Electroplating: Zinc, Nickel and Hard Chrome
Plating selection for corrosion, wear and conductivity, with pre-plate sizing, masking and post-plate dimension verification planned into the route.
Plating Selection and Control
Plating adds real thickness, so the value is in the selection and the size planning, not just the bath. KGL quotes the coating system the drawing needs, plans pre-plate dimensions or masking, and verifies thickness and post-plate dimensions on return. Zinc per ASTM B633, hard chrome per SAE-AMS-QQ-C-320, nickel per the drawing system, all through audited partner lines.
Film Thickness and Dimension Change We Plan To
The windows below come from our finishing standard, revision D, and are the values our quotes pre-size against.
| Process | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| Zinc, clear or blue | 5 to 8 | Profile 5 to 8; bores below 15 mm 3 to 5 |
| Zinc, thick-film blue | 12 to 18 | Profile 12 to 18; bores below 15 mm 3 to 5 |
| Zinc, yellow / iridescent / black | 5 to 10 | Profile 5 to 10; bores below 15 mm 2 to 4 |
| Electroless nickel, aluminum | 3 to 5 | Profile 3 to 5, bores 2 to 4 |
| Electroless nickel, steel or copper | 3 to 5 | Profile and bores 3 to 5 |
| High-phosphorus electroless nickel (9 to 12% P), steel | 10 to 12 | Profile and bores 10 to 12 |
| Electrolytic nickel, steel | 12 to 15 | Profile 12 to 15; bores below 3 mm unplated, above 3 mm 8 to 12 |
| Hard chrome, standard | 3 to 6 | Profile 3 to 6; bores and slots unplated |
| Hard chrome, heavy | 5 to 8 | Profile 5 to 8; bores and slots unplated |
| Silver plate | 3 to 5 | Profile and bores 3 to 5 |
| Gold plate | 0.3 to 0.5 | Profile and bores 0.3 to 0.5 |
| Nickel under silver on aluminum | Ni 2 to 3 + Ag 4 to 7 | Profile and bores 6 to 8 |
When to Choose It
| Goal | System | Spec seen on drawings |
|---|---|---|
| Corrosion barrier on steel brackets and fasteners | Zinc, clear trivalent chromate | ASTM B633 Type III, SC2, about 8 μm |
| Corrosion plus appearance on steel | Zinc, black chromate | per drawing class |
| Wear and corrosion on brass, copper, steel | Nickel plating | thickness per callout, post-plate verify |
| Dimensional wear surface, low friction | Hard chrome | SAE-AMS-QQ-C-320 Class 2E, about 20 μm |
| Conductive or solderable surface | Tin or nickel on copper alloys | thickness per callout |
Specifications We Control
| Item | Specification |
|---|---|
| Standards seen on KGL drawings | ASTM B633 (zinc, Type III clear chromate SC2), SAE-AMS-QQ-C-320 (hard chrome, Class 2E), drawing-specified nickel |
| Thickness control | Called out on drawing; measured on return per batch |
| Dimensional rule | Specified dimensions apply after plating; mask, pre-size or post-finish per route |
| Compliance | RoHS compatible routes standard; declarations per shipment |
| Lead time | 2 to 4 working days added to the route |
How We Run It and Check It
Verification on return: coating thickness spot check per batch, adhesion where specified, post-plate dimensions on features that carry tolerances, and appearance against the agreed face map. Adhesion and thickness reports travel with the shipment. For copper alloy contact parts, note that bare brass is often the better conductor call: we flag drawings where plating was specified by habit rather than function.
Material side: carbon steel, brass and copper, stainless steel. Alternative for aluminum: anodizing.
Cross entrances: by material | CNC machining | inspection and QC.
Frequently Asked Questions
Zinc, nickel or hard chrome: how do I choose?
Zinc (per ASTM B633) is the cheap corrosion barrier for steel brackets and fasteners, usually with clear trivalent chromate. Nickel builds a smooth, corrosion and wear resistant layer and is the default on brass and copper contact parts. Hard chrome (per SAE-AMS-QQ-C-320) is for wear surfaces that also carry dimensions, like gauge and slide faces.
Do dimensions apply before or after plating?
On the drawings we process, specified dimensions apply after plating, and the plating thickness is called out (for example clear zinc around 8 micrometers, hard chrome around 20 micrometers). We either pre-size the part, mask the features that cannot carry thickness, or post-finish. The route is agreed in the quote, not discovered at goods-in.
Can you meet RoHS on platings?
Yes, RoHS compatible routes are standard: trivalent chromate passivation on zinc instead of hexavalent, and declarations ship with the parts.
What about masking high-tolerance threads?
Threads and marked features are masked with plugs and tape per drawing, and pull-through is checked before packing. On precision fits we prefer pre-sizing where the design allows it, because masked edges always carry some buildup risk.
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