挤压时效态MB8镁合金在盐水中的腐蚀行为

摘要

The corrosion characteristics and corrosion mechanism of aged extrude MB8 magnesium alloy immersed in saline solution were investigated by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X­ray spectrometry (EDS). The results show that filiform corrosion and pitting corrosion are the main corrosion forms for MB8 alloy. After an induction period, filiform corrosion occurs coupling with anodic Mg dissolution at the leading edge of the corrosion front and hydrogen evolution on a cathodically activated corroded region behind. The second phases show significant effect on the propagation of filiform corrosion. The filiform corrosion grows in all directions due to the dispersively distributed second phases in the cross section, while the corrosion filament extends like bands due to the second phases distributed in bands in the longitudinal section. In the region without filiform corrosion, pitting occurs due to the galvanic effect of Mg matrix coupled with second phase particles.%　　采用光学显微镜(OM)、扫描电镜(SEM)和能谱分析(EDS)等手段研究挤压时效态MB8镁合金在盐水浸泡条件下的腐蚀特征，并探讨合金的腐蚀机理。结果表明：合金以丝状腐蚀和点蚀这两种局部腐蚀为主要的腐蚀形式。合金经过一定时间的诱导期后发生丝状腐蚀，腐蚀前端的丝头处发生镁基体的阳极溶解，已发生腐蚀的丝尾处作为活性阴极发生析氢反应；第二相粒子对丝状腐蚀的扩展具有重要影响，横截面上丝状腐蚀随着弥散分布的第二相粒子向四周扩展，而纵截面上腐蚀丝随着第二相粒子的带状分布呈长条带状形貌特征；在丝状腐蚀还未扩展到的区域由于第二相粒子与基体之间的腐蚀微电偶作用导致基体发生阳极溶解，从而产生点蚀。