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Avoiding Galvanic Corrosion

When selecting components for your cooling loop, you must consider their material compatibility as well as their individual performance. Although an aluminum cold plate paired with a copper-tubed heat exchanger might meet your thermal requirements, it is not a reliable cooling circuit. Copper and aluminum have widely different electrochemical potentials, so when they are combined in a cooling system, galvanic corrosion is likely. Galvanic corrosion (also called dissimilar metal corrosion) erodes the metal, causing leaks over time.

Galvanic Cell 

Figure 1: Galvanic Cell

In a cooling loop, metallic materials in electrochemical contact can form a galvanic cell, or battery (fig. 1). In a galvanic cell, when two metals with different electrical potentials are connected, there is a potential difference across them. The metal with the higher electrical potential becomes the anode, and the lower, the cathode. A current will flow from the anode to the cathode. The anode dissolves, or corrodes, to form ions. These ions drift into the water where they either stay in solution or react with other ions in the electrolyte. This process is known as galvanic corrosion.

A galvanic cell requires three elements:

  • Two electrochemically dissimilar metals,
  • An electrically conductive path between the two metals, and
  • An electrolyte to allow the flow of metal ions.

In a typical liquid cooling circuit, the plumbing provides the electrically conductive path, and the aqueous coolant provides the electrolyte. In the copper/aluminum scenario mentioned above, the aluminum is the anode, the copper is the cathode and the cooling fluid is the electrolyte. Over time, the aluminum corrodes as it dissolves into the water.

The galvanic corrosion rate depends on the electrical potential between the two metals. The Galvanic Series (fig. 2) orders metals based on the potential they exhibit in flowing seawater. The most reactive are at the top of the table, and the least reactive at the bottom.

Figure 2: Galvanic SeriesFigure 2: Galvanic Series

Fig 2. Galvanic Series*

  • Magnesium
  • Zinc
  • Aluminum (most types)
  • Iron, plain carbon and low alloy steels
  • Lead, high lead alloys
  • Tin plate, tin/lead solder
  • Chromium plated materials, chromium alloys, chromium type-steels
  • Brass
  • Copper
  • Nickel
  • Stainless steels
  • Silver
  • Gold

*adapted from MIL-STD-889

Elevated temperatures, which are likely in cooling loops, accelerate galvanic corrosion. A 10°C increase in temperature can approximately double the corrosion rate. Corrosion inhibitors can be added to the cooling water. This retards, but does not eliminate, galvanic corrosion. Corrosion inhibitors bind with the ions in solution to neutralize them. The inhibitors are consumed in this process so they need replacing regularly. Non-aqueous coolants, such as oils, eliminate galvanic corrosion because they do not support ions. However, thermal performance is sacrificed, as the thermal conductivities of heat transfer oils are generally significantly lower than water-based coolants.

To avoid galvanic corrosion, we highly recommend using the same materials, or materials with similar electrical potential, throughout your cooling loop. You should ensure that the plumbing, connectors and other components do not introduce a reactive metal into the system.

Using the same materials throughout your circuit does not mean that you have to sacrifice performance. Lytron offers high performance heat exchangers and cold plates with aluminum, copper and stainless steel fluid paths.

Fluid Path Copper Stainless Steel Aluminum
Heat Exchangers 6000 Series 4000 Series ES Series
OEM Coils Aspen Series
Cold Plates CP10 Tubed CP10 Tubed CP20 Flat Tubed
CP12 Tubed CP30 Vacuum Brazed
CP15 Tubed
CP25 Ascent Flat Tube
Copper Etched

Lytron's applications engineers are available to consult on component material compatibility. With careful design and component selection, you can ensure years of reliable, corrosion free service from your cooling loop.