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In the Institute of Metals Division Lecture of 1940, E. H. Dix, Jr.(1) discussed the acceleration of the rate of corrosion by high constant stresses. Experimental data obtained on this subject at the Aluminum Research Laboratories and a theory compatible with these facts were included in that lecture. The present paper contains data and ideas subsequently developed at the Aluminum Research Laboratories.

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Localized attack of metal specimens is often the result of electrochemical corrosion, not of simple chemical solution. The appearance of specimens suffering this type of attack has led laymen to attribute it to the presence of impurities in the corroding metal.However, impurities are only one possible cause for this type of attack.Other known or possible causes are: (1) grain boundaries, (2) orientation of grains,(3) differential grain size, (4) differential thermal treatment, (5) surface roughness, (6) local scratches or abrasions, (7) difference in shape, (8) differential strain, (9) differential pre-exposure to air or oxygen, IN MANY neutral solutions the corrosion of the common structural metals appears to be associated with the flow of electric currents between various parts of the metal surface at finite distances from one another. This statement is supported by much qualitative evidence, and in the case of steel ( 14) and of aluminum (7) the quantities of current flowing during corrosion account for the amount of corrosion which occurs.