Ultrasound attenuation plays a vital role in mechanical engineering for material characterization and non-destructive testing. Determining the attenuation parameter can be challenging in applications involving microstructural changes. This paper introduces a novel method for determining the ultrasound attenuation parameter using fringe spectrum analysis from a UFPR, enhancing the sensitivity in detecting attenuation parameter shifts with microstructural changes in aluminum alloy and providing a quantification of these shifts by employing a metric derived from standard method. The UFPR, drawing on principles from optical/microwave Fabry-Perot interferometry, offers fringe frequency domain analysis as an alternative to conventional time-or-frequency-domain analysis, providing deeper insight into material properties. Our research studied the sensitized aluminum alloys that the Al-Mg particles precipitate at the grain boundaries due to prolonged heat exposure, which is ambiguous with the ultrasound attenuation parameters determined from conventional methods.
Sensitization refers to the formation of magnesium precipitates at the grain boundaries when Al-Mg alloy is exposed to elevated temperatures for extended periods of time, which can lead to reduced corrosion resistance and increased susceptibility to stress corrosion cracking. Since sensitization occurs at the microstructure level, a measurement technique that can measure multiple locations rapidly and is highly sensitive to minute changes is called for. This paper explores laser-generated longitudinal ultrasonic guided waves for sensitization detection in aluminum alloy plates. The samples were heat-treated to induce sensitization, and the degree of sensitization was determined by the nitric acid mass loss tests. The longitudinal ultrasonic guided waves were generated using a high-power pulsed free-space laser and detected using a continuous fiber laser. A digital signal processing algorithm has been developed to analyze the time-frequency components of the acquired signal. The experimental results demonstrated that the state of sensitization can be characterized by ultrasound parameters, such as attenuation.
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