Small-invasive determination of iron content in coating of galvanized steel sheets by laser-induced breakdown spectroscopy

A new method was presented to determine the iron content in the coating of galvanized steel sheet based on laser-induced breakdown spectroscopy. The zinc-iron coating was characterized with a series of single laser pulses irradiated on the traversing sheet steel, each on a different steel sheet position. The influences of laser fluence and elemental depth distribution were studied and analyzed. To protect the corrosion performance of the coating and meet requirements for small-invasive measurement, the ablation size of the crater under different laser fluences was studied. Under the optimized experimental parameters, the diameter of ablation craters is about 50 mu m, and then, the Fe content in the coating was calibrated and analyzed by the linear standard calibration method. The calibration result, however, is not good. Considering that the Zn content in the coating was high and relatively constant, curve calibration was then carried out with the intensity ratio (I-Fe404: 58=I-Zn468:01) instead of the net line intensity of Fe, and then, the determination coefficient of calibration curve increases from 0.7713 to 0.9511, and the root-mean-square error decreases from 0.4832% to 0.1509%. The results prove that the laser-induced breakdown spectroscopy is an effective way for the analysis of the Fe content in the coating of galvanized steel sheet.