Electroless nickel plating on aluminium

Why electroless nickel on aluminium

Electroless nickel is deposited by a chemical reaction, not by an electric current, so it builds evenly over edges, bores, threads and the inside of cavities. On machined aluminium parts this gives:

• An even, predictable coating on tight-tolerance features
• A harder, more wear-resistant surface than bare aluminium
• Corrosion protection
• A base for silver or gold plating on RF housings and connector parts

How aluminium is prepared

Aluminium forms a thin, hard oxide film within seconds of meeting air, and plating does not bond to it. Each part is cleaned, etched to remove the oxide, desmutted, and then dipped in a zincate solution that replaces the oxide with a very thin layer of zinc. Electroless nickel is plated directly onto the zinc. See plating on aluminium for the full sequence.

Mid or high phosphorus

On RF filters, diplexers and cavities, magnetic layers in the coating can cause passive intermodulation (PIM). High-phosphorus electroless nickel is non-magnetic as plated, which is why it, or copper, is used under silver on these parts. If your part has a PIM requirement, put it on the drawing.

Thickness and tolerances

Because the coating builds evenly, it adds its thickness to every surface. A bore's diameter gets smaller by twice the coating thickness, and a shaft's gets larger by the same amount. Allow for this on tight-tolerance features, and mark any threads, tapped holes or mating faces that must stay uncoated so we can mask them.

Thickness is plated to your drawing and measured in-house by XRF, which does not damage the part. We supply an XRF thickness report with each batch.

Cast and die-cast parts

Machined parts from wrought aluminium alloys usually plate well. Cast and die-cast parts contain more silicon and can have fine porosity, which can trap solution and cause blisters after plating. They need an adjusted etch and careful rinsing. Tell us the alloy and how the part is made, so we can plan the pre-treatment.

Hardness and adhesion

Parts are supplied with the as-plated hardness. We do not bake electroless nickel for hardness; if your drawing calls for a heat treatment after plating, tell us in your enquiry. Adhesion is checked by thermal shock: plated parts are heated and then quenched in cold water, and the coating must not blister or flake.

Specifications

We plate electroless nickel to ASTM B733. Drawings may also cite ISO 4527, SAE AMS 2404 or AMS-C-26074; the electroless nickel page explains what each covers. Send the specification and revision with your drawing and we will confirm whether we can meet it.

What to send with your enquiry

• Aluminium alloy and temper, and whether the part is machined, cast or die-cast
• Mid or high phosphorus, or the ASTM B733 type
• Thickness in µm
• Threads, holes or faces to mask
• Whether silver or gold is plated over the electroless nickel
• Any PIM or non-magnetic requirement
• Quantity per lot and expected yearly volume