Cleaning & Corrosion Control
What is the primary corrosion-control function of the commercially pure aluminum 'cladding' metallurgically rolled onto Alclad aluminum-alloy sheet?
Answer
It provides sacrificial (galvanic) protection to the underlying alloy core
The pure-aluminum surface layer is anodic relative to the stronger core alloy, so it corrodes sacrificially and also resists corrosion better than the core—this is why abrasives must not be worked through the cladding into the core. Pure aluminum is softer and weaker than the alloy, so cladding does not harden the surface or add strength, and no coating permanently excludes all electrolyte.
Source: FAA-H-8083-30B AMT Handbook—General, Ch. 'Cleaning and Corrosion Control' / aluminum-alloy protection; AC 43.13-1B, Ch. 6
Not the answer
- It permanently seals the alloy so electrolyte can never reach it
- It substantially increases the tensile strength of the sheet
- It case-hardens the surface so abrasives cannot scratch it
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