Quality defects of galvanized layer

In recent years, with the surface quality continuous improvement of hot dip galvanized, the coating quality of the galvanized sheet has also been greatly improved. However, as cars and appliances of the two industries need high-grade galvanized steel sheet, which still have to solve the substrate surface contamination and uncoated points affect the quality of the galvanized coating.

Composition and source of a substrate surface contaminants
Hot dip galvanized substrate surface covered with a layer of black sludge pollutants. A mixture of contaminants from solids such as oil and iron particles, which about 30% to 50% iron and non-metallic solids. The hot rolled strip in a high-speed cold rolling process, part of the iron off from the surface of the roll and strip surface into the emulsion, contamination of the emulsion, the other part is stuck in the strip surface. In the strip rolling process, in addition to the emulsion due to the formation of high-temperature emulsion breaking film lubricant, as well as a small amount of oil residues in the strip surface and iron powder mixed pollutants, firmly glued to the strip surface. exports were unlikely to be blowing in the mill washed off.

Set layer type of quality defects
The types of defects that affect the coating quality can be broadly divided into:
(1) surface contamination;
(2) growth between the bump and metal compounds;
(3) uncoated point;
(4) embedded in people coating of zinc slag particles;
(5) pit;
(6) zn-Fe crystal growth in the coating.