-Zr is one biomedical magnesium alloy series which possesses low cytotoxicity,and Ce is chosen as an additional rare earth element to further improve the corrosion resistance.This study designed and prepared Mg-2Zn-0.4Zr-0.6Ce biomedical alloy,aiming to enhance the corrosion resistance and properties of the alloy through heat treatment and hot extrusion.And the effect of solution treatment,aging treatment,hot extrusion and recrystallization annealing has been investigated by means of OM?Optical Microscope?,SEM?Scanning Electron Microscope?,TEM?Transmission Electron Microscope?,immersion test,electrochemical test and tensile test.The result shows that the microstructure of the as-cast Mg-2Zn-0.4Zr-0.6Ce alloy mainly consists of ?-Mg and?Mg,Zn?11Ce.After solution treatment at different temperatures ranging from 430 to 470 ?,the most of secondary phases dissolve,the grains grow gradually.However,there still exist undissolved?Mg,Zn?11Ce phases,which is attributed to its high-temperature stability.Due to the reduction of second phases and homogenization of alloying element,solution treatment enha nces the corrosion resistance of the alloy,and the corrosion rate and corrosion curent Icorr in simulate body fluid?SBF?first decrease and then increase,the diameter of capacitive loop first increases and then decreases.When temperature is 450 ?,the lowest corrosion rate and Icorr is obtained.Meanwhile,the corrosion rate and Icorr are 0.7483 m·a-1 and 0.93 ?A·cm-2,respectively.Subsequently,the Mg-2Zn-0.4Zr-0.6Ce alloys quenched at 450 ? were aged at 250 ? for various time ranging from 8 to 24 h.After aging treament,the finer?Mg,Zn?11Ce phases precipitate,the amount of finer phases rises with the prolonged time.Because of the more micro-galvanic cells,corrosion rate and Icorr in the SBF increase,the diameter of capacitive loop decreases gradually with the prolonged time.The alloy aged for 8 h exhibits the lower corrosion rate and Icorr(0.8125 m·a-1 and 1.31 ?A·cm-2,respectively).Owing to dispersion strengthening,the te nsile strengh of alloy is improved.With the prolonged time,the tensile strength increases and elongation decreases gradually.When the aged time is 24 h,the tensile strength reach the maximum and is 209.4 MPa.Taking corrosion resistance into consider,the alloy aged for 12 h possesses the better comprehensive properties.Meanwhile,the tensile strength and elongation are 176.3 MPa and 12.8%,respectively,corrosion rate is 0.8573 mm·a-1.As-cast Mg-2Zn-0.4Zr-0.6Ce alloys were extruded at different temperatures ranging from 470 to 510 ?.The result shows that dynamic recrystallization occurs during hot extrusion,the microstructure of the extruded alloy consists of fine dynamic recrystallized?DRXed?grain and unDRXed grain.When the temperature rises,the volume fraction of DRXed grain gradually increases,while there is no obvious change in grain size,and the corrosion rate and Icorr in the SBF decrease and then increase,the capacitive arc diameter increases and then decreases.When temperature is 490 ?,the corrosion resistance is optimized,the corrosion rate and Icorr are 0.9337 mm·a-1 and 4.67 ?A·cm-2,respectively.Because of refinement strengthening and dislocation strengthening,the tensile strength of the extruded alloy is enhanced.With the extrusion temperature increasing,the tensile strength and elongation increases and then decreases.When extrusion temperature is 490 ?,the alloy exhibits the optimized comprehensive mechanical properties,the tensile strength and elongation are 259.1 MPa and 14.1% respectively.Subsequently,the Mg-2Zn-0.4Zr-0.6Ce alloys extruded at 490 ? were carried out with recrystallizaton annealing for 3 h at different temperatures ranging from 150 to 300 ?.After annealing treatment,recrystallization occurs,the unDRX grains disappear and the grains grow subsequently.With the increasing temperature,the corrosion rate and Icorr in the SBF decrease and then increase,the capacitive arc diameter increases and then decreases,the tensile strength decreases and elongation increases and then decreases.Corrosion current?Icorr?and grain size?d?meet the following equality: Icorr=a+bd-1/2 when annealed temperature is beyond 200?.Take corrosion resistance and mechanical properties into consideration,the alloy annealed at 200? for 3 h possesses the lowest corrosion current,and exhibits the optimized comprehensive properties.The tensile s trength and elongation are about 245.8 MPa and16.2%,respectively,and corrosion rate is about 0.7235 mm·a-1. |
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