Elaboration and Transformation Techniques

Several modes of elaboration are used for aluminium alloys casting, rolling, extmsion, etc. This is not an important factor. 

Roll casting does not significantly modify the corrosion resistance of alloys of the 1000 and 3000 series, and is said even to improve the resistance to pitting corrosion [4]. 

Cold working only has a minor effect on the corrosion resistance. At most, it changes the aspect of corrosion pits. In highly cold-worked metal, pits tend to propagate as so-called mole tunnels. 

Heat treatments of age-hardenable alloys—solution heat treatment, quenching and age hardening— lead to changes in the nature and the distribution of metallurgical constituents present in these alloys. They have an important influence on the susceptibility of these alloys to certain forms of corrosion, especially intercrystalline corrosion (see Section B.2.3) and stress corrosion (see Section B.2.5). 

Alloys 2017 and 2024 are known for their high sensitivity to the quenching rate. They have to be quenched very quickly in cold water as soon as they leave the solution heat treatment furnace. Otherwise, if the quenching rate is low or if the water temperature is too high, a high susceptibility to intercrystalline corrosion will result. The corrosion rate increases greatly with the temperature of the quenching water, as shown by the results obtained on 2024 reported in Table B.6.2. 

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