Poor Design against Corrosion after 4 days in salt spray chamber (SWAAT test): aluminium tube brazed to a copper tube with Zn-Al fillet. The galvanic potential difference between copper and aluminium causes massive galvanic corrosion on the aluminium tube to the left, which is less noble than the copper tube. Moreover, the zinc fillet in the brazing area has been heavily attacked by galvanic corrosion.

A heat exchanger consisting of copper tubes and aluminium fins will show excessive fin loss due to the large relative electric potential difference between copper and aluminium.

The same will happen to one of the materials in cases where the design consists of aluminium alloys that are not compatible in terms of galvanic potential. Likewise, the selection of filler material in a brazed joint may cause galvanic corrosion and attack the filler itself, or the joined materials.  

Good design against corrosion after 21 days in salt spray chamber (SWAAT test): Two aluminium tubes of the same alloy brazed with Al-Si. Very minor pitting corrosion was observed on the tubes.

A well-balanced alloy and fillet material selection in an all-aluminium heat exchanger will have a reduced fin loss compared to the traditional copper-aluminium concept.

Consequently, galvanic corrosion in all-aluminium heat exchangers is most often a result of poor design in terms of selection of materials to be joined and the joining method itself. If the material selection and joining method are properly considered, design against corrosion will prevent galvanic corrosion and contribute to a long-lived design, even in harsh environments.

With respect to the use of aluminium, there is a wide variety of alloys and joining methods that meets different needs for strength, corrosive characteristics and ductility. For support on design against corrosion, please contact Hydro here.