锌铝镁钢板表面黑点缺陷原因分析与控制

针对厚镀层锌铝镁产品出现的黑点缺陷,使用光学显微镜、激光共聚焦显微镜、扫描电镜、能谱、微区XRD对缺陷进行分析。结果表明,黑点位置富含共晶相,这是由于局部缺少凸出的先析出富锌相、共晶组织对光反射的特点以及镁化合物在空气中的氧化,导致其目视为黑色。使用中性盐雾试验对黑点样品及正常样品进行测试,并对其耐蚀机理进行了分析。结合现场工艺,通过优化冷却制度,增加镀层在凝固时的过冷度,抑制共晶相的局部富集,使该问题得到解决。

Analysis and control of black spot defects on surface of zinc-aluminum-magnesium steel sheet

Aiming at the black spot defects in thick layer of zinc-aluminum-magnesium products, the defects were analyzed by optical microscope, laser confocal microscope, scanning electron microscope, energy spectrum and micro-area XRD. The results show that the black spots are rich in the eutectic phase, which is due to local lack of protruding zinc rich phase precipitated first, light reflection characteristics of eutectic structure and magnesium compounds oxidized in the air. A neutral salt spray test was used to test the black spot samples and normal samples, and the corrosion resistance mechanism was analyzed. Combined with field process, by optimizing cooling process, supercooling degree of coating during solidification is increased and the local enrichment of eutectic phase is suppressed, so that the problem is solved.