Problem of Conventional Accelerated Corrosion Tests and Development of New Accelerated Corrosion Test: Development of New Accelerated Corrosion TestSimulating Electrical Appliance Environment (2)

摘要

As part of the effort to eliminate the use of hazardous substances in electrical appliances, the chromate coatings used in zinc-coated steel sheet are being replaced by chromate-free coatings. The objective of this study was to develop a new, accelerated corrosion-testing method for zinc-coated steel sheet, based on the actual environment of electrical appliances, that can accurately evaluate the corrosion resistance of the zinc-coated steel sheet with chromate-free coating that will be used from now on.The salt-spray test (SST) and the combined cyclic corrosion test (JASO M609-91) are the conventional accelerated corrosion tests that have been widely used until now in evaluating the corrosion resistance of zinc-coated steel sheet for electrical appliances. However, the results of these tests do not correlate well with the actual corrosion behavior of electrical appliances from the perspective of corrosion morphology and the ranking of corrosion resistance. It is suggested, therefore, that the conventional accelerated corrosion tests, SST and JASO M609-91, cannot be used to evaluate the corrosion resistance of zinc-coated steel sheet with chromate-free coating.Based on the actual corrosion behavior of electrical appliances and the inadequacy of the conventional accelerated corrosion tests, we have developed a new accelerated corrosion test for electrical appliances known as ACTE (Accelerated Corrosion Test for Electrical appliances). There is demonstrably a good correlation between the ACTE results and corrosion in actual environments. The ACTE test consists of a salt-deposition process and a cyclic wet/dry process. Since the test conditions simulate actual environments (use of artificial seawater, constant absolute humidity), the corrosion life of materials can be estimated in a wide range of use environments by varying the test conditions to obtain dependency data for the main corrosion factors (amount of deposited sea salt, etc.). ACTE makes it possible to obtain accurate evaluations of the corrosion resistance of zinc-coated steel sheet with chromate-free coating.