Volume Fraction Detection of Long Period Stacking Ordered Phases in Mg Alloys Based on Dual-Tree Complex Wavelet Packet Transform

The existence of long period stacking ordered (LPSO) strengthening phases greatly improves the mechanical properties of Mg alloys, such as tensile strength, compressive strength and ductility. Therefore, volume fraction detection of LPSO phases plays an important role in understanding the properties of the alloy. Aiming at the traditional volume fraction detection of LPSO phases in Mg alloys destroys the tested material, a nondestructive testing method based on acoustic attenuation signal is proposed. In order to improve the sensitivity of the signal to the LPSO phases content, the dual-tree complex wavelet packet transform (DTCWPT) is used to extract the feature frequency band. Regarding Mg alloys with different volume fractions of LPSO phases as the research specimens, the feature frequency bands are extracted by DTCWPT. The fitting equation between the energy attenuation coefficient of the feature frequency band signal and the volume fraction of LPSO phases is established, and is used to calculate the LPSO phases content of the testing specimen. The results show that the proposed method is able to reliably calculate the volume fraction of LPSO phases, the absolute error of the phases volume fraction of testing specimens are 2.5 and 3.1%, which are 1.2 and 0.8% less than the absolute error 3.7 and 3.9% calculated by WPT method, and also 2.3 and 1.6% less than the absolute error 4.8 and 4.7% calculated by the original signal. Therefore, the volume fraction detection method of LPSO phases based on DTCWPT is a better method, which opens up a new nondestructive detection method of volume fraction of LPSO phases in Mg alloys.