Phase transformations in 5xxx series aluminum alloys (AA) during sensitization impact the propagation of ultrasound through these materials in a quantifiable way. The effect of phase evolution on three experimentally measured acoustic parameters (longitudinal wave speed, shear wave speed, and longitudinal wave attenuation) in sensitized 5xxx AA was analyzed under the framework of the Johnson-Mehl-Avrami-Kolmogorov model. The phase transformation rate constant, k, and the Avrami exponent, n, were determined by fitting the experimental data with a developed model. At saturation, independent of k and n, the wave speed values agree with those measured individually for each phase. The k value for shear speed is higher for AA5456 than AA5083, reflecting that AA5456 reaches full sensitization earlier (per standard, the amount of Mg is higher in 5456 than in 5083). The k values for both shear and longitudinal wave speed match the Arrhenius equation for literature NAMLT data (for a given alloy type and heat treatment), the current data extending the existing range to higher temperatures. The difference between the effective k values obtained from the longitudinal-wave attenuation coefficient and wave-speed data reflects the important contribution of scattering to acoustic attenuation in a sensitized material. The values of n in the 1 to 2 range indicate a combination of 1D and 2D growth, pointing to beta-phase growth mostly at grain boundaries and at their intersections. At the highest processing temperature, n is higher, suggesting partial occurrence of 3D growth.
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1 February 2025
Research Article|
January 08 2025
Sensitization of 5xxx Series Aluminum Alloys Explored with an Adapted Johnson-Mehl-Avrami-Kolmogorov Model for Phase Evolution and Ultrasonics
S.P. Kharal;
S.P. Kharal
*Physics Department, University of Louisiana at Lafayette, Louisiana, 70504.
**Carbon and Composites Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37830.
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N.J. Jones;
N.J. Jones
***Physical Metallurgy and Fire Performance Branch, Naval Surface Warfare Center, Carderock Division, Potomac, Maryland, 20817.
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G. Petculescu
G. Petculescu
‡
*Physics Department, University of Louisiana at Lafayette, Louisiana, 70504.
‡Corresponding author. E-mail: [email protected].
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CORROSION (2025) 81 (2): 172–181.
Citation
S.P. Kharal, N.J. Jones, G. Petculescu; Sensitization of 5xxx Series Aluminum Alloys Explored with an Adapted Johnson-Mehl-Avrami-Kolmogorov Model for Phase Evolution and Ultrasonics. CORROSION 1 February 2025; 81 (2): 172–181. doi: https://doi.org/10.5006/4649
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