pH对脉冲电镀锌–镍–锰合金的影响

Effect of pH on pulse electroplating of zinc–nickel–manganese alloy

在Q235钢表面脉冲电镀Zn–Ni–Mn合金,镀液组成和工艺条件为:ZnSO_4·7H_2O 43.1 g/L,MnSO_4·H2_O 59.2 g/L,NiSO_4·6H_2O26.3 g/L,Na_3C_6H_5O_7·2H_2O 176.5 g/L,NH_4Cl 30 g/L,H_3BO_3 30 g/L,十二烷基硫酸钠(SDS)0.1 g/L,p H 4.5~6.0,温度30°C,平均电流密度30 m A/cm^2,脉冲占空比20%,脉冲周期1 ms,时间20 min。研究了pH对合金镀层元素组成、沉积速率、表面形貌和耐蚀性的影响。结果表明,随p H增大,沉积速率减小;镀层中锰含量升高,锌、镍含量降低;耐蚀性先增强后减弱。p H为5.0时,所得Zn–Ni–Mn合金镀层平整致密,Zn、Ni和Mn的质量分数分别为85.71%、5.03%和9.26%,中性盐雾试验96 h的保护等级为5级。与Zn–Ni合金镀层(Ni质量分数为12.88%)相比,Zn–Ni–Mn合金镀层的腐蚀电位正移了85 mV,腐蚀电流密度低了约2个数量级,耐蚀性更优。

Zn-Ni-Mn alloy pulse electroplating was conducted on Q235 steel substrate. The bath composition and process conditions are as follows： ZnSO4·7H20 43.1 g/L, MnSO4·H20 59.2 g/L, NiSO4·6H20 26.3 g/L, NaaC6HsO7·2H20 176.5 g/L, NH4C130 g/L, HaBO3 30 g/L, sodium dodecyl sulfate （SDS） 0.1 g/L, pH 4.5-6.0, temperature 30 ℃, average current density 30 mA/cm2, pulse duty cycle 20%, pulse period 1 ms, and time 20 rain. The effect of pH on elemental composition, electrodeposition rate, surface morphology and corrosion resistance of Zn-Ni-Mn alloy coating was studied. The results showed that with the increasing of pH, the electrodeposition rate is decreased, Mn content in alloy coating is increased while the Zn and Ni contents are decreased, and the corrosion resistance of alloy coating become better firstly and then worse. The coating obtained at pH 5.0 is smooth and compact with Zn 85.7wt% , Ni 5.03wt% and Mn 9.26wt%, and its protection performance is classified as grade 5 after neutral salt spray test for 96 h. Compared to the Zn-Ni alloy coating containing 12.88wt% Ni, the Zn-Ni-Mn alloy coating has a better corrosion resistance as shown by a more positive corrosion potential （shifted positively by 85 mV） and a lower corrosion current density （reduced by about 2 orders of magnitude）.