Why does Cl- corrode aluminum containers?

Question

I heard that $\ce{Cl^-}$ will corrode aluminum containers. Why? Is it because it would form a galvanic cell or produce coordination compounds?

Answer 1

In general, it should not. Under the right conditions, i.e. acidic conditions at high temperature on a freshly exposed (e.g. scratched) $\ce{Al}$ surface, you could get some oxidation to $\ce{AlCl3}$. One industrial process for producing $\ce{AlCl3}$ is via the reaction:

$$\ce{2 Al + 6 HCl → 2 AlCl3 + 3 H2}$$

at $\mathrm{600-800^oC}$. It would of course happen much more slowly, if at all, at lower temperatures and lower acidity.

The necessity of a freshly scratched surface is to expose the aluminum metal itself, as aluminum pretty rapidly forms a thin, inert oxide layer upon exposure to air or water.

In other words, in the absence of this perfect storm of conditions, aluminum cans should be very resistant to corrosion by $\ce{NaCl}$.