Corrosion Control - Galvanic Table
Originally published August 1997
Listed below is the latest galvanic table from MIL-STD-889. I have numbered
the materials for future discussion of characteristics. However, for any
combination of dissimilar metals, the metal with the lower number will
act as an anode and will corrode preferentially.
The table is the galvanic series of metals in sea water from Army Missile
Command Report RS-TR-67-11, "Practical Galvanic Series."
The Galvanic Table
End - Noble (Less Active, Cathodic)
- Mg alloy AZ-31B
- Mg alloy HK-31A
- Zinc (hot-dip, die cast, or plated)
- Beryllium (hot pressed)
- Al 7072 clad on 7075
- Al 2014-T3
- Al 1160-H14
- Al 7079-T6
- Cadmium (plated)
- Al 218 (die cast)
- Al 5052-0
- Al 5052-H12
- Al 5456-0, H353
- Al 5052-H32
- Al 1100-0
- Al 3003-H25
- Al 6061-T6
- Al A360 (die cast)
- Al 7075-T6
- Al 6061-0
- Al 2014-0
- Al 2024-T4
- Al 5052-H16
- Tin (plated)
- Stainless steel 430 (active)
- Steel 1010
- Iron (cast)
- Stainless steel 410 (active)
- Copper (plated, cast, or wrought)
- Nickel (plated)
- Chromium (Plated)
- AM350 (active)
- Stainless steel 310 (active)
- Stainless steel 301 (active)
- Stainless steel 304 (active)
- Stainless steel 430 (active)
- Stainless steel 410 (active)
- Stainless steel 17-7PH (active)
- Niobium (columbium) 1% Zr
- Brass, Yellow, 268
- Uranium 8% Mo.
- Brass, Naval, 464
- Yellow Brass
- Muntz Metal 280
- Brass (plated)
- Nickel-silver (18% Ni)
- Stainless steel 316L (active)
- Bronze 220
- Copper 110
- Red Brass
- Stainless steel 347 (active)
- Molybdenum, Commercial pure
- Copper-nickel 715
- Admiralty brass
- Stainless steel 202 (active)
- Bronze, Phosphor 534 (B-1)
- Monel 400
- Stainless steel 201 (active)
- Carpenter 20 (active)
- Stainless steel 321 (active)
- Stainless steel 316 (active)
- Stainless steel 309 (active)
- Stainless steel 17-7PH (passive)
- Silicone Bronze 655
- Stainless steel 304 (passive)
- Stainless steel 301 (passive)
- Stainless steel 321 (passive)
- Stainless steel 201 (passive)
- Stainless steel 286 (passive)
- Stainless steel 316L (passive)
- AM355 (active)
- Stainless steel 202 (passive)
- Carpenter 20 (passive)
- AM355 (passive)
- A286 (passive)
- Titanium 5A1, 2.5 Sn
- Titanium 13V, 11Cr, 3Al (annealed)
- Titanium 6Al, 4V (solution treated and aged)
- Titanium 6Al, 4V (anneal)
- Titanium 8Mn
- Titanium 13V, 11Cr 3Al (solution heat treated and aged)
- Titanium 75A
- AM350 (passive)
AC43.13, starting at Par 247, briefly covers several types of corrosion
and corrosion protection. The grouping of materials is an early method
of MS33586 which was superseded in 1969 by MIL-STD-889.
More on Galvanic Table (Almost straight from MIL-STD-889)
The Galvanic Table lists metals in the order of their relative activity
in sea water environment. The list begins with the more active (anodic)
metal and proceeds down the to the least active (cathodic) metal of the
A "galvanic series" applies to a particular electrolyte solution; hence
for each specific solution which is expected to be encountered for actual
use, a different order or series will ensue. The sea water galvanic series
is the most complete series that I know and I have not seen another series
published by either the Army, Navy, or Air Force. Civilian aircraft encounter
moisture and a salt of some kind.
Galvanic series relationships are useful as a guide for selecting metals
to be joined, will help the selection of metals having minimal tendency
to interact galvanically, or will indicate the need or degree of protection
to be applied to lessen the expected potential interactions.
