Understanding the Directional dependence of intergranular corrosion in aluminium alloys

Intergranular corrosion can lead to significant problems such as sub-critical crack growth or loss in section strength, potentially leading to failure, as well as a substantially increased maintenance burden. This type of corrosion is found in most types of aluminium alloys, but is a particularly significant problem in aerospace aluminium alloys. The form of intergranular corrosion can vary widely, and may depend on alloy composition, product form, environmental conditions and the presence or otherwise of local or global stresses. One notable example is the occurrence of intergranular corrosion due to atmospheric corrosion, in which salts and deposits deliquesce on the surface forming discrete corrosion cells. Intergranular corrosion of aluminium alloys is usually most rapid in the rolling or extrusion direction of wrought alloy. The reasons for this are not fully understood, and may include texture effects that produce highly susceptible grain boundaries, the inhomogeneous distribution of noble constituent particles, and stresses acting at a microscale. This paper will review and discuss the evidence for and against for the different effects mentioned.