Effect Of Ag And La On Microstructure And Properties Of Mg-0.5Sr Magnesium Alloy

As the lightest structural alloy,magnesium alloy has the advantages of low density,high specific strength and stiffness,and excellent electromagnetic shielding performance.It has broad application prospects in aerospace,electronics and national defense military fields.In addition,magnesium alloy has excellent biocompatibility and activity,and its elastic modulus is close to human bone,which can avoid stress shielding effect and promote human metabolism and new bone growth.Therefore,magnesium and magnesium alloys are considered to be a new generation of biodegradable metals with great potential in orthopedic applications.In this paper,Mg-0.5Sr alloy was taken as the research object,Ag and La elements were added during melting,and Mg0.5Sr-xAg-yla（x=0.5,1.0,1.5;y=1.0,1.5,2.0 wt%）bar with diameter of 10 mm were prepared by forward extrusion.The micro structure,mechanical properties and corrosion resistance of the alloy under different states were compared,and the cytotoxicity levels of alloying elements to cells were studied.The microstructure and phase composition of the alloy were analyzed by OM,SEM and XRD.The corrosion behavior of the alloy in Hank’s simulated body fluid was detected by electrochemical test and immersion corrosion test.The cytotoxicity of the alloy to C3H10 and RMSC cells was evaluated by CCK-8 technique.The main conclusions are as follows:（1）The micro structure of the alloy in different states is composed of α-Mg,Mg₁₇Sr₂,Mg₁₇La₂ and Mg₄Ag phases.With the increase of Ag and La content,the dot and block second phase gradually changed into strip.After extrusion,the grain of the alloy is refined and the distribution of second phase is more uniform.（2）The hardness of the alloy increase with the increase of Ag and La contents.The highest hardness value of EX-Mg-0.5Sr-1.5Ag-2.0La alloy is HV 69.86.The tensile strength of the alloy increases with the increase of La element content,and the elongation first increases and then decreases.The elongation of the alloy can be improved by increasing the content of Ag element.Mg-0.5Sr-0.5Ag-2.0 La alloy has the best comprehensive mechanical properties.The tensile fracture show a mixed of brittle-ductile fracture.After the aging peak treatment,the hardness of the alloy increased slightly,and the fracture mode does not change.（3）The similar arc of capacitive resistance of the alloys indicates the same type of corrosion.The EX-Mg-0.5Sr-0.5Ag-2.0La alloy has the largest arc resistance and the best corrosion resistance.After aging treatment,the open-circuit polarization curve moves to the negative direction,the current density increase and the corrosion resistance of the alloy deteriorates.（4）After immersion in Hank’s solution for 120 h,the surface corrosion products of Mg0.5Sr-xAg-yLa alloy are mainly Mg（OH）₂,mixed with MgO,Mg₃（PO₄）₂ and Ca（PO₃）₂.The corrosion resistance of the EX-Mg-0.5Sr-0.5Ag-2.0La alloy is the best.The corrosion resistance of the alloy increases with the increase of La element,and the corrosion resistance of the alloy decreases with the increase of Ag element content.After aging,the surface of the alloy has more black corrosion products,more hydrogen evolution and corrosion rate,and worse corrosion resistance.（5）The cytotoxicity of Mg-0.5Sr-xAg-yLa alloy to C3H10 and RMSC cells is grade 0 or 1 with the increase of the amount of Ag and La elements,which is not toxic and meeting the standards of medical biological materials.