Effects of pulse frequency and current density on microstructure and properties of biodegradable Fe-Zn alloy

Novel Fe-Zn alloys were prepared by pulse electrodeposition to solve the low corrosion rate of iron-based biodegradable materials for vascular stents. The effects of frequency and current density on the composition, microstructure, hardness, and corrosion characteristics of alloys were studied. The results manifested that all the Fe-Zn alloys prepared under the conditions studied here were supersaturated solid solutions. The composition and microstructure of the alloys exhibited a strong dependence on the frequency and current density. When the pulse frequency increased from 50 to 1000 Hz, the zinc content in alloy decreased from 7.2 wt.% to 2.1 wt.% with the grain coarsening. Besides, the low-zinc alloy had low hardness due to its slight lattice distortion and grain boundary strengthening. When the peak current density increased from 10 to 13 A/dm2, the oxygen content in alloy increased from 0.1 wt.% to 1.4 wt.%, and the microstructure changed from coarse columnar grain to fine nanocrystalline with the hardness of the alloy increasing sharply. Electrochemical and immersion tests in simulated body fluid (SBF) demonstrated that the corrosion rates of Fe-Zn alloys were higher than that of pure iron. The alloy containing 4.6% Zn was more prone to corrosion (0.267 mm·y−1 in immersion test) than other alloys while keeping relatively low hardness. The intrinsic causes of zinc to the accelerated corrosion of electrodeposited ferroalloy should be attributed to the decrease of corrosion potential, the increase of local corrosion, and the weak protection barrier caused by the corrosion products.