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Which corrosion problem arises where aluminium meets steel?

  • A.Stress corrosion cracking of the aluminium, which occurs only under a sustained tensile load in a damp environment
  • B.Galvanic corrosion of the aluminium
  • C.Galvanic corrosion of the steel, which is the less noble of the two metals and therefore corrodes preferentially
  • D.No corrosion occurs

Answer: B

Aluminium is anodic to steel, so in the presence of an electrolyte it corrodes preferentially and rapidly at the joint. Isolation using adhesive, coatings or non conducting washers is therefore essential wherever the two metals meet. Mixed material construction has made this a significant design consideration in modern vehicles.

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