Fengfan Zinc Nickel Alloy Black Trivalent Chromium Passivation TR-392

Product Overview

TR-392 is a black trivalent chromium passivation for zinc-nickel plating. It runs after the alloy layer and before the sealer, and it works by conversion rather than by dyeing: the trivalent chromium reacts with the zinc-nickel surface and becomes part of it, so the colour cannot lift off the way a dyed or silver-based blackening can. What leaves the bath is a dense, glossy black film, even in tone across flat faces, cut-outs and recesses — the deep black that automotive and aerospace drawings ask for, without the iridescent sheen that gives lesser passivates away.

The bath is tuned for zinc-nickel deposits carrying 12–15% nickel. That range gives the film its optimal receptivity and the deepest, most even colour. Deposits well outside it still passivate, but the black reads lighter and less consistently, so it is worth knowing your alloy before a line conversion.

It serves rack and barrel lines from one make-up, runs in a warm, low-temperature bath, and asks for nothing more elaborate than a PVC-lined tank, filtration and ordinary pH and titration control. An industrial metal plating shop moving off chromic acid keeps its carriers, its barrel and its rinse sequence, and changes only the passivation tank.

Typical work is small-to-medium steel parts with awkward geometry. A bracket with a U-shaped cutout, a raised hole boss and an angled tab is exactly the sort of shape this bath is expected to blacken evenly, corners included.

Specifications

Key Features

• Free of hexavalent chromium and cobalt. The film forms from a trivalent chromium matrix, so a shop leaving chromic acid behind also loses the toxic bath, the special handling and most of the waste-treatment burden.
• Colour that holds across the whole load. The reaction rate is stabilised at both ends of the current density range, so a bracket with deep recesses and a bracket with flat faces come out the same shade. Grey edges and the iridescent rainbow that plagues black passivates on shaped parts are what this bath is formulated to avoid.
• A conversion film rather than a dye. The chromium reacts with the alloy and becomes part of the surface, so the black does not rub off in handling, in assembly or in a wipe-down test. It also removes the need to keep a silver-based blackening agent in the line.
• Stable through the relief bake. High-tensile parts are baked after plating to release hydrogen. The film survives that thermal cycle with its colour and its corrosion resistance intact, which is not true of every black passivate on the market.
• One make-up for rack and barrel lines. The same bath and the same control points serve both line types, so a zinc nickel plating company running mixed work does not need two passivation tanks or two sets of additions.
• A base that accepts a topcoat. Organic sealers, topcoats and torque-modifying lubricants key onto the film without a pre-treatment, so the finish does not have to be stripped or re-activated before the next step in the line.

Rack & Barrel Line Fit

Both line types run from the same bath, with no separate make-up for either. The difference is in how the parts behave while they are wet.

On a rack, parts sit still and the solution reaches them from one direction, so heavy or shielded components need a little more dwell and a clear path for the bath. Contact points leave a small unpassivated mark, which is normally placed on a non-cosmetic face. Rack work is the natural choice for calipers and larger brackets, and for anything with a decorative surface that must not be touched — which is how most metal plating services handle that class of part.

In a barrel, the load tumbles and every surface keeps meeting fresh solution, which is why small clips, fasteners and connectors come out uniformly black even when they are packed densely. Do not overfill: a load that cannot move will show contact patches. A moderate load with steady rotation gives the most even result.

The step that catches most shops is transfer time. Parts that sit wet between the passivation tank and the first rinse keep reacting and the film keeps thickening. Keep the drag-out short and the rinse sequence close, and the colour stays where the bath put it.

Process Flow

1. Plate the zinc-nickel layer to the full thickness your specification calls for. The passivation converts the alloy it is given and cannot add protection the layer does not already carry.
2. Rinse twice after plating, so plating salts do not follow the work into the activation dip.
3. Activate. A short dip in dilute acid removes the oxide film that forms on the alloy and lets the passivation reach bare metal. Confirm the acid and strength our technical team recommends for your alloy before the first production load.
4. Rinse again, clean, before the passivation tank.
5. Passivate. Immerse the rack or barrel load and hold it for the full passivation time — short cycles leave the colour thin, long ones dull it. Watch pH and temperature here more closely than anywhere else in the metal plating process.
6. Rinse twice on the way out, keeping carry-over out of the following tank.
7. Seal. A post-dip sealer locks in the colour and delivers the last part of the corrosion performance.
8. Dry and cure to the sealer maker's schedule, then inspect against the master sample.

