几种电弧喷涂金属涂层在3.5%NaCl溶液中的腐蚀行为

Corrosion Behaviors of Several Kinds of Arc Sprayed Metal Coatings in 3.5%NaCl Solution

目的研究喷涂涂层的组织与耐蚀性。方法利用超音速电弧喷涂技术在20#钢表面分别制备了Zn-Al-Mg、Zn-Al和Zn涂层。采用扫描电镜观察Zn-Al-Mg涂层的组织形貌,用X射线衍射仪分析涂层的相结构。通过电化学试验,分析比较三种涂层在3.5%Na Cl溶液中的腐蚀行为。利用灰度法分析金相照片的灰度值,捕捉孔隙的位置和大小,并确定涂层孔隙率。采用万能拉伸试验机进行拉伸试验,测定涂层的结合强度。结果 Zn-Al-Mg伪合金涂层的组织致密,与基体结合良好,孔隙率为3.8%,结合强度为3.7 MPa,厚度约为300μm。由于存在耐蚀性极强的尖晶石氧化物,涂层的耐蚀性有所提高。Zn-Al-Mg涂层的腐蚀电流密度为1.249μA/cm2,低于Zn-Al涂层和纯Zn涂层;电化学反应电阻率Rt达到1356?·cm2,约为纯Zn涂层的2倍。结论 Zn-Al-Mg涂层组织致密,与基体结合良好,耐蚀性能优于Zn-Al涂层和纯Zn涂层。该涂层中存在耐蚀性极强的尖晶石结构氧化物,在腐蚀过程中,孔隙被腐蚀产物堵塞,有效阻止了腐蚀反应的进一步进行,自封闭特性起到了积极作用。

Objective To study the microstructure and anti-corrosion properties of several thermal sprayed coatings. Methods Zn-Al-Mg, Zn-Al and Zn coatings were prepared on 20# steel substrate by supersonic arc spraying. SEM was used to analyze the surface morphologies of the Zn-Al-Mg coatings, and X-ray diffraction was employed in examining the structure and phases of the coatings. Electrochemical experiments were conducted to compare the corrosion behavior of the Zn-Al-Mg coating with the pure Zn coating and Zn-Al coating in 3.5wt% NaCl solution. Gray method was used to analyze the gray value of the metallograph, capture the position and size of pores and determine the porosity of the coating. Tensile test was carried out by universal tensile testing machine to determine the bonding strength of the coating. Results The Zn-Al-Mg coating was compact and well bound with the substrate. The porosity of Zn-Al-Mg coatings was 3.8%, the bonding strength 3.7 MPa and the thick- ness 300μm. The highly corrosion-resistant spinel oxides in the coating were useful for improving the corrosion resistance. The Zn-Al-Mg coating showed low corrosion current density at 1.249μA/cm^2, which was lower than Zn-Al coating and pure Zn coating. The electrochemical resistivity of Zn-Al-Mg coating was 1356 Ω·cm^2, which was 2 times of the pure Zn coating. Conclusion The Zn-Al-Mg coating is compact and well binds with the substrate. It has higher corrosion resistance than the pure Zn coating and Zn-AI coating. The spinel oxides contained in the coating is strongly corrosion-resistant. During corrosion, micro pores in the coating are blocked by corrosion products, which effectively prevents further corrosion reaction. The self-sealing characteristic plays a positive role.