Microstructures And Properties Of Zinc-base Alloys For Bio-degradable Medical Materials

The Zn-Mg alloys with Mg additions of 35%,40%,45%,48%(mass fraction) and Zn-40Mg-Y alloys with Y additions of 0.3%,0.5%,0.7%,1.1%(mass fraction) in different cooling rate were prepared by conventional casting method.The effects of cooling rate and composition on the morphologies of microstructure, phase composition and mechanical properties of Zn-Mg alloys and Zn-Mg-Y alloys have been investigated by scanning electron microscope(SEM) equipped with energy-dispersive X-ray spectrometer(EDS),X-ray diffraction(XRD) and hardness instrument.The biocompatibility and biodegradability of Zn-Mg alloys and Zn-Mg-Y alloys were also studied by immersion corrosion in simulated body fluids and potentiodynamic polarization measurement.The experimental results of binary Zn-Mg alloys showed that there were four phases,MgZn₂,Mg₂Zn₃,MgZn and Mg₇Zn₃ in all the four alloys with different Mg additions.The hardness of all four alloys were enhanced by the increased of petal-like strengthening phase MgZn₂ increased by the Zn content increased.In the other hand,when the cooling rate decreased,the hardness of all the four alloys were also enhanced because of the ageing strengthening generated in the center of ingots.Immersion corrosion results showed that pH values of the immersion solution first rose sharply then declined a little,and then rose again but slowly, finally reached steadily.In the process of immersion,dense passivation film gradually generated on the surface of alloys,and the film flaked and reformed finally reached equilibrium,till the alloys completely changed into corrosion products.The pH result of Zn-40Mg alloy changed the most slowly,which indicated that the corrosion resistance of Zn-40Mg alloy was the best among the four alloys.Moreover,the lowest open circuit potentials of Zn-40Mg alloy in Polarization curve again suggested its best corrosion resistance.The experimental results of ternary Zn-Mg-Y alloys showed that there were alsoα-Mg solid solution phase,binary or ternary Y-included phases in all the four alloys besides the four phases in binary Zn-Mg alloys.With the increase of Y content and the falling of cooling rate,the primary phases MgZn₂ and Mg₂Zn₃ became less and coarse,and the eutectoid structure ofα-Mg and MgZn increased in quantity,at the same time,the dispersed Mg₇Zn₃ and Y-included phases increased in quantity and distributed uniformly,so the hardness of alloys gradually increased.In addition,we found a few of radialized flower-like phases which were termed as ternary quasicrystal Y-included phases.Immersion corrosion results were similar with that of Zn-Mg alloys.The pH result of Zn-40Mg-07 alloy changed the most slowly,and the open circuit potentials of Zn-40Mg-0.7 alloy was the lowest,this suggested that the corrosion resistance of Zn-40Mg-0.7 alloy was the best in the four alloys.