Applications

• Automotive fasteners. High-strength bolts finished with a zinc-nickel plating layer and this black passivate keep their appearance through ocean freight and years in a chassis. On a mixed bolt line the black also works as a visual identifier for a particular size or grade, which is why fastener plants specify it as much for the assembly line as for the customer.
• Brake calipers and chassis brackets. Exposed castings and brackets need a finish that reads as deliberate and survives road salt. The even black covers the whole part, including the areas a paint line struggles to reach.
• Fuel line and underbody fasteners. These are the parts that see the worst of the salt-spray regime, and they are the reason a 720-hour zinc-nickel specification exists in the first place.
• Commercial job shops. A shop running industrial metal plating on hydraulic fittings, electrical connectors and general hardware faces a different part shape every day. One bath that handles rack and barrel without changeover is worth more than a slightly better finish that only runs one way.
• OEM validation and electric-vehicle programmes. Materials engineers replacing cadmium and plain zinc on brackets and battery housings prepare CASS and NSS panels and cut cross-sections to check film density. A passivate that produces a consistent film is far easier to validate than one that shifts with current density.
• Decorative and aftermarket hardware. Where the black is the point — a visible bracket, a piece of exposed trim — the glossy finish replaces paint and e-coat while keeping the cathodic protection of the plating underneath.

Sealing & Post-Treatment

A sealer is not a correction for a weak passivate; it is the stage that protects the black and buys salt-spray time. The film is functional as it leaves the final rinse, but a sealing dip closes the surface, hardens it against scratching in packing and assembly, and lifts neutral salt spray well beyond what the passivate delivers alone. When a print calls for 720 hours of neutral salt spray on a zinc-nickel part, the sequence behind that number is plating, passivation and then a sealer — the last part of the figure is won at the sealing stage.

Sealers formulated for trivalent films, including the PN range, are the natural match. How concentrated you run the sealer sets how deep the black reads and how hard the surface becomes, so it is worth treating concentration as a specification decision rather than a line habit. The same film also accepts organic topcoats and torque-modifying lubricants, which is how a fastener line adjusts the coefficient of friction without disturbing the coating underneath.

Trial the sealer and the passivate together on panels before the line is committed, and confirm the dilution against your own salt-spray requirement rather than against a generic figure. The two stages behave as one system, and qualifying them separately usually costs a second round of trials.

Bath Control & Maintenance

• Impurity tolerance. Zinc and iron build up in every passivation bath as work passes through, and they are what usually shortens its life. This bath is formulated to tolerate both, so the colour stays consistent for longer between corrections and the tank does not have to be dumped the moment a little metal drags in.
• Check pH before you add anything. When the black comes up thin or slow, drift in the acid balance is the usual cause. Bring the bath back inside the working window from the specification table first, then look at additions.
• Simple control. A titration and a pH reading cover routine maintenance. There is no instrumental analysis to run and no specialist operator to train, which matters on a line where the passivation tank is nobody's full-time job.
• Standard tank and filtration. PVC-lined tanks and ordinary filtration are enough. Nothing here needs an unusual lining, a special heater or a separate waste stream.
• Bath life and the cost of a dump. Every dump costs a day of production and a full make-up. A bath that holds its balance longer is the cheapest kind of metal plating process improvement a line can make.

Ordering & Delivery

• Minimum order quantity. Varies by chemical; confirmed with our sales team per order.
• Packing. Supplied in plastic barrels, with the wider range available: 10 kg/box; 25 kg or 50 kg/bag; 20 kg/25 kg/30 kg/200 kg/drum; 1000 kg/IBC drum.
• Lead time. 2 weeks.
• Payment. 100% T/T in advance.
• Shipping. Per the terms agreed in the current contract.
• Documentation and warranty. Your sales contact confirms the paperwork with the order.
• Before you commit. Give your sales contact the alloy, the line type and the salt-spray target you are working to, and ask about sample availability for a panel trial.

Substrate Matching Guide

Technical Support & Model Matching

Choosing the right match is where most sourcing decisions stall. As a trading supplier, we keep one point of contact from first enquiry to after-sales: tell us what you are making and the conditions you work under, and we shortlist the closest matches from our supplier network, compare specifications and arrange samples before you commit to a bulk order. If something does not behave as expected, we work with the supplying partner on the cause and a practical fix, and stay with the case until it is settled. Email, WeChat or WhatsApp enquiries get a reply within 24 hours.

FAQ