Medium-phosphorus electroless nickel plating (ENP 79)

The balance between
mechanical performance and
anti-corrosion protection

Componenti meccanici con rivestimento uniforme di nichelatura chimica medio fosforo ENP 79

Medium-phosphorus
electroless nickel plating

The medium-phosphorus electroless nickel plating treatment, indicated in the Deltar procedure as ENP 79, is an autocatalytic nickel-phosphorus alloy with a P content between 5% and 9% by weight.
It is the most versatile choice among the three phosphorus levels: it offers an optimal compromise between the mechanical performance of low phosphorus and the anti-corrosion resistance of high phosphorus, without going to extremes on either characteristic.

Characteristics of the ENP 79 deposit

Medium phosphorus offers a balanced behaviour of the deposit:

Good “as deposited” hardness, intermediate between
low and high phosphorus
Good wear and corrosion resistance in moderately
aggressive environments
Excellent thickness uniformity, typical of
autocatalytic processes

When to choose medium phosphorus

Medium phosphorus is recommended when the component must balance more than one requirement without favouring just one:

Anti-corrosion protection in standard industrial
environments (not strongly aggressive)
Moderate wear resistance
Thickness uniformity on complex geometries

It is the most balanced choice in cases where neither maximum hardness
nor maximum anti-corrosion protection is the dominant design constraint.

Typical applications

Mechanical components for standard industrial environments/li>
Fittings and valves not intended for extreme environments
Automotive components and general engineering
Sealing elements and coupling seats in moderate environments

The ENP 79 process
at Deltar

The deposition process takes place chemically, without electric
current, through an autocatalytic process controlled
in every parameter:

Bath temperature: 88-91 °C
Bath pH: 4.9-5.3
Nickel concentration: 2.4-3.4 g/L
Continuous control of the composition with
dedicated electronic instrumentation and daily verification
by volumetric titration

The Deltar LS019 procedure complies with the main international
standards in the ENP sector: ASTM B117, B183, B322, B499, B571,
B578, B602, B636, B656, B689, B733, ISO 4527, MIL-C-26074.

Post-deposition
heat treatments

When required, the ENP 79 deposit can be subjected to heat treatment for two purposes:

Dehydrogenation (ASTM B733 Class 3): eliminates the hydrogen incorporated during deposition, prevents hydrogen embrittlement and improves coating adhesion

Hardness increase (ASTM B733 Class 2): further increases the surface hardness of the deposit with calibrated thermal cycles

Standard quality
controls

Each batch treated with ENP 79 is accompanied by control specimens (dimensions 50 × 100 × 1 mm in Fe, or supplied by the customer in a specific material) on which the standard tests are carried out:

Visual inspection
Thickness control (weighing method, ASTM B733 par. 9.3.5)
Adhesion impact test (ASTM B733 par. 9.4.2, ASTM B571)
Burnishing test (ASTM B571 par. 4.1)

On request, additional controls can be carried out: Vickers hardness, bend test, porosity test (ferroxyl), phosphorus determination, salt spray (ASTM B117). At the end of processing, Deltar issues an Inspection Certificate compliant with the EN 10204 3.1 standard.

What is needed for
a quick assessment

Technical drawing with areas to be treated and to be protected
Type of base material
Operating conditions (corrosion, wear, temperature)
Required thickness
Applicable specifications

Medium-phosphorus electroless nickel plating (ENP 79)

The balance between mechanical performance and anti-corrosion protection