Passivation Finish Service

Q: Can passivation be done on previously painted or coated parts?

No, not effectively. Paint or coatings block direct contact between the metal surface and passivation chemicals, preventing the oxide layer from forming. For coated parts, you’d first need to strip the coating (we offer pre-treatment services for this) before passivating, then re-coat if needed.

Q: Can passivation change the appearance of my parts?

No. The protective oxide layer from passivation is micro-thin, so it won’t dull, discolor, or alter your part’s surface finish—key for applications where looks matter. If you do want to adjust appearance (e.g., a matte finish, brighter polish, or color), consider processes like abrasive blasting, electroplating, or anodizing (for aluminum). These methods intentionally modify surface texture or add layers to achieve the desired look.

KingStar Mold’s passivation finish forms a protective layer, boosting metal parts’ corrosion resistance for harsh environments like automotive and aerospace. Our precision process ensures durability without compromising dimensional integrity.

Corrosion protection for tough conditions
Precision passivation, lasting metal durability
Safeguard components—automotive to aerospace

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Surface Conditions After Corrosion of Un-passivated And Passivated Metal Parts

(Click to Enlarge)

Overview of Passivation

Passivation is a chemical treatment that forms a thin, protective oxide layer on metal surfaces—most commonly stainless steel—neutralizing free iron and contaminants to resist corrosion. For anyone in manufacturing, you know raw metals like stainless steel can still corrode if free iron particles or contaminants linger. Our process dips parts in a controlled chemical bath, dissolving those impurities and leaving a chromium-rich oxide layer that acts like a shield. It’s subtle—you won’t see a glossy finish change—but in high-moisture automotive underbodies or chemical-exposed industrial valves, that layer is what keeps parts from rusting out months (or years) early.

From a shop floor perspective, passivation is about consistency. We calibrate bath concentrations and immersion times to match your part’s alloy—304 stainless needs a different touch than 316, for example. It’s not just about meeting specs; it’s ensuring that protective layer bonds evenly, even in tight crevices or threaded areas where corrosion loves to start. For parts that have to perform reliably, passivation is the quiet step that prevents costly failures down the line. However, it should be noted that passivation does not enhance the wear resistance of the component surface.

Other Surface Treatment

Applicable Materials of Passivation

Stainless Steels

The most common candidates, including 304, 316, and 400-series alloys. Their high chromium content reacts with passivating agents (like nitric or citric acid) to form a robust protective oxide layer, making them ideal for corrosion-prone applications.

High-Nickel Alloys

Materials such as Inconel and Hastelloy, used in extreme environments (e.g., high heat, chemicals), benefit from passivation to enhance their natural resistance to oxidation and pitting.

Certain Aluminum Alloys

While less common than for stainless steel, passivation (often using chromate or non-chromate solutions) helps protect specific aluminum grades from corrosion, particularly in aerospace and automotive parts.

Titanium

Though naturally resistant to corrosion, passivation can further stabilize its surface oxide layer, useful in medical implants and marine applications where long-term durability is critical.

Note: Passivation works best with chromium/nickel-rich metals (e.g., 304/316 stainless, Inconel) and select aluminum alloys (e.g., 6061), as their composition forms a protective oxide layer. It’s ineffective for low-chromium materials like carbon steel, 200-series stainless, or pure metals such as copper.

Our Metal Materials

KingStar’s Passivation Capabilities & Equipment

Capability	Details	Notes
Materials Handled	Stainless steel (304, 316, 400-series), high-nickel alloys, select aluminum	Passivation works best with chromium/nickel-rich metals (e.g., 304/316 stainless, Inconel) and select aluminum alloys
Process Options	Nitric acid passivation, citric acid passivation (RoHS-compliant)	Traditional nitric acid passivation requires adding highly toxic sodium dichromate, while citric acid + ultrasonic method is safer and eco-friendly
Reaction Temperature	From room temperature up to ~65°C	-
Passivation Time	10–30 minutes (varies by material, alloy, and part complexity)	-
Compliance Standards	ASTM A967 (stainless steel), AMS 2700 (aerospace-grade requirements)	-
Part Sizes	Small components (≤10mm) to large parts (up to 1200mm in length)	-
Quality Checks	Post-process testing (salt spray testing, oxide layer thickness measurement)	Detailed information will be provided later in this page

Manual Passivation/Cleaning System

Basket Dimensions: 36 inches x 48 inches x 24 inches high, accommodating parts of various sizes.
Tank Configuration: Includes a single ultrasonic cleaning tank, a single rinsing tank, dual passivation tanks (for nitric acid and citric acid), dual final rinsing tanks, and a drying tank.
Versatile Processes: Capable of rough cleaning/rinsing/drying, zero-residue cleaning/rinsing/drying, or zero-residue cleaning/passivation/drying in either passivation tank.
Water Treatment System: Equipped with water purification and deionization systems to ensure zero-residue cleaning and passivation results.
Control System: Features a color touchscreen HMI and PLC control, with 10 operational programs and remote access functionality for streamlined operation and monitoring.

