When Zinc Nickel Plating Is Better Than Galvanising

Zinc plating and hot-dip galvanising are two common surface finishes to protect steel from corrosion. But not all applications require the same properties. Here we discuss when the alloy finish has the edge.

Corrosion Hours on Salt-Spray Tests

Salt-spray testing results for corrosion hours to white rust for typical Zinc Nickel electroplating processes usually exceed 1,000 hours, whereas typical Zinc electroplating processes are typically in the range of 200 hours to 400 hours. The hot-dip galvanizing process can achieve similar results on typical structural steelwork but is generally not a suitable process for small machined parts.

Precision Parts With Tight Tolerances

Compared with the hot-dip galvanizing process, the thickness of the alloy finish deposited by electroplating can be accurately controlled to a uniform value of 8 to 15 microns. This ensures that the finish is suitable for precise components with small bores and threaded holes. Such parts can be plated to size to ensure that their dimensions are within the drawing tolerances.

High-Strength Steel and Embrittlement Risk

Zinc nickel is suitable for high strength steel components as it’s a process that does not introduce as much hydrogen into the metal as other electroplating processes. This is critical for components rated above 1,000 MPa as hydrogen embrittlement can cause them to fail. The post plate bake cycle also removes any remaining hydrogen from the steel part.

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Operating at Higher Temperatures

Galvanized coatings begin to degrade at temperatures of approximately 200°C, whereas the zinc nickel alloy finish is able to withstand temperatures of approximately 300°C, making it an ideal finish for exhaust brackets, brake components and other parts that operate near engines.

Automotive and Aerospace Approvals

Most original equipment manufacturers (OEMs) specify the use of a zinc nickel alloy plating in their specifications. At UDX, we have details of the surface treatment process specified in WSS-M21P17-A by Ford and in the surface treatment specifications of Airbus.

Paint and Topcoat Adhesion

The surface of the alloy can be chromate passivated and accepts primers. Paint systems can be applied to zinc nickel surfaces without additional surface preparation as is required with galvanized surfaces.

Therefore Zinc Nickel is the best option for precision parts made of high-strength steel.