Perforation of Coated Steel Panels on Automobiles and its Corrosion Mechanism

Abstract

The effect of galvanized corrosion steel sheets and zinc-rich primer coated steel sheets on the perforation corrosion of actual automobiles and the relevant corrosion mechanism was studied. Perforation occurred in 6-7 years for zinc-rich primer coated steel panels inside of door hems and after more than 14 years for galvanized steel sheets with 120g/m2 zinc coating mass in the lapped side-sill. Perforation corrosion of galvanized steel panels can be divided into 4 corrosion processes on the basis of measured perforation depth and analysis of iron rust for North American automobile bodies. The period in which zinc corrosion controls the corrosion of the steel substrate played a very important role in determining the period until perforation occurs in road salting regions.

Automotive Corrosion and Accelerated Corrosion Tests for Zinc Coated Steels

“…An investigations of corroded vehicles used in snowy areas showed that perforation corrosion of automotive parts tends to be prevented as the coating thickness increases. 26,27,29,30) Although sales of automobiles in tropical regions in Asia have increased in the last 10 years, there are still few reports on corrosion of vehicles in those environments. Therefore, this paper reports the corrosion of vehicles used in two different regions, snowy areas in Europe (Austria, Denmark and Sweden) and a tropical area in Asia (Thailand).…”

“…1. 27) The time to perforation corrosion is divided into the protection period by the zinc coating and the corrosion period of the steel substrate. The protection by the zinc coating is attributed to the good corrosion resistance of the zinc itself under the atmosphere (τ 1 ), sacrificial corrosion of zinc (τ 2 ) and protection by the deposited zinc corrosion products (τ 3 ).…”

“…The numbers in parentheses represent the coating thickness on one side. In the previous studies in North America, 27,32) it was clarified that zinc and zinc alloy coatings suppress corrosion of the steel in the early years of use period. Similar tendency was obtained in different regions in this study.…”

“…[20][21][22] Investigations of corrosion in vehicles in snowy areas have been carried out and reported in some publications. [23][24][25][26][27][28] Those investigations clarified the fact that the coating thickness is a more crucial factor than the alloy composition of the coating for prevention of cosmetic and perforation corrosion in automotive parts. On the other hand, corrosion of vehicles in tropical environments has not been fully understood, in spite of increasing sales of automobiles in Southeast Asia.…”

<i>In-Situ</i> Observation of Initial Stage Cosmetic Corrosion Behavior under Wet and Dry Conditions

“…The mechanism of "perforation corrosion" has been studied extensively based on an analysis of actual vehicles, 2) and the effects of anti-corrosion steel sheets under various corrosion environments have been clarified. 3) Regarding "cosmetic corrosion", in other words, "under-film corrosion", it is generally known that the anodic and cathodic sites are localized and show the morphology of macro corrosion.…”