Aluminum-base alloys intergranular corrosion

Austenitic stainless steels are the most significant class of corrosion-resistant alloys for which intergranular corrosion can be a major problem in their satisfactory use. The problem is most often encountered as a result of welding but also may result from stress-relief annealing or incorrect heat treatments. Intergranular corrosion also can occur in ferritic stainless steels and in nickel- and aluminum-base alloys. 

Fifty years ago, intergranular corrosion of the zinc—4% aluminum casting alloys was a problem because of high impurity levels, notably of lead, tin, and cadmium. The subsequent introduction of 99.99% zinc as the base for these casting alloys eliminated intergranular corrosion under normal service conditions. However, an inherent tendency for intergranular corrosion exists, and this defect can still occur if pure zinc-aluminum alloys are exposed to temperatures above about 70°C under wet or damp conditions. Research has... 

The method is based on the principle that if an aluminum alloy is susceptible to intergranular corrosion, this susceptibility will show as... 

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