Effects of additives on zinc electrodeposition from alkaline zincate solution

The effects of additives on the surface and cross-sectional morphologies of zinc deposits on iron substrate from alkalinezincate solution were characterized by scanning electron microscope(SEM).The cathodic reaction mechanisms under variousconcentrations of additives were investigated using cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)techniques.It is found that with increasing the additive A content in the bath solution,the nucleation overpotential(NOP)value isobviously increased and the inhibition effect is strengthened.This may be mainly due to the adsorption of additive A on the cathodicelectrode surface,which can cover the active sites and block the discharge reduction.The results of EIS analysis indicate that therate-determining step of zinc electrodeposition process is changed from mixed control step into electrochemical reduction step in thepresence of additive A.However,any quantity of additive B has little effect on the NOP value and the inhibition effect is not obvious.Furthermore,addition of additive A and additive B at the same time displays the strongest inhibition effect and shows a strongsynergism because of their co-adsorption on the cathodic electrode surface.

Performance tests of multi-metal zincate solutions with zinc sulfate and zinc oxide

Morphology of zinc alloy layer,from zincate solution with zinc sulfate and zinc oxide respectively,together with the consequent deposit was observed with SEM and back scattering electron image.EDS was applied to analyze the components of zinc alloy layer and the interface of high-Si aluminum alloy substrate-zinc alloy-deposit.Besides,the surface morphology of the zincated aluminum alloy after immersing in 3.5% NaCl solution for 7 d,is observed and the corrosion rate was calculate.Finally,tension test is conducted to quantify the adhesion between high-Si aluminum cast substrate and the deposit.The results show that,the zinc oxide contained zincating solution with sodium potassium tartrate and sodium citrate is a better one in multi-metal zincating solutions.The zinc alloy layer from this one gets stable performance,perfect adhesion with deposit,and good corrosion resistance.

Effect of non-cyanide zincation process parameters on the microstructure of the zincation layer on A356 alloys

The effects of non-cyanide zincation process parameters on the microstructure of the zincation layer on A356 alloy were investigated by scanning electronic microscope.With the increasing of zincation time,the zinc grain size and the number density increase gradually,and the zinc grains adhere each other.The zinc grain obtained in the double-dipping process is finer,compacter and more homogeneous than that obtained in the single-dipping process.With the increasing of the zincation temperature,the morphology of zinc grains changes from spherical shape to flake-like shape.However,higher zincation temperature results in the flaking off of the zincation layer from the matrix.The optimized zincation temperature is 20-30 ℃.The quality of the zincation layer obtained in a low concentration,non-cyanide and multi-element zincation solutions is much better than these obtained in conventional high concentration zincation solution,dilute zincation solutions or a dilute zincation solution containing nickel.In addition,the matrix alloy and the pre-treatment also have significant influence on the morphology of the zincation layer.