Wet/Dry Cycle Corrosion Behavior of Model Cut-Edge Formed on Pre-Painted Zinc Alloy Coated Steels by Laser Fabrication

Abstract

Laser machining technique, which used focusing pulse YAG laser beam irradiation, was applied to form area ratio of controlled model cut-edge on pre-painted zinc related coated steels. A corrosion behavior of formed model cut-edge was investigated by wet/dry cyclic corrosion test using 10 mol m-3 NaCl solutions in 80 % R.H. atmosphere. In high area ratio zinc specimens, red rust is observed on steel substrate at model cut-edge. The chromate inhibits corrosion of formed model cut-edge on pre-painted zinc coated steels. The behavior of corrosion penetration under the paint depends on composition of coating. In the case of painted zinc-55 mass% aluminum coated steel, zinc rich phase preferentially dissolved. The preferential zinc rich layer dissolution and corrosion products formation cause paint peel off.