镁合金在镀液中的腐蚀行为

Corrosion behavior of magnesium alloy in electroless nickel plating bath

通过腐蚀实验和阳极极化曲线研究了硫酸镍主盐配制的化学镀镍液成分和温度对 AZ91D镁合金的腐蚀行为的影响, 比较了碱式碳酸镍主盐和硫酸镍主盐两种镀镍液的腐蚀性以及施镀后的镀层质量。结果表明: 硫酸镍镀液的腐蚀性比碱式碳酸镍镀液大, 在低温下, 镁合金在硫酸镍镀液中表面的氟化镁膜不致密, 镀液对基材的腐蚀性高; 而在高温下, Mg2+与F-的反应性增强, 氟化反应完全, 形成的氟化镁钝化膜致密性高, 可保护镁合金基体免遭镀液的腐蚀。在施镀温度下, 镀液中F-的缓蚀作用, 可使SO2-4 离子对镁合金的腐蚀速率大大降低。

Through the corrosion experiments and the anodic polarization curves, the effects of composition of plating bath and temperature on corrosion behavior of magnesium alloy AZ91D in electroless nickel plating bath composed of nickel sulfate were studied. The corrosion behavior of AZ91D in the baths with nickel sulfate or with basic nickel carbonate and the quality of the coating obtained in both baths, were compared. The results show that corrosion of magnesium alloy in the bath with nickel sulfate is suffered more seriously than that in the bath with basic nickel carbonate. At low temperature, MgF_2 film on the surface of magnesium alloy in the bath with nickel sulfate is not compact and the coupons of magnesium alloy have a big corrosion rate, but at high temperature, the reactive of Mg^(2+) and F^- increases, and MgF_2 film on the surface of magnesium alloy becomes more compact. So MgF_2 film can prevent magnesium alloy from further corrosion. At the plating temperature beyond 70℃, the corrosion rate of magnesium alloy caused by SO^(2-)_4 in the bath is reduced in presence of F^-.