高强铝合金循环盐雾加速腐蚀行为与机理研究

Accelerated Corrosion Behavior and Mechanism of High-strength Aluminum Alloy by Cyclic Salt-spray Test

目的研究2A12铝合金在室内模拟及强化腐蚀环境下的腐蚀行为与机理,建立快速评价铝合金腐蚀寿命的加速试验方法。方法利用设计的室内加速腐蚀环境试验谱,通过实施模拟海洋大气环境效应的循环盐雾加速腐蚀试验,采用外观检查、SEM、XRD及电化学测试等手段,表征了暴露不同周期样品的腐蚀失重、腐蚀形貌、腐蚀产物成分、极化曲线及阻抗谱等腐蚀性能,分析和归纳了铝合金的加速腐蚀行为与机理。结果随着腐蚀暴露时间的延长,2A12样品腐蚀失重动力学符合幂函数规律且关系式为D=1.662t^(1.061),腐蚀速率呈现短暂降低后迅速增加再逐步下降的变化趋势;腐蚀形貌从腐蚀产物均匀分布到逐渐变得集中和突出表面,后期局部出现脱落,腐蚀产物成分均以Al_(2)O_(3)为主,与腐蚀机理分析的化学反应过程基本一致。极化曲线Tafel拟合结果表明,腐蚀电位整体呈现稳定并缓慢减小的变化趋势(‒0.509~‒0.392 V),腐蚀电流密度呈现先波动增加后减小的变化趋势(0.271~0.882 A/cm^(2));阻抗谱均在高频区表现为1个容抗弧,且容抗弧半径呈现“减小—增大—减小至稳定”的变化趋势;阻抗谱等效电路拟合结果表明,腐蚀产物膜电阻Rf呈现“增大—减小—增大—减小”的变化趋势,极化电阻Rp整体呈现先减小后增大的变化趋势。结论循环盐雾环境对高强铝合金腐蚀的加速效果显著,从腐蚀动力学、腐蚀产物形貌及成分、电化学特性等角度,能够比较全面地表征铝合金的加速腐蚀行为与机理,为进一步研究加速腐蚀试验的模拟性和相关性提供条件。

Although natural environmental tests were one realistic and accurate method for studying and evaluating the equipment corrosion life,but it had to be cost so many time and money for high-reliability and long-life products,which could not be accepted and carried out generally.Therefore,the artificial accelerated corrosion tests were developed to overcome the huge cost problem of time and money,such as cycle infiltration test,salt-spray test and so on.The simulation and relation characteristics to contrast with the outdoor results were key factors for designing and evaluating the accelerated testing methods,which could be considered as follows,(a)alternating wet and dry process of specimen surface;(b)corrosion kinetics laws;(c)morphology,composition and structure of corrosion products;(d)electrochemical properties and mechanisms of corrosion process.In this article,to study the corrosion behavior and mechanism of 2A12 aluminum alloy under the interior simulated and strengthened corrosion environment,and establish the accelerated test methods for evaluating the corrosion life of aluminum alloy.Utilizing the designed accelerated corrosion environment testing spectrum,accelerated corrosion tests by cyclic salt-spraying were performed to simulate marine atmospheric environment effect.By means of testing methods of scanning electron microscope,X ray diffraction,electrochemical and so on,the corrosion performance of specimens after different exposure time,such as corrosion weight loss,corrosion morphology,corrosion products composition,polarization curves and impedance spectroscopy were characterized.Accelerated corrosion behavior and mechanism of aluminum alloy were analyzed and concluded.With the corrosion exposure time extension,2A12 specimen corrosion weight loss conformed to power function law with the expression as D=1.662t^(1.061),and corrosion rate appeared the variation trend of reducing briefly,then increasing rapidly and then declining gradually.Corrosion morphology appeared that corrosion products distributed from uniform to concentrated and outstanding,and fallen off from the specimen surface in anaphase.The chemical constituents of corrosion products mainly contained Al_(2)O_(3),which was almost the same with chemical process by corrosion mechanism analysis.The results of polarization curve fitted by Tafel was indicated that corrosion potential appeared a steady and slowly decreasing trend(‒0.509-‒0.392 V),corrosion current density appeared a tendency for fluctuation to increase and then decrease(0.271-0.882 A/cm2);Electrochemical impedance spectroscopy performanced for one capacitive loop in high-frequency zone,and the radius of capacitive loops presented a trend of decrease,increase and decrease to stable.The results of EIS fitted by equivalent circuit was indicated that corrosion product film resistance appeared a trend of increase,decrease,increase and decrease,polarization resistance appeared a trend of a tendency to decrease and then increase.The interior accelerated corrosion testing was established to simulate and study the marine atmospheric environment corrosion of high-strength aluminum alloy.Experimental results showed that the corrosion accelerated effect was significant for high-strength aluminum alloy by cyclic salt-spray test,the corrosion behavior and mechanism of aluminum alloy could be characterized more comprehensively from the point of view of corrosion kinetics,corrosion morphologies,corrosion products constitutes and electrochemical characteristics,which could provide conditions for investigating the simulation and correlation of accelerated corrosion test.