Angstrom Automated Cleaning/Passivation System

Basket Dimensions: 22 inches x 28 inches x 15 inches high, suitable for smaller to medium-sized parts.
Tank Setup: Comprises a single cleaning tank, a single rinsing tank, dual-position dual passivation tanks (for citric acid and nitric acid), dual final rinsing tanks, and a single drying tank.
Flexible Processing Capabilities: Supports rough cleaning/rinsing/drying, zero-residue cleaning/rinsing/drying, or zero-residue cleaning/passivation/drying in either passivation tank.
Advanced Control System: Equipped with a color touchscreen HMI and PLC controls, featuring 10 operational programs and remote access for efficient management.
Automation Features:
- TRANSTAR II overhead robotic system: A traditional overhead setup with acid-resistant design, transferring baskets via hooks (lifting/lowering into tanks) to prevent contact between acidic fumes/liquids and automation components.
- Multi-position loading/unloading conveyors for streamlined automation.
- Automatic liquid level maintenance and filling system.
Water Treatment: Integrated water purification and deionization systems ensure zero-residue cleaning and passivation performance.

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General Passivation Workflow at KingStar

Pre-Cleaning (Ultrasonic Cleaning)
Parts are first placed in an ultrasonic cleaning tank to remove surface contaminants (oils, debris, or machining residues). High-frequency sound waves dislodge particles, ensuring the metal surface is ready for passivation.
Rinsing
After cleaning, parts move to a rinsing tank to wash away any remaining cleaning agents—critical for preventing chemical interference in the passivation step.
Passivation
Parts are submerged in either a nitric acid or citric acid tank (based on material and requirements). The acid dissolves free iron and impurities, prompting the formation of a protective chromium oxide layer on the metal surface.
Final Rinsing
Post-passivation, parts undergo a thorough rinse in deionized water (via our purification system) to eliminate residual acid, ensuring zero chemical residue.
Drying
Parts are transferred to a drying tank to remove moisture, preventing water spots and ensuring the protective oxide layer sets properly.
Quality Verification
Finished parts undergo checks (e.g., salt spray testing) to confirm the passivation layer meets standards—details covered in our quality section.

Tests & Standards for Passivation

Test Type	Description	Standard
Salt Spray Resistance Test	Parts are exposed to a saltwater mist in a testing chamber to simulate harsh, corrosive environments.	Minimum 2 hours
Free Iron Detection Test	An alternative to Water Immersion and High Humidity Tests, designed for large parts that cannot fit in tanks or cabinets.	Evaluates free iron presence (time not specified)
Water Immersion Evaluation	Parts are submerged in distilled water to check for corrosion or rust formation.	Minimum 24 hours
Ferroxyl Test (Potassium Ferricyanide-Nitric Acid)	A highly accurate test using a prepared solution to identify free iron; requires daily solution preparation and safe handling. Not suitable for some steel grades or food-processing parts.	Fast results (specific time not specified)
Copper Sulfate Spot Test	A fast test using copper sulfate solution to detect free iron; unsuitable for steel with <16% chromium or food-processing parts.	6 minutes (fast results)
High Humidity Exposure Test	Parts are exposed to high humidity in a controlled cabinet to evaluate resistance to moisture-induced corrosion.	Minimum 24 hours

Note: All tests listed comply with the ASTM A967 standard for passivation quality verification.

Frequently Asked Questions

Why do my parts develop a dark, etched look after passivation?webadmin2025-07-22T09:20:39+00:00

Why do my parts develop a dark, etched look after passivation?

This is often flash attack—a form of uncontrolled corrosion that happens when passivation isn’t properly managed. Unlike the micro-thin, protective oxide layer we aim for, flash attack creates a dark, unevenly etched surface, undoing the goal of corrosion resistance.

This is usually because:

Contaminated acid baths: Over time, free iron or debris from previous batches builds up in the solution, throwing off the chemical balance and triggering erratic etching.
Poor pre-cleaning: Oils, greases, or thermal oxides (from welding/heat treating) left on parts trap bubbles, so acid reacts unevenly—eating away at exposed spots while skipping others.
Mixed stainless grades: Putting 300-series and 400-series stainless in the same bath causes galvanic corrosion. The less noble metal (like 400-series) corrodes faster than it would alone, leading to a patchy mess.

