Investigation of laser irradiation effects on the hardness of Al 5086 alloy under different conditions

Laser irradiation effects on the hardness of Al 5086 alloy have been investigated by using KrF Excimer laser of 248 nm wavelength, 23 mJ pulse energy, 20 ns pulse duration, and 100 Hz repetition rate. The square-shape samples were irradiated in air as well as in vacuum (∼10⁻³ mbar) with a defocused beam of spot size 3.14 mm² at the target surface, where the laser fluence was 0.73 J/cm² and laser intensity ≈ 3.7 × 10⁷ W/cm². The number of shots were varied from 100 to 500, and its influence on the hardness profile and on the microstructure of the irradiated samples was analyzed. The surface hardness profile follows an increasing trend till 200 shots and afterwards it decreases in both the cases. The peak value of the surface hardness of laser-treated sample in air for 200 shots is 11% higher than for sample irradiated in vacuum and 48% higher than for un-irradiated sample. The surface hardness data for samples irradiated with 100-500 shots in air and in vacuum correlate very well with the dislocation line density derived from the XRD patterns, irrespective of the laser-treatment environment of samples prior to hardness measurements.