Mg-Gd-Y-Nd-Zr和MB8镁合金表面组织结构及其腐蚀行为

【作者】 刘俊；

【导师】 陈明安；

【作者基本信息】 中南大学 ， 材料加工工程， 2012， 硕士

【摘要】 基于原位腐蚀观察方法,采用光学显微镜(OM)、扫描电镜(SEM)和能谱分析(EDS)、盐水浸泡实验等手段研究了Mg-Gd-Y-Nd-Zr和MB8两种镁合金在盐溶液中的腐蚀行为,探讨了不同第二相在合金局部腐蚀中的作用机制；并运用等离子体离子注入Ti、N技术对两种镁合金进行表面改性处理,利用电子探针对注入后合金表面成分进行表征,综合运用动电位极化、析氢法及显微硬度等分析了等离子体离子注入Ti、N处理对两种镁合金表面性能的影响。Mg-Gd-Y-Nd-Zr合金腐蚀初期表现出典型的点蚀特征,富Gd和富Y粒子作为阴极相导致边缘基体相的优先溶解,富Zr粒子中的Mg和边缘α-Mg都优先发生腐蚀,并且腐蚀源的具体位置与第二相粒子和基体表面间的方位有关。在局部腐蚀过程中,具有更高稀土或锆含量的第二相微区表现出更好的耐蚀性能。此外,在第二相密集分布的区域,第二相粒子充当腐蚀屏障使得微区耐蚀性提高。MB8镁合金的腐蚀以丝状腐蚀和点蚀为特征。经过一定时间的诱导期,合金发生丝状腐蚀,并且腐蚀丝前端不断析出大量氢气泡。横截面上丝状腐蚀向四周扩展,而纵截面上腐蚀丝随第二相粒子的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。等离子体离子注入后两种镁合金的显微组织与表面形貌均未发生改变。Mg-Gd-Y-Nd-Zr注Ti和注N合金表面自腐蚀电位正移,腐蚀速率减小,且注N合金耐蚀性能更好；注Ti和注N改性处理使表层硬度相对于基体分别提高了36.8%和28.5%。MB8注Ti和注N合金在盐溶液中仍然发生丝状腐蚀,但腐蚀诱导期时间延长,抗Cl-的侵蚀能力增强,并且注入后合金丝状腐蚀扩展速率明显降低,注N合金的腐蚀速率最低；注Ti和注N改性处理使表层硬度相对于基体分别提高了26.0%和57.4%。更多还原

【Abstract】 Based on in-situ corrosion observation, the corrosion behaviors of Mg-Gd-Y-Nd-Zr and MB8magnesium alloys in3.5%NaCl solution, as well as the effect of various second phase particles on localized corrosion of both alloys, were investigated by optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and saline immersion test. Furthermore, surface modification of these two magnesium alloys was conducted by plasma immersion ion (Ti, N) implantation. Then, the chemical composition of alloys surface after ion implantation was characterized by electron probe micro-analysis (EPMA), and the influence of Ti, N implantation on the surface performance of both alloys was analyzed by means of dynamic potential polarization, hydrogen evolution technology and micro-hardness testing.As for Mg-Gd-Y-Nd-Zr alloy, pitting is the typical feature at the initial stage of corrosion. Gd-rich and Y-rich particles promoted corrosion of a-Mg as cathode of corrosion galvanic cell, while both Mg in Zr-rich particle and a-Mg close to Zr-rich phase corroded preferentially. Moreover, the exact location of corrosion was concerned with the orientation between second phase particle and the matrix. In the process of localized corrosion, the second phase with higher content of RE elements or Zr showed better corrosion resistant. Furthermore, the area distributed with intensive second phase particles exhibited better corrosion resistance, which was ascribed to the barrier effect derived from the interaction between particles.As for MB8magnesium alloy, filiform corrosion and pitting corrosion were the main corrosion forms. After an induction period, filiform corrosion occurred while there are a large number of hydrogen bubbles generated at the front end of the corrosion filament. Filiform corrosion grew in all directions to around in the cross section, while the corrosion filament extended as strips like the distribution of second phases in the vertical section. However, in the region without filiform corrosion, pitting occurred due to the galvanic effect of Mg matrix coupled with second phase particle.The surface morphology and microstructure of both magnesium alloys remained relatively unchanged after plasma ion implantation (PSII). For Mg-Gd-Y-Nd-Zr alloy after Ti, N plasma implantation respectively, the corrosion potential of surface shifted towards the anodic direction, and lower corrosion rate was obtained. Moreover, the N-implanted samples showed superior corrosion resistance than the Ti-implanted samples. The micro-hardness of modified layer of Ti-implanted and N-implanted Mg-Gd-Y-Nd-Zr alloy was enhanced by36.8%and28.5%, respectively. And with regard to MB8magnesium alloy, filiform corrosion still occurred in3.5%NaCl solution after Ti, N plasma implantation. But the differences were that the induction period was longer and the resistance of chloride ion attacks was advanced evidently. In addition, the growth rate of filiform corrosion was reduced after ion implantation, and a lower corrosion rate was obtained by N ion implantation. The micro-hardness of modified layer of Ti-implanted and N-implanted MB8alloy was also increased by26.0%and57.4%, respectively.更多还原