Research On The Microstructure And Properties Of Biomedical Magnesium-zinc Alloy Microtubes

Magnesium alloy is a very important lightweight structuralmaterial because of its low den-sity,high specific strength and specific stiffness.It is widely used in the fields of automotive,electronics,aerospace and other industries.Recently,Mg-Zn alloy with high mechanical proper-tiesand good biocompatibility is popular in biomedical material research filed.Growing research indicated that Mg-Zn showed potential to replace some inert materials,such as stainless steel and titanium alloy.However,previous studies on the biomedical magnesium alloy have highlighted on the larger-size bulk Mg alloy except some Mg alloy wire and micro-tube.Although the me-chanical properties,corrosion resistance and biocompatiblity of various Mg alloy bulk samples were systemically and detailedly investigated,in consideration of the great changes in the micro-structure and properties of the micro-tube during the processing,the pervious results have less direct assistance in the development of cardio and cerebral vascular stent.In order to promote the application of magnesium alloy in the biomedical field,the study on the magnesium alloy mi-cro-tube is necessary and urgent.In this paper,the microstructures,mechanical properties and corrosion resistance in vitroof magnesium alloy micro-tube were studied.The Mg-xZn(x=3、4、5、6wt.%)alloy bulk material and micro-tube were selected and analyzed.The optical microg-raphy(OM),scanning electronic micrography(SEM),X-ray diffraction(XRD),tensiletest at room temperature,electrochemical analysis and hydrogen evolution testin vitro were used to study their microstructure,mechanical properties andcorrosion properties.In comparison of the degradation properties of the annealing bulk Mg-xZn(x=3、4、5、6wt.%)alloy in vitro,we found that the second phase increased and the corrosion resistance re-duced with the increasing of Zn content,which increased the probability of corrosion in phase interfaces and accelerated the speed of hydrogen evolution.The results of electrochemical analy-sisshowed the self corrosion potential decreased and self corrosion current density increased with the increase of the Zn content.TheMg-xZn(x=3、4、5、6wt.%)alloy micro-tube showed obvious changes in microstructure and mechanical property compared with the corresponding raw materials.The grains were re-fined and complete recrystallization had occurredafter processing.In addition,the grain size de-creases with the increase of Zn content.When the content of zinc is lower than 5wt.%,the Mg-Zn alloys micro-tube with nearly single phase microstructure indicated a upward trend in mechanical properties.However,when the zinc content is up to 6wt.%,the many finer second phase particles distributed along the processing direction appeared and mechanical properties declined accordingly.The Mg-5Zn alloy micro-tube had the highest mechanical properties,and the ultimate tensile strength,yield strength andelongation were 305Mpa,235Mpa and 15.5%re-spectively.Hydrogen evolution test of the micro-tube Mg-Zn alloy indicated that the corrosion re-sistance increased with the increasing of Zn content when Zn content was below 5%.However,the corrosion rate increased significantlywhen the Zn content is 6wt.%.The results of electro-chemical analysis showed a similar tendency on corrosion potential and corrosion current density.We suggested that the increase of Zn content caused the solid solution Zn in the matrix after processing,which improved thecorrosion resistance of the matrix.Nevertheless,when the Zn content was improved to 6%,the incomplete-dissolved second phase quickened the corrosion of micro-tube in SBF by inducing galvanic corrosion occurred in phase interface.To summarized,when the Zn content varied from 3%to 6%,increasing the Zn content in Mg-Zn alloys micro-tube could improve both the mechanical properties and corrosion resistance which depended on its microstructure being single-phase.However,when the Zn content was increased to 6%,the incomplete dissolved second phase distributed along the processing direc-tion and formed the banded structure,reducing the mechanical properties and corrosion re-sistance.