Microstructure and corrosion resistance of as cast Mg-Nd-Gd-Sr-Zn-Zr alloys for biomedical applications

Mg-(4-x)Nd-xGd- 0.3Sr-0.2Zn-0.4Zr (wt-%, x=0, 1, 2 and 3) alloys were prepared by gravity casting. Microstructure was analysed by X-ray diffraction, optical microscopy and scanning electron microscopy respectively. The alpha-Mg and Mg41Nd5 phases existed in the as cast alloys with 4% and 3% Nd addition, while the new Mg3Gd was found in the alloys with 3% Gd addition. The volume fraction of the second phase reduced with increasing Gd addition and the microstructure was refined by the Gd addition. The corrosion resistance of the alloys was evaluated by mass loss, hydrogen evolution and Tafel polarisation tests. The results showed that the corrosion rate of the alloys decreased with increasing Gd addition even though the corrosion rates of the alloys obtained by different methods showed different values. Moreover, the corrosion morphologies of the alloys were uniform.