Microstructure And Properties Of New Biomedical Mg-Sc-Yb-Mn-Zr Alloy

Due to the good mechanical compatibility,biocompatibility and biodegradability of magnesium alloys,it has been widely concerned in the field of biomedicine materials.But because of fast degradation speed and uncontrollable degradation process that result from active property of magnesium,and poor plastic property with poor precision forming caused by HCP structure of magnesium,magnesium alloys in biomedical applications is limited.In recent years,rare earth elements and alloying modification have become the research focus of biomedical magnesium and its alloys.Because of its good mechanical properties,corrosion resistance and non-toxic,WE43magnesium alloy that contain Y and Nd and other rare earth elements has become the focus of many researchers.In order to develop a biomedical magnesium alloy that is more suitable for human environment,based on the composition of WE43 alloy,choose rare earth element of scandium（Sc）that the density is close to magnesium and ytterbium（Yb）of lanthanide element as alloying element to replace the rare earth elements in the WE43 alloy,and add Mn element which promotes the corrosion resistance of magnesium alloy and Zr element which promotes nucleation magnesium alloy.Mg-x Sc-y Yb-1.0Mn-0.5Zr（x=2,3,4,6;y=1,2,3,4）was prepared by casting of metal mould,then alloy was treated with solid solution,by optical microscope（OM）,field emission scanning electron microscopy（SEM）,room temperature tensile test and immersion test,respectively analyzes the effects of Sc elements and Yb elements on microstructure,mechanical properties and corrosion resistance of biomedical Mg-x Sc-y Yb-1.0Mn-0.5Zr alloy.Select Mg-6Sc-3Yb-1.0Mn-0.5Zr alloy with solid-solution state which has good mechanical properties and corrosion resistance for rolling,and comparatively analyse inherent law between the microstructure and properties of as-casting,solid-solution and rolling Mg-6Sc-3Yb-1.0Mn-0.5Zr alloy.The grain size of the as-cast Mg-x Sc-y Yb-1.0Mn-0.5Zr alloy was dendritic growth,and its average grain size was obviously refined with increase content of Yb element.The effect of Sc elements on the grain refinement of the biomedical as-cast Mg-x Sc-y Yb-1.0Mn-0.5Zr alloy is not obvious,and the excessive Sc element will increase the segregation in the grain boundary of the magnesium alloy.The second phase consists of Mg Sc,Mg₂Yb,Mn₂Sc and Mn₂Zr phase.Mg Sc and Mg₂Yb phase precipitates along grain boundary,and Mn₂Sc,Mn₂Zr phase precipitates in the grain interior.Pure Sc phase occurs when Sc element content is high.After solid-solution treatment,the segregation along the alloy grain boundary was eliminated,and the second phase consists of Mn₂Sc phase and Mn₂Zr phase.The average grain size was obviously refined with the increase of Sc element content.The increase content of Yb element can improve the strength of magnesium alloy through solid-solution strengthening and fine grain strengthening.Excessive Yb elements have a negative effect on the plasticity of the alloy,but the increase content of Sc element can improve the plasticity of biomedical Mg-x Sc-y Yb-1.0Mn-0.5Zr alloy,instead,the strength decreases.Biomedical Mg-6Sc-3Yb-1.0Mn-0.5Zr alloy has the best mechanical property.The tensile strength,yield strength and elongation of this alloy with as-cast state were 182MPa,81MPa and 11.6%.Although there is a decrease in the tensile strength and yield strength of this alloy with solid-solution state,elongation can reach28%.As-cast biomedical Mg-x Sc-y Yb-1.0Mn-0.5-Zr alloy corrosion resistance enhanced with the increase content of Sc and Yb element enhancement,solid-solution treatment that makes the alloy form a compact passivation film in the process of corrosion will improve biomedical Mg-x Sc-y Yb-1.0Mn-0.5Zr alloy in PBS simulated body fluids.Mg-6Sc-4Yb-1.0Mn-0.5Zr alloy with solid-solution state has the lowest rate of degradation of 0.72mm/a.Mg-6Sc-3Yb-1.0Mn-0.5Zr alloy with solid-solution state has excellent ductility,and the compression rate is up to 72%after rolling.The grain size of tihs alloy was obviously refined to 20μm,and the second phase could even reach the nanometer level.Due to work hardening of rolling,the strength of this alloy was greatly increased,the tensile strength reached 295MPa,and the elongation decreased significantly,only5.1%,and the fracture mechanism of this alloy with rolling state is mixed ductile-brittle fracture.Due to its refined grains and second phase,the corrosion resistance of biomedical Mg-x Sc-y Yb-1.0Mn-0.5Zr alloy with rolling state is better than as-casting and solid-solution state.The passivation film formed in the process of corrosion is more compact,and the corrosion is more homogenous.Compared with as-casting and solid-state alloys,the corrosion rate is lower,only 0.31mm/a.