Summary for zinc plated part rusted Discussion
Can a good zinc plated part get rusted? Amit Shah describes a spring that met a 10 micron zinc plating requirement and passed repeated salt spray tests, yet was found rusty by the final customer about 4–5 months after shipment. He asks whether moisture, storage conditions, manual assembly with plastic parts, carton packaging, or carton glue could be responsible, and how to relate a 6-hour salt spray requirement to real-world rust after months. The thread centers on the gap between laboratory corrosion testing and actual service/storage conditions. The key practical point is that passing salt spray does not guarantee long-term rust resistance in every environment, especially if parts are exposed to humidity, handling, packaging issues, or other post-plating contamination. The discussion implies the need to investigate the full supply chain and storage/packaging conditions rather than assuming the plating alone is at fault.
December 18, 2015
Q. Dear Sirs,
This is with respect to metal part in attached photos — which has got rusty.
1. Final Customer requirement is 6 hours Salt Spray.
As precaution my Customer and we follow the below:
Zinc plating – Minimum 10 micron coating thickness and Spring should pass minimum 24 hours salt spray test.
And rating should be more than 5 (that’s 4 times the requirement given by final customer).
Test Condition and test method for salt spray test: ISO 9227 Corrosion tests in artificial atmospheres–Salt spray tests
We recently got complaint from final customer per pictures attached:
We get this part done thru reputed plating vendor. Every lot has been salt spray tested by our plating supplier, then we are also doing every lot salt spray test and same is followed by our customer before assembling the parts at his end and then dispatching to final customer.
My customer stores all material in a heated room to avoid moisture.
Material sent June 2015 and complaint received on 15th Dec. 2015
What can be the reason for this part getting rusty —
1. Can it be moisture in Air at final customer?
2. Can one related reason for this metal part getting rusty after 4 -5 months (as no rust found before sea shipment)?
3. Parts have been assembled with plastics parts at our customer end manually?
4. Packing is in Carton boxes?
5. Can Glue of carton box – be culprit?
6. How to co relate with 6 hours of Salt Spray life required to rustiness after 4-5 months?
Please guide us.
Best Regards
Amit Shah
– INDIA