BS EN ISO 3613-2021 pdf download.Metallic and other inorganic coatings 一 Chromate conversion coatings on zinc, cadmium, aluminium-zinc alloys and zinc- aluminium alloys一Test methods.
In the case of a cadmium substrate, observe the appearance of the spot for 1 mm. The formation of a dark or black stain at least 5 s after the application of the test solution shall be deemed to indicate the presence of a colourless chromate conversion coating.
Black stain formation after more than 1 mm can be indicative of the presence of supplementary coatings, such as wax or oil.
For comparison purposes, test an untreated surface similarly. Untreated zinc and cadmium surfaces, or the surfaces that have been treated for the chromate conversion coating but do not have a continuous coating, will react with the lead acetate solution to form a black stain on the untreated or bare zinc and cadmium surfaces almost immediately, within 2 s to 5 s. after the application of the test solution.
No significance is to be placed upon any differences in the reaction time to black-spot formation between 1 mm and 3 mm on a zinc substrate, or between 5 s and 60 s on a cadmium substrate, with a colourless chromate conversion treatment. Factors such as substrate surface texture (roughness), chromate film thickness variations (due to processing conditions), variations in the ambient temperature of the test and precise pH control of the lead acetate solution have an influence on the reaction time, and therefore preclude any rating based upon times beyond those already stated. Similarly, the test cannot be used to compare the corrosion protection of chromate conversion coatings made from various types of chromate treatment solutions.
Because of the sensitivity of the method, the test is considered to be a quality control tool for the process. Items with damaged chromate layers should not be tested by this method.
Chromate conversion coatings exposed to temperatures above 60 °C will have considerably reduced resistance to corrosion in the accelerated test method (see .1O). They will show a black stain in less than 60 s on zinc and less than 5 son cadmium.
6.4 Test for the presence of a colourless chromate coating on zinc-aluminium (mass fraction of aluminium: 5 %) alloys
Expose the test specimen for 24 h to an accelerated damp heat test in accordance with IEC 60068-2-30.
The formation of a dark grey to black stain over the main part of the area shall be deemed to indicate the absence of a chromate conversion coating.
NOTE This test does not have any significant effect on the surface appearance if a chromate conversion coating is present.
6.5 Test for the presence of hexavalent chromium in both colourless and coloured chromate coatings
6.5.1 General
Carry out the following test methods for the presence of hexavalent chromium.BS EN ISO 3613 pdf download.