# Quantification of Sensitization in Aluminum–Magnesium Alloys Through Frequency-Dependent Ultrasonic Attenuation

## TL;DR

This paper introduces a new ultrasonic method to measure sensitization in aluminum-magnesium alloys, improving the accuracy of corrosion susceptibility assessment.

## Contribution

A time-frequency analysis technique is proposed to quantify sensitization using frequency-dependent ultrasonic attenuation.

## Key findings

- The frequency-attenuation slope correlates well with the degree of sensitization in Al–Mg alloys.
- The new method shows higher sensitivity and lower scattering than conventional ultrasonic techniques.
- Laser ultrasonic testing enables digital generation of narrowband signals for precise measurements.

## Abstract

Aluminum–Magnesium (Al–Mg) alloys undergo sensitization, i.e., the precipitations of β-phase (Al2Mg3) at the grain boundaries, when exposed to elevated temperature. This microstructural change increases the susceptibility of Al–Mg alloys to intergranular corrosion, exfoliation, and stress corrosion cracking. This study introduces a time-frequency analysis (TFA) technique to determine the frequency-dependent ultrasonic attenuation parameter and correlate the frequency-attenuation slope to the Degree of Sensitization (DoS) developed in heat-treated Al–Mg alloy samples. Broadband pitch-catch signal was generated using a laser ultrasonic testing (LUT) system, from which the narrowband pitch-catch signal at different frequencies can be digitally generated. The attenuation parameters of sensitized Al–Mg samples were determined from these narrowband pitch-catch signals using the primary pulse-first echo (PP-FE) method. By identifying the frequency range within which the attenuation parameter is linearly proportional to the frequency, the slopes of the frequency-attenuation relationship were determined and correlated with the DoS values of the sample plates. The experimental results validate that the frequency-attenuation slope has a higher sensitivity and lower scattering as compared to other conventional ultrasonic attenuation measurement techniques.