AZ91D镁合金电镀前处理工艺研究

为了得到适用于AZ91D镁合金的电镀前处理工艺,提高镀层与镁合金基体的结合力及镁合金的耐蚀性,采用正交试验方法研究了酸洗液中不同组分用量和酸洗时间对试样表面状态的影响,利用场发射扫描电子显微镜和X射线能谱仪分析了活化时间和浸锌时间对镁合金浸锌后表面形貌及微观成分,采用称重法考察了浸锌不同时段镁合金的质量变化,通过热震试验和中性盐雾试验研究了浸锌时间对后续镀层性能的影响。结果表明,AZ91D镁合金电镀的最佳前处理工艺为:先采用250 g/LCrO₃+20 mL/L浓硝酸溶液在室温下酸洗30 s,接着用200 mL/L H₃PO₄+100 g/L NH_4HF_2溶液在室温下活化60 s,再用以ZnSO₄·7H₂O和K₄P₂O₇·3H_2O为主的焦磷酸盐体系浸锌液浸渍150 s。

Study on pretreatment of AZ91D magnesium alloy before electroplating

In order to get a suitable pretreatment process for AZ91 D magnesium alloy before electroplating and improve the adhesion of a coating to magnesium substrate and its corrosion resistance,the effects of the bath composition and time for pickling on the surface state of magnesium alloy were studied by orthogonal test.The effects of activation time and zinc dipping time on the morphology and elemental composition of magnesium alloy surface after zinc dipping were analyzed using field-emission scanning electron microscope and X-ray energy-dispersive spectrometer.The mass variation of magnesium alloy after zinc dipping for different time was examined by weighing method,and the effect of zinc dipping time on the properties of subsequently electroplated coating was studied through thermal shock test and neutral salt spray test.The results showed that the optimal pretreatment process for magnesium alloy before electroplating were as follows:(a)pickling in 250 g/L CrO₃+20 mL/L concentrated nitric acid solution at room temperature for 30 s;(b)activating in 200 mL/L H₃PO₄+100 g/L NH4 HF2 solution at room temperature for 60 s secondly;and(c)zinc dipping in a pyrophosphate bath comprising ZnSO4·7 H2 O and K₄P₂O₇·3H₂O for 150 s.