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Friction stir processing (FSP) was performed on 12.7 mm thick AA5083-H321 (UNS A95083) plates that had received a 14 day sensitization treatment at 100°C. Two FSP parameters were studied: 240 RPM, 2.5 mm·s−1 with a forge-force of 17.8 kN and 2,000 RPM, 38.1 mm·s−1 with a forge-force of 44.5 kN. Salt bath heat treatments of sensitized (14 days at 100°C) non-FSP specimens were performed to determine the temperature necessary for elimination of sensitization. For all cases, the level of sensitization was assessed by nitric acid mass-loss tests (NAMLT). NAMLT results showed that processing of sensitized plates reduced mass loss to levels consistent with resistance to intergranular (IG) corrosion. The improved NAMLT response occurred not only in the stirred region, but also extended through regions of the heat-affected zone, experiencing temperatures of greater than approximately 250°C. A minimum temperature of 250°C for improved NAMLT response was corroborated by temperature measurement in the plates made during FSP as well as salt bath heat treatments. These data were also consistent with the Al-Mg phase diagram.
Reynolds et al. (Sat,) studied this question.