Hou Fengyan, Gorthy Rukmini, Mardon Ian, Tang Da, Goode Chris
Cirrus Materials Science Ltd., 5B Target Court, Auckland 0627, New Zealand.
ACS Omega. 2022 Mar 2;7(10):8570-8580. doi: 10.1021/acsomega.1c06442. eCollection 2022 Mar 15.
Low-density metals such as Mg and Al (and their alloys) are of high interest for lightweight engineering applications in various industries. Moisture sensitivity, poor tribology, and corrosion susceptibility limit the direct application of these light metals. Plasma electrolytic oxidation (PEO) is extensively used to passivate light metals against corrosion and enhance their mechanical properties. PEO processes in current use are often energy-intensive and use toxic electrolytes. Incorporating composite characteristics to PEO-treated surfaces typically requires modification of electrolytes with nanoparticle addition. Some applications also need post-treatment of oxidized coatings to ensure functionality. We report a versatile, environmentally friendly PEO process that uses organo-silicate electrolytes enriched with nitrogen-containing solutions. The single-step process produces ∼6 μm thick, uniform, adherent, and porous oxide coatings on AZ80 and Al6061 surfaces in 15 min. We evaluated the influence and effectiveness of in situ nitridation by comparing the coating properties with those on alloys treated in PEO electrolytes without nitrogen-containing chemicals. The two sets of coatings were porous with multilayered basalt-like topographies and were composed of metal oxides and metal silicates. Alloys treated in nitrogen-containing electrolytes exhibited the presence of oxynitrides. The use of nitrogen-containing PEO electrolytes resulted in coatings with enhanced mechanical behavior. We found that the corrosion resistance of coatings prepared using low voltages in this study was comparable to the traditional PEO-treated coatings reported in the literature. Nitridation of the coatings, however, appears to have a slightly negative influence on the coatings' corrosion resistance. Our future work will focus on improving the corrosion resistance of the mechanically resilient, nitride-containing PEO-treated coatings.
镁和铝等低密度金属（及其合金）在各行业的轻量化工程应用中备受关注。湿度敏感性、较差的摩擦学性能和易腐蚀性限制了这些轻金属的直接应用。等离子体电解氧化（PEO）被广泛用于使轻金属钝化以防止腐蚀并增强其机械性能。目前使用的PEO工艺通常能耗高且使用有毒电解质。将复合特性引入PEO处理过的表面通常需要通过添加纳米颗粒来改性电解质。一些应用还需要对氧化涂层进行后处理以确保其功能性。我们报道了一种通用的、环境友好的PEO工艺，该工艺使用富含含氮溶液的有机硅酸盐电解质。该单步工艺在15分钟内在AZ80和Al6061表面上制备出约6μm厚、均匀、附着性好且多孔的氧化物涂层。我们通过将涂层性能与在不含含氮化学品的PEO电解质中处理的合金上的涂层性能进行比较，评估了原位氮化的影响和有效性。这两组涂层都是多孔的，具有多层玄武岩状形貌，由金属氧化物和金属硅酸盐组成。在含氮电解质中处理的合金显示出氮氧化物的存在。使用含氮PEO电解质导致涂层具有增强的机械性能。我们发现，在本研究中使用低电压制备的涂层的耐腐蚀性与文献中报道的传统PEO处理涂层相当。然而，涂层的氮化似乎对涂层的耐腐蚀性有轻微的负面影响。我们未来的工作将集中在提高机械弹性好的含氮PEO处理涂层的耐腐蚀性上。
