镁合金等离子体电解氧化电解液中添加剂的相互作用

研究背景

镁合金等离子体电解氧化制备的膜层具有硬度高、耐磨性好、结合力强等优点。然而，由于该膜层主要由氧化镁组成，且存在多孔、微裂纹等缺陷，对材料腐蚀保护效果较差。通过向电解液中加入超细颗粒、有机添加剂等，可以在膜层中引入化学性质更为稳定的物相、减少膜层较大微孔数量和消除微裂纹等缺陷，从而提高膜层耐蚀性。但是，电解液中加入多种添加剂，属于多因素影响的范畴，目前已有研究多采用单因素法，并且未曾考虑所加添加剂之间的相互作用对膜层微观结构和耐蚀性能的影响。

近日，来自兰州理工大学的马颖教授、安凌云博士等人，基于正交实验并纳入交互项的试验设计理念，研究了等离子体电解氧化电解液中三种添加剂（TiC颗粒、分散剂PEG6000和阴离子表面活性剂SDS）分别对制备膜层的微观结构和耐蚀性的影响，以及三者之间存在的相互作用。研究发现，PEG6000、SDS和TiC颗粒三种添加剂对膜层耐蚀性的影响不同，其中TiC颗粒的影响最小，PEG6000的影响最大，SDS次之。当电解液中含有TiC颗粒时，可加入分散剂PEG6000和阴离子表面活性剂SDS，利用其交互作用防止TiC颗粒的团聚，增加其表面负电荷量，不仅提高了TiC颗粒的迁移率和沉积均匀性，而且使TiC更容易沉积到放电通道中，提高膜层致密性。此外，较小粒径的TiC颗粒，向阳极迁移也更为容易。因此，同时添加较小粒径TiC颗粒（0.05µm）、分散剂PEG6000和SDS时，利用其交互作用，制备的膜层腐蚀电流密度最低，为4.4×10-⁷A/cm²，膜层耐蚀性最好。本研究的实验设计采用多因素综合作用的分析模式，并且获得定性和定量的数据，为进一步寻找优化结果确定了方向、加快了收敛速度。表1 三种添加剂对镁合金耐蚀性影响的正交试验表格

该文章发表在《Journal of Magnesium and Alloys》2020年第八卷第2期：

[1] L. An, Y. Ma, L. Sun, Z. Wang, S. Wang, Investigation of mutual effects among additives in electrolyte for plasma electrolytic oxidation on magnesium alloys, Journal of Magnesium and Alloys 8(2) (2020) 523-536.

中文摘要

在有、无添加剂的碱性硅酸盐电解液中对AZ91D镁合金进行等离子体电解氧化处理，基于正交实验设计，研究添加剂TiC粒径、分散剂PEG6000和阴离子表面活性剂SDS三者间的相互作用。通过EPMA和EDS检测膜层中TiC的含量及分布状况，采用TT260数字式涡流测厚仪、XRD、SEM和电化学测试对膜层的厚度、物相组成、微观结构和耐蚀性能进行了研究。结果表明，本研究的实验设计是探究添加剂之间相互作用的关键所在。各添加剂及其之间的交互作用均会显著影响膜层中的TiC含量和膜层的耐蚀性。小粒径的TiC更易向阳极移动，且PEG6000和SDS间的交互作用通过有效防止小粒径TiC絮凝和增加其表面负电荷量，提高了TiC的迁移速率、沉积的均匀性以及TiC进入放电通道的几率，从而提高了膜层中优质物相TiC的含量和膜层的致密性。因此，当小粒径TiC、PEG6000和SDS三者都被添加到电解液中时，能很大程度地改善膜层的耐蚀性能。

Abstract

Plasma electrolytic oxidation (PEO) coatings were prepared on AZ91D magnesium alloys in alkaline silicate-based electrolyte with and without additives. The mutual effects among additives including TiC particles, dispersant polyethylene glycol 6000 (PEG6000) and anionic surfactant sodium dodecyl sulfate (SDS) were studied based on orthogonal experiment. The content and distribution of TiC deposited in the coatings were measured by EPMA and EDS. The thicknesses, phase compositions, microstructures and corrosion resistances of the coatings were examined by using TT260 eddy current thickness gage, XRD, SEM and electrochemical test, respectively. The results show that the experiment design of this study is the key to study the mutual effects among these additives. Each additive and their interactions all remarkably influence TiC content and corrosion resistance of the coatings. Smaller size TiC is much easier to migrate towards the anode, and the interaction between PEG6000 and SDS both effectively prevents its agglomeration and increases the number of its negative surface charges, which further increase the migration rate and the deposited uniformity of TiC and make TiC have more opportunity to deposit in the discharge channel. Thus, when smaller size TiC, PEG6000 and SDS are all added into the electrolyte, they could improve the anti-corrosion property of the coating to the largest extent attributed to higher TiC content and the densest microstructure of the coating.

来源：  JMACCMg