Formation and characterization of cerium conversion coatings on magnesium alloy

Chemical conversion treatment by rare earth metal salt solution was considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of magnesium alloys. In this study, cerium conversion coatings formed on AZ31 magnesium alloy were characterized and the formation mechanism was discussed. X-ray photoelectron spectroscopy （XPS） analysis showed that cerium conversion coating consisted of cerium hydroxides/oxides, in which both tetravalent cerium Ce（Ⅳ） and trivalent cerium Ce（Ⅲ） species co-existed. Cerium conversion coating was a two-layer structure. Atomic force microscopy （AFM） images revealed that the morphology of the inside layer was different from that of the outside one, which was responsible for the inherent adhesive weakness of the coating. Corrosion potential （Ecorr） measurements indicated that poor adhesion limited the improvement of the corrosion resistance of the coating. During the treating process, the increased pH value of the cerium salt solution led to the precipitation of cerium hydroxides/oxides. The formation kinetics of the coating followed a parabolic curve.     

AZ61镁合金轧制板材的腐蚀行为研究

采用动电位极化曲线和电化学阻抗谱方法研究了AZ61镁合金轧制板材的表面、侧面、截面在模拟海水中的腐蚀电化学行为,采用扫描电子显微镜对3个面的腐蚀形貌进行了观察。结果表明,AZ61镁合金轧制板材的表面、侧面、截面在模拟海水中的腐蚀均以孔蚀为主要特征;3个面腐蚀倾向由小到大的顺序为:表面<侧面<截面,耐蚀性能由优到劣的顺序为:表面>侧面>截面;造成3个面腐蚀行为及耐蚀性能不同的根本原因是轧制处理引起的材料微观组织的各向异性。     

NaCl介质中AZ31镁合金的动态电化学腐蚀行为研究

通过自腐蚀电位、电化学阻抗谱以及介质pH值测量研究AZ31镁合金在3.5%NaCl介质中的动态腐蚀行为,用光学显微镜、扫描电子显微镜对腐蚀形貌进行观察,讨论AZ31镁合金的腐蚀机理。结果表明:AZ31镁合金在3.5%NaCl介质中的耐蚀性能较差;腐蚀从局部区域开始,初期以点蚀为主要特征;由于Mg(OH)2等腐蚀产物结构松散、分布不均匀,不能有效阻止腐蚀的发展,致使镁合金表面在较短时间内被严重破坏。     

钼酸盐对镁合金在模拟冷却水中腐蚀的抑制作用

采用Tafel极化曲线、电化学阻抗谱方法研究了钼酸钠对AZ40镁合金在模拟冷却水中腐蚀的抑制作用,利用扫描电子显微镜(SEM)和能量色散谱(EDS)表征了试样的形貌及组成。结果表明,钼酸钠对镁合金在模拟冷却水中的腐蚀具有一定的抑制作用,钼酸钠浓度为1000 μg·g^-1时缓蚀效果最佳。钼酸钠的加入减弱了腐蚀性Cl^-在试样/介质界面的吸附,同时参与镁合金试样在模拟冷却水中表面膜的生成,使表面膜变得致密,从而较好地抑制镁合金的腐蚀;其缓蚀作用属于阳极抑制型缓蚀作用。