Assessment and Application
Technologies for Automotive Materials (Perforation)
—Techniques for Corrosion Resistance
and Perforation Feedback for Automotive Steel
Materials —
FUJITA Sakae KAJIYAMA Hiroshi KATO Chiaki
Abstract
The effect
of zinc and zinc alloy coated steel sheets
on cosmetic corrosion and perforation corrosion
in actual automobiles and the relevant corrosion
mechanisms were studied. The main factor affecting
cosmetic corrosion on the outside of outer
panels was the coating weight of the Zn or
Zn alloy coating rather than the type of coating.
Perforation occurred in 6-7 years inside of
door hems where Zn-rich primer coated steel
panels were used, whereas perforation corrosion
life was more than 14 years in galvanized
steel sheets with a 120g/m² Zn coating weight
in lapped side-sills. Measurements of the
perforation depth and analysis of the composition
of the iron rusts formed on automobile bodies
in North America showed that the perforation
corrosion process in hot-dip galvanized steel
sheets can be divided into 4 stages. The period
during which Zn corrosion products control
corrosion of the steel substrate plays a very
important role in determining the period until
perforation occurs in automobile bodies in
regions where road deicing salt is used.
