Investigation of corrosion resistance of pre-painted Zn-11%Al-3%Mg-0.2%Si alloy coated steel sheet through outdoor exposure test in Okinawa

  • K. Ueda
  • A. Takahashi
  • Y. Kubo

Abstract

Zn-11%Al-3%Mg-0.2%Si alloy coated steel sheet was well known as a coated steel exhibiting high corrosion
resistance. In order to develop and enhance the cut edge corrosion resistance of chromate –free prepainted
steel sheet, the corrosion resistance of the pre-painted Zn-11%Al-3%Mg-0.2%Si alloy coated steel
sheet (pre-painted SD) after 9.5 years of exposure test in Okinawa was evaluated and investigated in this
study. As a result, the corrosion resistance of pre-painted SD was better than that of pre-painted Zn-0.2%Al
coated steel sheet. The analysis of corrosion products of the corroded pre-painted SD by EPMA and XRD
were carried out. Simonkolleite; Zn5(OH)8Cl2
.H2O, gordaite; NaZn4(SO4)Cl(OH)6
.6H2O and zinc
aluminium carbonate hydroxide, Zn6Al2(OH)16CO3
.4H2O were found in the corrosion product under the paint
film and the corrosion product of Mg-rich was observed on the steel cut edge of pre-painted SD. From these
result, the mechanism of the cut edge corrosion resistance of pre-painted SD was discussed in the study.

Published
2013-06-06
Section
Memorie