Fig. 1. Laser cleaning equipment

Fig. 2. Schematic of laser scanning path and spot overlap

Fig. 3. XPS full spectrum of FV520B steel oxide layer sample

Fig. 4. Element contents of FV520B steel oxide layer sample prepared by polishing

Fig. 5. Roughness of prepared FV520B steel samples with and without oxide layer for different abrasive papers

Fig. 6. Roughness of FV520B steel oxide layer sample after cleaning when frequency is 20 kHz

Fig. 7. Surface morphologies of FV520B steel oxide layer samples before and after laser cleaning for different powers. (a) Before cleaning; (b) cleaning with power of 40 W; (c) cleaning with power of 80 W; (d) cleaning with power of 120 W; (e) cleaning with power of 160 W; (f) cleaning with power of 200 W

Fig. 8. SEM images of FV520B steel oxide layer samples after laser cleaning with different laser powers when pulse frequency is 20 kHz. (a) 40 W; (b) 80 W; (c) 120 W; (d) 160 W; (e) 200 W

Fig. 9. Surface morphologies of FV520B steel oxide layer samples after one time laser cleaning at different frequencies when laser power is 120 W. (a) 20 kHz; (b) 30 kHz;(c) 40 kHz; (d) 50 kHz

Fig. 10. Roughness of FV520B steel oxide layer sample after one time laser cleaning at different frequencies when laser power is 120 W

Fig. 11. Roughness of FV520B steel oxide layer sample after laser cleaning for different cleaning times when laser power is 120 W and pulse frequency is 20 kHz

Fig. 12. SEM images of oxide layer samples after laser cleaning with laser power of 120 W and pulse frequency of 20 kHz for different cleaning times. (a) One time; (b) two times; (c) three times; (d) four times; (e) five times; (f) ten times; (g) locally magnified region in dotted box of Fig.12 (b)

Fig. 13. Schematic of laser cleaning for FV520B steel oxide layer sample with laser power of 120 W and pulse frequency of 20 kHz

Fig. 14. Roughness histograms of oxide layer samples prepared after polishing with different grades of abrasive papers and after laser cleaning with laser power of 120 W and pulse frequency of 20 kHz for one time or two times

Fig. 15. Surface morphologies of oxide layer samples prepared after polishing with different grades of abrasive papers and after one time laser cleaning with 120 W/20 kHz. (a) 200#; (b) 400#; (c) 600#; (d) 800#

Table 1. Device parameters

Table 2. Element contents of FV520B steel plate

Table 3. Experimental parameters