Weathering Resistance of Wrought Alloys

There are three quantitative criteria for assessing the atmospheric corrosion of a metal  

As shown by the data listed in Table C.5.2, the mechanical characteristics do not change much for those alloys that show good resistance to atmospheric corrosion, namely 

The measurement of pitting depth is the most representative assessment of atmospheric corrosion of aluminium. It is carried out under an optical microscope at low magnification (in the order of 10 X to 20 X) by successive focussing on the rim and the bottom of the pit, the depth being given by the displacement of the lens. This method takes some time because at least five measurements have to be taken on the deepest pits that have been detected visually. These measurements can then be evaluated statistically (see Section B.4.4). 

The analysis of these data shows that the maximum pitting depth never exceeds 0.5 mm after 20 years of exposure [12]. Within the same alloy series, there may be dilferences between alloys, in the order of 0.1-0.2 mm, at most, after 20 years of exposure. 

The casting technology and the elaboration schedules of semi-products have undergone significant changes since 1935. On the basis of the available and usable results on several alloys, such as 1100, 3003, 6061 and 6082, it does not appear that the manufacturing conditions of semi-products, sheets or profiles have a significant 

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