镁合金化学镀中预处理氟化镁膜的特征与作用

对镁合金的表面前处理工艺进行研究,探讨氟化镁在化学镀层中的存在形式及作用。结果表明：酸浸使镁合金表面形成一层氧化物膜;活化过程生成的氟化镁不具备反应活性,对镁合金基体有保护作用,使之免于受镀液的过度腐蚀;对化学镀层断口进行SEM元素分布分析显示氟化镁层集中存在于镁合金基体与Ni-P镀层之间;但过度活化会导致化学镀层孔隙率升高,以3.5%NaCl溶液为介质的动电位极化测试表明,过度活化会导致化学镀层耐蚀性下降。

Effects and characteristics of MgF2 during electroless nickel plating of magnesium alloys

Pretreatment of magnesium alloy surface was studied. Effects of MgF2 in Ni-P coatings were emphatically discussed. The results show that a magnesium oxide layer is formed after acid etching, and the potential differences of different phases of magnesium alloys are reduced due to the presence of oxide layer. MgF2 layer is formed after activation which can protect magnesium substrate from corrosion of plating bath. The elemental distribution of cross section of Ni-P coating was investigated by scanning electron microscopy. The MgF2 layer exists between the magnesium alloy substrate and the Ni-P coating. Excessive activation can raise the porosity of Ni-P coating, and the potentiodynamic polarization indicates that excessive activation can lead to deterioration of corrosion resistance of the Ni-P coating.