MICROSTRUCTURE, MECHANICAL AND CORROSION PROPERTIES OF Mg-(4-x)Nd-xGd-Sr-Zn-Zr BIOMAGNESIUM ALLOYS
ZHANG Xiaobo1,2(), XUE Yajun1,2, WANG Zhangzhong1,2, HE Xiancong1,2, WANG Qiang3
1 School of Materials Engineering, Nanjing Institute of Technology, Nanjing 211167 2 Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing 211167 3 Jiangsu Konsung Equipment Co., Ltd, Danyang 212300
Cite this article:
ZHANG Xiaobo, XUE Yajun, WANG Zhangzhong, HE Xiancong, WANG Qiang. MICROSTRUCTURE, MECHANICAL AND CORROSION PROPERTIES OF Mg-(4-x)Nd-xGd-Sr-Zn-Zr BIOMAGNESIUM ALLOYS. Acta Metall Sin, 2014, 50(8): 979-988.
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 kinds of 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 microstructure 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 decreased 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 addition. 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 under 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.
Fund: Supported by National Natural Science Foundation of China (No.51301089), Natural Science Foundation of Jiangsu Province (No.BK20130745), Natural Science Foundation of Higher Education Institutions of Jiangsu Province (No.13KJB430014), Innovative Foundation Project of Nanjing Institute of Technology (No.CKJA201201) and Qing Lan Project of Jiangsu Province
Table 1 Parameters of T6 heat treatment for Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys
Fig.1 XRD spectra of the as-cast Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys
Fig.2 SEM images of the as-cast Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys
Fig.3 Eutectic microstructure of the as-cast alloy 2 (a) and its EDS result corresponding to the rectangle area in Fig.3a (b)
Fig.4 SEM images of the T6 state Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys
(a) x=0 (b) x=1 (c) x=2 (d) x=3
Fig.5 SEM images (a, d) and the EDS results (b, c, e) for alloy 2 (a, b, c) and alloy 3 (d, e) (Figs.5b and c correspond to the EDS analysis of positions A and B in Fig.5a, respectively; Fig.5e corresponds to the EDS analysis of rectangle area in Fig.5d)
Fig.6 Yield strength (a), ultimate tensile strength (b), elongation (c) and microhardness (d) of Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys
Fig.7 Corrosion rates of Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys immersed in simulate body fluid (SBF) for 120 h
Fig.8 Surface morphologies of the as-cast Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys immersed in SBF for 120 h after removing corrosion products
Fig.9 Surface morphology of the as-cast alloy 2 immersed in SBF for 120 h after removing corrosion products (a) and the EDS result of dendrite in the grain boundary (b)
Fig.10 Surface morphologies of the T6 state Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr alloys immersed in SBF for 120 h after removing corrosion products
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