Effect of immersion time on corrosion behavior of Mg-2Nd-0.5Zn-0.4Zr-1Y alloy in simulated body fluid

The purpose of this paper is to investigate the corrosion behavior of biodegradable Mg-2Nd-0.5Zn-0.4Zr-1Y alloy immersed in simulated body fluid (SBF) with different immersion times. The corrosion behavior of the materials in SBF was determined by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), electrochemical test and immersion tests. The results indicated that the Mg-2Nd-0.5Zn-0.4Zr-1Y alloy was comprised of α-Mg matrix, Mg₁₂Nd, Mg₂₄Y₅ and MgZn phases and the average grain size was about 60 μm. The corrosion started from the weak region between the eutectic phase/Zr-rich region and α-Mg matrix. The corrosion products were mainly composed of Mg(OH)₂, CaCO₃ and Ca₅(PO₄)₃(OH). The corrosion form of Mg-2Nd-0.5Zn-0.4Zr-1Y alloy was mainly pitting corrosion. With the prolongation of immersion time, the pitting began to grow and eventually developed into filiform corrosion. The degradation behavior of the alloy in SBF included main four stages: (a) stage 1: galvanic corrosion; (b) stage 2: pitting corrosion; (c) stage 3: accumulated hydrogen bursting the corrosion layer and (d) stage 4: lateral and longitudinal growth of pitting. (paper)