Avoiding Corrosion in Liquid Cooling Systems

Water and water/glycol solutions are the standard heat transfer fluids in industrial liquid cooling circuits, but their electrochemical activity also makes them corrosive toward the metals they contact. This article covers the three primary corrosion mechanisms — chemical corrosion, galvanic corrosion, and erosion corrosion — along with the design decisions, coolant chemistry, and maintenance practices that control each. The guidance is most relevant for liquid cold plates and plate-fin heat exchangers used in EV battery thermal management and ESS cooling. The pH ranges, chloride limits, and inhibitor types cited throughout are reference starting points. Actual values must be validated against the coolant supplier’s specification, the alloys and joining materials present, and the operating conditions.

Why Liquid Cooling Circuits Are Inherently Prone to Corrosion

Corrosion risk in liquid cooling circuits is built into the chemistry of water-based coolants and the metals they contact. Dissolved oxygen is the primary accelerator. In closed-loop systems, it is consumed during the first weeks of operation, after which the corrosion rate drops substantially. Open-loop systems replenish oxygen continuously through air exposure, sustaining higher corrosion rates throughout service.

Coolant pH, conductivity, inhibitor concentration, temperature, flow velocity, and the specific combination of wetted materials all interact to determine which corrosion mechanism dominates. No single parameter governs corrosion behavior in isolation.

Corrosion is classified as either general or localized. General corrosion produces uniform metal loss across a surface — predictable, and typically detectable before structural failure. Localized corrosion, primarily pitting, penetrates quickly through thin-walled components like cold plate channels, often causing leaks before any surface damage is visible.

Galvanic Corrosion: Dissimilar Metals and Electrochemical Risk

Galvanic corrosion occurs when two metals with different electrochemical potentials are electrically connected within a conductive coolant. The coolant acts as the electrolyte, and the less noble metal corrodes preferentially. The rate depends on the potential difference, coolant conductivity, pH, inhibitor chemistry, the anode-to-cathode area ratio, temperature, and whether an uninterrupted electrical path exists between the components.

Aluminum and copper are a high-risk pairing in conductive water-based coolants. Without appropriate inhibitor chemistry or galvanic isolation, an aluminum cold plate connected to copper or brass components in the same circuit is likely to experience accelerated attack. The actual rate, however, depends on all the variables above. Circuits combining aluminum with copper or brass should be evaluated against the specific coolant formulation rather than treated as universally prohibited. Some inhibitor packages are qualified for mixed-metal circuits. Where dissimilar metals cannot be avoided, dielectric unions can break the electrical path at material transitions.

Galvanic risk extends to every wetted component — fittings, connectors, valves, and clamps all contribute electrochemically. Material compatibility must be assessed for the complete fluid path.

Erosion Corrosion: Flow Geometry, Particles, and Component Flow Rate Limits

Erosion corrosion occurs when coolant velocity is sufficient to mechanically remove the protective oxide layer from metal surfaces. This exposes base metal to chemical attack before the oxide can reform, and the process self-reinforces as flow continues to strip each newly forming layer. Risk concentrates where flow direction or velocity changes abruptly — channel bends, inlet manifolds, abrupt diameter transitions, and areas downstream of turbulence-generating geometry.

There is no universal safe velocity threshold for all cold plates. Maximum flow rate must come from the component supplier’s data sheet and be validated against channel geometry, coolant chemistry, filtration quality, and pressure-drop limits for the specific installation.

Coolant containing suspended particles — from prior corrosion products, scale, or inadequate filtration — intensifies the erosion mechanism even at low bulk flow velocities. Particle filters are therefore a corrosion-control component, not only a cleanliness measure.

Control measures include larger-radius bends, gradual diameter changes at manifold entries, smooth internal channel finishes, reduced dissolved oxygen, and filtration appropriate to the channel geometry. Component-specified maximum flow rates must not be exceeded during commissioning or maintenance flushing.

Coolant Chemistry: pH, Inhibitors, and Monitoring

Effective coolant selection for aluminum cold plates addresses three interdependent controls: pH stability, inhibitor chemistry matched to the metals present, and glycol condition maintained within its service life.

pH: For aluminum-dominant cold plate circuits, many coolant suppliers specify a near-neutral to mildly alkaline pH range — commonly 7.0–8.5. This protects the aluminum oxide layer from both acidic pitting and alkaline dissolution. Mixed-metal circuits and glycol-based fluids may use different ranges, such as 8.0–10.5, depending on the inhibitor package and materials present. The coolant supplier’s specification is the controlling requirement; the ranges above are starting-point references only.

