硼酸钠浓度对镁合金阳极化的影响

EFFECTS OF CONCENTRATION OF SODIUM BORATE ON ANODIZING FOR MAGNESIUM ALLOY

采用电压-时间曲线、全浸腐蚀实验、极化曲线法、X射线衍射法(XRD)、扫描电镜(SEM)、能量色散谱仪(EDS)和X射线光电子能谱法(XPS)等方法研究了AZ91D镁合金在含不同浓度四硼酸钠的阳极化溶液中的阳极氧化行为和膜层的成分、结构.结果表明:在文中给定工艺中,AZ91D镁合金的阳极化过程可分为3个阶段:电火花出现之前的致密层生成阶段;少量小电火花出现的多孔层生成阶段;出现较大电火花的多孔膜层稳定生长阶段.阳极氧化过程中,随着阳极氧化溶液Na2B4O7浓度的升高,出现电火花的时间延长,出现电火花时的电压值升高;膜层厚度增加,膜层上的孔径增大.阳极化膜层中主要含有Mg2+、O2-、Si4+和B3+,主要相结构为MgO、MgSiO3和Mg3B2O6.四硼酸钠浓度对阳极化膜的耐蚀性影响较大,当四硼酸钠浓度为160 g/L时,膜层耐蚀性能最好.

The anodizing of AZ91D Mg alloy in the solution of different concentration of Na2B4O7 has been investigated by ways of voltage - time curve, immersion corrosion experiment, polarization curve, XRD, SEM, EDS and XPS respectively. The results show that the film- forming course can be divided into three stages： formation of dense layer before sparking, formation of porous layer accompanied with a bit of small sparking, and porous layer stable growth along with bigger sparking. With increasing concentration of Na2B4O7 in the solution of the anodizing, the time and voltage of sparking formation increase, the aperture and thickness of anodic oxide film become bigger. The anodic oxidation film contains Mg^2＋, O^2-, Si^4＋ and B^3＋, which is composed mainly of MgO, MgSiO3 and Mg3B2O6. The concentration of Na2B4O7 plays great effect on corrosion resistance of the said film. The film has best corrosion resistance when the concentration of Na2B4O7 in the anodic solution is 160 g/L. Key words： magnesium alloy, anodizing, sodium borate