dc.description.abstract | In this study, the micro-anode guided electroplating method was used to fabricate the Zn-Cu alloy microstructure. The electroplating system uses glass -tube coated platinum wire with a diameter of 125 μm as the anode, and PVC-coated copper wire with a diameter of 0.643 mm as the cathode, and contains copper sulfate, zinc sulfate, sodium citrate and sodium sulfate as auxiliary electrolytes in bath.It is expected to produce a biodegradable Zinc-rich Zn-Cu alloy microstructure. The research goal is to use Scanning Electron Microscope (SEM) to explore the effect of changing the parameters on the microstructure surface morphology in the original plating bath in the following order: 1. Add different concentrations of sodium sulfate (0.15 M, 0.30 M and 0.45 M ) 2. Change the pH value of the plating bath from 4.9 to 6.5 3. Add 1000ppm polyethylene glycol to improve the microstructure surface morphology as the optimized target. It was found that 0.15M sodium sulfate and plating bath acid and alkali were added and adjust the pH value to 6.5 to obtain the best surface morphology.
Fix the above conditions as the best conditions to obtain Zinc-rich Zn-Cu alloy as the goal, first reduce the concentration of copper sulfate in the plating bath and then increase the concentration of zinc sulfate, by increasing the ratio of zinc to copper [Zn2+/Cu2+] to analysis surface morphology (SEM), chemical composition(Energy-dispersive X-ray spectroscopy, EDS) mapping and line scan and the effect on crystal structure (X-ray diffractometer, XRD) of microstructure.Through cyclic voltammetry (cyclic voltammetry, CV )to analyze the reduction mechanism of Cu2+ and Zn2+ in the plating bath.
The results show that electroplating after adding 0.15 M sodium sulfate can increase the nucleation density to improve the microstructure surface morphology .Adjusting the pH value to 6.5 with ammonia can significantly change the fraction of the chelate compound in the plating bath. When Cu2CitH4- is substituted for Cu2CitH3-, the amount of copper reduction during plating will be greatly reduced. The microstructure morphology is improved. The addition of polyethylene glycol made the microstructure thinner, the surface morphology of the microstructure turned rough.
When the [Zn2+/Cu2+] reaches 50.00 and 66.67, the zinc content of the microstructure reaches 81± 2 at.% and 85± 1 at. %, and the EDS line scan and mapping results of the cross section show uniform distribution of composition.Observed by optical microscope (Optical Microscope, OM), cross-section of structure is dense if [Zn2+/Cu2+] higher than 33.33 .Higher [Zn2+/Cu2+] in bath leads less cracks and holes. Crystal structure analysis shows that when the [Zn2+/Cu2+] is 6.67 and 11.11, the corresponding structures are β CuZn phase + γ Cu5Zn8 phase and γ Cu5Zn8 phase + ε CuZn5 phase. When [Zn2+/Cu2+] is 33.33, 50.00 and 66.67, the corresponding structures are all ε CuZn5 phases.
The mechanical properties were measured with nanoindenter. When the [Zn2+/Cu2+] is 50.00 and 66.67, the hardness of microstructure can reach 2.91 ± 0.25 GPa and 2.86 ± 0.29 GPa, and the Young′s modulus is 47.21 ± 5. 37 GPa and 50.25 ± 2.27 GPa; the corrosion resistance is measured by electrochemical analysis, and the measured corrosion current density is 0.31 mA/cm2 and 0.45 mA/cm2. | en_US |