The Application of Lubricant Film Coated GA Steel

by Ming-Hao Liu, Heng-Shou Chang, Hsing-Lien Wu, Hung-Ping Wang

Publisher - *China Steel Corp., Taiwan, R.O.C. ** China Steel Corp., Taiwan, R.O.C. ***China Steel Corp., Taiwan, R.O.C.

Category - Engineering & IT

Galvannealed steel (GA) has both good corrosion resistance and weldability and thus has become the mainstream steel material used in auto industry. However, the high surface friction of the GA product makes formation fracture happen more easily during pressing process of auto panel. Though the surface lubricity can be improved through the control of coating layer structure or iron content while galvannealing, it is practically difficult to obtain in a real manufacturing line because of its various control parameters and the narrow control window for good coating layer structure. In recent years, the method of coating lubricant film is proposed as a major solution to improve surface lubricity. The lubricant film not only lubricates the surface but also widens the operation window of galvannealing process. In the application on auto outer panels, however, the streaky marks that tend to happen during film coating poses a surface appearance problem if they remain visible after electro-deposition paint coating. In this research, a method of increasing the surface roughness in order to improve streaky marks of lubricant coating film product will be introduced. The improved surface is verified to be satisfactory for the requirements of auto outer panel and the other properties are evaluated to be equivalent to those of the non-film-treated GA product. The lubricant film coated GA product for auto outer panels not only promotes lubricity with no negative effects, but also makes it possible for the same material to perform an even deeper formation.

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