Forensic Comparison of Automotive Aluminum Wheel Fragments Using Synchrotron Radiation X-ray Fluorescence with 18- and 116-keV Excitation X-rays.

The performance of synchrotron radiation X-ray fluorescence (SR-XRF) spectrometry for nondestructive discrimination of small fragments of automotive aluminum wheels was studied. Fragments (< 500 × 500 μm2 ) of 45 kinds of wheels were first analyzed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and then by SR-XRF. Despite the Mg/Al intensity ratio being a useful identification index, SEM-EDS was not efficient enough because of the absence of other meaningful indicators of comparison. Conversely, pairwise comparison was conducted and a 92.9% identification was achieved via SR-XRF using 18-keV X-rays. Trace heavy elements in the high-energy region were detected by SR-XRF using 116-keV X-rays, and an 82.9% identification was obtained. Combined use of 18- and 116-keV X-rays allowed 98.2% identification. Hence, SR-XRF is a powerful tool for nondestructive discrimination of automotive aluminum wheels with high precision using trace elements in a wide energy region.