2A12铝合金在EXCO溶液中腐蚀损伤形貌演化分析

目的探索2A12铝合金在EXCO溶液中腐蚀损伤形貌的演化规律。方法开展实验室内2A12铝合金的加速腐蚀实验。为实现表面粗糙度与腐蚀损伤相关性的定量研究,首先采用3D扫描成像仪对实验样品进行扫描,取得样品微观几何特征,实现表面粗糙度值的数字化定量表征。观察样品在EXCO溶液中腐蚀损伤的发生发展过程、腐蚀形貌的演化过程,测量腐蚀样品蚀坑深度,并分析表面粗糙度对样品腐蚀损伤的影响。结果当腐蚀时间不超过6 h时,2A12铝合金样品在EXCO溶液中的腐蚀类型主要为点蚀,随着时间的延长,将向全面腐蚀发展。粗糙度值高的试件表面有打磨时形成的较深表面纹理,这些纹理制约了点蚀坑的扩展,使蚀坑沿纹理的方向发展,有演化为微裂纹的可能性,蚀坑边界的不规则处也会萌生微裂纹。粗糙度值较小的样品,腐蚀损伤也较小,但粗糙度对腐蚀损伤的影响随时间的延长而减弱。结论常温下,2A12铝合金在EXCO溶液中首先发生点蚀,由于蚀坑向四周扩展的速度快于深度方向,使腐蚀类型从点蚀向全面腐蚀演变。表面粗糙度对2A12铝合金样品腐蚀损伤形貌的演化有重要影响,表面微观几何特征通过制约蚀坑扩展方向的方式来改变样品的腐蚀行为,并造成腐蚀损伤的明显差异。随着腐蚀时间的延长,材料逐渐失去其原有表面微观几何特征,表面粗糙度对腐蚀行为的影响下降。

Corrosion Damage Morphology Evolution of 2A12 Aluminum Alloy in EXCO Solution

Objective To explore the evolution of corrosion damage morphology of 2A12 aluminum alloy in EXCO solution. Methods Accelerated corrosion experiments of 2A12 aluminum alloy were carried out in laboratory. To quantitatively study the correlation between surface roughness and corrosion damage, a 3D scanning imaging instrument was used to scan the specimens to obtain the micro-geometric characteristics of them and have digital quantitative characterization of surface roughness. The occurrence and development of corrosion damage and the evolution of corrosion morphology in EXCO corrosion solution were observed. The pits depth of the specimens was measured and the effect of surface roughness on corrosion damage was analyzed. Results It was found that when the corrosion time did not exceed 6h, the corrosion type of 2A12 aluminum alloy specimens in EXCO solution was mainly pitting corrosion, which would develop toward general corrosion with the extension of time. There were some deep textures formed by grinding on the surface of specimen with high roughness value. These textures restricted the expansion of pit, and made the pit develop along the direction of the texture, which may evolve into micro cracks. Micro crack may also occur at the irregular boundary of pit. Specimens with lower surface roughness had less corrosion damage, but the effect of roughness on corrosion damage diminished over time. Conclusion At room temperature, 2A12 aluminum alloy firstly has pitting in EXCO solution, and the corrosion type evolves from pitting to general corrosion due to faster expansion of the pits to periphery than to depth. Surface roughness plays an important role in the evolution of corrosion damage morphology of 2A12 aluminum alloy specimens. Micro-geometric characteristics of the surface change the corrosion behavior of the specimens and cause obvious differences in corrosion damage by restricting the propagation direction of corrosion pits. With the extension of corrosion time, the material gradually loses its original surface micro-geometric characteristics, and the influence of surface roughness on corrosion behavior decreases.