preface
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This document has been prepared by Technical Committee ISO/TC 107, Metal and Other Inorganic Coatings, Subcommittee SC 7, Corrosion Testing.
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introduce
Decorative electrolytic nichcr and copper Nichcr coatings are made from multilayer nickel systems, including micro-discontinuous nickel, and applied to manufactured products to enhance their appearance and corrosion resistance.
These coating systems are characterized by unique corrosion mechanisms. Once corrosion has begun, the nickel layer dissolves preferentially (especially in the case of a bright nickel layer) : it acts as an anode for chromium (intended to act as a cathode). In addition, many tiny pores or cracks in the micro-discontinuous layer distribute corrosion currents throughout the surface. In this way, the electrical flow at a given corrosion site is greatly reduced, resulting in small pits held for longer periods of time that are invisible to the naked eye. In addition, corrosion penetration through the bright nickel layer is reduced, especially when a more advanced semi-bright nickel layer isolates it from the substrate or copper substrate.
Winter deicing salts, especially calcium chloride, cause a different type of corrosion. This particular corrosion phenomenon is characterized by slightly yellowing and less glossy spots on the surface, which are caused by complete dissolution of the chromium layer and partial deterioration of the microporous nickel layer. In this case, the bright nickel layer remains intact. This corrosion phenomenon occurs mainly in cold winter areas, using calcium chloride as a deicing agent in combination with dirt dust deposits.
Unfortunately, this corrosion phenomenon cannot be tested and evaluated using existing corrosion testing methods such as salt spray (see ISO 9227) and corrosion testing.
1 range
This document specifies equipment, reagents, and procedures for assessing the corrosion resistance of chrome plating parts in the presence of deicing salts (especially calcium chloride) in the laboratory.
This method is mainly suitable for chrome plated decorative parts, especially the exterior trim (automobile) parts with nickel chromium plating or copper nickel chromium plating.
This document simulates the specific corrosion of chromium plating deposits in winter in the presence of hygroscopic and corrosive deicing salts and conductive mud with high salt concentrations.
2 Normative references
The following files are referenced in the text in such a way that some or all of the content constitutes the requirements of this document. For dated references, citation-only versions apply. For undated references, the latest version of the reference (including any revisions) applies.
ISO 3696, Analytical laboratory water – specifications and test methods
3 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Deicing salt
Spray chemicals to control snow and ice on roads
Example: sodium chloride (rock salt), calcium chloride, and magnesium chloride.
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