A Guide to Electroless Nickel Phosphorus Levels

Executive Summary

• Corrosion resistance favors high phosphorus, and as-plated hardness favors medium phosphorus.
• A single requirement such as non-magnetic behavior can decide the phosphorus level before any detailed spec work.
• Micro Plating runs both phosphorus levels and backs each one with salt spray and hardness test data.

How To Choose The Right ENP Phosphorus Levels

Specifying electroless nickel means choosing between medium and high phosphorus. A wrong pick can surface later as a coating failure or a part sent back for stripping and replating. Sorting out the right level from a spec sheet is not an easy call.

At Micro Plating, we match each part to the right phosphorus level. You end up with a deposit built for its service conditions and no second trip through the plating line. Read on to learn more about the differences between medium and high phosphorus and how to specify the right one.

Get a Quote for High or Medium Phosphorus Electroless Nickel Plating

Medium and High Phosphorus Comparison

Micro Plating offers two electroless nickel phosphorus levels: medium and high. The correct range depends on the deposit properties the part requires.

Match Each Range to Performance Needs

Phosphorus content changes several properties of the finished deposit. The differences below help identify which range fits the part’s primary requirement.

• Phosphorus range: Medium-phosphorus deposits contain 6 to 9 percent phosphorus by weight compared with 10 to 12 percent for high-phosphorus deposits.
• Corrosion resistance: High phosphorus provides greater overall corrosion resistance than medium phosphorus.
• As-plated hardness: Medium phosphorus reaches greater hardness directly from the plating bath.
• Impact tolerance: High phosphorus stays more ductile as plated. That ductility lets it absorb impact and flexing better than medium phosphorus.
• Magnetic behavior: High phosphorus is non-magnetic as plated compared with the slight magnetism retained by medium phosphorus.
• Appearance: High phosphorus produces a semi-bright finish and is less prone to staining than medium phosphorus. Medium phosphorus produces a brighter finish.

Rule Out the Wrong Range Before Plating

A controlling requirement such as non-magnetic behavior can rule out one range before detailed specification work begins. Confirming that requirement early reduces the risk of applying a deposit that must be removed and replated.

Corrosion Resistance of Medium and High Phosphorus

Choose high phosphorus for acidic environments and medium phosphorus for alkaline or caustic environments. Deposit thickness must also match the required level of corrosion protection.

How Exposure and Thickness Determine Phosphorus Range

Chemical exposure determines which phosphorus range to consider first. Our test results show how deposit thickness affects high-phosphorus corrosion performance.

• Acidic service: Consider high phosphorus first for acidic environments involving hydrogen sulfide or carbon dioxide.
• Alkaline and mild indoor service: Consider medium phosphorus first for alkaline or caustic environments as well as personal handling and mild indoor exposure.
• Salt spray testing: ASTM B117 results showed our high-phosphorus deposits outperformed our medium-phosphorus deposits by more than 4 to 1.
• Extended salt spray testing: High-phosphorus deposits thicker than 0.001 inch withstood at least 1,000 hours of ASTM B117 testing on polished aluminum and carbon steel panels.
• Deposit porosity: Thicknesses above 0.0004 inch result in low to zero porosity in our high-phosphorus deposits and limit substrate exposure to corrosive media.

Reduce the Risk of Corrosion Failure

ASTM B117 compares relative corrosion resistance under controlled salt spray conditions and cannot by itself predict performance in actual service. Give us the chemicals, concentrations, and temperatures the part will encounter so we can confirm the phosphorus range and deposit thickness.

Hardness and Heat Treatment by Phosphorus Level

Choose medium phosphorus when the deposit needs greater hardness without heat treatment. Choose high phosphorus with heat treatment when the part needs greater corrosion resistance and higher final hardness.

Hardness Ranges Before and After Heat Treatment

Micro Plating’s medium-phosphorus deposits reach 54 to 65 Rc as plated. Our high-phosphorus deposits reach 40 to 48 Rc in the same condition. Medium phosphorus can meet a requirement within its range without a separate hardening step.

Heat treatment raises medium phosphorus to 65 to 68 Rc. A four-hour cycle at 550°F raises high phosphorus to 68 to 70 Rc and produces hardness comparable to hard chrome. The treated high-phosphorus deposit records 10 to 15 milligrams of weight loss under Taber Wear Index testing.

Control Heat Treatment Cost and Results

State whether the hardness requirement applies to the as-plated or heat-treated deposit. That distinction avoids unnecessary processing and gives us the correct hardness range for final inspection.

Specifying the Correct Phosphorus Level

The governing plating standard may already control deposit thickness and post-plating treatment. Part requirements identify the correct choice between the two electroless nickel phosphorus levels.

Build the Specification From Part Requirements

We plate electroless nickel to AMS 2404, ASTM B733, AMS-C-26074, MIL-C-26074, and MIL-DTL-32119 when those standards apply. Under AMS-C-26074 and MIL-C-26074, the grade sets minimum deposit thickness while the class sets the post-plating treatment.

State the phosphorus range on the drawing when the governing standard permits either medium or high phosphorus. Specify a range rather than an exact percentage because we tune the deposit within the range to the hardness the part requires.

Part geometry should not determine the phosphorus range because deposits in either range coat threads, recesses, and internal features uniformly. This coverage can eliminate post-plate polishing or machining. Our in-house X-ray fluorescence testing verifies the finished phosphorus content and coating thickness. Both ranges meet REACH AND RoHS requirements.

Resolve Potential Conflicts Before Production

Clear phosphorus, thickness, and heat-treatment requirements keep the drawing and purchase order consistent and give our laboratory measurable acceptance criteria. Send the complete drawing and specification with your quote request so we can confirm the phosphorus range before plating begins.

Choosing ENP Phosphorus Levels FAQ

Q: How does electroless nickel thickness affect finished dimensions?

A: A 0.0005-inch deposit increases a plated outside diameter by about 0.001 inch and reduces a plated bore by about 0.001 inch.

Q: How does the substrate surface affect the finished deposit?

A: Substrate condition influences the plated surface and deposit porosity so required finish values and defect limits should be stated before plating.

Q: Can selected areas of a part remain unplated?

A: Yes, we can use custom masking to keep specified features free of electroless nickel.

Q: Does heat treatment change properties besides hardness?

A: Heat treatment can reduce corrosion resistance and increase the magnetic response of a high-phosphorus deposit.

Which Phosphorous Levels Are Right For Your Application?

The choice between medium and high phosphorus comes down to the part’s requirements. Corrosion resistance, hardness, magnetism, and appearance each point toward one level or the other.

At Micro Plating, we match the phosphorus level to the required deposit properties and service conditions. We provide RoHS and REACH compliant electroless nickel plating services and specialize in alloying high phosphorus coatings.

Click below to learn more and get a quote.

Get a Quote for High or Medium Phosphorus Electroless Nickel Plating