Speaker
Description
The prevention of intermetallic dross particles like Fe2Al5 in strip galvanising is paramount in making good quality exposed automotive panels. These intermetallic dross particles can create small surface features which can adversely affect the final painting quality. The formation of intermetallic dross seems inevitable during the galvanising of steel as aluminium additions are necessary to improve the coating adhesion and to prevent the Fe-Zn alloying reaction. Based on the results of an initial laboratory study and on the outcome of several industrials trials, will be shown that adding up to 0.8 % Al to the zinc bath results in a large reduction in the amount of supersaturated Fe. The study also shows that the thickness of the inhibition layer does no longer depend on the Strip Entry Temperature (SET) nor on small variations in the Al %. The microstructure of the coating is characterised by small zinc grains with some multiphase regions. Laboratory and semi industrial tests demonstrate that this new product has a better resistance against tool pollution and galling. All other application properties like waviness, spot welding and adhesive bonding are similar or better than conventional GI. Hence this product is the new benchmark for exposed automotive GI panels.