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Temperature and annealing dependence of the longitudinal ultrasonic velocity in aluminum alloys
Published online by Cambridge University Press: 31 January 2011
Abstract
The longitudinal ultrasonic velocities of four commercial aluminum alloys and Al(1.8 wt.% Si) were measured between room temperature and the solidus temperatures. In all of the samples, the velocity deviated significantly from a linear temperature dependence at the highest temperatures. In commercially pure (1100) aluminum, this effect is found to be consistent with reported low-frequency damping and elastic modulus changes that are associated with dislocations or grain boundaries. In the four heat-treatable alloys studied, an additional contribution to the nonlinear temperature dependence arises from the dissolution of precipitates at elevated temperatures. Irreversible velocity changes occur during the first heating, as a result of the recovery from work-hardening and heat treatments which were performed during the production of the material. Small hysteretic changes above ∼ 250 °C are correlated with the precipitation and dissolution of alloying elements. The activation energy for the hysteretic changes in Al(1.8% Si) is found to be 0.82 eV, which is consistent with precipitation limited by silicon diffusion along grain boundaries.
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- Copyright © Materials Research Society 1993
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