The quality requirements of the trivalent chromium black zinc passivation process in the electroplating field usually include the following aspects:
1. Passivation film uniformity and color:
① The passivation film of the trivalent chromium black zinc passivation process should be uniform and continuous, with no bare substrate allowed.
② The color of the film layer should be in accordance with the provisions of the black, no miscellaneous colors, obvious spots or color differences.
2. Corrosion protection properties:
①Corrosion resistance is verified by salt spray testing (according to ASTM B117 or ISO 9227 standards). The test time (e.g. 48 hours, 72 hours, 96 hours, etc.) is determined by specific application standards and customer requirements.
Using Bigely black zinc passivate, salt spray can be achieved for up to 96 hours.
② For the time of the 1st appearance of rust (red rust) shall be in accordance with the specified standard requirements.
3. Adhesion test:
① The adhesion of passivation films is often evaluated by means of cross-hatch tests, tape-on-peel tests (e.g., ASTM D3359).
② It may also be necessary to verify the adhesion of the passivation layer when deformed or subjected to impact by bending tests or impact tests.
4. No hexavalent chromium:
①Passivation films shall be free of hexavalent chromium and comply with environmental directives such as RoHS and ELV.
②Use chromium-free or trivalent chromium-containing black zinc passivation solution to ensure the environmental safety of the treatment process.
5. Electrochemical properties:
For applications requiring electrical properties, parameters such as current potential or resistance of the passivation film also need to meet specific criteria.
6. Process control and detection:
① Requires control of temperature, concentration, pH and treatment time during passivation to ensure stable film quality.
②Rigorous testing of the production process and final results is required to ensure consistent high quality output.
7. Dryness and cleanliness:
After passivation treatment, the workpiece should be free of water and oil stains, kept dry and clean to prevent secondary contamination.
Each application area or customer may have its own specific requirements. Electroplating companies need to select a process based on these requirements when performing trivalent chromium black zinc passivation, or choose Bigely black zinc passivation solution if they have high requirements for salt spray duration, and carry out the appropriate quality testing and certification after completion.
If you are interested in black zinc passivation solution, please feel free to contact us.
