With zinc nickel electroplating, nickel is added to the solution used in the plating process. Typically the solution contains 12 to 15% nickel. Though not as common as standard zinc electro-plating, zinc nickel offers superior corrosion resistance. The major disadvantage of any electroplating process is that it can cause hydrogen embrittlement in fasteners with a tensile strength greater than 320 HV.
Usually, the corrosion resistance is enhanced by a post plating process called chromate passivation. This applies a thin coating on the zinc surface. To comply with RoHS and ELV directives, the solution used in this process must be hexavalent chrome free and the most common solutions used today use trivalent chrome.
As standard, all fasteners thast are case hardened and all fasteners with a property class of 8.8 or higher are heat treated after electroplating to help reduce the risk of hydrogen embrittlement. This process is called de-embrittlement but it does not guarantee that the risk of hydrogen embrittlement is removed completely. If any risk of hydrogen embrittlement is unacceptable than a non electroplated finish should be considered.
|Chromate Treatment||Thickness||White Rust||Red Rust||Appearance|
|Clear||8 microns||120 hours||720 hours||Transparent with slight Bluish tinge|
|Black||8 microns||240 hours||720 hours||Black|
|Heavy||8 microns||240 hours||720 hours||Iridescent Yellow|
|Black with top coat||8 microns||240 hours||1200 hours||Black|
Performance results are approximate only and are based on laboratory salt spray tests
Note: Due to the fact that fastening applications differ greatly, the above information is for guidance only and is correct to the best of our knowledge. The customer must satisfy themselves with the performance of the fastener and validity of the data. TR Fastenings will not be held responsible for any failure that may occur from the use of this information.