机械镀锌层外观、结合强度、钢基体

1)机械镀锌层外观呈灰色半光亮色，在特征部位(如螺纹、凹槽部位等)镀层呈现非光亮色。镀层覆盖完整，表面不存在起皮、折皱、夹杂、漏镀等缺陷。机械镀锌层在工件的边角、凹槽部位镀层!厚度相差更大。强化时延长时间、添加锡盐可提高镀层的平整度和光亮性。采用片状锌粉机械镀锌可提高镀层的外观质量。锌铝、锌镍、锌-稀土等复合镀层的外观质量优于机械镀锌层。

2)机械镀锌层划格试验不存在翘起或剥离现象，镀层具有较好的结合强度。镀层的拉伸破坏发生在镀层与基体界面，镀层与基体间的结合强度低于镀层内锌粉颗粒间的结合强度。随着镀层厚度的增加，镀层与基体间的结合强度逐渐降低。

3)机械镀锌层存在定的空隙，因为锌粉颗粒的移动和变形导致空隙体积减小而不能形成通孔，或镀层中存在微小尺寸通孔但不能对镀层的耐蚀性造成影响。镀层厚度对孔隙率影响不大。随着锌粉粒径的减少，镀层的致密度提高。随着强化时间的延长，镀层致密度提高。分别采用球状和片状锌粉制备的镀层均具有足够的致密度，镀层中不存在连通空隙。添加非锌微粉或其他金属盐制备锌基复合镀层(锌铝、锌镍、锌稀土等)对镀层的孔院率基本没有影响。

4) 机械镀锌层对钢基体可提供牺牲阳极保护，镀层在35g/L的NaCl溶液中均具有明显的活性溶解特征。采用片状锌粉制备镀层的耐蚀性要稍微优于球状锌粉制备的镀层。强化时间长短和镀后干燥加热温度高低对镀层的耐蚀性没有影响。锌基复合镀层(锌-铝、锌镍、锌-稀土等)的耐蚀性优于机械镀锌层。

1) The appearance of mechanical galvanizing coating is gray and semi-bright, and the coating is non-bright in characteristic parts (such as threads, grooves, etc.). The coating is completely covered, and there are no defects such as peeling, wrinkling, inclusions and leakage plating on the surface. Mechanical galvanizing coatings are deposited at the corner and groove of the workpiece! The thickness difference is greater. The flatness and brightness of the coating can be improved by prolonging the strengthening time and adding tin salt. Mechanical galvanizing with sheet zinc powder can improve the appearance quality of the coating. The appearance quality of zinc-aluminium, zinc-nickel and zinc-rare earth composite coatings is better than that of mechanical zinc plating.
2) There is no warping or peeling phenomenon in the mechanical galvanizing test, and the coating has good bonding strength. The tensile failure of the coating occurs at the interface between the coating and the matrix, and the bonding strength between the coating and the matrix is lower than that between the zinc powder particles in the coating. With the increase of coating thickness, the bonding strength between coating and matrix decreases gradually.
3) There are certain voids in mechanical zinc plating layer, because the movement and deformation of zinc powder particles lead to the reduction of void volume and can not form through holes, or there are micro-size through holes in the coating, but they can not affect the corrosion resistance of the coating. The thickness of the coating has little effect on the porosity. As the particle size of zinc powder decreases, the density of the coating increases. With the extension of strengthening time, the density of the coating increases. The coatings prepared by spherical and flaky zinc powders have sufficient density, and there are no connected voids in the coatings. Adding non-zinc powder or other metal salts to prepare zinc-based composite coatings (zinc-aluminium, zinc-nickel, zinc-rare earth, etc.) has little effect on the porosity of the coatings.
4) Mechanical zinc plating can provide sacrificial anode protection for steel substrate, and the coating has obvious active dissolution characteristics in 35 g/L NaCl solution. The corrosion resistance of the coating prepared with flake zinc powder is slightly better than that prepared with spherical zinc powder. The time of strengthening and the temperature of drying and heating after plating have no effect on the corrosion resistance of the coating. The corrosion resistance of zinc-based composite coatings (zinc-aluminium, zinc-nickel, zinc-rare earth, etc.) is better than that of mechanical zinc plating.

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