Perforation Corrosion at Lapped and Cold Formed Portions in Cold Rolled and Galvanized Sheet Steels

In order to prevent corrosive parts such as hood, trunklid, door and side sill in an automotive body from corrosion, a new perforation corrosion test to simulate the corrosion at lapped and cold formed portions was conducted on cold rolled, galvanized, and zinc rich primer coated steels.

Anti-perforation of galvanized steels with zinc of 95 or 128 g/m² and galvannealed steel with zinc-iron of 59 g/m² is remarkably improved compared to cold rolled DDQ mild steel so that they decrease the reduction in thickness to about 1/2 or 1/3. Especially galvannealed steel showed the highest protectivity.

On the other hand, effect of steel itself on perforation is also observed among three uncoated steels. The EDDQ high strength steel has excellent resistance. The reason can be attributed to low manganese content and lack of surface segregation of manganese due to short time continuous annealing.