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Ultrasonic Sensor for Determining the Degree of Sensitization in Alloys

The sensitization of aluminum alloys used in marine applications is a problem of enormous economic significance for both the private and the defense industries. In particular, Mg-rich aluminum alloys (5xxx-series, high-strength and corrosive-resistant) become sensitized when exposed to heat from the sun or from on-board sources. Sensitized aluminum is vulnerable to corrosion, exfoliation, and stress-corrosion cracking. Ultimately, structural failure becomes imminent if the material at high-stress points is sensitized. The current method of determining the degree of sensitization is the NAMLT test, a test that is destructive, requires large specimens, and is time consuming. Two existing alternative techniques (both currently in development) use eddy currents inspection and electrochemical surface corrosion, respectively. Both suffer from a very weak dependence of the measured parameter on sensitization. Researchers at the University of Louisiana at Lafayette (UL Lafayette) have invented a novel method of determining the degree of sensitization with a much larger sensitivity. This new method is nondestructive, as it employs ultrasonic waves generated and received by the same probe. Both the attenuation and the velocity of the wave are affected by the degree of sensitization, with the attenuation yielding a high resolution measurement, of a 20% change for full alloy sensitization, compared to the reported 0.05% for the eddy-currents method.