As a newly developed technique

friction stir welding（FSW） is widely applied in the areas of solid-phase welding. The fine defects in the weld seam are in characteristics of multi-tropism and clingy. To achieve the high accuracy and high resolution for the inspection needs of aluminum alloy FSW weld inspection

a method of micro-magnetic testing method based on magnetic signal distribution was proposed according to the weak paramagnetism under a natural geomagnetic field for the 7 A09 aluminum alloy. Specifically

a high-precision magnetic vector quantity sensor was used to collect magnetic induction intensity signal which changes slightly on the surface of weld and the magnetic anomaly signals of weld defects are accurately extracted from the complex original magnetic induction intensity signals through multi-scale property of wavelet transform

directly mapping weld defect information to the separated d1 signal curve. The results indicate that the micro-magnetic resolution for minor defects in aluminum alloy FSW welds can reach 0.2 mm

and the detection error of defect location is only 1.67%. Therefore

the micro-magnetic method can guarantee the non-destructive detection for aluminum alloy friction stir welding with complete coverage and high reliability.