Scanning microanalysis of Al alloys by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS), using microjoule UV laser pulses, was employed to conduct spectrochemical elemental microanalysis of commercially available aluminum alloys in air at atmospheric pressure. Multi-element 2D compositional mapping with a lateral resolution of about 10 μm in the surface plane of the sample was carried out to measure the precipitate distribution. The elemental composition of features less than 10 μm in size, such as precipitates in the aluminum alloy matrix, was determined by using single 8 μJ laser shots at 266 nm. Two main types of precipitates, namely Al–Cu–Fe–Mn (type I) and Al–Cu–Mg (type II) precipitates, were unambiguously distinguished in our LIBS experiments, in good agreement with electron microprobe X-ray analyzer measurements. It was also observed that the scanning led to the formation of an aluminum oxide layer with a thickness of about 1 μm in the neighboring regions of the laser-scanned area. An additional effect of laser plasma-induced shock wave cleaning of the deposited aluminum oxide layer in a circular region around each laser pulse was also observed. This cleaning effect extends beyond the 10 μm distance to the subsequent laser shot allowing the measurement of the elemental composition of the original surface despite the deposition of an aluminum oxide layer in the surrounding unscanned area.