Metal pitting corrosion characterized by scanning acoustic microscopy and binary image processing

[Display omitted] •SAM for detecting the localized corrosion degree of the metal under the rust layer is firstly reported.•Combined TAMI scanning with image processing method, the pitting depth can be characterized.•Under the C-scanning mode, one single pit on the 7050 aluminum alloy can be focused.•This work provides practical methods on mechanism study of the localized corrosion process. To evaluate the residual life and safe operation of metallic materials, it is crucial to accurately identify the intensity and depth of corrosion pits. Scanning acoustic microscopy (SAM) using tomographic acoustic microimaging (TAMI) under C-mode was employed to determine corrosion pit morphology and depth on aluminum alloy 7050, and the reults were cross-checked by optical microscopy. Maximum and average pitting depths of 204 μm and 80 μm, respectively, were determined by multilayer scannning, and a pitted area of 30 ∼ 40 % was calculated using binary image processing.