With the changing needs of various industries, an enhanced version of the gi sheet called zero spangle has emerged. This type of galvanized steel not only provides superior corrosion protection, but also has a smooth, visually appealing surface with zero spangle.
Zero Spangle GI Coil Passing cold rolled coil through a melted zinc bath, in order to coat the steel with a thin layer of zinc to provide corrosion resistance, is called hot dip galvanizing. Hot dip galvanized coils (GI coils) have many applications in construction/building, roofing, automotive parts, sections, profiled sheets, etc.
The production of spangles
Very large grains, termed "spangles," are produced on galvanized sheet steel coatings when lead is added to the zinc bath. The spangles have been attributed to melt undercooling prior to solidification. The present results indicate this is not the case, undercooling being less than 1 °C. The spangle diameter is shown to be dependent on the alloy addition to the bath, large spangles being obtained with Bi and Sb as well as Pb. The spangle size is related to the surface tension of the alloying addition, the size decreasing as the melt vapor surface tension of the alloying element increases. It is proposed that spangles form dendritically from a nucleus in the melt. Alloy additions with low interfacial energies and very limited solid solubility are highly concentrated ahead of the dendrite tip. This decreases the tip radius and increases the dendrite velocity, producing large grains. The basal plane orientation of the samples varies between 17 and 80 deg with respect to the steel sheet surface, which is inconsistent with basal plane dendritic growth in Zn along (1010) directions. It is proposed that solute additions to the melt and growth in a thin liquid layer can modify the dendrite growth direction, accounting for the spangle orientation.
