2006 Volume 55 Issue 8 Pages 356-363
In order to reduce hazardous substances in electrical appliances, the chromate coating used in zinc-coated steel sheets is being changed to chromate-free coating. The objective of this study was to develop a new accelerated corrosion test method for zinc-coated steel sheets based on the actual environment of electrical appliances, for appropriately evaluating the corrosion resistance of zinc-coated steel sheets with the chromate-free coatings that will be used from now on.
The conventional accelerated corrosion tests, which are the salt spray test (SST) and the combined cyclic corrosion test (JASO M609-91), have been widely used in evaluating the corrosion resistance of zinc-coated steel sheets for electrical appliances. However, these tests showed a low correlation with the actual corrosion behavior of electrical appliances from the perspective of corrosion morphology and the ranking of corrosion resistance. It is suggested that the conventional accelerated corrosion tests (SST, JASO M609-91) cannot be used for appropriately evaluating the corrosion resistance of zinc-coated steel sheets with the chromate-free coatings.
Based on the actual corrosion behavior of electrical appliances and inadequacies of the conventional accelerated corrosion tests, a new accelerated corrosion test for electrical appliances, “ACTE” (ACTE: Accelerated Corrosion Test for Electrical appliances) was developed. A good correlation between ACTE and corrosion in actual environments was demonstrated. ACTE consists of a salt deposition process and cyclic wet/dry process. As distinctive features of ACTE, the test conditions simulate actual environments (use of artificial seawater, constant absolute humidity), and it is possible to estimate the corrosion life of materials in a wide range of use environments by obtaining dependency data on the main corrosion factors (amount of deposited sea salt, etc.) by varying the test conditions. ACTE makes it possible to appropriately evaluate the corrosion resistance of zinc-coated steel sheets with chromate-free coatings.
