硅酸钠浓度对镁合金阳极化的影响

Effects of concentration of sodium silicate on anodizing for magnesium alloys

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硅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:在本文给定工艺中,AZ91D镁合金的阳极化过程可分为三个阶段: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Na2S iO3浓度的升高,出现电火花的时间缩短,出现电火花时的电压值降低;阳极化膜的颗粒度变大甚至膜层出现裂纹,膜层厚度基本不变.阳极化膜层中主要含有Mg2+、O2-、S i4+和B3+,主要相结构为MgO、MgS iO3和Mg3B2O6.硅酸钠浓度对阳极化膜的耐蚀性影响较大,当硅酸钠浓度为120g/L时,膜层耐蚀性能最好.

The anodizing of AZ91 D Mg alloys in the solution of different concentration of Na2SiO3 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 anodizing process can be divided into three stages：formation of dense film before sparking, formation of porous film accompanied with a bit of small spark, and porous film stable growth along with bigger spark. The time and voltage of spark formation decrease with increasing of Na2SiO3 concentration in the anodizing solution, while the granularity of anodic oxidation film becomes bigger and cracks occur even on the film, whereas the thickness of the film is approximately unchanged. The anodic oxidation film contains Mg^2 ＋ , O^2 - , Si^4＋ and B^3＋ , which is composed mainly of MgO, MgSiO3 and Mg3 B2O6. The concentration of Na2SiO3 plays great effect on corrosion resistance of the film. The film has best corrosion resistance when the concentration of Na2SiO3 in the anodizing solution is 120g/L.