Influence Of Electrolyte Composition And PH On The Microstructure And Properties Of The Electrodeposited Fe-Zn Alloy

Stent implantation is one of the effective methods to solve the disease of vascular stenosis.For iron-based biodegradable stent materials,the main problem is its low degradation rate.Addition of Zn element is an alternative strategy to improve the degradation rate of iron-based materials.Due to the large difference in melting point between Fe and Zn,Fe-Zn alloy is difficult to be prepared by the traditional metallurgical method.Our group had prepared Fe-Zn alloy by electrodeposition technology,but the alloy had high O content,large internal stress and was liable to brittle fracture.Therefore,based on the original chloride salt plating system,a new Fe-Zn electrodeposition solution containing boronic acid?H₃BO₃?and malonic acid?C₃H₄O₄?additives was redesigned.In this new system,the effect of the concentration of ascorbic acid?C₆H₈O₆?,saccharin sodium?C₆H₄SO₂NNaCO·2H₂O?and sodium citrate?C₆H₅Na₃O₇·2H₂O?,and the solution pH on the composition,microstructure and mechanical properties of electrodeposited Fe-Zn alloy were investigated.At the same time,the internal stress of Fe-Zn alloy prepared with different C₆H₄SO₂NNaCO·2H₂O content was tested by nanoindentation.The basic solution with different C₆H₅Na₃O₇·2H₂O content and pH levels was electrochemically analyzed by cyclic voltammetry to understand the co-deposition mechanism of Fe²⁺and Zn²⁺.Finally,the corrosion characteristics of Fe-Zn alloy with different microstructures were tested by the polarization curve and static immersion methods in simulated body fluid?SBF?to investigate the relationship between the deposited structure and its degradation performance.The results showed that the content of oxygen impurity in the alloy can be controlled by adding 30 g/L boric acid and 5.203 g/L malonic acid into the system.As the contents of the boric acid and malonic acid increased,the oxygen content was further reduced.When the content of antioxidant C₆H₈O₆ and flexible agent C₆H₄SO₂NNaCO·2H₂O in the plating solution was 5 g/L and 1.9 g/L,the deposit quality was good,and the oxygen content and residual stress were low.Keeping the solution pH at 2.35,when adjusting the sodium citrate concentration less than 5.147 g/L,the deposited alloy had a columnar crystal structure with low hardness and a?211?preferred orientation.While When the sodium citrate concentration was higher than 5.147 g/L,the alloy was fine-grained with higher hardness and was liable to brittle fracture due to the large internal stress.When the content of C₆H₅Na₃O₇·2H₂O was4.412 g/L and the pH value was increased to 2.70,or the content of C₆H₅Na₃O₇·2H₂O was kept at 5.882 g/L and the pH value was increased to 2.20,the alloy microstructure changed from columnar grain to fine grain,in a similar way as observed by controlling C₆H₅Na₃O₇·2H₂O content from low to high.The cyclic voltammetry tests on the base solution containing different sodium citrate or with different pH values showed that,with the increase of sodium citrate,the deposition potential of Fe²⁺was negatively shifted to be closer to that of Zn²⁺,which was favorable for Fe-Zn co-deposition.The effect of solution pH on the metal ion deposition potential was mainly achieved by affecting the dissociation form or complexation strength of C₆H₅Na₃O₇·2H₂O.The results of dynamic potential polarization curves and static immersion tests in simulated body fluid showed that,with the refinement of grains and increase of the Zn and O contents in the deposited alloy,its self-corrosion potential decreased from–0.45 V to–0.52 V,and its degradation rate increased from 0.358 mg/?cm²·d?to 1.258mg/?cm²·d?.