Intergranular CorrosionThe aluminum alloys that are given high strength by heat treating contain considerable amounts of copper or zinc. If those containing copper are not cooled rapidly enough in the heat-treating process to keep the copper uniformly distributed, there is a concentration of copper at die grain boundaries, setting up a potential difference there. Corrosion occurs in damp air, eating into die boundaries, causing "intergranular corrosion" and resultant brittleness, with lowered fatigue resistance from the notches thus formed. Precise control of the heating and quenching temperatures and times is a minimum requirement.
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