Behavior of β phase (Al3Mg2) in AA 5083 during friction stir welding

Friction stir welds of aluminum alloy 5083 are created at tool rotation speeds of 700, 1050, and 1600 rpm, with a fixed traveling speed of 100 mm/min. Stir welded structures, together with the as-received alloy, are subjected to a sensitization heat treatment of 175 °C for 240 h, which is known to produce severe sensitization in the as-received materials. It is demonstrated that stir welding dramatically reduces the sensitization response measured by the nitric acid mass loss test (NAMLT ASTM G67-93), suggesting that stir welding can be used to mitigate sensitization damage. The microstructures produced by the stir welding are evaluated using optical microscopy (OM), scanning electron microscopy (SEM), and an electron probe micro-analyzer (EPMA) to document the variations in the distribution of beta phase precipitates, which are believed to be responsible for this outcome.