Study On The Preparation,Microstructures And Properties Of Mg-Zn-Ca Alloy Wire For Biomaterial Application

Due to the excellent mechanical property,biocompatibility and biodegradability of magnesium alloys,magnesium alloy wires have attracted much attention in biomaterial field recent years for biomaterial applications including gastrointestinal anastomosis,hemoclip and sutures in wound closure.However,up to now,there is little research on medical magnesium alloy wire at home and abroad and there have been no reports on the fabrication of the Mg-Zn-Ca alloy wire through drawing process.In this paper,Mg-3.0wt%Zn-0.2wt%Ca alloy was selected as the original material.Mg-3Zn-0.2Ca alloy wire with 0.8 mm diameter were successfully prepared through casting,extruding,cold drawing combined with proper intermediated annealing process.The microstructure,texture,mechanical properties and corrosion behavior of Mg-3Zn-0.2Ca wire in simulated body fluid?SBF?were investigated systematically by optical microstructure observation,XRD,tensile test,EBSD analysis,hydrogen evolution test,electrochemical analysis and immersion test.In addition,the fluoride surface treatment of the wire was also carried out and its effect on the corrosion resistance of Mg-3Zn-0.2Ca wire was studied.Finally,a new type of biodegradable magnesium alloy skin staple was fabricated by Mg-3Zn-0.2Ca wire,and the feasibility of its application was preliminarily investigated.The main conclusions of this study were as follows:?1?By the detailed research of drawing process from?2 mm to?0.8 mm,the maximum accumulated cold deformation of 54.44%can be obtained by using the average single pass deformation of 8%,multi-pass continuous cold drawing combined with proper intermediate annealing.During the drawing process,the intermediate annealing was only carried out two times.After final annealing treatment,the average grain size of Mg-3Zn-0.2Ca wire was refined from 6.73?m to 3.96?m.The ultimate tensile strength,yield strength and elongation of the final as-annealed wire were 253 MPa,212 MPa and 9.2%,which showed good comprehensive mechanical properties.?2?EBSD analysis showed that a strong?0002?<10-10>//DD basal fiber texture system was formed after multi-pass cold drawing.After recrystallization annealing,the basal texture intensity of the wire decreased significantly,presenting the characteristics of random distribution,which was attributed to the Ca element added in the alloy.Moreover,the results also indicated that the LS surface of the wire was mainly composed of?0001?,?10-10?and?11-20?orientated grains,and the TS surface was mainly composed of?10-10?and?11-20?orientated grains.As can be known from the result of corrosion resistance,the corrosion resistance of TS surface was better than that of LS surface,which indicates that controlling texture components is an effective way to improve corrosion resistance of Mg alloy.?3?The corrosion rate of as-drawn Mg-3Zn-0.2Ca wire with the diameter of 0.8 mm was8.16 mm/y after immersing in SBF for 7 days.After annealing,the corrosion rate of the wire was reduced to 5.06 mm/y,and the corrosion behavior had been obviously improved.Additionally,the micro-cracks on the surface of the wire should be the main cause of the serious local corrosion and early fracture.The Mg-3Zn-0.2Ca wire with compact fluoride coating with a thickness of about 0.7?m was prepared by fluoride treatment.Experiments showed that the corrosion rate of HF-treated wire was reduced to 1.53 mm/y after immersing for 7 days,which indicates that fluoride treatment can effectively improve the corrosion resistance of Mg-3Zn-0.2Ca wire.?4?The study of Mg alloy skin staple showed that only a few twinning appeared in the bending area after closing,and no micro-cracks were observed,which indicated that the Mg-3Zn-0.2Ca skin staple exhibited a good formability.After closure,the MgF₂ coating on the bending part of the HF-treated staple did not crack under stress.The vitro immersion test showed that the untreated skin staple presented a relatively uniform corrosion behavior,and the mechanical integrity was maintained for about 7 days.The mechanical integrity of Mg-3Zn-0.2Ca skin staple was increased to about 11 days by fluoride treatment,which was close to meeting the clinical requirements of failure for about two weeks,and the degradation time was effectively extended.