Abstract
This research program evaluates the exfoliation corrosion properties of AA7136-T76 extrusions joined through friction stir welding (FSW). AA7136 is an aluminum alloy developed for high strength aerospace applications that also demand corrosion resistance. Extrusions were joined by FSW using a force of 26.7 kN, a welding velocity of 2.1 mm/s and a tool rotation speed of 250 RPM. Corrosion tests were performed in accordance with the requirements of ASTM G 34 and revealed a performance gradient across the weld – the weld center showing the greatest resistance to exfoliation corrosion and the thermo-mechanically affected zone adjacent to the tool shoulder showing the worst resistance to corrosion. Microscopy revealed that corrosion behavior is correlated with the distribution of MgZn₂ particles following supersaturation and cooling during FSW. In the weld center, coarse MgZn₂ particles were found on grain boundaries and within the grains alike, but near the TMAZ/HAZ boundary, large precipitates occurred on grain boundaries surrounded by precipitate free zones.

Key words
friction stir welding, aluminum, aluminum alloys, microstructure, corrosion

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