SECM对7075铝合金在NaCl溶液中的电化学腐蚀行为研究
发布时间：2018-11-22 14:12
【摘要】：铝及铝合金具有密度低、导电导热性好等优点,工业应用广泛。本文采用7075铝合金为研究材料,该材料是高速发展的航天航空产业以及船舶行业新型铝材。然而,沿海地区的飞机与船舰的服役环境复杂多变,海水中氯离子的存在是对金属材料的一大威胁,因此本文围绕7075铝合金在海洋环境中的腐蚀行为机理进行研究,结果如下:通过研究盐度对7075铝合金耐腐蚀性能的影响,获得该合金的腐蚀机理,研究结果表明:盐度增加致使Cl-对金属基体破坏加剧,合金表面逐渐出现微小孔洞,腐蚀电位正移,弥散指数降低,电极表面粗糙度增加,耐腐蚀性能下降。NaCl溶液中存在强活化作用的Cl-,7075铝合金腐蚀产物Al(OH)3的OH-逐渐被Cl-取代,合金表面氧化膜不断损坏,新的腐蚀产物AlCl3形成。在0.6 mol/LNaCl溶液中,室温环境,通过HCl与NaOH调节溶液p H值,研究7075铝合金在不同pH值条件下的耐腐蚀性能,研究结果表明:pH3~7,电荷传递电阻升高,电荷传递受阻,耐腐蚀性能增大。pH9~11,电极表面氧化膜稳定性降低,阻挡层溶解过程加快,腐蚀速度从0.0914 mm/a增加到2.1222mm/a,腐蚀加剧。强酸溶液中,电化学阻抗谱中感抗弧明显,存在不均匀点蚀。pH=7、9时,电化学阻抗谱中只出现1个容抗弧,为铝合金基体溶解过程。pH=11时,7075铝合金电化学腐蚀行为存在两个过程:阻挡层生成附着过程和阻挡层溶解反应过程。在扫描电镜(SEM)的基础上运用新型探针扫描技术扫描电化学显微镜(SECM)观测7075铝合金在0.6 mol/LNaCl溶液中浸泡腐蚀的表面形貌,研究结果表明:浸泡初期7075铝合金以点腐蚀为主,浸泡时间延长,金属基体逐渐溶解,溶液Al3+浓度增大,合金表面出现细小坑点,坑点分布稀疏,表面层状结构消失。在0.6 mol/LNaCl溶液中,7075铝合金中ZnAl相和ZnAlMg相腐蚀电位较高,与基体形成腐蚀微电解池,作阴极,腐蚀电位较低的铝基体作阳极,导致ZnAl相和ZnAlMg相周围的铝阳极溶解。
[Abstract]:Aluminum and aluminum alloys have the advantages of low density, good conductivity and thermal conductivity, so they are widely used in industry. In this paper, 7075 aluminum alloy is used as the research material, which is a new type of aluminum material in aerospace industry and ship industry. However, the service environment of aircraft and ships in coastal areas is complex and changeable, and the presence of chlorine ions in sea water is a great threat to metal materials. Therefore, the corrosion mechanism of 7075 aluminum alloy in marine environment is studied in this paper. The results are as follows: by studying the effect of salinity on corrosion resistance of 7075 aluminum alloy, the corrosion mechanism of 7075 aluminum alloy is obtained. The corrosion potential shifted positively, the dispersion index decreased, the surface roughness of the electrode increased, and the corrosion resistance decreased. The OH- of Al (OH) 3, a corrosion product of Cl-,7075 aluminum alloy with strong activation in NaCl solution, was gradually replaced by Cl-. The oxide film on the surface of the alloy is continuously damaged, and a new corrosion product, AlCl3, is formed. The corrosion resistance of 7075 aluminum alloy under different pH values was studied by adjusting pH value of 7075 aluminum alloy in 0. 6 mol/LNaCl solution at room temperature by HCl and NaOH. The results showed that the charge transfer resistance of pH3~7, was increased and the charge transfer was blocked. The stability of the oxide film on the surface of pH9~11, electrode is decreased, the dissolution process of the barrier layer is accelerated, and the corrosion rate is increased from 0.0914 mm/a to 2.122 mm / a. In the strong acid solution, the inductive arc is obvious in the electrochemical impedance spectrum, and there is inhomogeneous pitting corrosion. At pH=7, 9, there is only one capacitive arc in the electrochemical impedance spectrum, which is the dissolution process of aluminum alloy matrix. PH= 11:00, The electrochemical corrosion behavior of 7075 aluminum alloy has two processes: the formation of barrier layer adhesion process and the barrier layer dissolution reaction process. On the basis of scanning electron microscope (SEM), scanning electrochemical microscope (SECM) was used to observe the surface morphology of 7075 aluminum alloy immersed in 0.6 mol/LNaCl solution by scanning electrochemical microscope (SECM). The results show that the corrosion of 7075 aluminum alloy is mainly pitting corrosion at the beginning of soaking, the immersion time is prolonged, the metal matrix dissolves gradually, the concentration of Al3 in the solution increases, the surface of the alloy appears small pits, the distribution of the pits is sparse, and the layered structure of the surface disappears. In 0. 6 mol/LNaCl solution, the corrosion potential of ZnAl phase and ZnAlMg phase in 7075 aluminum alloy is higher. The corrosion microelectrolysis cell is formed with the substrate as cathode, and the aluminum substrate with lower corrosion potential is used as anode, which leads to the dissolution of aluminum anode around ZnAl phase and ZnAlMg phase.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178
