Corrosion Behavior And Room Temperature Mechanical Properties Of Novel Biodegradable Mg–Sn–Zn–Ca Alloys

The density and elastic modulus of magnesium and magnesium alloys are close to those of natural bones.As medical metal materials,it can effectively reduce the stress shielding effect.Magnesium is one of the essential elements of the human body and has excellent biocompatibility.Therefore,magnesium and its alloys have wide application prospects in the field of medical metal materials.In addition,magnesium and its alloys will gradually degrade after being implanted into the human body,without the need for secondary surgery,which greatly reduces the pain and economic burden of patients.However,the degradation rate of magnesium and its alloys in body fluids is relatively fast,which results in the loss of mechanical properties before the end of the healing process,which hindered their wide application as implant materials.At present,there are many studies on Mg–Sn series alloys,however,the addition of Zn and Ca elements to Mg–Sn series alloys and the hot rolling deformation of the alloys are relatively rare.In the present study,a novel hot–rolled Mg–xSn–1Zn–0.5Ca alloys have been developed for possible application as biodegradable implants.We combined element alloying with plastic deformation?hot rolling?to improve mechanical properties and corrosion resistance of biodegradable magnesium alloys and studied the influence of Sn content on the microstructure,room temperature mechanical properties and corrosion behavior of as-cast and hot-rolled Mg–x?1,3and 5 wt.%?Sn–1Zn–0.5Ca alloys.The Sn content in Mg–xSn–1Zn–0.5Ca alloys was optimized.In order to further improve the corrosion resistance of the magnesium alloys,HA coating and HA/GO composite coating were prepared on the surface of the hot-rolled Mg-1Sn-1Zn-0.5Ca alloy with better comprehensive performance.The influence of the coating on the corrosion resistance of the magnesium alloys was explored and the influence of GO on the coating was compared and analyzed.The main research results are as follows:?1?We compared and studied the as-cast Mg-xSn-1Zn-0.5Ca alloys with different Sn contents.It was found that the strength and plasticity increased gradually and the corrosion resistance decreased gradually with the increase of Sn content.The influence mechanism of the second phase and grain size on the strength and plasticity of the alloys was investigated,and the corrosion behavior of Mg-xSn-1Zn-0.5Ca alloys in the Hank's solution was revealed.It was found that the size and amount of the second phase had a significant influence on the corrosion resistance of the magnesium aloys.?2?A novel fine grain multi-pass rolling process of Mg-xSn-1Zn-0.5Ca alloys was developed.It was found that the recrystallization grain size of the rolled Mg-5Sn-1Zn-0.5Ca alloy was 6.6±1.1?m.With the increase of Sn content,the grain size gradually decreased,the number of the second phase significantly increased,the room temperature tensile strength?UTS?and yield strength?YS? slightly increased and the elongation gradually decreased.The fracture elongation at room temperature of Mg-1Sn-1Zn-0.5Ca aloy reached 15.3%.?3?Based on EBSD and the SEM analysis,the influence of Sn content?1,3 and 5 wt.%?on hot-rolled Mg-xSn-1Zn-0.5Ca alloys recrystallization behavior was studied.It was found that with the increase of Sn content,Mg-xSn-1Zn-0.5Ca alloysrecrystallizationvolumefractiondecreasedobviously, Mg-1Sn-1Zn-0.5Ca alloy almost completely recrystallization,the main reason is that Mg₂Sn grains inhibit grain boundary sliding,slow down the process of grain growth and inhibit the recrystal ization.?4?The results of electrochemical experiment and immersion experiment showed that the corrosion rate of the hot-rolled Mg-xSn-1Zn-0.5Ca alloys increased gradually with the increase of Sn content,the Mg–1Sn–1Zn–0.5Ca alloy showed the optimal corrosion resistance.It was found that Mg₂Sn had a more significant effect on corrosion resistance than grain size and the corrosion mechanism in the Hank's solution was explored.?5?The hydroxyapatite?HA?coating and hydroxyapatite/graphene oxide?HA/GO? composite coating were preparedin thesurface ofhot-rolled Mg-1Sn-1Zn-0.5Ca alloy with the better comprehensive performance.The effect of the coatings on the corrosion resistance of the magnesium alloy were compared.It was found that the HA/GO composite coating prepared at a deposition voltage of 10 V had the best corrosion resistance.The effect of GO on nucleation of hydroxyapatite crystal was revealed.