SAMPE Journal - November/December 2021 - 88

MEMBER NEWS / TECH TIDBITS
Moisture and Galvanic Corrosion
Effects on Composites
Dr. Scott W. Beckwith, FSAMPE
President and CTO, BTG Composites, Inc., Taylorsville, UT
Anodic
Fiber-reinforced composite materials and their manufactured structures,
almost always are subjected to a variety of environmental exposures during
their service lifetimes within field operational exposures. Some environments
may well be limited to very narrow ranges of temperature, humidity
(moisture), direct ultraviolet (UV) and durations over time. However, it is
always prudent to consider these environments and conduct appropriate
evaluations analytically and potentially via experiments on representative
material test coupons or subscale models, prior to proceeding into production.
Galvanic corrosion often comes to mind because it occurs with
the use of certain metals that exist within the Anodic (most active) range
when in adjacent contact with certain fiber reinforcement systems - such
as carbon and graphite. These fibers lie in the Cathodic (least active) range
of material scale as seen in Figure 1. Hence, galvanic corrosion must be considered
in design, such that use of the two must be separated from direct
contact if the metals shown with the red vertical line are required. There
are numerous ways to avoid such corrosive interactions when the Anodic
materials are desired in designed composites structures. Applications often
are required for bolted, riveted, pinned, dual material joints, lightning
strike applications, and other areas where carbon and/or graphite fibers
must exist mutually.
Potential solutions for avoiding of galvanic corrosion when carbon or graphite fibers are used in conjunction with
Anodic metals involve several following options:
* Use a glass fiber/resin interface layer in between the metal and carbon fiber material,
* Use a resin-rich layer between the carbon fiber material and metal,
* Use a permanent grease interface layer,
* Coat the metal with an adhesive or paint layer, and,
* Make sure that such actions above will remain permanent & not be subject to abrasive wear action over time.
(most active)
Magnesium alloys
Zinc
Alclad 7000 series aluminum alloys
5000 series aluminum alloys
7000 series aluminum alloys
Pure aluminum & alclad 2000 series alloys
Cadmium
2000 series aluminum alloys
Steel and iron
Lead
Chromium
Brass and bronze alloys
Copper
Stainless and heat resistant steels
Titanium
Silver
Nickel & nickel alloys
Gold
Graphite composites
Cathodic
(least active)
Figure 1. Anodic metals that interact with
carbon and graphite fibrous materials.
Considering that moisture effects (e.g. relative humidity (RH) and rain primarily) often must be considered -
there has been an extensive amount of research conducted in the 1980's on carbon and other fibrous materi88
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SAMPE Journal - November/December 2021

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