How we prevent it:

We refresh acid baths on a strict schedule, use RO/DI water to cut contaminants, and pre-treat parts with degreasers (or grinding/pickling for tough oxides). We also keep stainless grades separate—our dual tanks let us process different alloys safely. This attention to detail is why we rarely see flash attack in our work.

Can passivation be done on previously painted or coated parts?webadmin2025-07-22T09:10:39+00:00

Can passivation be done on previously painted or coated parts?

No, not effectively. Paint or coatings block direct contact between the metal surface and passivation chemicals, preventing the oxide layer from forming. For coated parts, you’d first need to strip the coating (we offer pre-treatment services for this) before passivating, then re-coat if needed.

How often should passivated parts be re-passivated?webadmin2025-07-22T09:09:35+00:00

How often should passivated parts be re-passivated?

It depends heavily on their environment and usage, but here are a few real-world examples from our clients to guide you:

Indoor machinery parts (e.g., stainless steel brackets in factory workshops): We’ve seen these last 5–7 years without re-passivation, as they’re sheltered from extreme moisture or chemicals.
Food processing equipment (e.g., 316 stainless conveyors): Regular cleaning with mild detergents can slowly degrade the oxide layer—most clients re-passivate every 2–3 years to stay compliant with food safety standards.
Marine components (e.g., boat hardware exposed to saltwater): The harsh, salty environment accelerates wear; we typically recommend re-passivation every 12–18 months to prevent pitting.

In general, watch for early signs of corrosion (tiny rust spots, discoloration) as your cue. Our team can also review your part’s material and use case to give a more precise timeline.

Is citric acid passivation as effective as nitric acid?webadmin2025-07-22T09:07:11+00:00

Is citric acid passivation as effective as nitric acid?

From what we’ve seen over years of running both processes, each holds its own—when matched to the right job.

Citric acid is our go-to for clients prioritizing safety and sustainability. We’ve used it extensively for food-grade equipment and medical parts, where toxic-free, RoHS-compliant processes are non-negotiable. It’s gentler to handle, easier to dispose of, and in our trials, it forms a reliably uniform oxide layer on 304 and 316 stainless—plenty tough for most industrial uses.

Nitric acid, though, is what we reach for when parts face extreme stress: think offshore drilling components or aerospace parts. Its stronger formula cuts through stubborn surface impurities (like heat-treat scale) that citric might miss, and we’ve found it delivers a slightly more robust layer for parts in constant contact with harsh chemicals.

We’ve fine-tuned both methods in our dual-tank setup, so whether you need eco-friendly compliance or heavy-duty resilience, we’ll pick the one that’s proven to work for your project.

Can passivation change the appearance of my parts?webadmin2025-07-22T09:28:23+00:00

Can passivation change the appearance of my parts?

No. The protective oxide layer from passivation is micro-thin, so it won’t dull, discolor, or alter your part’s surface finish—key for applications where looks matter.

If you do want to adjust appearance (e.g., a matte finish, brighter polish, or color), consider processes like abrasive blasting, electroplating, or anodizing (for aluminum). These methods intentionally modify surface texture or add layers to achieve the desired look.

What’s the difference between passivation and pickling?webadmin2025-07-22T08:53:04+00:00

What’s the difference between passivation and pickling?

Although both involve immersing metal parts in acid, they do not refer to the same process.

Passivation, as illustrated earlier, is all about protection. It uses mild acids (like nitric or citric) on already clean surfaces to dissolve free iron and spark the growth of a thin, invisible chromium oxide layer. This layer acts like a shield against rust and corrosion, and it doesn’t change how the part looks or feels—no rough spots, no color shifts. It’s a final step to keep parts durable long-term.

Pickling, by contrast, is a surface preparation process focused on stripping away unwanted materials. It uses more aggressive acids (such as hydrochloric or sulfuric acid) to dissolve mill scale, heat-treated oxides, rust, or heavy surface contaminants that form during manufacturing (e.g., welding, forging, or heat treatment). Unlike passivation, pickling intentionally removes a thin layer of the base metal, which can leave the surface slightly rougher or etched. While it cleans the surface, pickling does not create a protective layer on its own—parts often require passivation afterward to lock in corrosion resistance. You can put it in this way: pickling preps the surface to be “ready” for protection, while passivation delivers that protection.

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