不同Gd含量AZ31镁合金腐蚀行为的研究

发布时间：2018-03-11 18:16

本文选题：AZ31镁合金　切入点：稀土Gd　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：在资源和能源即将匮乏,环境污染不断加重的今天,镁合金由于其优异的性能而得到了汽车行业、电子行业以及航空航天等行业的关注。但由于镁合金较差的耐蚀性,使其在工业中的应用受到了一定程度的限制。截至目前,虽然相关科研人员已对镁合金的腐蚀与防护进行了大量的研究,也取得了一定的成果,但由于对镁合金腐蚀机制的认识还不够完善,致使其仍不能实现工业化的大规模应用。本实验先在氩气的保护下于井式电阻炉中精炼制备出不同Gd含量的4组AZ31镁合金,而后利用OM,SEM,EDS以及XRD等检测手段分析Gd的加入对合金相组成以及微观组织的影响。在室温和3.5%的中性Na_2SO_4溶液中进行AZ31-xGd合金失重实验和电化学实验的同时,对其在太原大气环境中进行大气腐蚀实验;待确定最佳稀土含量后,又研究了AZ31-4.12Gd合金在不同pH的Na_2SO_4溶液中的腐蚀行为。通过SEM观察合金表面腐蚀产物去除前、后的形貌变化,用XRD分析腐蚀产物的相组成,研究Gd的添加对AZ31-xGd合金晶粒尺寸、第二相以及腐蚀速率的影响,并在此基础上,进一步分析了AZ31-4.12Gd合金在不同pH的Na_2SO_4溶液中的腐蚀行为,这为大幅度的提高镁合金的耐蚀性以及扩大镁合金的应用范围提供了基础的实验数据。本研究的结论如下:1.静态失重实验中,随Gd的增加,合金的腐蚀速率会明显降低,尤其当Gd的添加量为4.12%时,合金的腐蚀速率最小,仅为0.675mg/(cm2.d-1),相比于未添加稀土Gd时的4.572mg/(cm2.d-1)下降了约85%。2.电化学实验中,Gd的加入在提高基体自腐蚀电位的同时,降低了腐蚀过程中的电流密度。尤其当Gd含量为4.12%时,自腐蚀电位会由-1.6987V提高至-1.5966V,同时腐蚀电流密度则会由6.7372×10-4mA降低至2.9315×10-4mA。此外,阻抗谱的实验结果与极化曲线的实验结果有很好的一致性。3.Gd的添加,一方面细化了晶粒,降低了基体相与析出相之间的微电偶腐蚀;另一方面,改变了基体中第二相的数量与分布,起到了降低腐蚀电流密度的作用。同时,新形成的Al2Gd相和固溶在基体中的Gd原子使基体表面形成了一层类似镀层一样的耐蚀保护膜,从而提高了合金的耐蚀性。4.AZ31-4.12Gd合金浸入不同pH的Na_2SO_4溶液中后,随溶液pH值的增加,合金的腐蚀速率会不断减小。此外,pH值的增加提高了基体的自腐蚀电位,降低了腐蚀过程中的电流密度,尤其当溶液的pH值为12时,合金的自腐蚀电位最大,同时腐蚀电流密度最小。这样的结果表明合金的耐蚀性会随溶液pH值的增大而增大。
[Abstract]:With the scarcity of resources and energy sources and the worsening of environmental pollution, magnesium alloys have attracted much attention from the automotive industry, electronics industry and aerospace industry because of their excellent performance. However, due to their poor corrosion resistance, The application of magnesium alloy in industry has been limited to a certain extent. Up to now, although the relevant researchers have done a lot of research on the corrosion and protection of magnesium alloy, some achievements have been made. However, the understanding of the corrosion mechanism of magnesium alloy is not perfect, so it can not realize the large-scale application of industrialization. In this experiment, four groups of AZ31 magnesium alloys with different Gd content were prepared by refining in well resistance furnace under the protection of argon gas. Then the influence of Gd addition on the phase composition and microstructure of the alloy was analyzed by OMS-SEMS-EDS and XRD. The weightlessness and electrochemical experiments of AZ31-xGd alloy were carried out at room temperature and in neutral Na_2SO_4 solution of 3.5% at the same time. After determining the optimum rare earth content, the corrosion behavior of AZ31-4.12Gd alloy in Na_2SO_4 solution with different pH was studied. The morphology changes before and after the removal of corrosion products on the surface of the alloy were observed by SEM. The phase composition of corrosion products was analyzed by XRD, and the effect of Gd addition on grain size, second phase and corrosion rate of AZ31-xGd alloy was studied. On the basis of this, the corrosion behavior of AZ31-4.12Gd alloy in different pH Na_2SO_4 solution was further analyzed. This provides the basic experimental data for greatly improving the corrosion resistance of magnesium alloys and expanding the scope of application of magnesium alloys. The conclusions of this study are as follows: 1. In static weightlessness experiments, the corrosion rate of the alloys decreases obviously with the increase of Gd. In particular, the corrosion rate of the alloy was the lowest when the addition of Gd was 4.12. The corrosion rate of the alloy was only 0.675 mg / m 路cm ~ (-2) 路d ~ (-1), which decreased by 850.2. the addition of Gd in the electrochemical experiment increased the self-corrosion potential of the substrate, compared with 4.572 mg / r 路cm ~ (-2) 路d ~ (-1) without adding rare earth Gd. When Gd content is 4.12, the corrosion potential increases from -1.6987V to -1.5966V, and the corrosion current density decreases from 6.7372 脳 10-4mA to 2.9315 脳 10-4mA. in addition, when Gd content is 4.12, the corrosion potential increases from -1.6987V to -1.5966V, and the corrosion current density decreases from 6.7372 脳 10-4mA to 2.9315 脳 10-4mA. The experimental results of impedance spectroscopy are in good agreement with the experimental results of polarization curves. 3. The addition of Gd not only refines the grain size and reduces the microgalvanic corrosion between the matrix phase and the precipitated phase, but also reduces the microgalvanic corrosion between the matrix phase and the precipitated phase. The number and distribution of the second phase in the substrate were changed, and the corrosion current density was decreased. Meanwhile, the newly formed Al2Gd phase and the Gd atom dissolved in the substrate resulted in the formation of a layer of corrosion resistant protective film similar to the coating on the substrate surface. The corrosion resistance of the alloy. 4.AZ31-4.12Gd alloy immersed in Na_2SO_4 solution with different pH value, the corrosion rate of the alloy will decrease with the increase of pH value of the solution, in addition, the increase of pH value increases the self-corrosion potential of the matrix. The corrosion current density is decreased, especially when the pH value of the solution is 12:00, the corrosion potential of the alloy is maximum and the corrosion current density is the lowest. The results show that the corrosion resistance of the alloy increases with the increase of the pH value of the solution.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178

【参考文献】