锡酸盐转化前处理对镁合金化学镀镍镀层的影响

Effects of Stannate Chemical Conversion Pretreatment on Electroless Nickel Plating of Magnesium Alloy

目的利用锡酸盐转化膜中间层避免化学镀镍镀层与金属基体的直接接触,降低其产生原电池腐蚀的趋势,提高镁合金化学镀镍层的耐蚀性及稳定性。方法采用锡酸盐化学转化膜技术在AZ31镁合金表面制备锡酸盐转化膜层,然后通过直接化学镀镍技术在该膜层上沉积Ni-P镀层。利用SEM、EDS、浸泡析氢、电化学测试等手段,研究了复合镀层的显微结构、相组成、耐蚀性。结果锡酸盐转化膜由细小均匀的球形颗粒堆积而成,颗粒之间存在空隙,为直接化学镀镍时镍磷的初始沉积提供了可能。化学转化膜表面沉积的化学镀镍层均匀致密,形成典型的胞状结构。基体-化学转化膜-化学镀Ni-P合金层三者之间的结合良好,保证了复合镀层优良的耐蚀性能。结论化学镀Ni-P层能够在不经过钯活化处理的条件下直接在锡酸盐转化膜上沉积,锡酸盐转化膜中间层避免了Ni-P阴极性镀层与阳极性镁基体的直接接触,降低了Ni-P镀层局部缺陷对整体防护效果的影响,提高了镀层的耐蚀性及耐久性。

The work aims to adopt middle layer of stannate conversion film to avoid the direct contact between electroless nickel plating coating and metal matrix, so as to reduce the trend of the galvanic corrosion and improve the corrosion resistance and stability of electroless nickel plating coating of magnesium alloy. The stannate chemical conversion film(SCC) was prepared on AZ31 magnesium alloy by stannate chemical conversion film technology and then the Ni-P coating was deposited on SCC layer by direct electroless nickel plating technology. The microstructure, phase composition and corrosion resistance of composite coatings were studied by SEM, EDS, Hydrogen Evolution Reaction test, electrochemical test, etc. The SCC film was composed of small uniform spherical particles, and there was a gap between the particles, which provided a possibility for the initial deposition of Ni-P alloy during the direct electroless nickel plating process. The electroless Ni-P coating deposited on the surface of the SCC film was uniform and dense with a typical cellular structure. The combination of matrix-chemical conversion film-electroless Ni-P alloy layer was good, which ensured the excellent corrosion resistance of the composite coating. The electroless Plating Ni-P coating can be deposited directly on the SCC film without palladium-activated treatment. The middle layer of the SCC film avoids the direct contact between the Ni-P alloy cathodic coating and the anodic magnesium matrix, reduces the influence of the local micro-defects of the Ni-P coating on the overall protection effect and improves the corrosion resistance and durability of the coating.