Unalloyed Aluminium Series

Within the BS series the corrosion resistance of unalloyed aluminium increases with increasing metal purity. 

Iron and silicon are the two main impurities of unalloyed aluminium in the 1000 series their total concentration determines the purity of the metal. The iron/silicon ratio is close to two, for most grades, unless it is deliberately modified, as with the 8000 series. The concentration of impurities can vary, depending on the alloy, from a few ppm (parts per million) in refined aluminium (1199) up to 1000-2000 ppm in most wrought alloys. The impurity level of casting alloys can be higher for alloys based on secondary aluminium. 

The dissolution potentials of alloys of the 5000 and 6000 series as well as those of magnesium and silicon-containing casting alloys of the series 40000 and 50000 are very close to each other, and very similar to that of unalloyed aluminium of the 1000 series (Table B.1.4). Therefore, there is no risk of galvanic corrosion between these materials. 

The 1.3-mm-thick aluminium sheets were manufactured in Neuhausen (Switzerland) in 1895. The composition of the metal corresponds to what was commonly achieved when the production of aluminium by molten salt electrolysis started (Table C.5.1). Very high in iron and siUcon, the metal contained 98.3% aluminium. In the last 50 years, when unalloyed aluminium (1000 series) has been used for this type of application, it contains at least 99.5% aluminium. 

In the 1000 series, the aluminium content has no important influence on the dissolution rate, which is the same for 1050, 1080 and 1199, as shown in Table E.5.10. The dissolution rate of unalloyed aluminium (1000 series) in nitric acid has been the subject of numerous... 

Parts made of the steel SAE 304 (X5CrNil8-10, DIN-Mat. No. 1.4301) were damaged by crevice corrosion after less than 6 months, whereas bolts made of the same material used as fasteners for unalloyed steel or aluminium were not damaged [114]. In condenser pipes cooled with seawater, the steels of the SAE 304 series failed after brief exposure due to massive pitting and crevice corrosion. [148]. The material also reacts to addition of chlorine to prevent fouling with an increased susceptibility to pitting corrosion [149]. 

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