什么是丝状腐蚀？
丝状腐蚀是一种特殊形式的腐蚀，发生在随机分布的线（如细丝）的薄涂层下。丝状腐蚀又称薄膜下腐蚀、丝状腐蚀或蜗杆腐蚀。
当暴露在温暖潮湿的大气空气中时，丝状腐蚀发生在涂有薄有机膜（通常为0.05至0.1毫米（2至4密耳）厚）的金属表面上。丝状腐蚀总是从涂层缺陷开始，例如划痕和薄弱点，例如胡须，切割边缘和孔洞。
如何检测丝状腐蚀？
丝状腐蚀可以在不使用显微镜的情况下目视识别。在涂层钢，铝和镁上观察到它具有锡，金，银，磷酸盐，搪瓷或漆的薄涂层。
以美国为例，识别丝状腐蚀耐性的标准测试是ASTM D 2803，“金属有机涂层耐丝状腐蚀性测试指南”。According to该测试，将涂层金属试样划刻到裸露的金属上，并在盐雾气氛下进行长达24小时，在蒸馏水中冲洗，然后湿放在25°C（77°F）和85%RH的封闭柜中。暴露时间通常从100到1000小时不等。测试结果显示涂层材料是否发生丝状腐蚀。
如何防止丝状腐蚀？
通常，通过将相对湿度降低到60%以下，可以防止丝状腐蚀。不幸的是，直接降低飞机和汽车等移动物体的湿度是不切实际的。然而，通过添加干燥风扇和加湿器，或通过在塑料包装中添加干燥剂，可以很容易地控制长期储存设施中保存的组件的湿度水平。
与单涂层体系相比，涂有两层环氧涂层体系和两层聚氨酯涂料的部件能够更好地抵抗丝状腐蚀。
当钢基体镀锌时，丝状腐蚀的机会降低。富锌底漆以及铬化和磷化底漆，以及坚韧、缓慢固化的聚氨酯和环氧树脂中间涂层，降低了钢基材上的丝状敏感性。铬酸锌底漆、铬酸阳极氧化、铬酸盐或铬酸盐-磷酸转化涂层在铝合金中提供了不同程度的丝状腐蚀缓解
Multi-layer coatings on metal surfaces slow the diffusion of moisture and have fewer penetrations and defect sites than single-coat paint systems. The multi-layer coating system resists penetration from mechanical abrasion and has fewer hills and valleys. Thicker coatings achieved through layer buildup and slower curing exhibit better resistance to filiform corrosion through reduced oxygen and moisture penetration, less solvent entrapment and fewer initiation sites. Powder coating systems are also beneficial because they are hot-melt, resulting in a tough coating with better moisture resistance. Smooth, well-prepared primed metal surfaces generally hold up better than rougher surfaces.
Steel, aluminum and magnesium are all chemically reactive. Their alloys contain intermetallic compounds that disperse, precipitate and agglomerate during hot rolling and annealing. Although these alloys generally have improved mechanical properties, recent studies have shown that their inhomogeneity (mixing) and the presence of surface-active layers increase their susceptibility to filiform corrosion.