Inhibitor selection by metal:

• Phosphates: effective on iron, steel, and most aluminum
• Tolyltriazole (TT) / benzotriazole (BT): effective on copper and brass; standard in mixed-metal circuit inhibitor packages
• Silicates: broad-spectrum at low concentrations; risk of deposits at higher concentrations or elevated temperatures
• Nitrites: effective on ferrous metals; not suitable at high concentrations where tin-lead solder is present
• Molybdates: effective on ferrous metals; widely used as a replacement for legacy chromate-based inhibitors

Inhibitors deplete through chemical consumption and thermal degradation. Concentration must be verified at scheduled intervals — elapsed time alone is not a reliable indicator.

Monitoring: A refractometer measures glycol concentration only. Inhibitor concentration requires a separate check — the coolant supplier’s test kit, a colorimetric or titration method, or laboratory analysis such as ICP or ion chromatography where closer monitoring is needed. pH and inhibitor levels should be re-verified within 24–48 hours of any flush or refill, once the system reaches operating temperature.

Standards and Test Methods for Corrosion Control

Specifying corrosion control should reference established test methods and guidelines rather than relying on generic parameters:

For EV and ESS applications, coolant qualification should also address thermal cycling stress on wetted joints, vibration exposure, and freeze-protection performance alongside corrosion resistance.

---

Aluminum Alloy and Brazing Design Considerations

Corrosion resistance in aluminum cold plates depends on cold plate design decisions — alloy selection, braze design, surface condition, and coolant compatibility — not coolant chemistry alone.

• Alloy selection: 3xxx-series alloys (manganese-based) are widely used in heat exchanger and brazing sheet applications for their corrosion performance across many coolant environments. 6xxx-series alloys (magnesium-silicon) offer higher structural strength and are common in machined or extruded cold plate bodies. Their corrosion behavior must be validated against chloride level, pH, surface treatment, and the joining process used.
• Braze cladding: In some brazing sheet designs, the cladding layer is formulated to be slightly more anodic than the core alloy. This provides a degree of sacrificial protection for the structural material — similar in principle to zinc anodes in marine corrosion protection. This should not be assumed for all brazed cold plates. The cladding alloy, filler alloy, core alloy composition, and post-braze surface condition must all be specified and validated for the intended application.
• Surface finish: Internal channel surface roughness creates localized turbulence that accelerates erosion corrosion at operating flow velocities. Smooth internal finishes and gradual port transitions reduce this risk without sacrificing thermal performance.

Our Water Cooling Plates are manufactured from aluminum alloys selected for EV and ESS environments, with channel geometry and surface specifications developed for long-term corrosion resistance.

Maintenance Schedule for Long-Term Corrosion Control

The following schedule supports ESS service life by catching coolant chemistry problems before they cause component damage.

pH outside the coolant supplier’s specified range should trigger immediate flushing and refilling. Attempting in-place pH correction while continuing to operate accelerates corrosion damage that cannot be reversed afterward.

Conclusion

Corrosion control in aluminum liquid cooling circuits requires matching coolant chemistry, material selection, and maintenance practice to the conditions of each specific system. The failure modes that most consistently cause service interruptions in EV and ESS applications — pitting from halide contamination, galvanic attack at mixed-metal junctions, and erosion at high-velocity channel geometry — each have defined engineering controls. These are most effective when addressed at the design stage.

In the cold plates we design for EV battery and ESS thermal management, three variables most consistently determine long-term corrosion resistance: alloy and braze cladding specification, inlet water quality at commissioning, and inhibitor chemistry maintained throughout service. Systems that enter service within the coolant supplier’s specified pH and inhibitor range — and are kept there through scheduled monitoring — routinely achieve their design life without corrosion-related failures.

Engineers evaluating cold plate options for corrosion-sensitive EV or ESS applications are welcome to contact us with their circuit architecture, coolant chemistry, material list, and operating conditions for a compatibility review. Our Water Cooling Plates are available with application engineering support covering alloy selection, pressure testing, and coolant compatibility.

FAQ