Study On Microstructure Evolution And Corrosion Properties Of Biomedical Mg-3Zn-0.2Ca Alloy Processed Of Different Thermal Deformations

Recent years, magnesium and its alloys as biodegradable implant materials become a hot spot.But as biomedical alloys, magnesium alloys in the body have a rapid degradation rate, it can not maintain the mechanical properties for a long time.Therefore, the corrosion resistance of magnesium alloys attract more attention. Moreover, the poor deformation of magnesium alloy has become a key issue of its practical application. Therefore, this paper researched deformation process of Mg-3Zn-0.2Ca alloy by using conventional hot extrusion and equal channel angular pressing(ECAP). The changes in microstructure of Mg-3Zn-0.2Ca alloy and its degradation behavior in simulated body fluid(SBF) after the different deformatoin process were investigated by different methods, which provided a reference for the deformation process design and its impact on the microstructure and corrosion behavior of magnesium alloy.In this paper, Mg-3.0wt%Zn-0.2wt%Ca alloy was prepared by the vacuum melting.Conventional hot extrusion and ECAP were uesd for Mg-3Zn-0.2Ca alloys deformation.The corrosion behavior of the composites was investigated by electrochemical tests and in vitro degradation properties tests. According to above analysis, the following conclusions can be drawn:1.After hot extruding of extruded ratio about 57:1, the grain size of as-cast Mg-3Zn-0.2Ca alloys was reduced obviously.The grain size of as-cast Mg-3Zn-0.2Ca alloys was about 70μm,but after extrusion, the grain size was reduced to 3μm. The corrosion resistance of as-cast Mg-3Zn-0.2Ca alloys was poorer than that of extrusion alloy sheet.After a week’s immersion, as-cast Mg-3Zn-0.2Ca alloys and extrusion alloy sheet generated corrosion products are mainly Mg(OH)2 and HA.2.The suitable temperature of ECAP of as-cast Mg-3Zn-0.2Ca alloys was 280℃and ECAP optimum speed was 60mm/min.3.The ECAP process could effectively refine the grain size of as-cast Mg-3Zn-0.2Ca alloys, and with the increasing of deformation passes, alloy microstructure was more homogeneous. When deformation passes of the samples were less than 8 passes in path A, the microstructure in different directions sectional were varied greatly. After 8 passes, the microstructure of the samples in three directions are constituted with uniform fine isometric crystal. Phase composition and orientation of the crystal plane of samples did not change a lot during different extrusion pasess. The second phase in extrusion samples should be Mg4Zn7 and Ca2Mg6Zn3. After the ECAP, most of the textures in(0001)plane were paralleled to ND.With the increasing of ECAP passes, Vickers hardness of alloys increased first and then decreased. The variation in hardness depends on texture orientation and intensity.4.After extruded eight passes, the corrosion resistance of the alloy was significantly lower than the low passes of alloy extrusion, that is, with the increase of the pressing passes,grain has been refined, whole the corrosion resistance of Mg-3Zn-0.2Ca alloys has decreased.Samples of ND sectional have poor corrosion resistance than that of ED and TD sectionals,consistent with the electrochemical test results. The texture with most(0001)plane paralleled to ND, which may be the reason of different corrosion resistance.