The electrochemical properties of the Zn-Ni plating baths and the structure andperformance of the obtained deposits were investigated.The results show that the nickel content of theobtained deposits is incereased with decreasing of Zn ̄(2+)/Ni ̄(2+) ratio in the baths and with increasing ofcathodic current density;The cathode current efficiency is increased with increasing of Zn [Ⅱ]content in the bath and with decreasing of cathodic current density.The ZN-11 additive used is thereaction product of heterocyclic compound and polyamines with epichlorohydrin,it has a higheradsorptivity on Hg-electrede at potential between -0.16~-1.68 V (vs. Hg/HgO,1 mol·L ̄(-1)KOH). It is found that zinc and nickel are codeposited anomalously due to the inhibition effect ofZN-11 additive on nickel deposition and the catalytic effect of the used complexing agent on zincdeposition.The results of X-ray diffraction analysis show that zinc-nickel alloy deposits with nickel content>10.6 wt%possess γ phase alone with preferred orientation of (330)+(411) of complex cubic.The zinc-nickel alloy deposits are bright with hard ness 220 to 270 Hv.The corrcoion experimence in5% NaCl solution shows that zinc-nickel alloy deposit with nickel content about 13 wt% behavesmaximum protection to steel.The zinc-nickel alloy deposit with nickel content<10.6 wt% behavesanodic protection to steel,and with nickel content in the range of 10.6~14.5 wt% behaves mixedprotection of anodic and cathdic.On the base of the conclusions obtained above,a new technology of alkaline bright zinc-nickelalloy plating has been suggested.The optimum bath composition is found to be 4 to 10 g·L ̄(-1) of ZnO,70 to 120 g·L ̄(-1) of NaOH,4 to 15 mL·L ̄(-1) Ni complexing compound, 0.05 to 0.3 g·L ̄(-1) ofaromatic aldehyde and 0.5 to 3 mL·L ̄(-1) ZN-11 additive,Zn ̄(2+)/Ni ̄(2+) ratio(wt.)is 4 to 10. Thebath operates in 15~65℃ and with cathodic current density 0.2~10 A·dm ̄(-2).The industrialpractice shows that,the suggested bath is stable, and the deposits obtained are bright,corrosionresistive and the nickel contents are controllable conveniently in the range of 9~2 0 percent.


Alkaline, Plating, Electredeposition, Zinc-nickel alloy

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