Mg-(4-x)Nd-xGd-Sr-Zn-Zr生物镁合金的组织、力学和腐蚀性能

MICROSTRUCTURE,MECHANICALAND CORROSION PROPERTIES OF Mg-(4-x)Nd-xGd-Sr-Zn-Zr BIOMAGNESIUM ALLOYS

采用重力浇铸法制备了Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr(质量分数,%,x=0,1,2,3)4组合金,并对其进行了固溶+人工时效热处理(T6).利用XRD对铸态合金的物相进行分析,采用SEM观察合金的组织,采用拉伸试验机和显微硬度计测试合金的室温拉伸性能和显微硬度,采用失重法评价合金在模拟体液中的腐蚀速率,并对腐蚀形貌进行观察.结果表明,随着Gd部分取代Nd,铸态合金的组织先细化后又变粗,第二相含量逐渐减少,室温力学性能和耐蚀性能均提高.而对于T6态合金,强度和硬度均比不含Gd的合金要低,耐蚀性能则优于不含Gd的合金.

Magnesium and its alloys have been widely studied as biomaterials for over a decade due to their good biocompatibility, good bio-mechanical properties and biodegradation in human body. However, most of them are commercial magnesium alloys, which are not taken biocompatibility into account. Even though some novel magnesium alloys were developed recently, there are still no biodegradable magnesium alloys available for clinical application because of the rapid corrosion rate and localized corrosion mechanism. In order to develop new kindsof biodegradable magnesium alloys with excellent mechanical properties and corrosion resistance in simulated body fluid, four alloys with nominal composition Mg-（4-x）Nd-xGd-0.3Sr-0.2Zn-0.4Zr （mass fraction, %, x-=0, 1, 2, 3） were prepared by gravity casting on the basis of previous studied Mg-Nd-Zn-Zr alloys, and solution treatment ＋ artificial aging treatment （T6） was conducted on the as-cast alloys. The phases were identified using XRD, the mi- crostructure was observed with SEM, the tensile properties and microhardness were carried out using tensile test machine and microhardness tester, the corrosion rate of the alloys was evaluated in simulated body fluid by mass loss method, and corrosion morphology was observed by SEM. It was found that Mg41Nd5 phase was formed in grain boundaries when Gd addition was less than Nd, while Mg3Gd was formed when Gd addition was more than Nd. The microstructure was refined firstly but was coarsen finally, and the volume fraction of the second phase de- creased with increasing Gd addition due to relatively large solubility of Gd in Mg matrix than Nd. The mechanical properties at room temperature and corrosion resistance of the as-cast alloys at 37.5 ℃ were improved with Gd ad- dition. As for the T6 state alloys, the strength and microhardness of the alloys with Gd addition were lower than those of the alloy without Gd, which indicates that the precipitation strengthening effect of Gd is weaker than that of Nd. Nevertheless, the corrosion resistance of the alloys with Gd addition was better than the alloy without Gd un- der T6 condition. The four alloys both under as-cast and T6 conditions exhibit relatively uniform corrosion mode, which is a desired corrosion characterization for degradable biomaterial.