Microstructure and microhardness study of laser bent Al-2024-T3

Abstract

Microstructure and microhardness profile of laser bent AA 2024-T3 sheets were obtained to determine the effects of such a process on this material. A fast-axial flow CO2 laser unit (TEM00) was used at 250, 500, and 800 W continuous wave to bend the samples; scanning velocities ranged from 10 to 80 mm/s while laser spot diameters used were 1, 5, and 10 mm. Characterization techniques included light microscopy, scanning electron microscopy, and Vickers microhardness. Laser bending process variables were arranged into a parameter called accumulated energy density (AED) in J/mm2. Light microscopy observations and microhardness results revealed that there was no damage to the microstructure for AED values less than 25 J/mm2. At these AED values, the microhardness level across the depth is closer to the average value of the as-received material (150.9+/−2.7 Hv). However, some AED values resulted in samples with microhardness above and below that number. Higher microhardness levels were attributed to a small grain size and a localized T6 temper while the lower values were associated with grain growth. For AED values between 25 and 125 J/mm2 subgrain structures and dispersoids at grain boundaries were observed under scanning electron microscopy. Partial melting at recrystallized grain boundaries was the principal form of damage. Remelting of the upper region of the sheet underneath the alclad layer took place leaving a cast structure. For AED values of 125 and 250 J/mm2, the alclad layer fused to the substrate. For AED values that caused partial melting and a considerable fusion drop in the microhardness value was observed.