Generally, the closer one metal is to another in the series, the more
compatible they will be, i.e., the galvanic effects will be minimal. Conversely,
the farther one metal is from another, the greater the corrosion will be.
Notice that graphite is at the bottom of the table. Think of the corrosion
potential if you put a big hunk of graphite on a small piece of magnesium.
In a galvanic couple, the metal higher in the series (or the smaller
the number I have given it) represents the anode, and will corrode preferentially
in the environment.
Types of Protection
Metals widely separated in the galvanic series must be protected if they
are to be joined. Appropriate measures should be taken to avoid contact.
This can be accomplished by several methods:
Sacrificial - by applying to the cathodic member a sacrificial coating
having a potential similar to or near that of the anodic member. If you
are designing for a sacrificial element, the sacrificial element should
be on the anodic side and smaller. Cadmium plate (No. 10) on steel bolts
(No. 81) holding 2024-T4 (No. 25) plates will sacrifice the cadmium instead
of corroding the Aluminum. This is one reason for using new bolts that
have the Cad plate intact. (Don't use Cad plate with Titanium (No. 82
through 88). But that's another story.)
Sealing - by sealing to insure that faying surfaces are water-tight.
(We have "talked" about this before.)
Resistance - by painting or coating all surfaces to increase the
resistance of the electrical circuit. (We have "talked" about this only
in terms of primer and sealant on fayed surfaces. There is still more that
can be done by design selection.)
The (Non-Aerodynamic) Area Rule
To avoid corrosion, avoid a small anodic area relative to the cathodic
Corollary I - Use LARGE ANODE AREA.
Corollary II - The larger the relative anode area, the lower the galvanic
current density on the anode, the lesser the attack.
Corollary III - The amount of galvanic corrosion may be considered as
proportional to the Cathode/Anode area ratio.
Corollary IV - Design for a SMALL Cathodic/Anodic Ratio (CAR). (When
designing, remember your small CAR.)
Corollary V - The same metal or more noble (cathodic, higher number in the table)
metals should be used for small fasteners and bolts.
Sea Water Environments
Metals exposed to sea water environments shall be corrosion and stress
corrosion resistant or shall be processed to resist corrosion and stress-corrosion.
Irrespective of metals involved, all exposed edges should be sealed with
a suitable sealant material conforming to MIL-S-8802. When non-compatible
materials are joined, an interposing material compatible with each shall
Material other than true metals, i.e., non-metallic materials which must
be considered as metallic materials, unless there is supporting evidence
to the contrary. If these material are essentially free of corrosive agents
(salts), free of acid or alkaline materials (neutral pH), and free of carbon
or metallic particles, not subject to biodeterioration or will not support
fungal growth, and do not absorb or wick water, then these may be considered
non-metallics suitable for joining to metals.
Many materials classed non-metallic will initiate corrosion of metals
to which they are joined, e.g., cellulosic reinforced plastics, carbon
or metal loaded resin materials, asbestos-cement composites.
More Precautions for Joining
Where it becomes necessary that relatively incompatible metals must be
assembled, the following precautions and joining methods are provided for
alleviation of galvanic corrosion.
For Electrical Connection - Select materials which are indicated
to be more compatible in accordance with the galvanic series.
Design metal couples so that the area of the cathode is smaller (appreciably)
than the area of the anodic metal. For example, bolts or screws of stainless
steel for fastening aluminum sheet, but not reverse.
Interpose a compatible metallic gasket or washer between the dissimilar
metals prior to fastening.
Plate the cathodic member with a metal compatible to the anode.
Select a electrically conductive sealant. (More on these later.)
Not For Electrical Conductors - Interpose a non-absorbing, inert
gasket material or washer between the dissimilar materials prior to connecting
Seal all faying edges to preclude the entrance of liquids.
Apply corrosion-inhibiting pastes or compounds under heads of screws
or bolts inserted into dissimilar metal surfaces whether or not the fasteners
had been previously plated or otherwise treated. In some instances, it
may be feasible to apply an organic coating to the faying surfaces prior
to assembly. This would be applicable to joints which are not required
to be electrically conductive.
Where practicable or where it will not interfere with the proposed use
of the assembly, the external joint should be coated externally with an
effective paint system.
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Revised -- 8 April 1998