$($a$)$ The following data are for the pitting of pure aluminum in chloride solutions for a short$-$term

immersion of $24h[67].$ What is the pitting potential for aluminum in $0\mathrm{.}6$MNaCl $($the

chloride ion concentration in seawater$)?$

$($b$)$ How does the value for pure aluminum in the short$-$term immersion test compare with the

pitting potential of aluminum alloys as determined from the long$-$term practical immersion

tests in Table $10\mathrm{.}5?$

$($c$)$ If there is a difference between the two values, explain why.

Table $10\mathrm{.}5$ Corrosion behavior of various aluminum alloys in seawater after $1-$year immersion $[25]$

${?}^{\text{a}\text{A}\text{l}\text{l}\text{o}\text{y}}1100$ is commercially pure aluminum. The other alloys have the following principal additions: $2000$ series,

$Cu$;$3000$ series, $Mn$;$5000$ series, $Mg$;$6000$ series, $Mg$ and $Si$;$7000$ series, $Zn.$ The amount of the alloy addition

is generally $3-5wt\%.$