AZ91D镁合金新型均一化前处理化学镀Ni-P合金的研究

Electroless Ni-P Plating on AZ91D Magnesium Alloy with a New Homogenization Pretreatment

采用新型环保均一化前处理工艺在AZ91D镁合金表面制备了化学镀Ni-P镀层。利用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)研究了镀层的微观形貌、成分和相结构。通过电化学方法和热震实验评价了镀层的电化学腐蚀行为和结合力。结果表明,经前处理后基体表面的β相(Mg17Al12)被选择性去除,表面组织均一化,从而得到了均匀致密的浸Zn层。Ni-P镀层均匀致密,P含量为7.0%,具有非晶结构。与AZ91D基体相比,Ni-P镀层的自腐蚀电位正移了1.136V,自腐蚀电流密度降低了两个数量级,表明镀层具有优良的耐腐蚀性能。热震实验表明镀层与基体之间结合良好。

A new environment-friendly homogenization pretreatment process was adopted for the electroless nickel plating on AZ91D magnesium alloy. Then, the morphologies, chemical composition and microstructure of the pretreated layer and the formed Ni-P coating were studied using scanning electronic microscopy(SEM), energy-dispersive X-ray spectroscopy(EDS) and X-ray diffraction spectroscopy(XRD). It was indicated that a dense Zn film formed on the substrate surface after the homogenization pretreatment, due to the selective removal of β phase during the processing.As the result, the subsequently formed Ni-P coating was uniform, compact and defect-free with P content around 7.0%, which was characterized as an amorphous matter by XRD. Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests revealed that the Ni-P coating could significantly improve the corrosion resistance of AZ91D magnesium alloy with an obvious positive shifting of corrosion potential by 1.136 V and a dramatic reduce of corrosion current density by two orders of magnitude. Furthermore the obtained Ni-P coating showed excellent adhesion to AZ91D substrate.