Damage Behavior of 7075 Aluminum Alloy and Its Protective Coating Under Laser Irradiation and High-Speed Airflow

Under continuous-wave laser irradiation, 7075 aluminum alloy is susceptible to melting and through-thickness penetration, while high-speed airflow may modify its thermal response and damage evolution. Bare and Cu–Ag–Zn-coated 7075 aluminum alloy targets were examined at airflow velocities of 510 and 1020 m/s using an 8 kW, 1080 nm laser with a 3 cm spot diameter. Melting onset and penetration breakdown were identified from image sequences sampled at 0.1 s intervals; back-surface temperature and transmitted-power measurements provided supporting evidence. For bare targets, the descriptive mean breakdown times were 1.97 and 1.95 s at 510 and 1020 m/s, respectively, compared with 4.13 s in a non-concurrent static reference study. The corresponding melting-onset times (1.03 and 1.05 s) were close to the static reference value of 1.17 s. For coated targets at 1020 m/s, three observed breakdown times (23.6, 50.0, and 51.2 s) yielded a descriptive mean of 41.6 s, approximately 21 times the bare-target mean of 1.95 s. A separate two-specimen subset (Batches 2 and 4), excluding the record associated with suspected coating damage of unverified origin, yielded a mean of 50.6 s (approximately 26 times); this subset ratio is not a stable performance metric. At 510 m/s, the three coated specimens showed neither visible melting nor penetration within their respective 30, 50, and 60 s observation windows, yielding right-censored bounds of >30, >50, and >60 s without an estimable arithmetic mean. In the two coated specimens with identifiable melting onset at 1020 m/s, melting was delayed by approximately 48.7 s relative to the bare-target mean, whereas the subsequent melting-to-breakdown intervals were 0.8–1.0 s. All comparisons are descriptive and limited to the tested conditions; neither velocity dependence nor the relative contributions of airflow-induced mechanisms can be established.