Effect of the MOPA Laser Cleaning Parameters on the Surface Evolution of the Epoxy Coating on AH36 Steel

High-power laser cleaning has been extensively adopted to remove organic coatings, but pulse duration, pulse energy, and overlap rate must be adjusted to limit residue and thermally affected surface modification. In this work, a 1000 W MOPA pulsed fiber laser was used to strip a 75 ± 5 μm thick iron-red epoxy primer from AH36 marine steel. Single-factor tests and an L9(3³) orthogonal design were evaluated using image-derived paint removal rate (PRR), surface roughness (Ra), SEM morphology, and energy-dispersive X-ray spectroscopy (EDS); every processing condition was repeated on five independently prepared coupons. Increasing pulse energy from 5.0 to 12.5 mJ raised the mean PRR from 79.01% to 99.67%, although the improvement above 7.5 mJ was marginal. At 70% overlap, PRR reached 99.12%, Fe was 77.7 wt.%, C was 8.1 wt.%, and Ra reached 4.196 μm, showing that high Fe exposure alone did not define the best surface state. Descriptive range values from the replicated L9 runs gave the apparent PRR order overlap rate > power > pulse duration; since the archived worksheet retained only run means, the small differences among the ranges cannot be tested against within-run error and are not treated as statistically significant. Run 2 (300 ns, 6.00 mJ at 100 kHz, and 60% overlap) was selected from the tested combinations as a multi-index engineering compromise rather than as a predicted optimum. It produced PRR = 99.90% and Ra = 1.308 μm. Pull-off testing used three dollies per recoated condition; the mean strength of the laser-cleaned condition was 5.20 MPa and failure was predominantly cohesive within the epoxy.