Aluminum Alloy Defects Detection Method Research Based On Pulsed Eddy Current

Aluminum alloy has been widely spread with a large number of applications in the aerospace equipment manufacturing industry in recent years attribute to its great metal material properties, such as good plasticity, low density and high strength. But the defects and metal corrosion in the aluminum alloy may affect the normal operation of devices, even to cause hidden trouble to safety, therefore, perform effective and rapid detection to the aluminum alloy is quite necessary and important. Considering that the detection technology based on pulsed eddy current(PEC) has a very great application advantage in the surface and subsurface defects detection, and the material loss quantitative assessment, after contraposing several most common types of aluminum alloy defects, the defects detection method based on PEC is studied in this paper. The specific work include following aspects:1. PEC testing theory researches. The function principle of PEC technolog is analyzed on the theoretical basis of the eddy current effect, and the excitation signal feature is taken into consideration to specifically study the PEC detection depth. Mathematical model is built with Maxwell equations to study the interactions between different physical quantities during the detection. Further, a proper simulation model for detection is constructed and finite element simulation is conducted with COMSOL software to have an intuitive analysis about the PEC testing process, which verifies the detection principle of PEC introduced in the paper.2. PEC testing system experimental system build. System function mudule including an excitation signal generator, detection probe, signal conditioning circuit and data acquisition and processing module are designed and completed.3. Detection signals processing and analysis. In order to improve the signal to noise ratio while retaining the original signal to maximum extent, digital low-pass filter and progressive average methods is adopted to suppress the high-frequency noise mixed in the detection signal. Then the feature analysis to the detection signal is conducted in time and frequency domain respectively to extract signal features as the peak value and the peak time in the time domain, and the fundamental component amplitude in the frequency domain, and the amplitude ratio of the fundamental component and the third-harmonic component is first used as a feature in the frequency for later detection experiments.4. Defects detection experiment and result analysis. The detection experimental system is used to detect three common types of defects appear in aluminum alloy, including the surface defect, subsurface defects and thickness loss due to mental corrosion, the corresponding relationship between the defects’ parameters and feature values extracted from the detection signal is studied comprehensively.According to the detection results, the differential signal is adopted to determine the absence of defects in the specimen, and the surface and subsurface defects with different depths, the specimen thickness loss status are qualitatively distinguished by the signal features extracted from the time domain and frequency domain, and the surface defect is differentiated from the other subsurface defects, the detection results verified the feasibility of PEC detection method.