热镀铝锌板黑线缺陷原因分析

Analysis of Black Line Defects in Hot-dip Al-Zn Sheets

为了查找薄规格热镀铝锌板黑线缺陷产生原因,采用ZEISS Merlin Compact场发射扫描电镜及其附带的OXFORD X-max N型能谱仪等分析技术对热镀铝锌钢板黑线缺陷表面、截面以及腐蚀去掉镀层后的钢铁基板表面进行了微观形貌观察和化学成分分析。结果表明:热镀铝锌钢板上表面黑线缺陷是由于钢铁基板划伤致使钝化膜较厚所致;热镀铝锌钢板下表面黑线缺陷是由于下表面镀层发生凹陷微变形致使钝化膜较厚所致。热镀铝锌钢板表面划伤以及镀层凹陷造成与周围其他位置对光的反射不同,形成了视觉上的黑线缺陷。

In order to identify the causes of black line defects in thin specification hot-dip Al-Zn sheets,a ZEISS Merlin Compact field emission scanning electron microscope(SEM)and an attached OXFORD X-max N type energy spectrometer were utilized to analyze the surface and cross-section of black line defects in hot-dip Al-Zn steel plates,as well as the microstructure observation and chemical composition of the steel substrate surface after corrosion and removal of the coating.Analysis was also conducted on the steel substrate surface after the coating had been removed by corrosion.Results showed that the black line defects on the upper surface of the hot-dip Al-Zn steel sheet were caused by a thicker pas-sive film due to scratches on the steel substrate.On the lower surface of the hot-dip Al-Zn sheet,the black line defects were attributed to a thicker passive film resulting from concave micro-deformations of the lower surface coating.Scratches on the surface and depressions of the coating of the Al-Zn steel sheet were found to cause different reflections of light from the rest of the surrounding area,forming a visually perceived black line defect.