The Study On The Microstructure, Tensile Properties And Corrosion Behavior Of Low-Alloyed Biomedical Mg-Sn-Al-Zn Alloys

Magnesiumalloys,withgoodbiocompatibilityand mechanical-compatibility,can be developed as next generation promising biomaterials.Firstly,due to the similar density and elastic modulus between magnesium alloy and human bone,the implant of magnesium alloy has a good stress shielding effect.Secondly,the magnesium alloy has good degradable properties,and is easily degraded in the biological liquid environment to form Mg²⁺,which is involved in metabolic excretion,and is non-toxic and harmless to the human body.Finally,the Mg²⁺affects various biological enzymes in living organisms,participates in the activities of the nervous system and muscles of the organism.However,commercial magnesium alloy has a relatively high corrosion rate,and thus the toughness and strength in the biological fluid environment will be accompanied by a serious failure phenomenon with the increased implantation time,which greatly hinders the promotion and application of biomedical magnesium alloy.The low alloying can effectively refine the microstructure,modify the texture and improve the deformability of the magnesium alloy,thereby improving the tensile properties and corrosion resistance of the Mg-Sn based dilute alloy.In this paper,the low-alloyed Mg-Sn-Al-Zn extruded alloy is the research object.The dependence of tensile properties of the studied alloys on the microstructure characteristics?the grain size and second phase type?and deformation texture was analyzed.At the same time,through the hydrogen evolution test and electrochemical test of the studied alloys,the corrosion rate and corrosion process of the studied alloys in simulated body fluids were investigated.Finally,the immersion experiment of the alloy was conducted and the influence of the grain size,structure and orientation as well as the corrosion product layer on the corrosion behavior ofthe studied alloys was analyzed.The results of this study are as follows:?1?The extruded Mg-Sn-Al-Zn exhibits a typical bimodal structure consisting mainly of dynamically recrystallized grains and undynamically recrystallized bands along the extrusion direction.Fine nanosecond phase Mg₂Sn particles and typical basal fiber textures are present in the matrix of the alloy.Among the extruded alloys,Mg-0.5Sn-1Al-1Zn alloy has the highest comprehensive mechanical properties,tensile yield strength?TYS?of 292 MPa,tensile strength?UTS?of 308 MPa,and elongation?EL?.26.5%.The improvement of the comprehensive mechanical properties of the experimental alloy is mainly the result of grain boundary strengthening,texture strengthening and solid solution strengthening.?2?The open circuit potential value?OCP?of the extruded experimental alloy reached a steady state,indicating that corrosion products were present on the surface of the alloy substrate.The polarization curves all show asymmetric structure.The polarization fitting data proves that the corrosion rate?P_i?of Mg-0.5Sn-1Al-1Zn alloy is the lowest,which is 6.07mm/a.The corrosion resistance of Mg-1.0Sn-1Al-1Zn alloy is the worst,which is 12.4mm/a.Further analysis shows that the difference in electrochemical behavior of the experimental alloy is mainly due to the protective effect of the corrosion product layer on the substrate,resulting in a change in the corrosion resistance?R_p?.?3?The corrosion product analysis results of the extruded alloy show that the corrosion product film is mainly composed of a mixed product of MgO,Mg?OH?₂,SnO₂ and MgCl₂.Among them,SnO₂ can effectively improve the protection effect of corrosion products on the alloy matrix.The soaking experiment of the extruded alloy can obtain the mixed corrosion of the body fluid corrosion type of the alloy as micro-galvanic corrosion and its induced pitting corrosion.The effect of different body fluids on the low-alloyed Mg-Sn-Al-Zn alloy is mainly affected by the microstructure?the potential difference between Second phase particle and substrate,grain size,grain orientation?.And the impact of the macroscopic morphology?corrosion product layer?.