镁合金表面的锌系磷化及阴极电泳

Zinc phosphate film and cathodic electro-coat deposition on magnesium alloy

采用在磷化液中添加Ce(NO3)3及腐蚀抑制剂的方法,在镁合金表面制备了均匀致密的锌系磷化膜,在磷化膜上进行阴极电泳处理制备的涂层具有良好的附着力和耐蚀性.在磷化液中加入稀土添加剂可使锌系磷化膜致密无裂纹,磷化膜在阴极电泳和烘烤固化过程中的失重率较低.当磷化液中Ce(NO3)3的质量浓度为1.5 g/L时,磷化膜的组织最致密,电泳漆膜的附着力和耐蚀性也最好.在镁合金的锌系磷化膜上沉积20μm阴极电泳涂层,耐盐雾腐蚀时间可达720 h以上,沉积35μm阴极电泳涂层时,耐盐雾腐蚀时间可达1 000 h以上.试验结果表明,“稀土锌系磷化+低温阴极电泳”工艺适合于镁合金的表面防腐处理.

An uniform and fine zinc phosphate film on AZ91D magnesium alloy was prepared by using a phosphating bath containing Ce （ NO3 ） 3 and a corrosion inhibitor. The experimental results showed that the addition of Ce （NO3 ）3 in the phosphating bath made phosphate film finer and non-crack. Very dense phosphate coating was obtained from the phosphating bath containing 1.5 g/L Ce （ NO3 ） 3. Cathodic electro-paint was then coated on the phosphated magnesium alloy. The addition of Ce （NO3 ）3 alSO reduced the weight loss of phosphate coating during the electro-coating and drying processes. The cathodic electro-coat of 35μm thickness plus phosphate coating on the AZ91D magnesium alloy can bear 1 000 h salt fog test without corrosion. It is thus concluded that the zinc phosphate film ＋ cathodic electro-paint is an effective technique for protection of magnesium alloy.