In situ elevated temperature transmission electron microscopy of sensitized aluminum–magnesium alloy treated by ultrasonic impact treatment

In situ transmission electron microscopy (TEM) analysis shows that submicrometer grains formed by ultrasonic impact treatment (UIT) of sensitized 5456-H116 Al–Mg alloy products are thermally stable up to ∼300 °C which is consistent with previous research on annealing of heavily deformed Al–Mg. Grain growth occurs above 300 °C with significant growth at ∼400 °C. Grain growth continued upon heating to 450 °C; the grain size did not significantly increase when the temperature was held at 450 °C long term. In situ TEM revealed a duplex microstructure that was not fully recrystallized. The activation energy for grain growth was determined to be ∼32 kJ/mol. The submicrometer grains produced by UIT offer improved resistance to fatigue and corrosion. The majority of sensitized 5456-H116 failures are sensitive to the material's surface properties and operational service temperature; the stability of the submicrometer grains in the UIT Al–Mg makes them more stable in practical operations where increase in the material temperature is an issue.