Corrosion behavior of a novel Mg-13Li-X alloy with different grain sizes by rapid solidification rate

As degradable biomaterials,the higher degradation rate of Mg-Li alloys in the physiological environment is the main challenge for the implant applications.In order to try and overcome this limitation,the present work was dedicated to studying the corrosion behavior of a novel Mg-13Li-X alloy fabricated by a rapid solidification process(RSP).The special Mg-13Li-X alloy was immersed in Hank’s balanced salt solution(HBSS),and the influence of immersion time on corrosion rate was analyzed.X-ray diffraction(XRD)and scanning electron microscopy(SEM),complemented with electrochemical techniques such as potentiodynamic polarization curves and electrochemical impedance spectroscopy,were applied.Microstructural characterization indicates that the mean grain sizes of RSP Mg-13Li-X alloy are 4.2,8.2 and 12.7μm with the solidification rate decreasing.By contrast,the conventional as-cast Mg-13Li-X alloy has an average grain size of about 150μm.The results of electrochemical test indicate that the sample with 4.2μm in grain size has the most positive corrosion potential(E_(corr))of−1.354 V and the minimum corrosion current(I_(corr))of 5.830×10^(−7)A·cm^(−2)after immersion for 2 h in HBSS.Therefore,the finest grain size can improve the polarization resistance of the alloy,reduce its corrosion current density and increase its corrosion resistance.However,because the weak layer of the corrosion product which consists of Mg(OH)_(2) does not afford strong protection,the corrosion resistance becomes worse after immersion for longer periods.