Differing microstructural properties of 7075-T6 sheet and 7075-T651 extruded aluminium alloy

This paper details an initial study of the differences, if any, in corrosion behaviour between 7075-T6 sheet and 7075-T651 extruded aluminium alloy. The study involved a visual inspection of the grain structure of each material and an analysis of the grain sizes. It was found that there is a significant difference in the grain sizes of the two materials; the extruded material had grains that were approximately 15-20% of the size of the sheet grains. Also, the grains in the sheet material were wider, with a length-to-width aspect ratio of 1.5 (compared with 1.3 for the extruded material). Finally, the grains in the extruded material appeared to form a semi-continuous line of grain boundaries, possibly facilitating the growth of laminar intergranular corrosion; the sheet material contained higher-angle grain boundary junctions which should limit the amount of laminar intergranular corrosion produced and promote networked intergranular corrosion. Further testing will involve corroding specimens and investigating the size, shape and depth of the corrosion produced