Applications
Zinc-nickel plating is usually applied where specifiers want the highest performance with the lowest deposit thickness. By specifying zinc-nickel, components can resist more than 1000 hours neutral salt spray (ISO 9227 & ASTM B117) with no effect on the dimensional tolerance of threaded components. Components typically plated with zinc-nickel include:
- Automotive – Fluid transfer tubes which can be deformed into their required shape after plating
- Automotive – Fasteners, particularly in areas of high corrosion (underhood, chassis joints)
- Electronic – Connectors, as a direct replacement for cadmium to provide corrosion resistance and high electrical conductivity
- Aerospace and defense – Joining components in contact with aluminum.
The preferred alloy composition for zinc-nickel plating is 12 – 15% nickel, with the remainder being zinc. This alloy gives exceptional sacrificial corrosion resistance and can be readily passivated. To achieve this alloy, zinc-nickel is usually plated from an alkaline electrolyte. For some applications, including the plating of brake castings, acid zinc-nickel can be used.
Coating Advantages
Advantages of MacDermid Enthone zinc-nickel plating processes:
- Excellent corrosion resistance
- Good alloy distribution
- Excellent deposit distribution (alkaline)
- Compatible for TriPass hexavalent-chromium free passivates
- Compatible with TriPass 7000 series cobalt-free passivates
- Friction properties can be modified with Torque 'N' Tension fluids
- Specified and approved by many automobile manufacturers
Enviralloy® Sprint
Enviralloy Sprint is suitable for both rack and barrel zinc-nickel plating applications that require 12 -15% nickel alloy coverage. These deposits meet demanding automotive specifications for extended resistance to corrosion. This process is recommended for applications requiring high yield productivity and maximum corrosion resistance.
The as-plated deposit is a uniform silver-grey, which can be further enhanced by passivation with PERMAPASS™ ULTRA IV and sealing with ENSEAL XD40. Where a black finish is required, passivating with TriPass ELV 5700 and sealing with TRIDIP will give a uniform, iridescent-free, deep black finish.
Enviralloy Ni 12 -15 G2 / Alkaline
Primarily designed as a barrel system, Enviralloy Ni 12-15 G2 delivers operational consistency and ease of use with increased deposit brightness. This is achieved even at the lower end of the nickel alloy range. Existing Enviralloy Ni 12-15 can also be converted to the new system.
Enviralloy NiFlex 12 / Alkaline
Designed primarily for zinc-nickel plating components which are post-plate deformed, such as fluid transfer tubes. Enviralloy Niflex 12 produces a semi-bright zinc-nickel deposit with a consistent alloy composition in the range within 12 - 15% nickel and good thickness distribution across a wide range of current densities and operating conditions.
Enviralloy NiSpeed / Alkaline
Enviralloy NiSpeed is a rack process with high cathode efficiency. This helps to ensure fast zinc-nickel plating rates and improved production yields. Enviralloy NiSpeed yields a consistent nickel content of 12-15% across a wide range of current densities and operating conditions.
ZINCROLYTE KCL-NI / Acid
ZINCROLYTE avoids the need for 'duplex' coatings normally applied when plating brake calipers in alkaline based zinc-nickel. It offers substantial benefits over earlier acid zinc-nickel plating alloy technology, namely consistency in both deposit and alloy distribution; critical when zinc-nickel plating complicated castings.
Post-plate Passivation
Zinc-nickel deposits are passivated to further enhance the corrosion resistance of the deposit. Recent legislation including End of Life Vehicle Directive (ELV) and Restriction of the use of certain Hazardous Substances (RoHS) has led to new, high performance, passivation systems based on trivalent chromium.
Topcoats
Finally a topcoat can be applied to the zinc-nickel plating and trivalent passivation coatings. The choice of topcoat depends on the application.
Advantages of topcoats include:
- Production proven
- Edictable torque and tension characteristics
- Improved corrosion resistance after post-plating deformation operations
- Resistance to thermal shock (heat exposure) testing
