SurTec 680 Chromitierung/Chromiting Chromium(VI)-free Thick Layer Passivation for Zinc and Zinc Alloys

Problem

Possible Cause

Remedy

slight white clouds in/on the Chromiting layer

a) if the clouds are already visible on the plated zinc (after activation)

check the quality of the parts, the pretreatment and the zinc plating process

b) insufficient rinsing and drying conditions

check the pH-value of the activation (≤ 2); shorten the rinsing times: in total < 2 min; check the pH of the last rinse (best: 5-6); optimize the drying process: first cold drying (air blow), then dry 10-15 min at 60-80°C

c) pH-value of the Chromiting bath is too high

correct the pH with nitric acid to pH 1.8

d) loss of complexing agent SurTec 680 KCT (high zinc contents lead to precipitation of complexing agent)

add SurTec 680 KCT in steps of 1 g/l (for 1 g/l zinc add 2 g/l SurTec 680 KCT)

yellowish Chromiting layer c

content of iron in the bath is too high

find out the source of the iron contamination and prevent it; further dissolution of iron can be reduced by adding SurTec 660 B; for continuous input of iron we recommend the installation of an ion exchange system (SurTec 680 IAT)

pale colour of the Chromiting layer, bad corrosion protection

working parameters of the Chromiting are not correct

check concentration, pH-value, agitation temperature and application time - and correct these parameters if necessary

discolouration of the Chromiting layers after 1-4 weeks

a) inadequate storage conditions

high humidity, high temperatures and salts on the part’s surface impair the Chromiting layers

b) too thin zinc layer

possible migration of base metal cations can lead to discolouration => increase the plating time

c) metal impurities in the zinc bath or the Chromiting bath

keep the electrolyte free from metal impurities; for the Chromiting bath: use the ion exchange SurTec 680 IAT for eliminating metal impurities

d) in case of using a sealer: be aware that it is not too alkaline and that the resulting layer is not too thick

dilute the sealing bath; adjust the pH-value as low as possible