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Ultrasonic Studies for Microstructural Characterization of A98090 Aluminum-Lithium Alloy

Ultrasonic velocities and attenuation measurements in the temperature range of 303 to 500 K (85.7 to 440 °F) have been carried out on UNS A98090 Al-Li alloy, in the as received (temper T8771) and heat treated (755 K [899 °F] for 1 h) followed by natural aging conditions. A high power ultrasonic process control system has been used for the measurements. Transducers (longitudinal and shear) with a fundamental operating frequency of 5 MHz have been used. The changes in longitudinal modulus, shear modulus, bulk modulus, Young’s modulus and Poisson’s ratio with temperature have been computed. Significant variations in ultrasonic velocities and attenuation in the temperature range of 450 to 480 K (350 to 404 °F) are attributed to formation, growth and dissolution of δ´ (Al3Li) precipitates. A pronounced peak in the ultrasonic velocities and the elastic moduli and a dip in the attenuation and the Poisson’s ratio at 470 K (386 °F) are attributed to the formation and growth of δ´ (Al3Li) precipitates. As the temperature is increased beyond 470 K (386 °F), the δ´ precipitates start dissolving, leading to a reduction in the velocities and an increase in the attenuation, thus restoring the original trend.

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