本文编号：2349601
[Abstract]:Aluminum and aluminum alloys have the advantages of low density, good conductivity and thermal conductivity, so they are widely used in industry. In this paper, 7075 aluminum alloy is used as the research material, which is a new type of aluminum material in aerospace industry and ship industry. However, the service environment of aircraft and ships in coastal areas is complex and changeable, and the presence of chlorine ions in sea water is a great threat to metal materials. Therefore, the corrosion mechanism of 7075 aluminum alloy in marine environment is studied in this paper. The results are as follows: by studying the effect of salinity on corrosion resistance of 7075 aluminum alloy, the corrosion mechanism of 7075 aluminum alloy is obtained. The corrosion potential shifted positively, the dispersion index decreased, the surface roughness of the electrode increased, and the corrosion resistance decreased. The OH- of Al (OH) 3, a corrosion product of Cl-,7075 aluminum alloy with strong activation in NaCl solution, was gradually replaced by Cl-. The oxide film on the surface of the alloy is continuously damaged, and a new corrosion product, AlCl3, is formed. The corrosion resistance of 7075 aluminum alloy under different pH values was studied by adjusting pH value of 7075 aluminum alloy in 0. 6 mol/LNaCl solution at room temperature by HCl and NaOH. The results showed that the charge transfer resistance of pH3~7, was increased and the charge transfer was blocked. The stability of the oxide film on the surface of pH9~11, electrode is decreased, the dissolution process of the barrier layer is accelerated, and the corrosion rate is increased from 0.0914 mm/a to 2.122 mm / a. In the strong acid solution, the inductive arc is obvious in the electrochemical impedance spectrum, and there is inhomogeneous pitting corrosion. At pH=7, 9, there is only one capacitive arc in the electrochemical impedance spectrum, which is the dissolution process of aluminum alloy matrix. PH= 11:00, The electrochemical corrosion behavior of 7075 aluminum alloy has two processes: the formation of barrier layer adhesion process and the barrier layer dissolution reaction process. On the basis of scanning electron microscope (SEM), scanning electrochemical microscope (SECM) was used to observe the surface morphology of 7075 aluminum alloy immersed in 0.6 mol/LNaCl solution by scanning electrochemical microscope (SECM). The results show that the corrosion of 7075 aluminum alloy is mainly pitting corrosion at the beginning of soaking, the immersion time is prolonged, the metal matrix dissolves gradually, the concentration of Al3 in the solution increases, the surface of the alloy appears small pits, the distribution of the pits is sparse, and the layered structure of the surface disappears. In 0. 6 mol/LNaCl solution, the corrosion potential of ZnAl phase and ZnAlMg phase in 7075 aluminum alloy is higher. The corrosion microelectrolysis cell is formed with the substrate as cathode, and the aluminum substrate with lower corrosion potential is used as anode, which leads to the dissolution of aluminum anode around ZnAl phase and ZnAlMg phase.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178
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